Response of the 1-5 day-aged ovine corpus luteum to prostaglandin F2alpha

The hypothesis that, in the ewe, prostaglandin (PG) F2alpha administration on day 3 after ovulation is followed by luteolysis and ovulation was tested using 24 animals. The ewes were treated with a dose of a PGF2alpha analogue (delprostenate, 160 microg) on days 1 (n=8), 3 (n=8) or 5 (n=8) after ovulation, was established by transrectal ultrasonography. Daily scanning and blood sampling were performed to determine ovarian changes and progesterone serum concentrations by radioinmunoassay. The treatment induced a sharp decrease of progesterone concentrations followed by oestrus and ovulation in all ewes treated on days 3 and 5 and in one ewe treated on day 1 (8/8, 8/8, 1/8; P<0.05). Seven ewes treated on day 1 did not respond to PGF2alpha treatment and had an inter-ovulatory cycle of normal length (17.4 +/- 0.5 days). However, the profile of progesterone concentrations during the cycle of these ewes was delayed 1 day (P<0.05) compared with a control cycle. The overall interval between PGF2alpha and oestrus for the 17 responding ewes was 42.4 +/- 2.3 h. In 15 of these ewes the ovulatory follicle was originated from the first follicular wave and the ovulation occurred at 60.8 +/- 1.8 h after PGF2alpha treatment. The other two responding ewes ovulated an ovulatory follicle originated from the second follicular wave between 72 and 96 h after treatment. These results support the hypothesis and suggest that refractoriness to PGF2alpha of the recently formed corpus luteum (CL) may be restricted to the first 1-2 days post-ovulation.     

An ultrasonographic study of luteal function in breeds of sheep with different ovulation rates

Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n = 12 and prolific pure-bred Finn sheep, n = 7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 +/- 0.2 and 5.3 +/- 0.2 mm, respectively; P < 0.001). The mean volume of luteal structures was higher (P < 0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0 = day of ovulation). This accounted for the higher (P < 0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 +/- 0.3 and 1.7 +/- 0.2, respectively; P < 0.05). Mean serum progesterone concentrations were higher (P < 0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r > or = 0.40, P < 0.02), and during luteal growth and regression (r > 0.60, P < or = 0.00001) but not during mid-cycle in white-faced ewes (r = 0.16; P = 0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P < 0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P = 0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P = 0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.     

LH and FSH concentration and follicular development in Nellore heifers submitted to fixed-time artificial insemination protocols with different progesterone concentrations

Nine heifers were pre-synchronized (PGF2α, 12 days) and assigned into three groups with 6 repetitions each: (1) CL (～8 days old, n=13); (2) DIB+CL (n=18); (3) DIB+EB (150 μg of PGF2α and 2mg estradiol benzoate, n=18). After progesterone (P4) device removal (8 days) and/or final PGF2α, heifers were injected with either GnRH or EB in a 3×2 factorial totalling 49 observations (5 were excluded). The blood sampling schedule: every 12 h during P4 period; for LH pulse frequency on Days 3-5, every 15 min for 6 h during P4 period; after P4 removal and EB treatment, samples were collected every 3 h for 24 h or after GnRH every 1 h for 10 h. Ovarian follicle number and diameter were evaluated by ultrasonography every 12 h until the last blood sample and then 24 h and 48 h later. After device insertion (12 h), the DIB+CL group had a lesser LH concentration than the DIB+EB group. After 36 h, all DIB+CL-treated heifers had less LH than CL-heifers, and after 60 h, the DIB+EB group had less LH than the CL-group. Considering all P4 groups combined, LH peak amplitude was greater after GnRH compared to EB treatment but total area of LH peak amplitude and time to first peak was less. The CL-group had fewer follicles and a greater largest follicle diameter than DIB+CL and DIB+EB groups. When treated with EB, the DIB+CL group had a lesser ovulation rate at 24 h than the CL- and DIB+EB-groups. Fixed time artificial insemination (FTAI) protocols promoted a pre-ovulatory LH peak, independent of previous exposure to the DIB coupled with a CL or not. The progesterone excess interfered with FSH and LH secretion, follicular development and ovulation within 24 h.     

Duration of oestrus, ovulation rate, time of ovulation and plasma LH, total oestrogen and progesterone in Galway adult ewes and ewe lambs

The mean duration of oestrus, ovulation rate, duration of the preovulatory LH discharge, time interval between sponge removal and beginning of the LH discharge, total LH discharged, maximum LH value observed and the concentration of progesterone in the peripheral plasma during the luteal phase of the oestrous cycle was similar in Galway adult ewes and 8-month-old ewe lambs after treatment with intravaginal sponges containing 30 mg cronolone for 12 days and injection of 500 i.u. PMSG. The interval between sponge removal and the onset of oestrus was shorter for adults than for ewe lambs; the interval between the onset of oestrus and the beginning of the LH discharge was longer in adults. During the period 12-36 h after sponge removal the mean plasma total oestrogen concentration was significantly higher in lambs than in adults. In a separate study of the time of ovulation in Galway ewe lambs given the same progestagen-PMSG treatment, ovulation did not occur in any lamb before 17 h after the onset of oestrus and the majority ovulated close to the end of oestrus.     

Comparison of the effect of natural mating, LH, and GnRH on interval to ovulation and luteal function in llamas

Gonadotropins and GnRH have been used to electively induce ovulation in llamas and alpacas, but critical evaluation of the natural interval to ovulation after mating has not been performed nor has a direct comparison of the effects of natural mating versus hormone treatments on this interval and subsequent luteal development. The objectives of this study were to compare the effects of hormonal treatments and natural mating on ovulation induction, interval to ovulation, and luteal development in llamas. The ovaries of llamas were examined by transrectal ultrasonography once daily. Llamas with a large follicle were assigned randomly to be: (1) mated with an intact male (mated; n=10); (2) given 5 mg of LH im (LH; n=11); or (3) 50 microg of GnRH im (GnRH; n=10). Ultrasound examinations were performed every 4h from treatment (day 0) to ovulation and thereafter once daily for 15 consecutive days to monitor CL growth and regression (n=5 per group). Plasma progesterone concentrations were measured at days 0, 3, 6, 9, and 12 after treatment to evaluate CL function. The size of the largest preovulatory follicle at the time of treatment did not differ among groups (11+/-0.6, 10.5+/-0.8, 11.8+/-0.9 mm, for mated, LH, and GnRH groups, respectively; P=0.6). No differences were detected among groups (mated, LH, and GnRH) in ovulation rate (80%, 91%, 80%, respectively; P=0.6), or interval from treatment to ovulation (30.0+/-0.5, 29.3+/-0.6, 29.3+/-0.7h, respectively; P=0.9). Similarly, no differences were detected among groups (mated, LH, and GnRH) in maximum CL diameter (14.2+/-0.3, 13.2+/-0.5, and 13.0+/-0.7 mm, respectively; P=0.5), the day of maximum CL diameter (7.6+/-0.2, 7.6+/-0.2, and 7.4+/-0.4 mm, respectively; P=0.6), or the day on which the CL began to regress (12.3+/-0.3 [non-pregnant, n=3], 11.8+/-0.6, 12.2+/-0.4, respectively; P=0.4). The diameter of the CL and plasma progesterone concentrations changed over days (P<0.0001) but the profiles did not differ among groups. In summary, ovulation rate, interval to ovulation, and luteal development were similar among llamas that were mated naturally or treated with LH or GnRH. We conclude that both hormonal preparations are equally reliable for inducing ovulation and suitable for synchronization for artificial insemination or embryo transfer program.     

Characterization of plasma progesterone concentrations for two distinct luteal morphologies in mares

Plasma progesterone concentrations in mares were determined in two experiments during the time that the luteal glands were detectable by transrectal ultrasonography. In both experiments, corpora lutea were classified into two tupes of morphologies based on their ultrasonic appearance: centrally nonechogenic luteal glands (fluid-filled) and uniformly echogenic luteal glands (non-fluid-filled). In Experiment 1, daily blood samples were taken from horse mares during August through October and May through July. There were no significant effects of season or luteal morphology on progesterone concentration. There was a significant main effect of day, but no day-by-season or day-by-morphology interactions. Progesterone increased significantly between Days 1 and 3 (mean progesterone concentration, 2.5 vs 5.2 ng/ml, respectively), between Days 3 and 4 (5.2 vs 7.8 ng/ml), and between Days 4 and 5 (7.8 vs 11.0 ng/ml). Progesterone did not decrease significantly until between Days 11 and 15 (11.6 and 6.1 ng/ml). Subsequent decreases occurred between Days 15 and 16 (6.1 vs 3.9 ng/ml), and Days 16 and 17 (3.9 vs 2.5 ng/ml). In Experiment 2, blood samples were obtained from pony mares at 1 2 - h intervals for 3 h before and 2 h after the defined onset of luteal development (end of evacuation of the ovulatory follicle). Additional blood samples were taken at 5, 8 and 12 h after the onset of luteal development, and thereafter at 12-h intervals for 5d. There were no significant differences between centrally nonechogenic luteal glands (n = 7) and uniformly echogenic luteal glands (n = 5) during the first 5 d of luteal development. There was no time-by-morphology interaction, but there was a significant time effect. The first significant increase in progesterone concentration occurred between Hours 12 and 24 (0.5 vs 1.1 ng/ml). Additional increases were detected between Hours 24 and 36 (1.1 vs 2.6 ng/ml), Hours 36 and 48 (2.6 vs 4.3 ng/ml), Hours 48 and 60 (4.3 vs 6.1 ng/ml), Hours 60 and 72 (6.1 vs 9.4 ng/ml), and Hours 72 and 96 (9.4 vs 13.8 ng/ml). The hypothesis was supported that fluid-filled corpora lutea do not differ from non-fluid-filled corpora lutea with regard to progesterone production.     

Luteinizing hormone receptors and progesterone content in porcine corpora lutea after prostaglandin F2 alpha

The effect of prostaglandin F2 alpha (PGF2 alpha) on luteinizing hormone (LH) receptors, weight and progesterone content of corpora lutea (CL), and serum progesterone concentrations was studied in gilts. Fifteen gilts were hysterectomized between Days 9 to 11 of the estrous cycle. Twelve gilts were injected i.m. with 10 mg of PGF2 alpha and 3 with saline on Day 20. Ovaries were surgically removed from each of 3 gilts at 4, 8, 12 and 24 h following PGF2 alpha treatment and from the 3 control gilts 12 h following saline injection. Jugular blood samples for progesterone analysis were collected from all gilts at 0, 2 and 4 h following treatment and at 8, 12 and 24 h for gilts from which ovaries were removed at 8, 12 and 24 h, respectively. Mean serum progesterone and CL progesterone concentrations decreased within 4 h after PGF2 alpha treatment (P less than 0.05) and remained low through 24 h after treatment. The number of unoccupied LH receptors decreased by 4 h (P less than 0.05) and this trend continued through 24 h. There were no differences in luteal weight or affinity of unoccupied LH receptors of luteal tissue at 4, 8 12 and 24 h after PGF2 alpha when compared to luteal tissue from controls. These data indicate that during PGF2 alpha-induced luteolysis in the pig, luteal progesterone, serum progesterone concentrations and the number of LH receptors decrease simultaneously.     

Estradiol benzoate given 0 or 24 h after the end of a progestagen treatment in postpartum suckled beef cows

The objective of Experiment 1 was to compare the effects of estradiol benzoate (EB) given 0 or 24h after the end of a progestagen treatment on ovulation and CL formation in anestrous cows. Twenty cows were treated with an intravaginal sponge containing 250 mg of medroxiprogesterone acetate (MPA). At sponge insertion, each cow received 3 mg EB and 10 mg MPA im. At device removal, cows received 0.7 mg EB either at that time (EB0) or 24h later (EB24). Ultrasound examinations and blood sampling to determine plasma progesterone concentrations were performed to detect ovulation and CL formation. Ovulation occurred in 77.8 and 81.8% cows in the EB0 and EB24 groups, respectively. Diameter of the ovulatory follicle (EB0 = 10.9 +/- 0.5mm; EB24 = 12.1 +/- 0.8 mm; P = 0.26) and the interval from sponge removal to ovulation (median = 3 days; P = 0.64) did not differ between treatments. Among the cows that ovulated (n = 16), short-lived CL were present in 2/7 and 2/9 cows in the EB0 and EB24 groups, respectively. Plasma progesterone concentrations and CL area did not differ between treatments (P > 0.05). In Experiment 2, cows were treated with the same protocol as in Experiment 1, but at sponge withdrawal all cows received 250 microg cloprostenol and timed artificial insemination (TAI) was performed 48 h after sponge removal. In Replicate 1 (n = 204 multiparous cows), pregnancy rates were 45.0 and 47.5% for EB0 and EB24, respectively (P > 0.05). In Replicate 2 (n = 69 primiparous cows) pregnancy rate did not differ between EB0 and EB24 (51.4% versus 52.9%). In conclusion, EB given 0 or 24h after the end of a progestagen treatment had the same effect on ovulation rate, time to ovulation, diameter of the ovulatory follicle, incidence of short-lived CL, luteal tissue area, and plasma progesterone concentrations of normal lifespan CL, and pregnancy rate after TAI in suckled beef cows.     

Relationship between ultrasonic characteristics of the corpus luteum, plasma progesterone concentration and early pregnancy diagnosis in Friesian mares

The purpose of the present study was to evaluate the change in cross-sectional area of the early corpus luteum (CL) and progesterone production in relation to subsequent pregnancy diagnosis. The cross-sectional area of the CL of 75 Friesian brood mares was measured by ultrasonography on Day 1 or 2 and Day 8 or 9 after ovulation. The change in cross-sectional area was expressed in a volume ratio. Plasma progesterone concentrations were measured on Days 8 to 9, and ultrasonography to determine pregnancy status was carried out on Day 17. The data obtained were analyzed by using a multiple logistic regression model. There were significant differences in the age, volume ratio and progesterone concentration between pregnant and nonpregnant mares. Pregnancy on Day 17 was related to the change in size of the CL up to Days 8 to 9 and progesterone concentration on Days 8 to 9. These differences between pregnant and nonpregnant mares might reflect the first luteal response to pregnancy.     

Milk and Serum Progesterone Levels in Mares after Ovulation

Twenty-four Finnhorse mares were examined by rectal palpation and ultrasonography every 6 h during late oestrus to determine the time of ovulation. Milk and serum samples were collected every 6 h after the detected ovulation for progesterone analysis. The progesterone rises took place within 0–54 h and 0–60 h after ovulation, in milk and serum, respectively. Statistically significant differences (p < 0.05) in progesterone levels were observed for the first time 12–18 h and 18–24 h after ovulation, in serum and milk, respectively, as compared to progesterone levels 0–6 h after ovulation.     

Progesterone and follicular changes in postpartum noncyclic dairy cows after treatment with progesterone and estradiol or with progesterone, GnRH, PGF2alpha, and estradiol

A previous study showed that noncyclic dairy cows treated with 10 microg of GnRH and a progesterone-releasing CIDR insert on Day 0, 25 mg of PGF2alpha and CIDR removal on Day 7, followed by 1 mg estradiol benzoate on Day 9 for those cows that still had not shown estrus (CGPE program) had higher conception rate (47% vs. 29%) than cows treated only with CIDR and estradiol benzoate as above (CE program). This study was to investigate the mechanisms by which the CGPE program improved conception rate compared with the CE program. Sixteen noncyclic Holstein-Friesian cows were randomly assigned to 2 groups balanced for the size and growth pattern of the dominant follicles, which were determined by ultrasonography over a 3-d period. One group received the above CGPE treatment, and the other group received the CE treatment. Follicular and luteal development were monitored by daily ultrasonography. Blood samples were collected daily from Day -2 to Day 11, and thereafter milk samples were collected thrice weekly for a further 24 d. Blood and milk samples were analyzed for progesterone. The GnRH treatment induced ovulation in 7 of 8 cows, resulting in elevated (P<0.05) progesterone concentrations between Days 4 and 7 for cows in the CGPE group. All induced CL underwent luteolysis by 24 h after PGF2alpha treatment. Within 5 d of CIDR removal, 7 of 8 cows in both the CE and CGPE groups ovulated. The interval from emergence of the ovulatory follicle to ovulation was similar (P=0.32) but less (P<0.05) variable for the CGPE group (9.0+/-0.3 d) compared with the CE group (10.3+/-1.2 d). Progesterone concentration in milk samples was similar between the two groups up to 10 d after ovulation. In summary, the GnRH treatment induced ovulation or turnover of dominant follicles, induced a synchronized initiation of a new follicular wave, and increased the progesterone concentration from 4 d after treatment. These could be the reasons for the increased conception rate of cows treated with the CGPE program.     

Expression of ghrelin and the ghrelin receptor in different stages of porcine corpus luteum development and the inhibitory effects of ghrelin on progesterone secretion, 3β-hydroxysteroid dehydrogenase (3β-honestly significant difference (HSD)) activity and protein expression

Recent studies have suggested that ghrelin plays a direct role in controlling female reproduction. The aim of the present study was to investigate the mRNA and protein expression of ghrelin and its receptor (via real time PCR, Western blot and immunohistochemistry analysis, respectively) in porcine corpora lutea (CL) collected during early (CL1: 1-2 days after ovulation), middle (CL2: 7-10 after ovulation), and late luteal phase (CL3: 13-15 after ovulation). Ghrelin expression and concentration of both acylated and unacylated forms of ghrelin significantly increased during CL development. Immunohistochemistry analysis shown localization of ghrelin protein in the cytoplasm of large luteal cells. No changes in the expression of the ghrelin receptor were observed. Direct in vitro effects of ghrelin on progesterone (P4) secretion and 3-beta-hydroxysteroid dehydrogenase (3β-honestly significant difference (HSD)) activity, which were measured by the conversion of pregnenolone (P5) to P4, and 3β-HSD protein expression were then analyzed. To assess 3β-HSD activities, mature luteal cells were first cultured for 24 h with ghrelin at 100, 250, 500 and 1000 pg/mL with P5, or with aminoglutethimide (AMG). AMG is an inhibitor of CYP11A1-mediated hydroxylation; an addition of AMG and P5 enabled P4 production to serve as an index of 3β-HSD activity. Inhibitory effects of ghrelin on P4 secretion, 3β-HSD activity and protein expression were observed. In conclusion, the presence of ghrelin and its receptor in porcine corpora lutea and the direct inhibitory effects of ghrelin on luteal P4 secretion and 3β-HSD suggest potential auto/paracrine regulation by ghrelin in the luteal phase of ovary function.     

Regression and resurgence of the CL following PGF2alpha treatment 3 days after ovulation in mares

The present study was designed to characterize and compare the physiology and ultrasonographic morphology of the corpus luteum (CL) during regression and resurgence following a single dose of native prostaglandin F2alpha (PGF) given 3 days after ovulation, with a more conventional treatment given 10 days after ovulation. On the day of pre-treatment ovulation (Day 0), horse mares were randomly assigned to receive PGF (Lutalyse; 10 mg/mare, i.m.) on Day 3 (17 mares) or Day 10 (17 mares). Beginning on either Days 3 or 10, follicle and CL data and blood samples were collected daily until post-treatment ovulation. Functional and structural regression of the CL in response to PGF treatment were similar in both the Day 3 and 10 groups, as indicated by an abrupt decrease in circulating concentrations of progesterone, decrease in luteal gland diameter and increase in luteal tissue echogenicity. As a result, the mean +/- S.E.M. interovulatory interval was shorter (P < 0.0001) in the Day 3 group (13.2 +/- 0.9 days) than in the Day 10 group (19.2 +/- 0.7 days). Within the Day 3 group, functional resurgence of the CL was detected in 75% of the mares (12 of 16) beginning 3 days after PGF treatment, as indicated by transient major (6 mares) and minor (6 mares) increases (P < 0.05 and < 0.1, respectively) in progesterone. Correspondingly, mean length of the interovulatory interval was longer (P < 0.03) in mares with major resurgence (15.8 +/- 1.6 days) than in mares with minor (11.2 +/- 1.2 days) and no resurgences (13.5 +/- 0.3 days) in progesterone. Structural resurgence of the CL in the Day 3 group and functional and structural resurgence in the Day 10 group were not detected. In conclusion, PGF treatment 3 days after ovulation resulted in structural and functional regression of the CL and hastened the interval to the next ovulation, despite post-treatment resurgences in progesterone.     

Ovarian capillary blood flow in seasonally anoestrous ewes induced to ovulate by treatment with GnRH

The microsphere technique was used to obtain estimates of ovarian capillary blood flow near ovulation, in 8 seasonally anoestrous ewes, which were induced to ovulate by GnRH therapy. Plasma progesterone concentrations were monitored in jugular blood sampled between Days 4 and 7 after the onset of the preovulatory LH surge. The ewes were then slaughtered. Three of the ewes were treated with a single injection of 20 mg progesterone before GnRH therapy. In these ewes and 1 other, plasma progesterone values increased after ovulation and reached 1.0 ng/ml on Day 7 following the preovulatory LH surge (normal, functional CL), whilst in the other 4 ewes progesterone concentrations increased initially then declined to 0.5 ng/ml by Day 7 (abnormal CL). In the ewes exhibiting normal luteal function, the mean ovarian capillary blood flow was significantly greater (P less than 0.01) than that for ewes having abnormal luteal function. Irrespective of the type of CL produced, capillary blood flow was significantly greater (P less than 0.05) in ovulatory ovaries than in non-ovulatory ovaries. These findings indicate that the rate of capillary blood flow in ovaries near ovulation may be a critical factor in normal development and maturation of preovulatory follicles and function of subsequently formed CL.     

Relationship between maternal plasma progesterone concentration and interferon-tau synthesis by the conceptus in cattle

The objective of this study was to determine the relationship between maternal progesterone concentration and conceptus synthesis of interferon-tau as an index of conceptus viability at the time of maternal recognition of pregnancy. Heifers of mixed beef breeds were randomly assigned to receive 1 of 2 treatments: 1) intramuscular injection of 1500 IU hCG on Day 5 after artificial insemination (AI; n = 12) or 2) intramuscular injection of saline on Day 5 after AI (n = 17). Ovaries were scanned daily by transrectal real-time ultrasonography. Progesterone concentrations were determined from daily blood samples collected from the jugular vein. Heifers were slaughtered on Day 18 after AI and conceptus tissues were collected. These were incubated individually at 37 degrees C in RPMI medium, and supernatant collected after 24 h. Conceptus secretory products in the supernatant were analyzed for interferon concentration by antiviral assay using vesicular stomatitis virus. Transrectal ultrasonography showed all heifers that received hCG had at least 1 extra corpus luteum (CL) in addition to the spontaneous CL formed from the previous ovulation (10 with 2 CL, 2 with 3 CL). A significant increase in plasma progesterone concentration was detected in pregnant heifers treated with hCG (n = 9) vs pregnant control heifers (n = 11; P < 0.001). There was a tendency for an increase (P = 0.059) in synthesis of interferon-tau by conceptuses from hCG-treated heifers compared to control heifers. Maternal plasma progesterone concentrations were correlated with interferon-tau production by the conceptuses (r = 0.593, P < 0.006), suggesting that higher maternal progesterone may provide a more suitable environment for the developing conceptus.     

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.     

Administration of gonadotropin-releasing hormone during metoestrus in cattle: influence on luteal function and cycle length

Gonadotropin-releasing hormone (GnRH) has been used to warrant the success of artificial insemination by accurately timing occurrence of ovulation. In practical conditions, GnRH may be administered too late, after ovulation, with an eventual reduction in pregnancy rate. The aim of this study was to investigate whether GnRH administration after ovulation would have a negative effect on luteal function.Three cows and six heifers of the Finnish Ayrshire breed were used. Oestruses were synchronised. After detection of ovulation, one of the following treatments was implemented: gonadorelin (250 microg, i.m.) at either 0-24h (T1) or 24-48h (T2) post-ovulation or control (no gonadorelin, C). Every animal was assigned once to each of these three manipulations. Ultrasonography was performed on days 1, 4 or 5, 7 or 8, 11 or 12, 14 or 15 post-ovulation and daily from the beginning of the next oestrous signs until ovulation (day 0=day of ovulation). Blood samples for progesterone (P(4)) determinations were collected daily from day 1 after the occurrence of ovulation until recording of the next oestrus. Administration of GnRH during metoestrus did not induce ovulation of either large or small follicles and, thus, no accessory corpora lutea (CL) were formed. In T1, on day 14 or 15, the diameter of CL was 1.3+/-0.3mm smaller than in C (P<0.01), but no differences were found either on days 11 or 12 or on the same days of the T2 and C treatments. No significant differences in levels or profiles of P(4) curves were found between GnRH treatments and control. Neither had the treatments any effects on the length of the oestrous cycle. In conclusion, GnRH treatment during metoestrus does not seem to alter subsequent luteal function and, thus, this does not explain previous reports of reduced fertility post-treatment.     

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   

Maintenance of the corpus luteum after uterine transfer of trophoblastic vesicles to cyclic cows and ewes

One or two trophoblastic vesicles (0.4-2 mm diam.) from cow (Day 14) or ewe (Day 11-13) embryos without their disc were transferred, after culture for 24 h, into recipients. Each vesicle was transferred into the uterine horn ipsilateral to the CL by the cervical route in heifers and surgically in ewes on Day 12 of the oestrous cycle. In cows, daily measurements of plasma progesterone concentrations and checks for return to oestrus showed that the CL was maintained in 8 out of 12 recipients. These 8 cows had 25- to 37-day cycles while 4 recipient heifers returned to oestrus normally. Three recipients with an extended cycle were slaughtered. The dissected uterus showed that trophoblastic vesicles had developed in the uterine horns. In ewes, the serum progesterone curve, determined in each recipient, showed that the CL was maintained in 7 out of 12 recipients. These 7 ewes had 20- to 54-day cycles and the other 5 ewes had a normal cycle of 15-19 days comparable to that of 17.0 +/- 0.5 days for the 6 control ewes. Whenever the CL was maintained, high blood progesterone levels were followed by rapid luteolysis. In cattle and sheep, therefore, a trophoblastic vesicle transferred into the uterus can develop in vivo, secreting the embryonic signals when there is no embryonic disc control and transforming the cyclic CL into a CL of pregnancy in about 60% of the cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of oestradiol treatment during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span in anoestrous ewes

In sheep, induction of ovulation during anoestrus is accompanied by a high incidence of short luteal phases, though pre-treatment with progesterone can overcome this problem. We have investigated the effects of supplementing oestradiol during GnRH-induced ovulation on subsequent PGF2alpha release and luteal life span. Thirty anoestrous crossbred ewes received 250 ng GnRH i.v. at 2 h intervals for 48 h to induce ovulation either alone (group 1; n=10) or in association with either an i.m. injection of 20 mg progesterone 3 days earlier (group 2; n=10) or 3 i.m. injections of 10 microg oestradiol at 8 h intervals on the second day of GnRH treatment (group 3; n=10). Laparoscopy, performed 3 days following GnRH to confirm ovulation and 8 days later, coupled with plasma progesterone analysis were used to determine luteal life span. On day 4 following GnRH, plasma samples were collected at 20 min intervals for 8 h to monitor PGF2alpha release. One ewe from group 1 failed to ovulate and was excluded from further analysis. All groups showed an increase (P<0.01) in plasma oestradiol during GnRH treatment, with group 3 showing a marked (P<0.001) increase over that seen in the other two groups. In group 1 there were 1.4+/-0.2 PGF2alpha episodes/ewe/8 h. In group 2, pre-treatment with progesterone caused the complete inhibition of PGF2alpha episodes (0 episodes/ewe/8 h) while in group 3, treatment with oestradiol resulted in a significant reduction (0.3+/-0.1 episodes/ewe/8 h) compared with group 1 (P<0.01). In group 1, 9/9 ewes exhibited short cycles compared with 2/10 ewes in group 2 (P<0.01). In group 3 the proportion of ewes showing short cycles 7/10 ewes was not significantly different from the other groups. While treatment with oestradiol caused a significant attenuation of PGF2alpha release, this was associated with only a partial reduction in the incidence of short cycles.