Effect of exogenous FSH on estrus, ovulation and endogenous hormone release in dairy cows

Fifteen lactating Holstein cows were randomly allotted to receive either 0 mg (group 0), 32 mg (group 1) or 50 mg (group 2) porcine follicle stimulating hormone (FSH-P) injected in 10 fractions at 12 hr intervals beginning on day 9 of the estrous cycle. All cows received 25 mg prostaglandin (PG) on day 11. Jugular blood samples were collected from cows in all groups at 6 hr intervals beginning on day 7 and continuing through expression of estrus. Mean duration to occurrence of estrus and preovulatory LH surge after PG injection was reduced (P<.05) by injection of FSH-P. Mean number of ovulations increased (P<.05) progressively with increased dose of FSH-P. Mean peripheral progesterone declined more uniformly in FSH-P treated cows after PG and increased earlier (P<.05) after estrus in group 2 cows compared to group 0 and 1 cows. Mean plasma estradiol-17beta elevated (P<.05) after PG injection in both FSH-P-treated groups compared to group 0 cows. Both LH and FSH increased (P<.05) for 36 hr after initiation of FSH-P injection in groups 1 and 2, then declined until after PG injection. Peak LH and FSH occurred more uniformly following PG in treated cows. Results indicate that FSH-P increased endogenous gonadotropin release, estradiol-17beta, ovulation rate and reduced duration to estrus and preovulatory gonadotropin release after PG. Injection of 50 mg FSH-P increased plasma estradiol-17beta and ovulation rate compared to injection of 32 mg FSH-P.     

Ovulatory response, and plasma concentrations of luteinizing hormone and progesterone following administration of synthetic mammalian or chicken luteinizing hormone-releasing hormone relative to the first or second ovulation in the sequence of the domestic hen

Experiments were conducted to investigate hypophyseal and follicular competency at two distinct stages of the hen's egg laying sequence: 1) 14 h prior to the first (C1) ovulation of a sequence (27 h following the previous ovulation); and 2) 14 h prior to the second (C2) ovulation of a sequence (13 h following the previous ovulation). When a single dose of mammalian luteinizing hormone-releasing hormone (mLHRH) or chicken luteinizing hormone-releasing hormone (cLHRH) was injected 14 h prior to a C1 ovulation, premature ovulation was induced in 19 of 20 hens. In contrast, ovulation was premature in only 1 of 20 hens when mLHRH or cLHRH was injected 14 h prior to a C2 ovulation. There was no difference between the two stages of the sequence in the amount of luteinizing hormone (LH) released for up to 60 min following a single i.v. injection of 20 micrograms mLHRH. However, only prior to a C1 ovulation did LH levels further increase to reach preovulatory concentrations. By contrast, progesterone (P4) concentrations were increased within the first 60 min to a lesser extent in hens injected prior to a C2 ovulation compared to a C1 ovulation. In C2-injected birds, P4 fell to levels that were not different from vehicle-injected controls by 45 to 60 min following injection, whereas P4 secretion was maintained in hens injected prior to a C1 ovulation. We suggest that the lack of sustained LH secretion following treatment with either species of LHRH 14 h prior to a C2 ovulation is related to follicular immaturity with respect to ability to produce and secrete P4. At the dosage administered, there was no difference in the ability of mLHRH compared to cLHRH to release LH at either stage of the sequence. Finally, two successive injections of mLHRH at 14 and 13 h prior to a C2 ovulation induced premature ovulation in 6 of 11 hens. It is suggested that LH, and possibly P4, exerts a priming effect on the largest preovulatory follicle to initiate fully potentiated P4 production and secretion.     

The influence of estradiol-17beta and progesterone on peripheral serum concentrations of luteinizing hormone and follicle stimulating hormone in the ovariectomized ewe

Serum gonadotropin concentrations were high and variable and fluctuated episodically in short and long term ovariectomized ewes. Treatment with solid silastic implants releasing progesterone (serum levels 1.81 +/- 0.16 ng/ml) had no consistent effect. Treatment with implants releasing estradiol-17beta significantly depressed mean serum gonadotropin concentrations and peak height to values usually seen in intact ewes. This occurred regardless of implant size and serum estradiol-17beta concentrations (range 11 +/- 0.3 pg/ml to 98 +/- 12.8 pg/ml). Progesterone and estradiol-17beta together significantly depressed the frequency of peaks in LH concentration. Following progesterone removal, 95% of the ewes treated with progesterone and estradiol-17beta implants experienced a transient increase in serum LH concentrations similar to the preovulatory surge in intact ewes. Eighty-four percent of the LH surges were accompanied by a surge in serum FSH concentrations. However, following progesterone removal, 5.1 +/- 2.1 FSH surges were observed over six days. Gonadotropin surges occurred regardless of estradiol-17beta implant size and with or without the influence of supplemental estradiol-17beta.     

Frequency of luteinizing hormone surges and egg production rate in turkey hens

Whether the interval between preovulatory surges of LH was different between lines of turkey hens with either poor (RBC3 line, peak at 55%) or excellent rate of egg production (Egg line, peak at 85%) was examined. Laying hens were cannulated and bled hourly for 10 days at peak of production. A constant light photoschedule was used to avoid diurnal masking of innate circadian rhythms. The mean interval between LH surges in the RBC3 line was longer than in the Egg line and had a higher coefficient of variation. A few longer LH surge intervals (72 h) were found in some RBC3 line hens (2 of 7 hens), but none were found in Egg line hens (0 of 11 hens). All progesterone (P4) surges were coupled with LH surges, but not all LH-P4 surges were coupled with ovipositions (blind LH-P(4) surges). The percentage of blind LH-P4 surges was not different between lines. The baseline concentration of LH was higher in Egg line than RBC3 line hens, but LH surge amplitude, and surge duration were not different. The baseline and surge amplitude concentrations of P4 were not different between lines, nor was the concentration of estradiol-17beta. The longer interval between LH surges was the major factor tested that was associated with the poorer egg production rate in RBC3 line hens in comparison to Egg line hens. A higher incidence of blind LH surges further contributed to lower egg production in RBC3 line turkey hens.     

Expression of messenger RNA for gonadotropin receptor in the granulosa layer during the ovulatory cycle of hens.

The present experiments were conducted to evaluate the mRNA levels of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) in granulosa layers during the ovulatory cycle of hens, in relation to the release of LH and steroid hormones. After the release of LH, progesterone (P4) and estradiol-17beta (E2), found 4-5 h before ovulation, LHR and FSHR mRNA levels were observed to decrease in the granulosa layers of the largest (F1) and second largest (F2) preovulatory follicles, with the greatest in the LHR mRNA level of F1. P4 concentrations in the granulosa layers of F1 and F2 increased 4-5 h before ovulation, with greater in F1 than in F2. F2 concentrations in the theca layers were greater in F2 than in F1 throughout the ovulatory cycle. Also, the injection of ovine LH caused decreases in the mRNA levels of LHR and FSHR in the granulosa layers. However, these decreases were abolished by the injection of aminoglutethimide, an inhibitor of steroid synthesis. These results suggest that in hen granulosa cells, the mRNA levels of not only LHR but also FSHR are down-regulated by LH and the down-regulation may be mediated steroid hormones.     

Gonadotropin-releasing hormone at estrus: luteinizing hormone, estradiol, and progesterone during the periestrual and postinsemination periods in dairy cattle

Administering gonadotropin-releasing hormone (GnRH) improved conception rates in our previous studies. Our objective was to determine if the effect of GnRH was mediated through serum luteinizing hormone (LH) and/or by altered secretion of serum progesterone (P) and estradiol-17 beta (E) during the periestrual and post-insemination periods. Cattle were given either GnRH (n = 54) or saline (n = 55) at 72 h and inseminated artificially (AI) 80 h after the second of two injections of either prostaglandin F2 alpha or its analog, cloprostenol. Progesterone and E were measured in blood serum collected during 3 wk after AI (estrus) from 60 females. Blood was collected for LH determinations via indwelling jugular cannulae from 14 cows and 11 heifers. Collections were taken every 4 h from 32 to 108 h after the second PGF injection (PGF-2) (periestrual period) and at more frequent intervals during 240 min after administration of GnRH (n = 18) or saline (n = 7). Ten females had a spontaneous preovulatory LH surge before GnRH treatment (GnRH-spontaneous), whereas GnRH induced the preovulatory LH surge in six females. A spontaneous LH surge appeared to be initiated in two heifers at or near the time of GnRH treatment (spontaneous and/or induced). The remaining seven cows had spontaneous LH surges with no subsequent change in LH after saline treatment. Serum P during the 21 days after estrus was lower (p less than 0.05) in both pregnant and nonpregnant (open) cattle treated previously with GnRH compared with saline. Serum P during the first week after estrus was greater (p less than 0.01) and increased (p less than 0.05) more rapidly in saline controls and in GnRH-spontaneous cattle than in those exhibiting GnRH-induced or GnRH-spontaneous and/or-induced surges of LH. Conception rate of cattle receiving GnRH was higher (p = 0.06) than that of saline-treated controls. These data suggest that GnRH treatment at insemination initiated the preovulatory LH surge in some cattle, but serum P in both pregnant and open cows was compromised during the luteal phase after GnRH treatment. Improved fertility may be associated with delayed or slowly rising concentrations of serum progesterone after ovulation.     

Preovulatory secretion of progesterone, luteinizing hormone, and prolactin in 4-day and 5-day cycling rats

Timing of ovulation and changes in plasma progesterone, luteinizing hormone (LH), and prolactin (PRL) during periovulatory stages were determined in Holtzman rats exhibiting regular 4- or 5-day cycles under a daily artificial illumination from 0500 to 1900 h. The 5-day cycling rats ovulated between 0130 and 0930 h on estrus, whereas some of the 4-day cycling animals ovulated as early as about 0130 h and others as late as 1130 h on estrus. Onset time of preovulatory LH and progesterone surges was about 1500 h on proestrus in both the 4- and the 5-day cycling rats. Peak levels of plasma LH and progesterone were measured at 1700 to 1900 h on proestrus, while the first rises and peak values of plasma PRL were evident a few hours earlier than those of plasma LH in the rats with two cycle lengths. Plasma LH levels at 1900 h on proestrus as well as plasma progesterone levels at 1600 and 2300 h on proestrus and at 0130 and 0330 h on estrus were significantly lower in the 5-day cycling rats than in the 4-day cycling animals (p less than 0.05). In contrast, PRL levels from 1500 through 2300 h on proestrus remained consistently higher in 5-day cycling rats than in 4-day cycling rats, and significant differences in PRL levels between these rats were apparent at 1500, 1600, and 2100 h (p less than 0.05-0.01). Thus, these results demonstrate that the 5-day cycling rats exhibit the attenuated magnitude of LH surge accompanied by the augmented preovulatory PRL release, and that plasma progesterone levels reflect the magnitude of LH surge. A tentative working hypothesis concerning the etiology of the 5-day cycle has been proposed.     

Changes in peripheral levels of bioactive and immunoreactive inhibin, estradiol-17 beta, progesterone, luteinizing hormone, and follicle-stimulating hormone associated with follicular development in cows induced to superovulate with equine chorionic gonadotropin.

Changes in concentrations of bioactive and immunoreactive (ir-) inhibin, estradiol-17 beta, progesterone, LH, and FSH in peripheral blood were determined in cows induced to superovulate with eCG. The pattern of follicular growth was also characterized by daily ultrasonographic examination. Hormonal profiles and follicular development during the intact estrous cycle of the same animals before eCG treatment served as controls. Equine CG increased the number of follicles of various sizes (small, greater than or equal to 4 less than 7, medium, greater than or equal to 7 less than 10; large, greater than or equal to 10 mm in diameter) by 4 days after administration. The second growth of large follicles occurred within 1 day after superovulation. Inhibin bioactivity in jugular vein blood was detectable 48 h after eCG injection (44 h before LH peak), whereas it was not detected before administration of eCG or during control cycles. Circulating levels of bioactive inhibin further increased during the two waves of growth of large follicles. The highest activity of inhibin was noted at the time of the preovulatory LH peak (0 h). Thereafter, bioactivity of inhibin in peripheral plasma dropped from 0 to 24 h after the LH peak, and the activity increased again at 72 h compared to the value at -44 h. Plasma levels of ir-inhibin showed a pattern similar to changes in bioactive inhibin in the eCG-treated cows. Plasma concentrations of estradiol-17 beta also increased concomitantly with two waves of growth of large follicles. There was no correlation between plasma levels of progesterone and inhibin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Temporal relations between plasma concentrations of luteinizing hormone, follicle-stimulating hormone, estradiol-17beta, progesterone, prolactin, and alpha-melanocyte-stimulating hormone during the follicular, ovulatory, and early luteal phase in the bitch

Compared with other domestic animals, relatively little is known about the changes in, and temporal relations between, reproductive hormones around the time of ovulation in the domestic bitch. Therefore, plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17beta, progesterone, prolactin (PRL), and alpha-melanocyte-stimulating hormone (alpha-MSH) were determined one to six times daily from the start of the follicular phase until 5 days after the estimated day of ovulation in six Beagle bitches. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. A pre-ovulatory PRL or alpha-MSH surge was not observed. The pre-ovulatory FSH and LH surges started concomitantly in four bitches, but in two bitches the FSH surge started 12 h earlier than the LH surge. The FSH surge (110+/-8 h) lasted significantly longer than the LH surge (36+/-5 h). In contrast with the pre-ovulatory FSH surge, the pre-ovulatory LH surge was bifurcated in four of six bitches. The mean plasma LH concentrations before (1.9+/-0.4 microg/L) and after (1.9+/-0.3 microg/L) the LH surge were similar, but the mean plasma FSH concentration before the FSH surge (1.6+/-0.3 U/L) was significantly lower than that after the FSH surge (3.1+/-0.2 U/L). In most bitches the highest plasma estradiol-17beta concentration coincided with or followed the start of the pre-ovulatory LH surge. In five of the six bitches the plasma progesterone concentration started to rise just before or concurrently with the start of the LH surge. In conclusion, the results of this study provide evidence for the differential regulation of the secretion of LH and FSH in the bitch. In addition, the interrelationship of the plasma profiles of estradiol-17beta and LH suggests a positive feedback effect of estradiol-17beta on LH surge release. The start of the pre-ovulatory LH surge is associated with an increase in the plasma progesterone concentration in this species.     

Ability of progesterone to reverse anti-androgen (hydroxyflutamide)-induced interference with the preovulatory LH surge and ovulation in PMSG-primed immature rats

In Exp. 1, PMSG was injected to 26-day-old prepubertal rats to induce ovulations. On Day 2 (2 days later, the equivalent of the day of pro-oestrus) they received at 08:00 h 5 mg hydroxyflutamide or vehicle and at 12:00 h 2 mg progesterone or testosterone or vehicle. Animals were killed at 18:00 h on Day 2 or at 09:00 h on Day 3. Progesterone but not testosterone restored the preovulatory LH surge and ovulation in hydroxyflutamide-treated rats. In Exp. 2, 2 mg progesterone or testosterone were injected between 10:30 and 11:00 h on Day 2, to advance the pro-oestrous LH surge and ovulation in PMSG-primed prepubertal rats. Injection of hydroxyflutamide abolished the ability of progesterone to advance the LH surge or ovulation. Testosterone did not induce the advancement of LH surge or ovulation. In Exp. 3, ovariectomized prepubertal rats implanted with oestradiol-17 beta showed significantly (P less than 0.01) elevated serum LH concentrations at 18:00 h over those observed at 10:00 h. Progesterone injection to these animals further elevated the serum LH concentrations at 18:00 h, in a dose-dependent manner, with maximal values resulting from 1 mg progesterone. Hydroxyflutamide treatment significantly (P less than 0.003) reduced the serum LH values in rats receiving 0-1 mg progesterone but 2 mg progesterone were able to overcome this inhibition. It is concluded that progesterone but not testosterone can reverse the effects of hydroxyflutamide on the preovulatory LH surge and ovulation. It appears that hydroxyflutamide may interfere with progesterone action in induction of the LH surge, suggesting a hitherto undescribed anti-progestagenic action of hydroxyflutamide.     

Estrogen - Induced release of luteinizing hormone in prepubertal and postpubertal heifers

This experiment was designed to determine the age at which estradiol-17beta (E(2)) first induces a preovulatory-like surge of luteinizing hormone (LH) in prepubertal heifers. Responses of prepubertal animals 3 to 4 and 5 to 6 months of age were compared with those of postpubertal heifers that received 25 mg prostaglandin F(2)alpha at 0800 hr on day 15 of the estrous cycle. E(2) (500mug) induced surges of LH in 1 5 heifers 3 to 4 months of age, 3 3 heifers 5 to 6 months of age and 5 5 postpubertal heifers. Duration of response and interval between E(2) injection and peak of the response were longer in postpubertal heifers than in those 5 to 6 months old (P<0.10). Peak response and total amount of LH released were greater in animals 5 to 6 months old (P<0.10). Only one prepubertal heifer had elevated concentrations of progesterone following an LH surge. Four of 5 postpubertal heifers receiving E(2) and 3 of 4 postpubertal heifers receiving corn oil had corpora lutea and similar patterns of progesterone concentrations. We conclude that ability to release an LH surge in response to E(2) develops in heifers between 3 and 5 months of age, but that this induced surge does not cause ovulation.     

Effects of reducing the remating interval after parturition on the fertility and plasma concentrations of luteinizing hormone, prolactin, oestradiol-17 beta and progesterone in lactating domestic rabbits

Primiparous crossbred does were remated on Day 1 (n = 15) or 14 (n = 25) post partum and killed on Day 10 post coitum to assess their fertility. Blood samples were taken during the pre- (0-12 h post coitum) and post- (1-10 days post coitum) ovulatory periods and plasma was assayed for luteinizing hormone (LH), prolactin, oestradiol-17 beta and progesterone. Ovulation response was significantly greater (P less than 0.01) and ovulation rate significantly lower (P less than 0.001) in does mated on Day 1 than in those mated on Day 14 post partum. Does failing to ovulate on Day 14 post partum exhibited no preovulatory LH surge and had significantly lower (P less than 0.05) premating concentrations of oestradiol-17 beta and prolactin than those ovulating at this time. No significant differences in hormone concentrations were observed during the preovulatory period between does ovulating on Days 1 and 14 post partum, with the exception of oestradiol-17 beta. Concentrations of this hormone were significantly lower (P less than 0.01) in does mated on Day 1, at 1 h post coitum. We conclude that (i) fertility was affected by the remating interval after parturition, (ii) ovulation failure was associated with an absence of the preovulatory LH surge and a reduction in premating concentrations of oestradiol-17 beta and prolactin and (iii) the lower ovulation rate in early lactation was apparently caused by a reduction in ovarian competence to respond to the gonadotrophic stimulus.     

Temporal relationships among estrus, body temperature, milk yield, progesterone and luteinizing hormone levels, and ovulation in dairy cows

Estrous cycles of 10 postpartum cyclic Holstein cows were synchronized using prostaglandin f(2alpha) (PGF(2alpha)) given twice 12 d apart to study the relationship of the onset of estrus, body temperature, milk yield, luteinizing hormone (LH) and progesterone concentration to ovulation. Blood samples and body temperatures (vaginal and rectal) were taken every 4 h until ovulation, starting 4 h prior to the second PGF(2alpha) treatment. All cows were observed for estrus following the second administration of PGF(2alpha). Ultrasound scanning of the ovaries commenced at standing estrus and thereafter every 2 h until the disappearance of the fluid filled preovulatory follicle (ovulation). Two cows failed to ovulate and became cystic following the second PGF(2alpha) treatment. The remaining eight cows exhibited a decline in progesterone to <1.0 ng/ml within 28 h, standing estrus and a measurable rise (> 1.0 degrees C) in vaginal but not rectal temperature, and ovulated 90 +/- 10 h after the second PGF(2alpha) treatment. Onset of standing estrus, LH peak and vaginal temperature were highly correlated (P<0.05) with time of ovulation (0.82, 0.81 and 0.74, respectively). Intervals to ovulation tended to depend upon parity. Pluriparous (n = 4) and biparous (n = 4) cows ovulated within 24 and 30 +/- 3 h from the onset of standing estrus; 22 and 31 +/- 2 h from the LH peak; and 22 and 27 +/- 3 h from peak vaginal temperature (mean +/- standard error of the mean), respectively. The results indicated that the onset of standing estrus and rise in vaginal temperature are good practical parameters for predicting ovulation time in dairy cattle.     

Effects of indomethacin and aminoglutethimide phosphate in vivo on luteinizing-hormone-induced alterations of cyclic adenosine monophosphate, prostaglandin F, and steroid levels in preovulatory rat ovaries.

Changes in levels of cyclic adenosine monophosphate (cAMP), prostaglandin F (PGF), progesterone, testosterone, and estradiol-17beta, in preovulatory rat ovaries induced by exogenous luteinizing hormone (LH) have been measured. Ovarian cAMP reached maximal levels 15 min and 1h after LH administration by intravenous and intraperitoneal routes, respectively, and then declined to pre-LH levels by 8 h. Progesterone levels in ovaries and serum rose approximately in parallel with cAMP, but remained elevated throughout the 8-h sampling period. Ovarian testosterone increased to maximal levels 1 h after LH injection, followed by a rapid decline to below pre-LH levels. Ovarian estradiol-17beat concentrations declined steadily throughout the sampling period, reaching almost undetectable levels 8 h after LH treatment. Elevated ovarian PGF levels were observed only at the 4- and 8-h sampling times. Indomethacin treatment, 1 h before LH, prevented the LH-induced increase in ovarian PGF levels, depressed PGF values considerably in saline-injected controls but produced no significant inhibition of ovarian cAMP and progesterone levels. Aminoglutethimide phosphate depressed ovarian concentrations of all three steroids (progesterone, testosterone, and estradiol-17beta) to essentially undetectable levels, both in control and LH-injected rats, but did not alter the LH-induced changes in ovarian cAMP and PGF levels. These observations support the concept of cAMP as a mediator of the LH-induced alterations of ovarian steroidogenesis in vivo during the preovulatory period, but argue against an obligatory role of PGF in this process.     

Estradiol-induced blockade of ovulation in the cow: effects on luteinizing hormone release and follicular fluid steroids

Administration of 10 mg estradiol valerate (EV) to nonlactating Holstein cows on Days 16 of the estrous cycle prevented ovulation in 7 of 8 cows for 14 days post-injection. In these 7 cows, the timing of luteolysis and the luteinizing hormone (LH) surge was variable but within the normal range. At 14 days post-treatment, each of these cows had a large (greater than 10 mm) follicle, with 558 +/- 98 ng/ml estradiol-17 beta, 120 +/- 31 ng/ml testosterone, and 31 +/- 2 ng/ml progesterone in follicular fluid (means +/- SE). A second group of animals was then either treated with EV as before (n = 22), or not injected (control, n = 17) and ovariectomized on either Day 17, Day 18.5, Day 20, or Day 21.5 (24, 60, 96, or 132 h post-EV). Treatment with EV did not influence the timing of luteolysis, but surges of LH occurred earlier (59 +/- 8 h post-EV vs. 100 +/- 11 h in controls). The interval from luteolysis to LH peak was reduced from 44 +/- 6 h (controls) to 6.9 +/- 1.5 h (treated). Histologically, the largest follicle in controls tended to be atretic before luteolysis, but nonatretic afterwards, whereas the largest follicle in treated animals always tended to be atretic. Nonatretic follicles contained high concentrations of estradiol (408 +/- 59 ng/ml) and moderate amounts of testosterone (107 +/- 33 ng/ml) and progesterone (101 +/- 21 ng/ml), whereas atretic follicles contained low concentrations of estradiol (8 +/- 4 ng/ml) and testosterone (12 +/- 4 ng/ml), and either low (56 +/- 24 ng/ml) or very high (602 +/- 344 ng/ml) concentrations of progesterone. This study suggests that EV prevents ovulation by inducing atresia of the potential preovulatory follicle, which is replaced by a healthy large follicle by 14 days post-treatment.     

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.     

Dose-related effects of luteinizing hormone on the pattern of steroidogenesis and cyclic adenosine monophosphate release in superfused preovulatory rat follicles

The secretion of steroids and the release of cAMP in response to repeated luteinizing hormone (LH) stimulation were examined during superfusion of isolated preovulatory rat follicles. A high dose of ovine LH (1 microgram/ml for 20 min) caused a prolonged increase in the secretion of progesterone (P) and 20 alpha-dihydroprogesterone (20 alpha-OHP) and a transient increase in the secretion of testosterone (T) and estradiol-17 beta (E2), and was accompanied by a peak of cAMP release. A single pulse of LH at a low dose level (10 mg/ml for 20 min) gave a limited increase in T secretion, but no clear change in P, 20 alpha-OHP and E2 secretion or cAMP release. When the follicles were challenged with a second pulse of LH (at 1 microgram/ml), the response varied according to the dose of LH delivered in the preceding pulse. Following exposure to the high dose of LH, the follicles were partially refractory to the second LH challenge in terms of cAMP and P and the secretion of T and E2 remained low. The low dose of LH, however, had a conditioning effect on the follicles since the response to the second LH challenge was amplified in terms of P, 20 alpha-OHP and cAMP. In this case a secondary increase in T and E2 secretion was found. The differential response to varying doses of LH are likely to reflect the physiological control of steroidogenesis during final follicular maturation.     

Changes in plasma concentrations of luteinizing hormone,progesterone, and estradiol-17beta in peripubertal turkey hens under constant or diurnal lighting

Possible circadian fluctuations and long-term changes in concentrations of reproductive hormones in peripubertal female birds is poorly documented in comparison with mammalian species. Our objective was to document changes in concentrations of several reproductive hormones the several days before and after initial pubertal preovulatory surges of LH in turkey hens photostimulated with either constant (24L:0D) or diurnal (14L:10D) lighting. The hens were cannulated for hourly blood sampling, starting 10 days after photostimulation and continuing until all hens had laid at least two eggs. First eggs were oviposited between 16 and 24 days after photostimulation, and egg production ranged from two to nine eggs/hen during the experimental period. With both lighting treatments, concentrations of LH declined slightly, concentrations of progesterone (P(4)) increased, and concentrations of estradiol-17beta (E(2)) were constant the 3-4 days prior to initial LH surges with no circadian fluctuations in hormone concentrations. Most (10 of 13) initial preovulatory surges of LH were coupled with ovulations, and all LH surges were coupled with P(4) surges. Those LH and P(4) surges not coupled with ovulations (blind surges) occurred with both lighting treatments, but the incidence of blind surges was higher with diurnal lighting. The interval between LH and P(4) surges was longer between the first and second surges than between subsequent surges, when the interval was approximately 26 h. The duration of LH surges (7.4 +/- 3.0 h) was shorter than that of P(4) surges (10.0 +/- 2.0 h). We conclude that, in the peripubertal female turkey, 1) prior to puberty (first LH-P(4) surges), there are no circadian fluctuations in concentrations of LH, P(4), and E(2), 2) 3 days prior to initial LH surges, E(2) concentrations are stable, LH concentrations decline slightly, and P(4) concentrations increase, and 3) surges of LH are coupled to surges of P(4) but LH-P(4) surges are not always coupled to ovipositions (blind surges), possibly because of internal ovulations.     

Changes in luteinizing hormone-releasing hormone content of discrete hypothalamic areas associated with spontaneous and induced preovulatory luteinizing hormone surges in the domestic hen

It is widely assumed that luteinizing hormone-releasing hormone (LHRH) neuronal activation is involved in the preovulatory surge of LH in the hen. In addition, this LH surge may be initiated by ovarian progesterone (P4) release. Thus, spontaneous and P4-induced LH surges should be associated with acute changes in LHRH content of discrete hypothalamic areas associated with LHRH cell bodies and/or LHRH axon terminals. Medial preoptic area (mPOA) and infundibulum (INF) LHRH content was measured by radioimmunoassay at intervals before, at, and following peak LH levels of a spontaneous preovulatory surge of LH, as well as when this surge was advanced by P4 administration in laying hens. Nonlaying birds served as additional controls. Levels of serum LH, P4, 17 beta-estradiol and pituitary LH were also measured. Increased (P less than 0.05) LHRH content in mPOA without changes in the INF are associated with peak serum LH levels of the spontaneous LH surge. By contrast, decreased (P less than 0.05) LHRH content in both mPOA and INF is associated with peak serum LH levels when the spontaneous surge was advanced 8 h by P4 administration to laying hens. Medial preoptic area and INF LHRH contents were significantly lower (P less than 0.05) in nonlaying than in laying hens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interference with the preovulatory luteinizing hormone surge and blockade of ovulation in immature pregnant mare's serum gonadotropin-primed rats with the anti-androgenic drug, hydroxyflutamide

The involvement of androgens in the control of ovulation has been assessed by administration of the androgen antagonist, hydroxyflutamide, to prepubertal rats treated with pregnant mare's serum gonadotropin (PMSG) to induce first estrus and ovulation. Without human chorionic gonadotropin (hCG) injection, only 46% of rats that received six 5-mg, s.c. injections of hydroxyflutamide at 12-h intervals, beginning an hour before s.c. injection of 4 IU PMSG on Day-2 (Day 0 = the day of proestrus), had ovulated a mean of 1.3 +/- 0.4 oocytes per rat when killed on the morning of Day 1, whereas 92% of sesame oil-treated controls had ovulated a mean of 6.9 +/- 0.6 oocytes. After i.p. injection of hCG at 1600 h on Day 0, 92% of hydroxyflutamide-treated rats ovulated a mean of 8.3 +/- 1.2 oocytes compared to 100% of controls, which ovulated 7.3 +/- 0.4 oocytes per rat: these groups were not significantly different from each other, nor from control rats that received no hCG. Thus, exogenous hCG completely overcame the inhibitory effect of hydroxyflutamide on ovulation. Rats treated with PMSG and hydroxyflutamide without hCG were killed either on the morning of Day 0 to determine serum and ovarian steroid levels or on the afternoon of Day 0 to determine serum LH levels. Serum levels of estradiol-17 beta and testosterone in hydroxyflutamide-treated rats were significantly higher (178% and 75%, respectively; p less than 0.01) than levels observed in controls on the morning of Day 0. Ovarian concentrations of the steroids were also elevated in hydroxyflutamide-treated rats (p less than 0.01 for testosterone only).(ABSTRACT TRUNCATED AT 250 WORDS)