Effects of a 6-day treatment with medroxyprogesterone acetate after prostaglandin F2 alpha-induced luteolysis at midcycle on antral follicular development and ovulation rate in nonprolific Western white-faced ewes

Medroxyprogesterone acetate (MAP) from intravaginal sponges prolongs the lifespan of large ovarian follicles when administered after prostaglandin F2alpha (PGF2alpha)-induced luteolysis early in the luteal phase of ewes. The present study was designed to determine whether a PGF2alpha/MAP treatment applied at midcycle would alter the pattern of antral follicle growth and increase ovulation rate in nonprolific ewes. A single injection of PGF2alpha (15 mg, i.m.) was given, and an intravaginal MAP (60 mg) sponge was inserted for 6 days, on approximately Day 8 after ovulation, in 7 (experiment 1), 8 (experiment 2) or 11 (experiment 3) ultrasonographically monitored, cycling Western white-faced ewes; seven ewes (experiment 1) served as untreated controls. Blood samples were collected each day and also every 12 min for 6 h, halfway through the period of treatment with MAP (experiment 1), or every 4 h, from 1 day before to 1 day after sponging (experiment 2). Seventeen of 26 treated ewes (experiment 1, n = 6; experiment 2, n = 5; experiment 3, n = 6) ovulated 1 to 6 days after PGF2alpha, but this did not affect the emergence of ensuing follicular waves (experiments 1 and 2). These ovulations, confirmed by laparotomy and histological examinations of the ovaries (experiment 3), were not preceded by an increase in LH/FSH secretion and did not result in corpora lutea, as evidenced by transrectal ultrasonography and RIA of serum progesterone (experiments 1 and 2). Following the removal of MAP sponges, the mean ovulation rate was 3.1 +/- 0.4 in treated ewes and 2.0 +/- 0.3 in control ewes (experiment 1; P < 0.05). In experiments 1 and 2, the ovulation rate after treatment (3.1 +/- 0.4 and 2.8 +/- 0.4) was also greater than the pretreatment rate (1.9 +/- 0.3 and 1.9 +/- 0.1, respectively). Ovulations of follicles from two consecutive waves before ovulation were seen in five treated but only in two control ewes (experiment 1), and in seven ewes in experiment 2. There were no significant differences between the MAP-treated and control ewes in mean daily serum concentrations of FSH and estradiol, and no differences in the parameters of LH/FSH secretion, based on frequent blood sampling. Treatment of nonprolific Western white-faced ewes with PGF2alpha and MAP at midcycle changed follicular dynamics and increased ovulation rate by approximately 50%. These effects of MAP, in the absence of luteal progesterone, may not be mediated by changes in gonadotropin secretion.     

Suppression of plasma FSH concentrations with bovine follicular fluid blocks ovulation in GnRH-treated seasonally anoestrous ewes

The specific requirement for FSH in the final stages of preovulatory follicle development was assessed in seasonally anoestrous ewes given 2-h injections of GnRH (250 ng/injection), with (N = 10) or without (N = 10) concurrent treatment with bovine follicular fluid (bFF: 2 ml given i.v. at 8-h intervals). Treatment with bFF significantly (P less than 0.01) suppressed plasma FSH concentrations, but, at least for the first 30 h of treatment, did not influence the magnitude of GnRH-induced LH episodes (mean max. conc. 3.00 +/- 0.39 and 3.63 +/- 0.51 ng/ml for bFF-treated and control ewes, respectively). Of 10 animals treated with GnRH for 72 h, 5/5 control ewes showed oestrus and ovulated whereas 0/5 bFF-treated ewes showed oestrus or ovulated in response to GnRH treatment. There was, however, a transient (13.2 +/- 1.0 h) increase in plasma LH concentrations in the ewes given bFF (mean max. conc. 4.64 +/- 1.57 ng/ml), which was coincident with the preovulatory LH surge recorded in animals given GnRH alone. In 10 GnRH-treated ewes slaughtered after 32 h of treatment, the mean diameter of the largest antral follicle was significantly (P less than 0.001) greater in control ewes (5.92 +/- 0.17 mm) than in animals that were also given bFF (3.94 +/- 0.14 mm). In addition, the incidence of atresia in the 3 largest antral follicles present at this time was greater in bFF-treated ewes. These results show that, when plasma FSH concentrations are suppressed by administration of bFF, although the magnitude of GnRH-induced LH episodes is unchanged, preovulatory follicular development is impaired and ovulation does not occur.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of subluteal levels of exogenous progesterone on follicular dynamics and endocrine patterns during early luteal phase of the ewe

Nineteen Corriedale ewes were treated with an im dose of a PGF2alpha during the luteal phase to synchronize estrus. After ovulation had been detected by using ultrasonography (Day 0); the ewes were randomly assigned to 2 different groups. In 11 ewes a CIDR, which had previously been used for 10 d, was inserted on the fourth day after ovulation. The ewes then received a dose of PGF2alpha on Day 5 to induce luteolysis. The CIDR remained in place until the end of the experiment (Day 9). Control ewes (n = 8) received no treatment. Blood samples were taken daily for estradiol, progesterone and FSH determinations. In the untreated ewes, 2 follicular waves were detected in all of the animals throughout the monitoring period, with a mean wave interval of 4.5 d. The total number of follicles which were > or =2 mm decreased from Day 0 to Day 4 (8.8+/-1.0 to 5.3+/-0.6; P< or =0.05) and then increased at Day 7 (7.5+/-0.9; P< or =0.05). The growth profiles of both the largest and the second largest follicles of Wave 1 showed significant divergence, while no divergence was observed in Wave 2. Serum estradiol concentrations decreased significantly from the day before to the day of ovulation and then increased again during the growing phase of the largest follicle of Wave 1. Concentrations of FSH were high on the day of emergence of both waves, but while a significant decline was observed after emergence in Wave 1, the levels remained high in Wave 2. In 8 of the 11 treated ewes, the largest follicle of Wave 1 was still present on the ninth day after ovulation (persistent follicle). In the other 3 ewes, the largest follicle of Wave 1 was already regressing on the day that the treatment was administered, and the largest follicle that was present on Day 9 originated from Wave 2 (nonpersistent follicle). In persistent follicle ewes, the largest follicle of Wave 1 prolonged its lifespan significantly, attaining the maximum diameter (Day 8.1+/-0.8) later than in untreated (Day 3.0+/-0.4) and nonpersisted follicle ewes (Day 2.0+/-0.6). The total number of follicles decreased in persistent follicle ewes between Day 0 and Day 4 (7.9+/-1.5 to 4.5+/-0.5, respectively; P< or =0.05) and remained low until the end of the experiment. Progesterone concentrations (nmol/L) between Days 6 and 9 were significantly different between untreated and persistent follicle ewes (12.8+/-1.0 vs. 9.4+/-1.0, P< or =0.02). The present study confirms that the largest follicle of Wave 1 is dominant in the ewe and that subluteal progesterone concentrations can prolong its lifespan and extend this dominance.     

Differential regulation of the secretion of luteinizing hormone and follicle-stimulating hormone around the time of ovulation in the bitch

Plasma concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined 3-6 times daily in six Beagle bitches from the start of the follicular phase until 5 d after the estimated day of ovulation. The aim of the study was to gain more detailed information regarding the changes in and the temporal relation between these hormones around the time of ovulation. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. The mean duration of the pre-ovulatory FSH surge (110 +/- 8 h) was significantly longer than that of the pre-ovulatory LH surge (36 +/- 5 h). The FSH surge started concomitantly with the pre-ovulatory LH surge in four bitches, and 12 h before the start of the LH surge in the other two bitches. The pre-ovulatory LH surge had a bifurcated pattern in four bitches. The mean plasma LH concentration before (1.9 +/- 0.4 microg/L) and after (1.9 +/- 0.3 microg/L) the pre-ovulatory LH surge were similar. The mean plasma FSH concentration during the period 72-28 h before the pre-ovulatory LH surge (1.6 +/- 0.3 U/L) was lower (P < 0.001) than that during the period 100-144 h after the pre-ovulatory LH surge (3.1 +/- 0.2U/L). In conclusion, this study demonstrated concurrent pre-ovulatory surges of FSH and LH and provided more evidence for differential regulation of the secretion of FSH and LH.     

Effects of medroxyprogesterone acetate (MAP) on ovarian antral follicle development, gonadotrophin secretion and response to ovulation induction with gonadotrophin-releasing hormone (GnRH) in seasonally anoestrous ewes

When ovulation is induced with gonadotrophin-releasing hormone (GnRH) in anoestrous ewes, a proportion of animals fail to form normal (full-lifespan) corpora lutea (CL). Progesterone treatment before GnRH prevents luteal inadequacy. It remains uncertain whether a similar effect, achieved with medroxyprogesterone acetate (MAP) from intravaginal sponges, is mediated by influences on growing ovarian follicles and/or secretion of gonadotrophic hormones, before and after GnRH treatment. Two experiments were performed, on 13 and 11 anoestrous Western white-faced ewes, respectively. Seven and six ewes, respectively, received MAP-containing sponges (60 mg) for 14 days; the remaining ewes served as untreated controls. To test the effect of timing of GnRH administration after pre-treatment with MAP-releasing sponges, GnRH injections (250 ng every 2h for 24h followed by a bolus injection of 125 microg of GnRH i.v.) were given either immediately (Experiment 1) or 24h after sponge removal in the treated ewes (Experiment 2). Ovarian follicular dynamics (follicles reaching >or=5mm in size) and development of luteal structures were monitored using transrectal ultrasonography. In Experiment 1, the mean ovulation rate (0.7+/-0.3 and 1.0+/-0.4) and proportion of ovulating ewes (57 and 67%, respectively) did not vary (P>0.05) between MAP-treated and control ewes. Normal (full-lifespan) CL were detected in 29% of treated and 67% of control ewes (P>0.05). In Experiment 2, the mean ovulation rate (2.3+/-0.2 and 1.2+/-0.6; P<0.05) and percentage of ewes with normal (full-lifespan) CL (100 and 40%, respectively; P<0.10) were greater in the treated compared to control ewes. In Experiment 1, the mean peak concentration of the GnRH-induced LH surge was lower (P<0.05) in MAP-treated than in control ewes. There were no significant differences between MAP-treated and control ewes in the characteristics of follicular waves, mean daily serum FSH concentrations, and secretory parameters of LH/FSH, based on intensive blood sampling conducted 1 day before sponging and 1 day before sponge removal. It is concluded that treatment with MAP has no effect on the tonic secretion of LH/FSH or follicular wave development in anoestrous ewes. However, the GnRH-stimulated LH discharge was attenuated in the ewes that received MAP-impregnated sponges for 14 days and were treated with GnRH immediately after sponge withdrawal. Ovulatory response and CL formation were increased when GnRH was administered 24 h after sponge removal.     

Synchronization of follicular wave emergence in the seasonally anestrous ewe: the effects of estradiol with or without medroxyprogesterone acetate

Fertility is often lower in anestrous compared to cyclic ewes, after conventional estrus synchronization. We hypothesized that synchronization of ovarian follicular waves and ovulation could improve fertility at controlled breeding in anestrous ewes. Estradiol-17beta synchronizes follicular waves in cattle. The objectives of the present experiments were to study the effect of an estradiol injection, with or without a 12-d medroxyprogesterone acetate (MAP) sponge treatment, on synchronization of follicular waves and ovulation in anestrous ewes. Twenty ewes received sesame oil (n=8) or estradiol-17beta (350 microg; n=12). Eleven ewes received MAP sponges for 12d and were treated with oil (n=5) or estradiol-17beta (n=6) 6d before sponge removal. Saline (n=6) or eCG (n=6) was subsequently given to separate groups of ewes at sponge removal in the MAP/estradiol-17beta protocol. Estradiol treatment alone produced a peak in serum FSH concentrations (4.73+/-0.53 vs. 2.36+/-0.39 ng/mL for treatment vs. control; mean+/-S.E.M.) after a short-lived (6 h) suppression. Six of twelve ewes given estradiol missed a follicular wave around the time of estradiol injection. Medroxyprogesterone acetate-treated ewes given estradiol had more prolonged suppression of serum FSH concentrations (6-18 h) and a delay in the induced FSH peak (32.3+/-3.3 vs. 17.5+/-0.5 h). Wave emergence was delayed (5.7+/-0.3 vs. 1.4+/-0.7d from the time of estradiol injection), synchronized, and occurred at a predictable time (5-7 vs. 0-4d) compared to ewes given MAP alone. All ewes given eCG ovulated 3-4d after injection; this predictable time of ovulation may be efficacious for AI and embryo transfer.     

Plasma concentrations of gonadotrophins, preovulatory follicular development and luteal function associated with bovine follicular fluid-induced delay of oestrus in heifers

In Exp. 1, injections of 10 ml bovine follicular fluid (bFF, i.v. or s.c.), given twice daily for 3 days after injection of a luteolytic dose of PGF-2 alpha, delayed the onset of oestrus in 3 of 6 heifers to 8 or 9 days after PGF-2 alpha, as compared with 2 or 3 days after PGF-2 alpha in control heifers. Mean plasma concentrations of FSH and LH during the injection period were not different from those in saline-injected heifers. In Exp. 2, i.v. injections of 20 ml bFF twice daily for 3 days uniformly delayed oestrus to 8 days after PGF-2 alpha (N = 4) and injections of 20 ml bFF i.v. every 6 h for 24h on the day of PGF-2 alpha injection delayed oestrus to 5.0 +/- 0.6 days after PGF-2 alpha as compared with 2.8 +/- 0.3 days for control heifers. In both treatment groups, plasma concentrations of FSH were suppressed during the injection period and increased transiently after treatment, but plasma concentrations of LH during the injection period were not different from those of control heifers. Plasma levels of oestradiol in heifers given bFF remained basal for 2 or 3 days after treatment, then increased several days before the delayed oestrus, in a manner similar to that in control heifers, and elicited normal preovulatory surges of LH and FSH. Plasma concentrations of progesterone and the length of the next oestrous cycle were normal, indicating formation of functional corpora lutea. Therefore, bFF treatments appear to delay oestrus by selectively suppressing plasma FSH, without affecting LH, and delaying the development of the preovulatory follicle. These results suggest that FSH may be critical to support the growth and development of the preovulatory follicle after luteolysis in cows.     

Examination of the relative role of FSH and LH in the mechanism of ovulatory follicle selection in sheep

The GnRH-antagonist suppression-ovarian autotransplant model (n = 18) was used to examine the relative roles of temporal changes in FSH and LH stimulation on follicle development and selection. Follicle development was stimulated by infusion with oFSH for 3 days and treatments applied for 60 h after progestagen sponge withdrawal and before delivery of an ovulatory stimulus. In Expt 1, there was continuous infusion of FSH with or without small amplitude high frequency LH pulses, or withdrawal of FSH with or without pulsatile LH. In Expt 2, there was acute or gradual withdrawal of FSH at sponge withdrawal with pulsatile LH. The patterns of follicle development and basal and pulsatile ovarian hormone secretion were determined. The maintenance of FSH throughout the artificial follicular phase resulted in multiple follicle development and ovulation (3.3 +/- 0.3). Pulsatile LH stimulated steroid secretion (P < 0.001) but had little effect on ovulation rates (3.8 +/- 0.8) when FSH was maintained. However, withdrawal of FSH in the absence of LH resulted in atresia of the ovulatory follicles and anovulation whereas, when FSH was withdrawn in the presence of LH, preovulatory follicle development was maintained in some animals (3/6 and 5/9 in Expts 1 and 2, respectively) and these ewes had lower (P < 0.05) ovulation rates (1-2 ovulations per ewe). When FSH was withdrawn gradually in the presence of pulsatile LH, 9/9 animals ovulated with ovulation rates in the normal range. These results indicate that ovulatory follicles can transfer their gonadotrophic dependence from FSH to LH. It is hypothesized that the ability of a follicle to respond to this switch in gonadotrophic support is central to the mechanism of follicle selection.     

Follicular and FSH dynamics in ewes with a history of high and low ovulation rates

Daily transrectal ultrasound scanning and twice-daily blood sampling were used to monitor the temporal relationships between FSH concentrations and follicle development during complete interovulatory intervals for ewes in which the ovulation rate in each of the 2 previous years was high or low (> or = 3 and < or = 2 ovulations, respectively). Follicles that reached > or = 5 mm were used to define a follicular wave and were tracked retrospectively to 3 mm (emergence). The hypothesis that FSH surges (identified with a computer program) and follicular waves (retrospectively determined based on ultrasound scanning) are temporally associated was supported in both groups by the emergence of an anovulatory or ovulatory follicular wave near the peak of an FSH surge. Further support for the hypothesis was a significant increase in FSH concentrations before and a significant decrease after follicular-wave emergence in both groups independent of the identification of FSH surges. Ewes with a history of high ovulation rates had smaller follicles (anovulatory and ovulatory) and more ovulations, but the 2 groups were similar in the number of ovulatory follicular waves and associated FSH surges, number and characteristics of the FSH surges, and mean FSH concentrations per interovulatory interval. Surges of FSH were periodic (every 3 or 4 d) regardless of the ovulation-rate group or follicle response. In ewes with a low ovulation rate, the nonovulatory FSH surges were most frequently associated with emergence of detected anovulatory follicular waves. In ewes with a high ovulation rate, more FSH surges were not associated with a detected follicular wave, as defined, presumably because the largest follicle did not reach 5 mm. The results indicated that the factors resulting in a high ovulation rate were not exerted through circulatory patterns or concentrations of FSH but involved a shorter growth phase and smaller maximal diameter of follicles.     

Effects of oestradiol on LH, FSH and prolactin in ovariectomized ewes

This study was conducted to test the hypothesis that the rate (dose/time) at which oestradiol-17 beta (oestradiol) is presented to the hypothalamo-pituitary axis influences secretion of LH, FSH and prolactin. A computer-controlled infusion system was used to produce linearly increasing serum concentrations of oestradiol in ovariectomized ewes over a period of 60 h. Serum samples were collected from ewes every 2 h from 8 h before to 92 h after start of infusion, and assayed for oestradiol, LH, FSH and prolactin. Rates of oestradiol increase were categorized into high (0.61-1.78 pg/h), medium (0.13-0.60 pg/h) and low (0.01-0.12 pg/h). Ewes receiving high rates of oestradiol (N = 11) responded with a surge of LH 12.7 +/- 2.0 h after oestradiol began to increase, whereas ewes receiving medium (N = 15) and low (N = 11) rates of oestradiol responded with a surge of LH at 19.4 +/- 1.7 and 30.9 +/- 2.0 h, respectively. None of the surges of LH was accompanied by a surge of FSH. Serum concentrations of FSH decreased and prolactin increased in ewes receiving high and medium rates of oestradiol, when compared to saline-infused ewes (N = 8; P less than 0.05). We conclude that rate of increase in serum concentrations of oestradiol controls the time of the surge of LH and secretion of prolactin and FSH in ovariectomized ewes. We also suggest that the mechanism by which oestradiol induces a surge of LH may be different from the mechanism by which oestradiol induces a surge of FSH.     

Differences in the plasma concentrations of FSH and LH in ovariectomized Booroola FF and ++ ewes

During 12 sampling days before ovariectomy the mean plasma FSH but not LH concentrations in FF ewes were higher (P less than 0.01) than those in ++ ewes (16 ewes/genotype). After ovariectomy increases in the concentrations of FSH and LH were noted for ewes of both genotypes within 3-4 h and the rates of increase of FSH and LH were 0.18 ng ml-1 h-1 and 0.09 ng ml-1 h-1 respectively for the first 15 h. From Days 1 to 12 after ovariectomy, the overall mean +/- s.e.m. concentrations for FSH in the FF and ++ ewes were 8.1 +/- 0.6 and 7.1 +/- 0.4 ng/ml respectively and for LH they were 2.7 +/- 0.3 and 2.1 +/- 0.2 ng/ml: these differences were not statistically significant (P = 0.09 for both FSH and LH; Student's t test). However, when the frequencies of high FSH or LH values after ovariectomy were compared with respect to genotype over time, significant F gene-specific differences were noted (P less than 0.01 for both FSH and LH; median test). In Exp. 2 another 21 ewes/genotype were blood sampled every 2nd day from Days 2 to 60 after ovariectomy and the plasma concentrations of FSH and LH were more frequently higher in FF than in ++ ewes (P less than 0.01 for FSH and LH). The F gene-specific differences in LH concentration, observed at 21-36 days after ovariectomy were due to higher mean LH amplitudes (P less than 0.025) but not LH peak frequency in FF than in ++ ewes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormone secretion in the asian elephant (Elephas maximus): characterization of ovulatory and anovulatory luteinizing hormone surges.

In the elephant, two distinct LH surges occur 3 wk apart during the nonluteal phase of the estrous cycle, but only the second surge (ovLH) induces ovulation. The function of the first, anovulatory surge (anLH) is unknown, nor is it clear what regulates the timing of these two surges. To further study this observation in the Asian elephant, serum concentrations of LH, FSH, progesterone, inhibin, estradiol, and prolactin were quantified throughout the estrous cycle to establish temporal hormonal relationships. To examine long-term dynamics of hormone secretion, analyses were conducted in weekly blood samples collected from 3 Asian elephants for up to 3 yr. To determine whether differences existed in secretory patterns between the anLH and ovLH surges, daily blood samples were analyzed from 21 nonluteal-phase periods from 7 Asian elephants. During the nonluteal phase, serum LH was elevated for 1-2 days during anLH and ovLH surges with no differences in peak concentration between the two surges. The anLH surge occurred 19.9+/-1.2 days after the end of the luteal phase and was followed by the ovLH surge 20.8+/-0.5 days later. Serum FSH concentrations were highest at the beginning of the nonluteal phase and gradually declined to nadir concentrations within 4 days of the ovLH surge. FSH remained low until after the ovLH surge and then increased during the luteal phase. Serum inhibin concentrations were negatively correlated with FSH during the nonluteal phase (r = -0.53). Concentrations of estradiol and prolactin fluctuated throughout the estrous cycle with no discernible patterns evident. In sum, there were no clear differences in associated hormone secretory patterns between the anLH and ovLH surge. However, elevated FSH at the beginning of the nonluteal phase may be important for follicle recruitment, with the first anLH surge acting to complete the follicle selection process before ovulation.     

LH surge in Nelore cows (Bos indicus), after induced estrus or after ovarian superestimulation

Considering that there is limited information about the preovulatory LH surge in Zebu cattle (Bos indicus), the purpose of the present work was to assess the LH surge in Nelore cows during the estrous cycle and after ovarian superestimulation of ovarian follicular development with FSH. This information is particularly important to improve superovulatory protocols associated with fixed-time artificial insemination. Nelore cows (n=12) had their estrus synchronized with an intravaginal device containing progesterone (CIDR-B) associated with estradiol benzoate administration (EB, 2.5 mg, i.m., Day 0). Eight days later all animals were treated with PGF2alpha (Day 8) in the morning (8:00 h) and at night, when CIDR devices were removed (20:00 h). Starting 38h after the first PGF2alpha injection, blood sampling and ovarian ultrasonography took place every 4h, during 37 consecutive hours. Frequent handling may have resulted in a stress-induced suppression of LH secretion resulting in only 3 of 12 cows having ovulations at 46.7+/-4.9 and 72.3+/-3.8 h, respectively, after removal of CIDR-B. Thirty days later, the same animals received the described hormonal treatment associated with FSH (Folltropin), total dose=200 mg) administered twice a day, during 4 consecutive days, starting on Day 5. Thirty-six hours after the first injection of PGF2alpha, to minimize stress, only seven blood samples were collected at 4h interval each, and ultrasonography was performed every 12 h until ovulation. In 11 of 12 cows (92%) the LH surge and ovulation were observed 34.6+/-1.6 and 59.5+/-1.9 h, respectively, after removal of progesterone source. The maximum values for LH in those animals were 19.0+/-2.6 ng/ml (mean+/-S.E.M.). It is concluded that, in Nelore cows submitted to a ovarian superstimulation protocol, the LH surge occurs approximately 35 h after removal of intravaginal device containing progesterone, and approximately 12h before the LH surge observed after an induced estrus without ovarian superstimulation.     

Bromocriptine-induced premature oestrus is associated with changes in the pulsatile secretion pattern of follicle-stimulating hormone in beagle bitches

The secretory profiles of LH and FSH were investigated before and during the administration of bromocriptine in six beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 6 h every 2 weeks until the next ovulation. Bromocriptine treatment was started 100 days after ovulation. Both before and after bromocriptine treatment, LH and FSH pulses occurred together. The mean duration of the FSH pulse (120 min) was significantly longer than that of the LH pulse (80 min). The interoestrous interval in the bitches treated with bromocriptine was significantly shorter than that of the preceding cycle (160 +/- 3 versus 206 +/- 24 days). The mean basal plasma FSH concentration (7.4 +/- 0.6 versus 6.1 +/- 0.7 iu l-1) and the mean area under the curve for FSH (46.6 +/- 4.7 versus 40.4 +/- 4.4 iu l-1 in 6 h) increased significantly after the start of the bromocriptine treatment. In contrast, the differences in mean basal plasma LH concentration (2.1 +/- 0.2 versus 2.0 +/- 0.2 micrograms l-1) and the mean area under the curve for LH (19.0 +/- 3.1 versus 19.5 +/- 2.5 micrograms l-1 in 6 h) between the day before and 14 days after the start of the bromocriptine treatment were not significant. Bromocriptine administration also lowered the mean amplitude of the FSH pulse and shortened the mean duration of the FSH pulse, without influencing the LH pulse. In addition to demonstrating the concurrent pulsatile secretion of LH and FSH, the results of the present study demonstrate that the bromocriptine-induced shortening of the interoestrous interval in the bitch is associated with an increase in plasma FSH concentration without a concomitant increase in plasma LH concentration. This finding indicates that treatment with the dopamine agonist bromocriptine increase plasma FSH to a concentration that results in the enhancement of follicle development.     

The effect of the infusion of insulin during the luteal phase of the estrous cycle on the ovulation rate and on plasma concentrations of LH, FSH and glucose in ewes

The role of insulin in mediating pituitary responses to nutrition was investigated in 30 mature Border Leicester X Merino ewes. The ewes were infused with saline (n = 15) or bovine insulin at 0.4 IU/kg/d (n = 15) for 72 h during the luteal phase of the estrous cycle The ewes were housed in individual pens and were fed, ad libitum, a diet of low quality straw. Their estrous cycles were synchronized with prostaglandin (PG), with infusions given over Days 9 to 11 of the estrous cycle. A further injection of PG was given at the end of the infusion, and the subsequent ovulation rate was determined by endoscopy 12 d later. Blood samples were collected every 4 h from Day 8 until 52 h after the final PG injection for the determination of plasma FSH, insulin and glucose concentrations. On Day 11 blood samples were also taken every 20 min for 24 h for the determination of LH pulse characteristics. During the infusion of insulin, its concentration rose 4-fold and remained elevated until the end of infusion, when it fell to pretreatment concentrations. Glucose concentrations were significantly reduced during the insulin infusion and rose to pretreatment concentrations after infusion. In control ewes glucose and insulin concentrations did not change. Ovulation rate of treated ewes was not affected by the insulin (1.9 +/- 0.07) compared with that of control ewes (2.0 +/- 0.10). Neither were FSH concentrations affected by treatment with insulin, although a significant interaction of treatment with time was observed in the 36 h after infusion. The pre-ovulatory decline in FSH concentrations was delayed by about 8 h in the insulin treated ewes. The mean (+/- SEM) LH pulse frequency (4.3 +/- 0.4 vs 1.8 +/- 0.3 pulses per 24 h) and the mean (+/- SEM) concentration of LH (0.48 +/- 0.04 vs 0.32 +/- 0.03 ng/ml) were both significantly reduced by insulin. These results indicate that insulin-induced hypoglycaemia inhibits LH secretion in cyclic ewes and implicates insulin as a mediator of normal hypothalamo-pituitary function.     

Ovarian response to gonadotropin treatment initiated relative to wave emergence in ultrasonographically monitored ewes

Follicular recruitment and luteal response to superovulatory treatment initiated relative to the status of the first wave of the ovine estrous cycle (Wave 1) were studied. All ewes (n = 25) received an intravaginal progestagen sponge to synchronize estrous cycles, and ewes were monitored daily by transrectal ultrasonography. Multiple-dose FSH treatment (total dose = 100 mg NIH-FSH-P1) was initiated on the day of ovulation (Day 0 group) in 16 ewes. In the remaining 9 ewes, FSH treatment was started 3 d after emergence of the largest follicle of Wave 1 (Day 3 group). Ewes received PGF(2alpha) with the last 2 FSH treatments to induce luteolysis. Daily blood samples were taken to determine progesterone profiles and to evaluate the luteal response subsequent to superovulation. The ovulation rate was determined by ultrasonography and correlated with direct observation of the ovaries during laparotomy 5 to 6 d after superovulatory estrus when the uterus was flushed to collect embryos. Results confirmed that follicular recruitment was suppressed by the presence of a large, growing follicle. In the Day 0 and Day 3 groups, respectively, mean numbers (+/- SEM) of large follicles (>/= 4 mm) recruited were 6.4 +/- 0.6 and 2.7 +/- 0.7 (P < 0.01) at 48 h after the onset of treatment, and 6.7 +/- 0.5 and 5.1 +/- 0.6 (P = 0.08) at 72 h after the onset of treatment. Ovulation rates were 5.6 +/- 0.8 and 3.3 +/- 0.8 in the respective groups (P < 0.05). The number of transferable embryos was 1.8 +/- 0.5 and 0.3 +/- 0.2 in the respective groups (P < 0.05). Short luteal phases (相似文献   

Rapid recovery of estrogen-induced pituitary gonadotropin surges after luteectomy in rhesus monkeys

In the presence of a functional corpus luteum, positive estrogen feedback on the surge modes of gonadotropin secretion is blocked in rhesus monkeys. We investigated the effects of luteectomy (Lx) on the time required for recovery of pituitary responsiveness (LH/FSH surges) to positive estrogen feedback. Estradiol-17 beta-3- benzoate (EB, 50 microgram/kg sc) was given: 1) 24th prior to, 2) the day of, or 3) 24 h after luteal ablation. Daily measurements of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17 beta (e2) and progesterone (P) were made on each monkey for 5 days. Serum P fell to undetectable levels within 24 h after Lx, whereas E2 levels in circulation peaked within 24h after injection of EB. Among early follicular phase monkeys, this EB treatment results in typical midcycle type LH/FSH surges within 48h. Lx alone was not soon followed by significant changes in pituitary gonadotropin secretion. When circulating P levels were undetectable the pituitary responded fully to EB; that is, typical midcycle type FSH/LH surges occurred. When serum P was in the midst of declining after Lx, gonadotropin surges were present, but attenuated. However, when P levels remained elevated for more than 24 h after EB injection, the surge modes of FSH/LH secretion remained fully blocked. These results demonstrate that the suppressive influence of luteal secretions (principally progesterone) on positive estrogen feedback regulation of the surge modes of pituitary gonadotropin secretion is quite transient in these primates.     

Effects of bovine follicular fluid inhibin on serum gonadotrophin concentrations in ewes during oestrus

Experiments were conducted with ewes to investigate the effects of an enriched bovine follicular fluid inhibin preparation (INH) on gonadotrophin secretion after the onset of oestrus. Administration of INH (10 mg) 1 h after the onset of oestrus did not significantly alter the preovulatory FSH and LH surges or the second FSH peak. To determine the effects of INH on the second FSH surge, ewes were treated with saline (N = 7) or INH (N = 10) at 4 h (10 mg) and 24 h (5 mg) after the peak of the preovulatory LH surge. The second FSH surge was delayed about 24 h (P less than 0.05) in ewes treated with INH; however, the delay did not alter the interval to the next oestrus. In a third experiment, 16 ewes were assigned to 4 groups in a 2 x 2 factorial with the main effects being ovariectomy at 4 h and INH treatment (10 mg) at 4, 20 and 36 h after the peak of the LH surge. Controls received sham ovariectomy and saline injection as appropriate. Ovariectomy resulted in a rapid increase in serum FSH but not LH and this was delayed (P less than 0.05) by INH treatment. These results indicate that inhibin has a selective inhibitory action on FSH secretion in ewes and suggests that the second FSH surge results from increased basal FSH secretion due to decreased endogenous inhibin levels.     

Ovarian and endocrine responses to prostaglandin F2alpha (PGF2alpha) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F(2alpha) (PGF(2alpha)) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF(2alpha) (15 mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF(2alpha) treatment (2.3+/-0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7+/-0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF(2alpha) injection (3.0+/-0.6 ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF(2alpha) treatment (2.0+/-0.3 ovulations/ewe; P>0.05). The mean interval from PGF(2alpha) to emergence of the next follicular wave (1.0+/-0.4 and 4.0+/-0.0 d, respectively; P<0.001) and the interval from PGF(2alpha) treatment to the next FSH peak (0 and 3.5+/-0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7+/-0.2, and six ewes ovulated both before and after the onset of estrus (3.0+/-0.5 ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1+/-0.3 or 5.5+/-0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF(2alpha) at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF(2alpha)-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.     

Role of increased estradiol on altering the follicle diameters and gonadotropin concentrations that have been reported for double-ovulating heifers

During the preovulatory period in heifers that ovulate from two compared to one follicle, circulating concentrations of estradiol-17β (E2) are greater, diameter of follicles and concentration of FSH are reduced, and the LH surge occurs sooner. The effect of increased E2 on the reported characteristics of double ovulation was studied by treating heifers with 0.07 mg E2, 0.09 mg E2, or vehicle in four treatments at 6-h intervals (n=6 heifers/group), beginning at the time of expected follicle deviation (largest follicle, 8.5mm). There were no significant differences on follicle diameters or hormone concentrations between the 0.07 and 0.09 mg E2 groups, and heifers were combined into one E2 group (n=12). The E2 treatments induced concomitant preovulatory surges in LH and FSH at 34.0 ± 2.6h after first treatment, compared to 57.6 ± 4.5h in the vehicle group (P<0.0002). The E2 treatments did not affect FSH concentrations during the preovulatory gonadotropin surge. The diameter of the preovulatory follicle at the LH peak was smaller (P<0.0001) in the E2-treated group (10.2 ± 0.2mm) than in the vehicle group (13.1 ± 0.6mm). The hypothesis was not supported that the previously reported increase in circulating E2 in heifers with double preovulatory follicles accounts for the reported lesser concentrations in the preovulatory FSH surge in heifers with double ovulations. Hypotheses were supported that the reported earlier occurrence of the preovulatory LH surge and smaller preovulatory follicles in heifers with double ovulations are attributable to the reported increase in E2 from the double preovulatory follicles.