Delay In Ovulation Research Articles

Efficacy of altrenogest administration to postpone ovulation and subsequent fertility in mares

A recent report suggested administration of altrenogest during the follicular phase could postpone ovulation. Based on these results, two questions were generated. We first hypothesized that by initiating a altrenogest treatment earlier in the estrous cycle, a greater and/or more consistent delay in ovulation would result. Second, we hypothesized that exposure to elevated progestin concentrations might alter viability of the ovulatory follicle and oocyte. The focus of the first experiment was to determine if initiation of altrenogest treatment at different stages of the estrous cycle would yield a more predictable time to ovulation, whereas the second experiment was designed to determine whether mares receiving altrenogest during estrus had compromised fertility. In the first experiment thirty mares of mixed light breed, ranging in age from 5-15 years, were randomly assigned to one of three groups. The two treated groups received altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 30 or 35 mm in diameter was detected. Control mares were not treated. Mares treated with altrenogest whether initiated at the detection of a 30 or 35 mm follicle demonstrated similar (P>.05) day to ovulation interval when adjusted to 35 mm (5.4 and 5.6 days, respectively). Both treated groups demonstrated a delayed interval (P<.05) when compared to control (3.9 days). Thirty-six mares of similar breed and age, were randomly assigned to two groups for use in the second experiment. All mares were monitored daily via transrectal ultrasonography from the time a 35 mm or greater follicle was detected until ovulation. Treated mares received daily doses of altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 35 mm or greater was detected. Control mares received no treatment. Fertility data were collected from mares inseminated every other day with 500 million motile spermatozoa from one of two stallions with proven fertility. Pregnancy data were collected via transrectal ultrasonography at days 12, 14 and 16 post-ovulation. Ovulation data were collected from 27 control cycles and 26 treated cycles. Contrary to previous reports and Experiment 1, no difference (P=0.35) was noted between groups with respect to days to ovulation. Control mares averaged 4.14 days and treated mares averaged 4.7 days to ovulation from initial detection of a 35 mm follicle. Fertility data were also similar (P=0.8) between control and treated mares (66.6% and 61.5% per cycle, respectively). Interestingly, a greater number (P=0.017) of treated cycles (5/26) resulted in follicular regression than did control cycles (0/27). While these data suggest that this dosage of altrenogest may not postpone ovulation, it did appear related to increased incidence of follicular regression. Fertility was unaffected, however, in those mares that ovulated. Further studies are needed in which initiation at different stages of estrus and different doses of altrenogest are used.

Update on adolescent contraception

Recent advances in OCPs include less androgenic progestins and lower doses of ethinyl estradiol. All low-dose OCPs are safe in terms of venous thrombosis risk in appropriately chosen patients. DMPA is a safe and effective long-acting contraceptive agent; clinical attention should be directed to its most common side effect, irregular bleeding. DMPA does not seem to affect mood, and it is uncertain what impact it has on weight changes. More research needs to be conducted on its impact on adolescent bone metabolism. Norplant continues to be the only subdermal contraceptive implant marketed in the United States. It provides safe and effective contraception and has the best continuation rate of all types of hormonal contraception. Its most common side effect is irregular bleeding. Norplant may be especially well suited for adolescents who have recently been pregnant or who are not tolerating other types of contraception. Emergency postcoital contraception continues to be underused in the United States, with a lack of awareness among patients and clinicians. Mechanisms of action include a delay in ovulation and interference with implantation. Research and public health groups are striving to increase patient and provider awareness and use of emergency contraception.

Energy Balance of Dairy Cattle in Relation to Milk Production Variables and Fertility

Variables derived from milk yield records were investigated to find an easy to measure and readily available indicator of the energy balance status of a lactating cow. Weekly energy balances during the first 180 d in milk (DIM) were calculated from weekly yield, live weight, and energy intake records for 470 first lactation heifers. The energy balance curve for each cow was estimated using a random regression model. From each curve, three measures were calculated to describe the energy balance status: 1) total energy deficit in early lactation, 2) interval for return to positive energy balance, and 3) lowest value (nadir) for energy balance. Mean energy deficit per lactation was 776.8 MJ of NEL/d, interval for return to positive energy balance was 41.47 d, and nadir was –33.72 MJ of NEL/d. Regression analysis to relate these variables to interval to start of luteal activity (measured using progesterone profiles) showed that a low nadir of energy balance was related to delayed resumption of luteal activity. In general, a 10 MJ of NEL/d lower nadir of energy balance corresponded to a delay of ovulation of 1.25 d. A relatively strong decrease in fat percentage during early lactation was significantly correlated with lower nadir of energy balance, larger energy deficit, and later return to positive energy balance. The maximal correlation was between nadir of energy balance and a decrease of milk fat percentage. This correlation remained above 0.60 throughout the first 26 DIM but dropped to 0.14 at 180 DIM. Large decreases in milk fat percentage were related to high initial fat percentages at the start of lactation and slightly lower fat percentages later during lactation. Hence, we concluded that a decrease in fat percentage during early lactation might serve as an indicator of energy balance.

Geographic and annual variation in reproductive cycles in the Tasmanian spotted snow skink, Niveoscincus ocellatus (Squamata : Scincidae)

We studied the reproductive cycle of two populations of the spotted snow skink, Niveoscincus ocellatus, over a three-year period. This species is widespread in Tasmania and its distribution overlaps those of other species in the genus that show two distinct reproductive strategies: annual reproduction that is completed within one season, and biennial reproduction in which females carry advanced embryos throughout winter hibernation. We chose populations representative of the climatic extremes of the species’ distribution, within these areas of overlap. Niveoscincus ocellatus maintains the same basic reproductive strategy in both populations: summer gestation, primary autumn mating with obligate sperm storage by females, secondary mating in spring, and predominantly spring vitellogenesis and ovulation. In both populations all females reproduce annually, suggesting that reproductive frequency is not constrained by availability of energy. However, we found distinct differences in the timing of ovulation and parturition. Females from our subalpine site ovulated approximately one month later than those from our warmer, lowland site; parturition was delayed by the same period so gestation length was unchanged. The delay in ovulation results in gestation proceeding over the warmest months at the cold site. The annual reproductive cycle of this species appears to constrain its distribution to the lower altitudinal/climatic range of alpine Niveoscincus species. There were minor annual differences in the timing of reproductive events at each site, which we attribute to variation in thermal conditions and the amount of precipitation.

Effects of body condition at calving, post-partum nutrition and calf access on the interval from calving to first ovulation in beef cows: Cow performance and metabolism

The prolonged interval from calving to first ovulation in beef cows is primarily due to the suckling-mediated inhibition of pulsatile LH release. Undernutrition both before and after calving also suppresses LH release, reduces ovarian follicular growth and delays ovulation. The interactive effects of these factors on the interval from calving to first ovulation in beef cows were quantified by studying the incidence of ovulation, following acute calf isolation and once-a-day suckling (restricted access), after emergence of the fourth follicular wave post partum in cows in differing body condition at calving and offered low or high planes of nutrition after calving.The experiment was a 2 x 2 x 2 factorial design, in which the factors were body condition score at calving (Low v. Moderate), feeding level after calving (0.6 v. 1.0 MJ ME/d/kg M0.75), and restricted (once-a-day) v. ad libitum access and suckling. The experiment, duplicated at each of the four participating sites, involved 16 Simmental, 16 Sarda, 16 Brown Swiss and 16 Hereford x Friesian multi-parous cows. Follicle growth was monitored daily from day 21 post partum until the earlier of second ovulation or Day 90 post partum using transrectal ovarian ultrasonography.

Efficacy of short-term administration of altrenogest to postpone ovulation in mares

Estrogen from a growing follicle stimulates the preovulatory surge of luteinizing hormone (LH) while progesterone (P) is known to suppress LH. The possibility exists that administration of P, in the presence of an ovulatory follicle, would sufficiently suppress LH and, therefore, delay ovulation. The objective of this research was to elucidate the potential for oral administration of altrenogest (17-Allyl-17β-hydroxyestra-4,9,11-trien-3-one) to postpone ovulation of a preovulatory follicle (35 mm) for approximately two days. Fourteen light-horse mares, ranging in age from two to 19 years, were randomly assigned to one of three treatments (A-.044 mg/kg BW altrenogest for two days; B-.088 mg/kg BW altrenogest for two days; and C- no altrenogest). Mares began treatment when a 35-mm or greater follicle was observed via real-time transrectal ultrasonography. Both number of days until ovulation and follicular maintenance differed between treated and control mares. Number of days until ovulation was increased (P<.05) for mares in treatment A when compared with the control mares. Follicular diameter maintenance, a measurement of follicular diameter throughout treatment, also increased (P<.05) for mares in treatment A when compared with the control mares. Mean LH concentration was not different between mares treated with altrenogest at either treatment dose when compared with the control mares. Pregnancy rates and embryonic vesicle size change were also measured to determine potential effects of altrenogest administration. No differences (P>.05) were found in either characteristic. Short-term administration of altrenogest increased the number of days to ovulation. Further study is warranted to prove conclusively that altrenogest increases follicular maintenance, alters the preovulatory LH surge, and has no detrimental effects upon reproductive efficiency.

Ovulatory delay alters postnatal growth, behavior, and brain structure in rats

To investigate the effect of a delay in ovulation on postnatal growth and development in resultant rat offspring, a 1-day ovulatory delay was induced by sodium pentobarbital, animals mated, and the offspring monitored. There were no differences between control and 1-day delayed offspring in the number of live or dead births, number of males or females, nor in the ratio of sexes. Delayed pups had a slightly lower birth weight, but then recovered to weigh more than controls by day 12. In the first two weeks post-parturition, delayed pups displayed an earlier ability to reorient themselves in a negative geotaxis test, but no differences by the righting reflex and reflex suspension tests. At postnatal day (pnd) 28, delayed pups exhibited decreased activity in a continuous corridor test, but no alterations in gait. At this time, the brains of delayed animals revealed thickening of cortical layers V plus VI. There were significant correlations between various developmental endpoints (body weight, negative geotaxis, continuous corridor activity, and gait) and the cortical layer thicknesses. The results indicate that ovulatory delay produces changes in brain cortical thickness, with correlative changes in growth and behavior. Although the mechanisms by which ovulatory delay alters postnatal development and brain structure are unknown, ovulatory delay may alter the uterine environment during early pregnancy.

Effect of follicular phase administration of mifepristone (RU486) on blastocyst implantation in the rhesus monkey

In the present study our aim was to test two hypotheses: 1) inhibition of preovulatory phase progesterone action can inhibit or delay ovulation, and 2) inhibition of preovulatory phase progesterone action can inhibit postovulatory phase endometrial receptivity for blastocyst implantation. Female rhesus monkeys showing normal cycle lengths were randomly assigned to two groups: group 1 (n = 5) and group 2 (n = 7). The pretreatment cycles were monitored for ovulatory pattern and, in treatment cycles, females were allowed to cohabit with males from cycle days 6 to 28; group 1 animals received vehicle alone, and group 2 animals received mifepristone (RU486, subcutaneously), 1 mg/animal 3 consecutive cycle days (days 7, 8, and 9 for 26-day pretreatment cycle length; and days 8, 9, and 10 for 28-day pretreatment cycle length). Follicular phase mifepristone resulted in a delay of ovulation (p < 0.01) when compared with pooled data of pretreatment and treatment cycles of group 1 and pretreatment cycles of group 2. Despite delay of ovulation, there was only a 20% decrease in the incidence of pregnancy in group 2 as compared with that in group 1. However, a delay (p < 0.05) in the appearance of CG was noted in follicular phase mifepristone-treated cycles as compared with control treatment cycles. On the other hand, ovulation could not be detected in three monkeys in group 2; and, of these, two cycles were extended, but all three cycles were negative for CG. These results support earlier reports that follicular phase mifepristone can inhibit or disrupt follicular maturation, and delay ovulation. However, follicular phase mifepristone failed to inhibit implantation, because gonadal hormones, including progesterone, resume normal functions once ovulation takes place.

Effect of tumor necrosis factor-α on progesterone production by granulosa cells in laying hens of different genetic lines

In vitro progesterone production by granulosa cells in the presence or absence of human recombinant tumor necrosis factor-alpha (hrTNF-α) was measured at 10, 20, and 30 wk of egg production in White Leghorn hens selected for high (HA)- or low-antibody (LA) response to sheep red blood cell challenge. Isolated granulosa cells from the three largest preovulatory follicles (F1–F3) were incubated with 5 or 250 ng/ml hrTNF-α, and progesterone production was determined by the use of a validated radioimmunoassay. F1, F2, and F3 granulosa cells from HA hens produced more (P ⩽ 0.05) progesterone (140.8, 107.2, and 49.7 ng/ml) than LA hens (109.4, 78.9, and 26.9 ng/ml). The treatment of granulosa cells with hrTNF-α consistently inhibited (P ⩽ 0.05) progesterone secretion by all follicles among HA and LA hens, but not always at both doses. Generally, 5 ng/ml hrTNF-α was the maximum inhibitory dose. In the laying hen, a decrease in steroid production in response to cytokines may upset the steroid balance created by follicular hierarchy and inhibit or delay ovulation.

Adiposity and Androstenedione Production in Relation to Delayed Ovulation in the Indian bat, Scotophilus heathi

Observations on body weight, circulating androstenedione concentrations and morphology of ovarian stroma were made in Scotophilus heathi during the period of delayed ovulation to make a comparison with polycystic ovarian syndrome in women. Body weight of bats increased from a level of 31.00 ± 0.30 g in August and reached a peak of 45.00 ± 0.46 g in November. This increase in body weight was due to accumulation of adipose tissue. The body weight declined gradually from December onwards and finally reached a basal level in March. The circulating androstenedione concentration showed a gradual increase from 36.80 ± 15.54 ng/ml in August and reached a peak level of 220.50 ± 50.10 ng/ml in November. Androstenedione concentration reached the lowest level in the March, just before ovulation. Morphological study showed extensive distribution of luteinized stromal cells or interstitial cells (ICs). Morphometric study showed that during the period of ovulatory delay, more than 75% area of the ovary was occupied by the ICs. Hyperandrogenism, anovulation, obesity (fat deposition) and stromal hyperthecosis present during delayed ovulation in S. heathi may serve as an experimental model for some aspects of the polycystic ovarian condition in women.

Role of leptin in the neuroendocrine response to fasting.

A total deficiency in or resistance to the protein leptin causes severe obesity. As leptin levels rise with increasing adiposity in rodents and man, it is proposed to act as a negative feedback 'adipostatic signal' to brain centres controlling energy homeostasis, limiting obesity in times of nutritional abundance. Starvation is also a threat to homeostasis that triggers adaptive responses, but whether leptin plays a role in the physiology of starvation is unknown. Leptin concentration falls during starvation and totally leptin-deficient ob/ob mice have neuroendocrine abnormalities similar to those of starvation, suggesting that this may be the case. Here we show that preventing the starvation-induced fall in leptin with exogenous leptin substantially blunts the changes in gonadal, adrenal and thyroid axes in male mice, and prevents the starvation-induced delay in ovulation in female mice. In contrast, leptin repletion during this period of starvation has little or no effect on body weight, blood glucose or ketones. We propose that regulation of the neuroendocrine system during starvation could be the main physiological role of leptin.

Characterization of Pregnancy Outcome Following Thiram-Induced Ovulatory Delay in the Female Rat

Characterization of Pregnancy Outcome Following Thiram-Induced Ovulatory Delay in the Female Rat

Characterization of pregnancy outcome following thiram-induced ovulatory delay in the female rat

A single injection of the dithiocarbamate fungicide, thiram, suppresses the proestrous surge of LH and delays ovulation for 24 h. In this study, we examined fertility after a thiram-induced delayed ovulation. Females were injected with thiram (50 mg/kg, IP) on proestrus (1300 h) and mated on the following evening. Control and thiram-treated, but nondelayed, females were injected and mated on the same day. The number of females in the thiram-delayed group that became pregnant was reduced and litter size on GD 20 was reduced; however, no obvious morphological anomalies were seen. The number of pregnant females and litter size was not altered in the thiram-nondelayed rats, indicating that it is the thiram-induced delay in ovulation and not the exposure to thiram per se that was responsible for altered pregnancy outcome. On GD 7 and 11, the number of live fetuses per litter was reduced in the delayed females, but the number of implantation sites was not different from controls. On GD 11 the mean developmental score, head length, crown-rump length, and somite number in the delayed group were also reduced, indicating retarded development of live embryos. These results demonstrate that delayed ovulation induced by a single thiram exposure does not alter the number of oocytes released or the number that implant. However, the concepti from these females are compromised during midgestation.

Antiprogestins: mechanism of action and contraceptive potential.

Antiprogestins are characterized by substitutions at the 11 beta and 17 alpha positions of the steroid ring system and bind strongly to both progesterone and glucocorticoid receptors. Although they function predominantly as antiprogestins and antiglucocorticoids, on occasion they display progestin agonistic and even antiestrogenic properties. The most common clinical use of the antiprogestin mifepristone is to induce a medical abortion in the early stages of pregnancy. Progesterone maintains the endometrium, transforming it from a proliferative to a secretory state. It also facilitates the luteinizing hormone surge, which initiates ovulation. As a consequence, antiprogestins may also have contraceptive potential. Although antiprogestins do delay ovulation, this effect is inconsistent unless high doses are given, and under these circumstances, the antiprogestin effect is associated with unopposed estrogen action on the endometrium. Very low doses of antiprogestins do not affect hormonal secretion or ovulation or alter bleeding patterns, but they do have contraceptive potential by inducing profound alterations in endometrial morphology. Mifepristone is also a very effective and safe postcoital agent. This new class of pharmacological agents has numerous other gynecological and obstetrical indications, such as endometriosis, uterine myoma, and expulsion of the fetus in the case of fetal death in utero. Antiprogestins may also be used in the treatment of steroid-dependent tumors. There are also therapeutic implications consequent to their antiglucocorticoid properties.

Delay in Ovulation and Fertilization and Asynchronous Pronuclear Development in Aged Hamsters.

Ova were collected from young (9-12-week old) and aged (43-53-week old) golden hamsters at various times before and after fertilization to decide the timing of ovulation, sperm penetration and pronuclear formation. Ovulation was delayed 1 h in the aged animals, although overall ovulation rate did not differ statistically between young and aged animals. Sperm penetration also showed another 1 h delay in aged hamsters. The types of abnormalities during early fertilization were asynchronous development of male and female pronuclei, polyspermy, polygyny and pycnosis. Asynchronous development of the male and female pronuclei, mainly a delay in the development of the male pronucleus, was found more often in the aged females (8.2%), contrasting 3.1% (P<0.01) in the young females. Polyspermy accounted for a small proportion of the abnormalities in both groups (0.5 and 0.4% in the young and aged groups, respectively), whereas abnormalities observed only in the aged group were polygyny (5.5%) and pycnosis (0.4%). It is suggested that increased abnormalities of fertilization observed in the aged hamsters (approximately 15% of the total ova) may be directly related to delayed ovulation and fertilization attributed to defective ova and deteriorated reproductive ability of the aged females. These delays in ovulation and fertilization may be the main factors causing the preimplantation wastage of embryos in the aged hamsters.

‘No Nation Can Rise Above the Level of its Women’: New Thoughts on Maternal Nutrition the Caroline Walker Lecture 1993

In the human life cycle the period of highest susceptibility to hazards is before and around conception. A long historical record shows that an inadequate maternal diet, including a deficiency of single nutrients, depresses sex hormone levels, which reduces the rate of ovulatory maturation, delays ovulation and slows down embryonic growth producing smaller babies and defects in children. A slow-down in ovulatory maturation can also cause damage to the genome or mutations including chromosomal aberrations. Many toxic substances also cause mutations. Some essential nutrients and many substances in food, such as chlorophyll, not classified as ‘essential’, are nevertheless antimutagens. A modest-but-adequate standard of nutrition for women of reproductive age is summarized.

Biodegradable estradiol microspheres do not affect uterine involution or characteristics of postpartum estrus in mares

Quarterhorse mares were used to investigate effects of estradiol-17β on uterine involution, duration of estrus, interval to ovulation, and fertility achieved by breeding on the first postpartum estrus. On the day of foaling, mares were injected with biodegradable poly (DL-lactide) microspheres containing either 100 mg estradiol-17β (25 mares) or no drug (27 mares). The treatment period was considered to last for 12 to 15 d. Estrus was determined by teasing mares (n=16) with a stallion. Ovulation was detected by transrectal ultrasonographic examination of ovaries (n=48). On Days 6, 11 and 16 post partum, transrectal ultrasonography was used to measure cross-sectional diameters of the uterine body, uterine horns, and fluid within the uterine lumen (n=28). Uteri were swabbed for bacteriologic culture, and uterine biopsies were obtained from the previously gravid uterine horn on Days 11 and 16 post partum, for assessment of endometritis and morphometric analysis of endometrial histioarchitecture (n=19). Twenty-two mares were bred on foal-heat, and pregnancy was determined by transrectal ultrasonography on 14 to 16 and 30 to 35 d after breeding. With only one exception (diameter of previously gravid uterine horn on Day 11), mean values for all measures of uterine involution did not differ between treatment groups (P > 0.05). No differences were detected between treatment group means for length of estrus or interval to ovulation (P > 0.05). No differences were detected between treatment group liklihoods for recovery of potential bacterial pathogens, presence of endometritis, or presence of intrauterine fluid at 11 or 16 d post partum (P > 0.05). Pregnancy rate of mares treated with estradiol ( 5 11 ; 45%) was not different from that of control mares ( 9 11 ; 82%; P > 0.05). Estradiol treatment did not hasten uterine involution, increase duration of estrus, delay ovulation, or increase fertility in these postpartum mares.

Mammary somatosensory pathways are not required for suckling-mediated inhibition of luteinizing hormone secretion and delay of ovulation in cows.

Four experiments were conducted to evaluate endocrine, lactational, and reproductive features of an experimental animal model employing complete neural disconnection of the udder in beef cows and then to utilize the validated model to study the role of mammary somatosensory pathways in suckling-mediated anovulation. For experiment 1, crossbred beef cows (n = 16) were randomly assigned to suckled/sham-operated control, weaned (calf removed)/sham-operated control, and suckled/mammary-denervated groups between Days 14 and 18 postcalving. Ten additional cows were randomly divided into weaned or suckled unoperated control groups (experiment 2). Complete mammary anesthesia was attained in all denervated cows (experiment 1), but sensory perception was not affected in sham-operated controls. Prolactin release patterns were markedly depressed by denervation; however, oxytocin release, milk production, and calf growth rates were not affected. Although acute sham surgery attenuated weaning-induced increases in LH pulse and ovulation frequency (experiment 1), normal responses to weaning were observed in unoperated controls (experiment 2) as well as in sham-operated cows 1 yr later (experiment 3). Finally, denervated-suckled cows (n = 22) that had been denervated before conception (experiment 4) exhibited LH secretion patterns and mean postpartum intervals to luteal activity similar to those of intact-suckled cows (n = 16). In contrast, the intact-weaned group (n = 16; calves weaned at birth) responded within 2 wk postcalving with an increased frequency of LH pulses, and intervals to onset of luteal activity were shortened compared to those in the other groups. Suckling-mediated anovulation is not dependent upon mammary somatosensory cues.

Influence of the Formamidine Pesticide Chlordimeform on Ovulation in the Female Hamster: Dissociable Shifts in the Luteinizing Hormone Surge and Oocyte Release

The formamidine pesticide chlordimeform (CDF) has been found to interfere with the hormonal control of ovulation in the rat by a presumptive disruption in the catecholaminergic regulation of the midcycle surge of luteinizing hormone (LH). While the brain hypothalamic mechanisms underlying generation of the hamster surge have not been as well-defined, there is evidence for an adrenergic component. The present experiments were designed to investigate the effects of CDF on ovulation in the golden hamster and whether any observed alterations are associated with differences in the appearance of the surge. Intraperitoneal CDF injections (0, 75, 150, or 200 mg/kg) at 1400 hr on proestrus caused a dose-related reduction in oocytes retrieved at 0700 hr on the day of estrus. Additional experiments demonstrated that this effect was due to a delay in ovulation and not a decrease in the complement of oocytes released. Doses of 150 or 200 mg/kg at 1100 hr or 200 mg/kg at 1600 hr were without a comparable ovulatory effect. Characterization of the LH surge indicated that there was a dose-related delay, but that this effect was not sufficient to account for the delay in ovulation. Animals dosed at 1100 hr (150 or 200 mg/kg) exhibited shifts in the surge identical to those animals injected at 1400 hr, but did not show any such detectable effects on the time of oocyte release. CDF administered at 1100 or 1400 hr also caused alterations in serum estradiol and progesterone, even at a relatively low dose of 37.5 mg/kg. The results indicate that CDF given at a time just prior to the preovulatory rise in LH is able to impede ovulation in the hamster by possibly influencing some ovulatory event(s) triggered by the surge. Also, the ability of CDF to alter the timing of LH release is consistent with catecholaminergic participation in the generation of the gonadotropin signal stimulating the final events leading to ovulation. Under the present conditions, this perturbation can be characterized as a delay in the LH trigger, rather than a blockade.

The ability of steroid-free bovine follicular fluid to suppress FSH secretion and delay ovulation persists in heifers actively immunized against inhibin

Previous reports indicate that administration of steroid-free bovine follicular fluid (bFF) to intact heifers suppresses plasma FSH levels and delays the timing of ovulation. In addition, cessation of bFF treatment is associated with a rebound hypersecretion of FSH. To test the hypothesis that these effects of bFF are mediated by inhibin, we have compared the responses to bFF treatment in heifers actively immunized against the N-terminal sequence of inhibin alpha subunit (bI alpha(1-29)Tyr30-ovalbumin) with those in ovalbumin-immunized controls. Oestrous cycles were synchronized, and inhibin-immune (n = 10) and control (n = 10) heifers were subdivided into two groups which received either 5 ml bFF (n = 5) or 5 ml bovine serum (n = 5) every 4 h for a 60 h period starting 8 h before prostaglandin (PG)-induced luteolysis. Blood was withdrawn every 4 h for 10 days starting 30 h before luteolysis and ovaries were examined daily by ultrasonography. Overall, mean ovulation rate in bI alpha(1-29)Tyr30-immunized heifers was 44% higher (P < 0.02) than in controls. Inhibin antibody titres tested in bI alpha(1-29)Tyr30-immunized heifers before (19 +/- 3%), during (19 +/- 3%) and after (20 +/- 3%) bFF treatment did not differ. In the pretreatment period (i.e. mid-luteal phase), plasma FSH levels were 32% (P < 0.05) higher in inhibin-immunized than in control heifers. During administration of bFF to control heifers, plasma FSH was suppressed to a level 40% lower than in serum-treated heifers (P < 0.02). Unexpectedly, bFF suppressed FSH to a similar extent in inhibin-immunized heifers (37% lower than in the serum-treated group; P < 0.025). Similarly, a post-bFF rebound hypersecretion of FSH was observed in both control (P < 0.05) and inhibin-immunized (P < 0.05) heifers, although the FSH rebound lasted about 24 h longer in the latter group (P < 0.001). The timing of the preovulatory LH surge in control (86 +/- 7 h post-PG) and immunized (81 +/- 6 h post-PG) groups treated with serum was similar as was the timing of the preovulatory rise in plasma oestradiol and the subsequent rise in plasma progesterone. However, bFF treatment delayed (P < 0.001) the preovulatory surges of LH and oestradiol and the subsequent rise in plasma progesterone to a similar extent (> 4 days) in both control and inhibin-immunized groups.(ABSTRACT TRUNCATED AT 400 WORDS)