Roles of pulsatile release of LH in the development and maintenance of corpus luteum function in the goat

The roles of the pulsatile release of LH in the functional development and maintenance of the corpus luteum (CL) during the estrus cycle in the goat were examined using a potent GnRH antagonist. In Experiment 1, to assess the inhibitory effects of the GnRH antagonist on the release of LH during the estrus cycle, 9 goats were divided into 3 groups. Goats in Group I received only saline on Days 0 (day of ovulation), 5, 10 and 15. Goats in Group II received the GnRH antagonist (50 microg/kg, s.c.) on the days mentioned for Group I to inhibit endogenous LH during the periods of luteal development and maintenance. Goats in Group III received saline on Days 0 and 5 and then the GnRH antagonist on Days 10 and 15 to inhibit LH during the period of luteal maintenance. Serial blood sampling took place on Days 1, 3, 5, 8, 13 and 18 to characterize the LH pulses. The LH pulses were observed throughout the estrus cycle in Group I but were completely abolished in Group II. In Group III, the pulsatile release of LH was observed from Day 1 to 8, but the LH pulses were completely abolished on Days 13 and 18. In Experiment 2, 16 goats were divided into the same 3 groups as in Experiment 1 to examine the effects of the GnRH antagonist on the luteal function. The concentration of progesterone in the plasma in Group I increased after ovulation, reached a maximum level around Day 12, and subsequently returned to the basal level on Day 17. The concentrations of progesterone in Group II rose after ovulation, but reached a plateau around Day 6 and maintained the level up to Day 9, then rapidly decreased from Day 9 to 10 to the basal level. The concentrations of progesterone in Group II were lower on Days 7 to 15 than those in Group I (P<0.01). The concentrations of progesterone in Group III increased after ovulation, reached a maximum level around Day 8, then dropped from Day 10 to 13 to the basal level. The concentrations of progesterone in Group III on Days 11 to 15 were lower than those in Group I (P<0.05 on Day 11, P<0.01 on Days 12 to 15). These results demonstrate that endogenous LH is essential for normal development and maintenance of the CL function during the estrus cycle in the goat. Further, this study suggests that while the functional maintenance of the caprine CL depends entirely on LH support, such functional dependence during early CL development is only partial.     

Induction of luteal regression in the marmoset monkey (Callithrix jacchus) by a gonadotrophin-releasing hormone antagonist and the effects on subsequent follicular development

Doses of 100 or 200 micrograms of a novel GnRH antagonist ([N-acetyl-D beta Na11-D-pCl-Phe2-D-Phe3-D-Arg6-Phe7-Arg8-D-Ala10]NH2 GnRH) (4 animals/dose) were administered on Days 10/11 of the luteal phase and induced a marked suppression of circulating bioactive LH and progesterone concentrations within 1 day of treatment (P less than 0.01). Thereafter, progesterone concentrations remained low or undetectable until after the next ovulation. Similar results were obtained when 200 micrograms antagonist were given on Days 5/6 of the luteal phase (N = 4). The interval from injection of antagonist (200 micrograms but not 100 micrograms) to ovulation (based on a rise in progesterone above 10 ng/ml) was significantly longer than that from prostaglandin-induced luteal regression to ovulation in control cycles (N = 4/treatment) (range, 13-15 days after antagonist vs 8-10 days after prostaglandin, P less than 0.01). This delay of 4-5 days was equivalent to the duration for which LH concentrations were significantly suppressed by 200 micrograms antagonist when administered to ovariectomized animals (N = 3). Corpus luteum function during the cycle after GnRH antagonist treatment appeared normal according to the pattern of circulating progesterone. These results show that corpus luteum function and preovulatory follicular development in the marmoset monkey are dependent on pituitary gonadotrophin secretion.     

Deslorelin on Day 8 or 12 postovulation does not luteinize follicles during an artificially maintained diestrous phase in the mare

Practical estrus synchronization schemes are needed for mares. The Ovsynch synchronization protocol for cattle involves the administration of gonadotropin-releasing hormone (GnRH) to induce ovulation or luteinization of dominant follicles during the luteal phase and prostaglandin 7 days later to cause regression of any luteal tissue and development of a preovulatory follicle. An Ovsynch-type synchronization program potentially could be developed for horses if luteinization or ovulation of diestrous follicles occurred in response to GnRH treatment. The objective of this study was to determine if administration of the GnRH agonist, deslorelin acetate, on Day 8 or 12 postovulation would induce luteinization or ovulation of diestrous follicles in the mare. The model used was cycling mares maintained in an artificial luteal phase by administration of a synthetic progestin following prostaglandin-induced luteal regression. On the day of ovulation, 21 light horse mares were randomly assigned to one of three groups: (1) no GnRH, altrenogest from Days 5 to 15 postovulation with prostaglandin on Day 15; (2) GnRH on Day 8, altrenogest from Days 5 to 15 with prostaglandin given on Day 6 to induce luteolysis of the primary corpus luteum, an implant containing 2.1mg of deslorelin acetate inserted on Day 8 and removed on Day 10, with a second prostaglandin treatment on Day 15; (3) GnRH on Day 12, altrenogest from Days 9 to 19, prostaglandin on Day 10, a deslorelin acetate implant injected on Day 12 (subsequently removed on Day 14), and a second dose of prostaglandin administered on Day 19. Follicular development was monitored every other day from Day 5 until a 30-mm sized follicle was observed, and then daily to detection of ovulation. Serum progesterone concentrations were determined daily for 12 consecutive days. Progesterone concentrations in Group 1 remained elevated until approximately Day 12 postovulation. Prostaglandin administration on Day 15 resulted in complete luteolysis in all seven mares. In Group 2, progesterone concentrations in six of seven mares declined to baseline after prostaglandin treatment. No increase in serum progesterone was noted in any of the six mares that were given GnRH on Day 8, including three mares that had diestrous follicles > or =30mm in diameter at the time of treatment. Similarly, progesterone concentrations in six of seven mares in Group 3 declined to baseline after prostaglandin and there was no increase in progesterone after administration of GnRH on Day 12. No ultrasound evidence of luteinization or ovulation of diestrous follicles were noted after GnRH administration in any mares of Group 2 or 3. In conclusion, administration of the GnRH agonist deslorelin acetate to mares failed to induce luteinization or ovulation of diestrous follicles. Consequently, the Ovsynch program (as used in cattle) has little efficacy for synchronization of estrus in mares.     

Increase in ovulation rate after treatment of ewes with bovine follicular fluid in the luteal phase of the oestrous cycle

Administration of charcoal-treated bovine follicular fluid to Damline ewes twice daily (i.v.) from Days 1 to 11 of the luteal phase (Day 0 = oestrus) resulted in a delay in the onset of oestrous behaviour and a significant increase in ovulation rate following cloprostenol-induced luteolysis on Day 12. During follicular fluid treatment plasma levels of FSH in samples withdrawn just before injection of follicular fluid at 09:00 h (i.e. 16 h after previous injection of follicular fluid) were initially suppressed, but by Day 8 of treatment had returned to those of controls. However, the injection of follicular fluid at 09:00 h on Day 8 still caused a significant suppression of FSH as measured during a 6-h sampling period. Basal LH levels were higher throughout treatment due to a significant increase in amplitude and frequency of pulsatile secretion. After cloprostenol-induced luteal regression at the end of treatment on Day 12, plasma levels of FSH increased 4-fold over those of controls and remained higher until the preovulatory LH surge. While LH concentrations were initially higher relative to those of controls, there was no significant difference in the amount of LH released immediately before or during the preovulatory surge. These results suggest that the increase in ovulation rate observed during treatment with bovine follicular fluid is associated with the change in the pattern of gonadotrophin secretion in the luteal and follicular phases of the cycle.     

Alterations in hypophysial responsiveness to synthetic GnRH at different postpartum intervals in Murrah buffalo (Bubalus bubalis )

The objective of this study was to investigate the hypophysial responsiveness to GnRH at different intervals post partum in Murrah buffalo. Plasma LH and FSH levels were measured at 1 h before and upto 6 h subsequent to the administration of GnRH (1 ug/kg body weight) or saline on Days 2, 20 and 35 post partum in 2 groups of buffalo (n=4 each). Plasma progesterone levels were measured in samples collected once daily from Day 3 to Day 46 post partum. Pretreatment basal LH levels exhibited a progressive increase from Day 2 through Day 35 post partum, while the basal FSH levels increased only until Day 20 post partum. Following a highly subdued LH response to GnRH on Day 2 post partum, a 408% increase (P < 0.01) was observed in the total LH released in response to GnRH on Day 20 post partum, followed by a 20% reduction (non-significant) over Days 20 to 35 post partum. The interval from parturition was highly correlated with total LH released (r = 0.711, P < 0.01). Unlike LH, a substantial amount of FSH was released following GnRH treatment on Day 2 post partum, which was not significantly different from the FSH response on Days 20 and 35 post partum. The LH and FSH response to GnRH was not significantly different between animals in which luteal activity resumed and in those which showed no luteal activity post partum. While pointing to a dramatic enhancement in the hypophysial responsiveness to GnRH between Days 2 and 20 post partum, these results suggest that pituitary responsiveness to GnRH does not appear to be the limiting factor for resumption of estrous cycles by Day 35 post partum in Murrah buffalo.     

Effectiveness of an antagonist to gonadotrophin releasing hormone on the FSH and LH response to GnRH in perifused equine pituitary cells,and in seasonally acyclic mares

We wish to use a gonadotrophin-releasing hormone (GnRH) antagonist in the mare as a tool for investigating the control of the oestrous cycle. The aim of this study was to test the effectiveness of the antagonist cetrorelix by testing both in vitro, using perifused equine anterior pituitary cells, and in vivo in seasonally acyclic mares. Pituitary cells were prepared and after 3-4 days incubation, loaded onto columns and given four pulses of GnRH (at 0, 30, 60 and 90 min; dose-response study). After the second GnRH pulse, infusion of cetrorelix began (0, 100, 1000 and 2000 pmol/l) and continued until the end of the experiment. To mimic luteal phase conditions, cells were pre-incubated and perifused with progesterone (25 nmol/l) and GnRH pulses given at 0, 90, 180 and 270 min. Cetrorelix (0 or 1000 pmol/l) began after the second GnRH pulse. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were measured in 5 min fractions. Both FSH and LH response areas (above baseline) after GnRH were inhibited by 1000 pmol/l cetrorelix (P < 0.01, P < 0.01, respectively) but not by 100 pmol/l cetrorelix. Similarly, in the presence of progesterone, cetrorelix inhibited the FSH (P < 0.001) and LH (P = 0.0002) response area. Seasonally acyclic mares, pre-treated for 3 days with progesterone (150 mg i.m. per day) were given cetrorelix as (i) a loading dose of 1 microg/kg then infusion at 2.2 ng/(kg min) for 90 min, (ii) a s.c. injection at 20 microg/kg, (iii) infusion at 2.2 ng/(kg min) for 48 h, and (iv) no cetrorelix (control mares). At 90 min, 6, 24 and 48 h after cetrorelix was first administered, mares were given a bolus injection of GnRH (22.2 ng/kg i.v.) and the FSH and LH responses measured. All doses of cetrorelix inhibited the FSH response at 90 min. The response was no longer suppressed at 6 h in the 90 min infusion group, showing a rapid recovery from inhibition. At 24 h, the FSH responses in the injected and 48 h infusion group were suppressed. The LH concentrations were low and showed no significant changes. This study has defined the time course and dose of cetrorelix with respect to its effect on FSH in the horse. It is concluded that cetrorelix could be used to elucidate the role of FSH in follicular development in cyclic mares.     

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.     

Pulsatile LH secretion and ovarian follicular wave emergence and growth in anestrous ewes

The objective of this study was to determine if pulsatile LH secretion was needed for ovarian follicular wave emergence and growth in the anestrous ewe. In Experiment 1, ewes were either large or small (10 × 0.47 or 5 × 0.47 cm, respectively; n = 5/group) sc implants releasing estradiol-17 beta for 10 d (Day 0 = day of implant insertion), to suppress pulsed LH secretion, but not FSH secretion. Five sham-operated control ewes received no implants. In Experiment 2, 12 ewes received large estradiol-releasing implants for 12 d (Day 0 = day of implant insertion); six were given GnRH (200 ng IV) every 4 h for the last 6 d that the implants were in place (to reinitiate pulsed LH secretion) whereas six Control ewes were given saline. Ovarian ultrasonography and blood sampling were done daily; blood samples were also taken every 12 min for 6 h on Days 5 and 9, and on Days 6 and 12 of the treatment period in Experiments 1 and 2, respectively. Treatment with estradiol blocked pulsatile LH secretion (P < 0.001). In Experiment 1, implant treatment halted follicular wave emergence between Days 2 and 10. In Experiment 2, follicular waves were suppressed during treatment with estradiol, but resumed following GnRH treatment. In both experiments, the range of peaks in serum FSH concentrations that preceded and triggered follicular wave emergence was almost the same as control ewes and those given estradiol implants alone or with GnRH; mean concentrations did not differ (P < 0.05). We concluded that some level of pulsatile LH secretion was required for the emergence of follicular waves that were triggered by peaks in serum FSH concentrations in the anestrous ewe.     

Pituitary and ovarian responses of post-partum acyclic beef cows to continuous long-term GnRH and GnRH agonist treatment

Post-partum acyclic beef cows received continuous long-term treatment with GnRH (200 or 400 ng/kg body wt/h) or the GnRH agonist buserelin (5.5 or 11 ng/kg body wt/h) using s.c. osmotic minipumps which were designed to remain active for 28 days. All treatments increased circulating LH concentrations whereas FSH remained unchanged. Ovulation and corpus luteum (CL) formation as judged by progesterone concentrations greater than or equal to 1 ng/ml occurred in 0/5 control, 4/5 200 ng GnRH, 4/4 400 ng GnRH, 4/5 5.5 ng buserelin and 3/5 11 ng buserelin cows. The outstanding features of the progesterone profiles were the synchrony, both within and across groups, in values greater than or equal to 1 ng/ml around Day 6, and the fact that most CL were short-lived (4-6 days). Only 3 cows, one each from the 400 ng GnRH, 5.5 ng buserelin and 11 ng buserelin groups, showed evidence of extended CL function. Cows failed to show a second ovulation which was anticipated around Day 10 and this could have been due to insufficient FSH to stimulate early follicular development, or the absence of an endogenously driven LH surge. The highest LH concentrations for the respective groups were observed on Days 2 and 6 and by Day 10 LH was declining, although concentrations did remain higher than in controls up to Day 20.(ABSTRACT TRUNCATED AT 250 WORDS)     

Superstimulation of ovarian follicular growth with FSH oocyte recovery, and embryo production from Zebu (Bos indicus) calves: effects of treatment with a GnRH agonist or antagonist

The capacity of heifer calves of a late sexually maturing Zebu (Bos indicus) genotype to respond to superstimulation with FSH at a young age and in vitro oocyte development were examined. Some calves were treated with a GnRH agonist (deslorelin) or antagonist (cetrorelix) to determine whether altering plasma concentrations of LH would influence follicular responses to FSH and oocyte developmental competency. Brahman calves (3-mo-old; 140 +/- 3 kg) were randomly assigned to 3 groups: control (n = 10); deslorelin treatment from Day -8 to 3 (n = 10); and cetrorelix treatment from Day -3 to 2 (n = 10). All calves were stimulated with FSH from Day 0 to 2, and were ovariectomized on Day 3 to determine follicular responses to FSH and to recover oocytes for in vitro procedures. Before treatment with FSH, heifers receiving deslorelin had greater (P < 0.001) plasma LH (0.30 +/- 0.01 ng/ml) than control heifers (0.17 +/- 0.02 ng/ml), while plasma LH was reduced (P < 0.05) in heifers treated with cetrorelix (0.13 +/- 0.01 ng/ml). Control heifers had a surge release of LH during treatment with FSH, but this did not occur in heifers treated with deslorelin or cetrorelix. All heifers had large numbers of follicles > or = 2 mm (approximately 60 follicles) after superstimulation with FSH, and there were no differences (P > 0.10) between groups. Total numbers of oocytes recovered and cultured also did not differ (P > 0.05) for control heifers and heifers treated with deslorelin or cetrorelix. Fertilization and cleavage rates were similar for the 3 groups, and developmental rates to blastocysts were also similar. Zebu heifers respond well to superstimulation with FSH at a young age, and their oocytes are developmentally competent.     

Passive immunization of the pig against gonadotropin releasing hormone during the follicular phase of the estrous cycle

Three experiments were conducted to determine the effects of passively immunizing pigs against gonadotropin releasing hormone (GnRH) during the follicular phase of the estrous cycle. In Experiment 1, sows were given GnRH antibodies at weaning and they lacked estrogen secretion during the five days immediately after weaning and had delayed returns to estrus. In Experiment 2, gilts passively immunized against GnRH on Day 16 or 17 of the estrous cycle (Day 0 = first day of estrus) had lower (P<0.03) concentrations of estradiol-17beta than control gilts, and they did not exhibited estrus at the expected time (Days 18 to 22). When observed three weeks after passive immunization, control gilts had corpora lutea present on their ovaries, whereas GnRH-immunized gilts had follicles and no corpora lutea. The amount of GnRH antiserum given did not alter (P<0.05) serum concentrations of LH or pulsatile release of LH in sows and gilts. In Experiment 3, prepuberal gilts were given 1,000 IU PMSG at 0 h and GnRH antiserum at 72 and 120 h. This treatment lowered the preovulatory surge of LH and FSH, but it did not alter serum estradiol-17beta concentrations, the proportion of pigs exhibiting estrus, or the ovulation rate. These results indicate that passive immunization of pigs against GnRH before initiation of or during the early part of the follicular phase of the estrous cycle retards follicular development, whereas administration of GnRH antibodies during the latter stages of follicular development does not have an affect. Since the concentration of antibodies was not high enough to alter basal or pulsatile LH secretion, the mechanism of action of the GnRH antiserum may involve a direct ovarian action.     

Induction of follicular development and ovulation in seasonally acyclic mares using gonadotrophin-releasing hormones and progesterone.

Deeply acyclic (seasonally anovulatory) mares were treated with GnRH or a GnRH analogue to induce follicular development and ovulation. Courses of GnRH (3--4) were administered at approximately 10-day intervals to reproduce the gonadotrophin surges which precede ovulation in the normal cycle. Exogenous progesterone was administered in an attempt to reproduce the luteal phase pattern. Induced serum FSH concentrations were comparable to those causing follicular development in the normal cycle, but induced LH levels were lower and of shorter duration than those of the periovulatory surge. Three of 4 mares treated with GnRH appeared to ovulate, but did not establish CL. Nine of 10 mares given GnRH analogue also developed follicles during the final treatment course, as did mares treated with progesterone only, while only 1 of 5 untreated control mares showed any ovarian development. Failure to induce final follicular maturation and CL development by this treatment regimen may be due to an inadequate LH surge at the time of the expected ovulation associated with the low preovulatory oestradiol-17 beta surge, possibly caused by the preceding FSH stimulation being inadequate or inappropriate. Progesterone treatment increased baseline FSH concentrations in GnRH-treated mares, and also stimulated follicular development in mares not treated with GnRH, indicating a possible role for progesterone in folliculogenesis and, indirectly, ovulation.     

Effects of gonadotrophin-releasing hormone and prostaglandin F-2 alpha on corpus luteum function and timing of the subsequent ovulation in the mare

Standard bred mares that were cycling normally were treated beginning on Days 9 or 10 of the oestrous cycle with repeated pulses of GnRH (20 micrograms/h) and/or a single injection of prostaglandin (PG)F-2 alpha (alfaprostol, 3 mg), and were subsequently bled and palpated daily until the next ovulation. GnRH treatment increased serum concentrations of LH and progesterone at 4 days after the start of treatment compared to controls. The combination of PGF-2 alpha + GnRH treatment resulted in an immediate decline in serum progesterone values, and subsequently decreased the interval to next ovulation by 4.5 days compared to controls. Mean serum concentrations of FSH were not different among treatment groups 4 days after the start of treatment, and there was a consistent trend among all treatment groups for decreasing concentrations of FSH within the 6 days before ovulation. We conclude that, under our experimental conditions, pulsatile administration of GnRH provides a short-term luteotrophic stimulus, probably by the elevation in serum LH, but that this stimulus cannot indefinitely prevent the luteolytic effects of exogenously administered PGF-2 alpha. Although GnRH treatment combined with PGF-2 alpha injection hastened the impending ovulation, this regimen was no more effective than PGF-2 alpha treatment alone.     

Effect of purified llama ovulation-inducing factor (OIF) on ovarian function in cattle

Two experiments were designed to determine the effect of purified ovulation inducing factor (OIF) on ovarian function in cattle. In Experiment 1, prepubertal heifers (n = 11 per group) were treated on Day 5 (Day 0 = day of follicular wave emergence) of the follicular wave with an intramuscular dose of saline (1 mL), GnRH (100 μg), or purified OIF (1 mg/100 kg body weight). Ovulation occurred in 9/11 heifers treated with GnRH, and 1/11 heifers in each of the OIF- and saline-treated groups (P < 0.05). Compared to saline-treated controls, OIF treatment was associated with a smaller dominant follicle diameter (P < 0.01), a rise in plasma FSH concentration (P < 0.1), and earlier emergence of the next follicular wave (P < 0.05). In Experiment 2, sexually mature heifers were given either GnRH or purified OIF on Days 3, 6 or 9 of the first follicular wave (i.e., early growing, early static, or late static phase of the dominant follicle; n = 5 per group per day), or were untreated (n = 10). In heifers treated with OIF on Day 6, the dominant follicle diameter profile tended to be smaller than in controls, and was associated with a rise (P < 0.05) in plasma FSH concentrations. A similar rise in FSH was detected after OIF treatment on Day 9. Compared to untreated controls, treatment with OIF and GnRH was associated with a larger CL diameter (Days 3 and 6 groups; P < 0.05) and a greater concentration of plasma progesterone (Days 6 and 9 groups; P < 0.05). Treatment with purified OIF did not induce ovulation in heifers, but hastened new follicular wave emergence in prepubertal heifers, influenced follicular dynamics in a phase-specific manner in mature heifers, and was luteotrophic.     

Synchronous fluctuations of LH and FSH in plasma samples collected daily during the estrous cycle in mares

Circulating concentrations of LH and FSH in each of 12 mares were measured in daily blood samples from 3 d before until 3 d after an interovulatory interval (ovulation=Day 0). The interval was normalized to its mean length (22 d) and partitioned into periods relative to high and low (first significant increase and decrease: Days 3 and 14, respectively) mean FSH concentrations. The resulting experimental periods were as follows: 1) Days −3 to 2 corresponding to the periovulatory period, 2) Days 3 to 14 corresponding to the luteal period, and 3) Days −7 to 3 corresponding to the follicular-periovulatory period. An adaptive threshold method was used to detect peak concentrations of LH and FSH fluctuations. There was no significant difference in the number of detected LH fluctuations per mare among the 3 periods (means, 1.2, 1.8, 1.6 fluctuations, respectively). However, more (P<0.05) FSH fluctuations per mare were detected during the luteal period (mean, 2.4 fluctuations) than during the periovulatory period (mean, 0.5 fluctuations) and follicular-periovulatory period (mean, 1.2 fluctuations). Synchronous LH and FSH fluctuations, defined as the simultaneous detection of peak concentrations of fluctuations, occurred more (P<0.05) often per mare during the luteal period (mean, 1.3 fluctuations) than during the periovulatory period (mean, 0.1 fluctuations) and follicular-periovulatory period (mean, 0.2 fluctuations). During the luteal period, concentrations of LH peaked (P<0.05) during FSH fluctuations and, conversely, concentrations of FSH peaked (P<0.05) during LH fluctuations, indicating a high degree of coupling between the 2 gonadotropins. In summary, fluctuations of LH and FSH occurred in synchrony with a high degree of coupling between them during the luteal period, but not during the periovulatory and follicular-periovulatory periods.     

Effect of FSH deprivation at specific times on follicular maturation in the bonnet monkey (Macaca radiata)

Cyclic monkeys were deprived of FSH for specific periods on different days of the follicular phase by injecting them with minimal doses of an FSH antiserum characterized for specificity and bioneutralizing ability. The effect of the antiserum on follicular maturation was assessed by determining (a) serum oestrogen concentrations through the midcycle period, (b) serum progesterone concentrations as an index of ovulation and luteal function, (c) laparoscopic examination of the surface of the ovary when necessary, and (d) overall cycle length. While antiserum injection on Day 5 of the cycle caused delay in the oestrogen surge from Days 9 to 11, injection on Day 6 led to the occurrence of two oestrogen surges, on Days 9 and 14. Laparoscopic examination showed that the earlier follicle had disappeared and a new follicle had appeared by Day 14. Antiserum injection on Day 7 of the cycle arrested further growth of the maturing follicle, but a new follicle appeared 9 days later, as indicated by a surge of oestrogen on Day 16. Injection of antiserum beyond Day 7 had no effect on follicular development, ovulation and luteal function. These observations suggest that the mature follicle becomes relatively independent of FSH support about 48 h before ovulation and this event could be a marker for follicular dominance.     

FSH and LH concentrations in periparturient mares.

The influence of the ovaries and presence of a foal on periparturient concentrations of FSH and LH were studied in 19 Pony mares. In intact and ovariectomized mares, mean concentrations of FSH fluctuated between 1.1and 9.9 ng/ml on Days -14 to-1 before parturition (Day 0). A surge of FSH occurred in all mares in association with parturition. From Days 1 to 10, the high levels of FSH gradually decreased in the intact group to the minimal concentrations that occur during oestrus, but remained elevated in the ovariectomized mares. There were no significant pre-partum changes in LH in either type of mare. Post-partum changes in LH concentrations increased at a similar rate in ovariectomized and intact mares. The presence of a foal significantly lengthened the interval to first oestrus, depressed LH levels on Days 6--10 and decreased the FSH concentrations as averaged over the 10 days before the first ovulation after parturition.     

Controlling interrelationships of progesterone/LH and estradiol/LH in mares

The interrelationships of progesterone, estradiol, and LH were studied in mares (n=9), beginning at the first ovulation (Day 0) of an interovulatory interval. An increase in mean progesterone concentrations began on Day 0 and reached maximum on Day 6, with luteolysis beginning on Day 14. A common progesterone threshold concentration of about 2 ng/ml for a negative effect on LH occurred at the beginning and end of the luteal phase. Progesterone and LH concentrations decreased at a similar rate from Day 6 until the onset of luteolysis on Day 14, consistent with a decreasing positive effect of LH on progesterone. Concentrations of LH during the increase in the ovulatory surge consisted of two linear regression segments involving a rate of 0.4 ng/ml/day for Days 14-22 and 1.8 ng/ml/day for Day 22 to 1 day after the second ovulation. The end of the first segment and beginning of the second segment was 2 days before ovulation and was the day the ovulatory estradiol surge was at a peak.     

Endocrine and ultrasound evaluation of the response to PGF 2alpha and GnRH given at different stages of the luteal phase in cyclic ewes

To investigate the effects of prostaglandin (PGF 2alpha) plus GnRH at different stages of the luteal phase 13 ewes received PGF 2alpha on Day 9 of the synchronized cycle, followed 36 h later by GnRH. This control regimen resulted in ovulation and normal corpus luteum (CL) function. In the next cycle, the ewes were treated simultaneously with PGF 2alpha and GnRH either on Day 4 (early, n = 7) or Day 9 (late, n = 6). Ovarian activity was monitored daily by ultrasonography, and blood samples were obtained to monitor hormonal patterns. Size of the largest follicle present when GnRH was administered was similar in all groups, but the preceding growth rate was greatest for the early group. In the 36 h after injection of PGF 2alpha, serum progesterone (P4) had declined to basal levels in the control cycles when GnRH was administered, but P4 concentrations were higher in the early group and were highest in the late group when the GnRH was administered with PGF 2alpha. The LH surges induced by GnRH were highest in the control cycles, and were lower in the 2 treated groups. In the early group, 6 of 7 ewes demonstrated ovulation within 48 h of GnRH, resulting in the formation of normal CL. In the late group, ovulation was delayed for about 5 d in 4 of 6 ewes, and subsequent luteal function was normal; no ovulation was detected in the other 2 ewes of this group, but the follicles became luteinized, resulting in a normal P4 profile in one and subnormal in the other. These results suggest that follicles present during the early luteal phase are capable of ovulating and forming fully functional CL in response to exogenous GnRH. In contrast, follicles present during the late luteal phase fail to ovulate in response to GnRH while P4 levels are high, even though the LH stimulus is adequate; however, these follicles persist and subsequently ovulate after P4 levels have decreased. Therefore, the endocrine milieu to which a follicle was exposed may be more important than its size in determining its ability to undergo ovulation and development into a normal CL.     

Relation between levels of circulating ovarian steroids and pituitary gonadotropin content during the menstrual cycle of the rhesus monkey

Anterior pituitary glands were removed from 27 intact cycling rhesus monkeys sacrificed in the early (Day 2), mid (Days 6--9) and late (Days 11--12) follicular phase, and in the early and late luteal phase (3--5 and 10--15 days after the midcycle luteinizing hormone (LH) surge). Assignment of cycle stage was confirmed by the pattern of circulating steroid and gonadotropin levels seen in the blood samples taken daily throughout the cycle. The anterior pituitary glands were weighed, stored at -30 degrees C and assayed for LH and follicle-stimulating hormone (FSH) content by specific radioimmunoassays. Serum estradiol levels and pituitary LH and FSH contents rose simultaneously during the follicular phase. After the preovulatory gonadotropin surge, pituitary LH content was low and invariant. Pituitary FSH content reached a nadir in the early luteal phase and tended to rise in the late luteal phase. Multiple correlation analyses revealed that there is a positive correlation between rising levels of estradiol in the circulation and pituitary LH (p = 0.003) and FSH (p = 0.017) content, and that there is a significant negative correlation between circulating progesterone levels and pituitary FSH content (p = 0.002). Pituitary LH content is less strongly related to circulating progesterone levels. There was no significant difference in the wet weights of the anterior pituitary glands during the five phases of the menstrual cycle studied.