Consequences of increasing or decreasing plasma FSH concentrations during the preovulatory period in Romney ewes

Romney ewes were infused with ovine FSH (NIADDK-oFSH-16) for 48 h from the initiation of luteolysis with cloprostenol. Doses of 2.5 or 5 micrograms/h which partly or completely prevented the normal preovulatory decline in plasma FSH concentrations caused a significant increase in mean ovulation rates. Ovulation rates were not increased significantly if the FSH (5 micrograms/h) was infused for only 20 h starting from the initiation of luteolysis or 24 h later. Infusion of a less potent and relatively impure preparation of FSH (i.e. FSH-P) at 0.5 mg/h for 48 h after cloprostenol treatment also increased the mean ovulation rate significantly. However, if the FSH-P was given for only the first 24 h, or if the start of the infusion was delayed for more than 12 h, mean ovulation rates were not increased significantly. Infusion of LH (NIADDK-oLH-25, 5 micrograms/h) for 48 h from the initiation of luteolysis decreased the mean ovulation rate significantly. Administration of bovine follicular fluid to suppress plasma FSH concentrations below normal during the first 24 h after cloprostenol injection did not delay oestrus. However, oestrus was delayed by approximately 2 days if plasma FSH concentrations were reduced by bovine follicular fluid 24 h after the initiation of luteolysis. As ovulation rate increased, the mean weight of individual corpora lutea of each ewe decreased. In ewes with a single ovulation, most corpora lutea weighed greater than 600 mg, but as the ovulation rate increased the proportion of corpora lutea present weighing less than 400 mg rose steadily.(ABSTRACT TRUNCATED AT 250 WORDS)     

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 During follicular fluid treatment plasma levels of FSH in samples withdrawn just before injection of follicular fluid at 09:00 h (i.e. 16 h after previous injection of follicular fluid) were initially suppressed, but by Day 8 of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.     

Suppression of the secondary FSH surge with bovine follicular fluid is associated with delayed ovarian follicular development in heifers

Holstein heifers were given 5 injections (twice/day) of 10 ml charcoal-extracted bovine follicular fluid (bFF; N = 6) or 10 ml saline (N = 5) beginning 12 h after the onset of oestrus. Blood samples were collected for determination of plasma concentrations of FSH, LH, progesterone and oestradiol-17 beta. Treatment with bFF suppressed the secondary FSH surge (P less than 0.01). Cessation of bFF injections was followed by a rebound period during which FSH was elevated compared with controls (P less than 0.01). Daily ultrasonographic examinations revealed that follicular growth occurred in waves, with 4 of 5 control heifers exhibiting 3 waves and the other 2 waves. In contrast, 5 of 6 bFF-treated animals exhibited 2 waves and the other 3 waves. Appearance of follicles in the first wave was delayed in bFF-treated heifers (Day 3.3 +/- 0.3 compared with Day 1.4 +/- 0.2; P less than 0.0001) and appearance of the dominant follicle of the first wave was delayed (Day 4.5 +/- 0.3 compared with Day 1.8 +/- 0.2; P less than 0.0001). Follicles in the second wave appeared later in animals treated with bFF (Day 12.7 +/- 0.4 compared with Day 10.4 +/- 0.6; P less than 0.01), and the dominant follicle of this wave also appeared later (Day 13.0 +/- 0.5 compared with Day 10.6 +/- 0.5; P less than 0.01). Oestradiol-17 beta increased during the early luteal phase, but this increase occurred later in heifers treated with bFF (peak concentrations on Day 6.3 +/- 0.6 compared with Day 4.2 +/- 0.2; P less than 0.05). LH, progesterone and cycle length were not affected by bFF. Delayed follicular growth associated with suppression of FSH suggests that the secondary FSH surge is important in the initiation of follicular development early in the bovine oestrous cycle, and thus may play a role in the regulation of ovarian follicular dynamics.     

Follicular dynamics and temporal relationships among body temperature, oestrus, the surge of luteinizing hormone and ovulation in Holstein heifers treated with norgestomet

The effects of chronic treatment with norgestomet on follicular dynamics, corpus luteum growth and function as well as the temporal relationships among body temperature, oestrous behaviour, the luteinizing hormone (LH) surge and ovulation following implant removal were studied in 16 Holstein heifers. Oestrous cycles of the heifers were initially synchronized using 2 injections of prostaglandin F-2 alpha (PGF-2 alpha) 12 days apart. The heifers were then implanted with a norgestomet ear implant for 9 days, beginning either at the middle of the synchronized cycle (dioestrus) or at the end of the synchronized cycle (pro-oestrus). Follicular dynamics, corpus luteum growth and regression, and plasma progesterone were not affected by norgestomet treatment at dioestrus. The dominant follicle present at the time of norgestomet implantation in the pro-oestrus group was maintained during the 9-day implant period of 6 of 8 heifers and ovulated after implant removal. Time from implant removal to onset of standing oestrus and time to LH peak following implant removal were highly correlated with the time of ovulation (r = 0.92 and 0.96, respectively). Onset of standing oestrus and the LH peak and the onset of standing oestrus and peak vaginal and rectal temperatures were also highly correlated (r = 0.96, 0.82 and 0.81, respectively). It is concluded that any decrease in pregnancy rates following treatment with norgestomet is not due to asynchrony among oestrus, the LH surge and ovulation.     

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

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

Ovulation rate and embryo survival in Damline ewes after treatment with bovine follicular fluid in the luteal phase of the oestrous cycle

Treatment of Damline ewes with twice daily i.v. injections of bovine follicular fluid during the luteal phase for 10, 6 or 2 days before prostaglandin-induced luteolysis resulted in an increase in ovulation rate. This was associated with a large rebound increase in plasma concentrations of FSH after the last injection of bovine follicular fluid. While conception rate was not affected by bovine follicular fluid treatment, a higher percentage embryonic loss was observed between Days 3 and 34 of pregnancy in the 10-day treatment group only compared to controls. This reflected the increase in ovulation rate above the optimum for embryonic survival in this breed. The present results suggest that the increase in ovulation rate induced by bovine follicular fluid treatment in the luteal phase of the cycle before mating would result in a significant increase in the number of lambs born.     

Simultaneous injection of follicle stimulating hormone (FSH) and the prostaglandin F2alpha analog cloprostenol (PGF) disrupts follicular activity in diestrous dairy cows

Simultaneous injections of PGF and FSH or saline were given to 32 Holstein cows to test their combined ability to improve estrous and ovulation synchrony beyond that of PGF alone. All the cows were randomly assigned to receive PGF on either Day 8 or Day 10 of the estrous cycle (estrus = Day 0), and all the cows in each group were further assigned to simultaneous injection of either FSH or saline. Regression of the corpus luteum (CL), return to estrus and follicular activity were monitored by plasma progesterone assay, twice-daily estrous detection and ultrasonographic examination, respectively. Plasma progesterone concentrations declined to <1.0 ng/ml at 24 hours after PGF treatment in all the cows and FSH did not affect this decline. Return to estrus was not affected by FSH treatment in cows treated on Day 8 or Day 10; however, FSH disrupted normal follicular activity and either delayed normal ovulation following estrus or induced premature ovulation or cyst formation in 4 of 8 PGF/FSH (Day 8) cows and 5 of 8 PGF/FSH (Day 10) cows. These data indicate that exogenous FSH administered simultaneously with a luteolytic does of PGF does not maintain viability of large, dominant follicles and, therefore, is not an effective method for the synchronization of estrus and ovulation.     

Effect of enucleation of the corpus luteum at different stages of the luteal phase of the human menstrual cycle on subsequent follicular development

To investigate the mechanism of suppression of follicular development during the luteal phase of the human menstrual cycle, the corpus luteum was enucleated surgically from 10 women at various times after ovulation. In the 24 h after CL enucleation there was an immediate and rapid fall in the concentration of oestradiol and progesterone and a temporary decline in the concentration of FSH and LH. Within 3 days, however, all 10 women showed evidence of renewed follicular activity as indicated by a progressive rise in the concentration of oestradiol. This rise was preceded by a rise in the concentration of FSH and LH, and ovulation, as indicated by a mid-cycle surge in LH and rise in the concentration of plasma progesterone, occurred 16-19 days after enucleation. There was no significant difference in the time to ovulation following enucleation at different times of the luteal phase. The post-operative follicular phase, measured from the time of enucleation, was 3 days longer than that observed pre-operatively from the first day of menstrual bleeding. In the follicular phase of post-operative cycles the concentration of FSH was higher and that of oestradiol lower than the corresponding values before surgery. These results indicate that the absence of healthy antral follicles in the luteal phase of the cycle is due to the inhibitory effects of the corpus luteum. The fact that, after CL enucleation, emergence of the dominant follicle was always preceded by a rise in the concentration of FSH and LH suggests that suppression of gonadotrophins by ovarian steroids secreted by the corpus luteum is responsible for the inhibition of follicular development during the luteal phase of the cycle.     

Blood flow changes and vascular appearance in preovulatory follicles and corpora lutea in immature, pregnant mare's serum gonadotropin-treated rats

In the present study, synchronized follicular growth, ovulations, and luteogenesis were prematurely induced in 26-day-old immature rats by the s.c. injection of 4 IU of pregnant mare's serum gonadotropin (PMSG) at 2100 h. Relative blood flow of follicles/corpora lutea, fallopian tube, and uterus was measured with radioactive microspheres during the periovulatory period (Day 28, 1700 h-Day 31, 1300 h). Also, follicular/corpus luteal light microscopy and plasma progesterone were studied at the same intervals after PMSG injection. It was found that the relative follicular blood flow did not increase after the endogenous gonadotropin surge (Day 29, 0300-0500 h) and toward ovulation (Day 29, 1300-1500 h). During the same time period, light microscopy showed an interstitial edema and extravasation of erythrocytes appearing in the follicular wall near the time of ovulation. The relative blood flow reached its nadir in the young corpus luteum (21 h after ovulation) and increased thereafter (i.e., 48 h after ovulation). Plasma progesterone showed a preovulatory increase and then declined just prior to the ovulatory period. Between 24 and 48 h after ovulation, parallel increases in relative blood flow, morphological vascularization, morphological luteinization, and plasma progesterone levels were observed in the growing corpus luteum. These data indicate that a functional relationship between blood flow and steroid output may exist within the ovarian follicle and corpus luteum.     

Evidence for the action of bovine follicular fluid factor(s) other than inhibin in suppressing follicular development and delaying oestrus in heifers.

The aim of this study was to investigate the importance of inhibin in the delay in return to oestrus in heifers induced by steroid-stripped bovine follicular fluid (bFF). Oestrous activity was synchronized in 18 Hereford x Friesian heifers with two injections of prostaglandin (PG) 12 days apart. At the time of the second PG injection (time 0), the animals were assigned at random to one of three experimental groups and received i.v. injections of 20 ml saline (controls, n = 6), whole bFF (FF group, n = 6) or bFF in which the bioactive inhibin content had been reduced by > 95% by immunoaffinity chromatography (-INH group, n = 6; inhibin content approximately 0.8 ml whole bFF) every 8 h for 2 days. In a dose-response study, 2.5 ml whole bFF was insufficient to delay oestrus consistently following a similar synchronization regimen. Blood samples were taken every 8 h, initially before each injection and then subsequently for a further 9 days for hormone analysis. Animals were observed every 8 h throughout the experiment for signs of behavioural oestrus. The ovaries of all animals were examined using real-time ultrasonography about 30 h after the second PG injection. Treatment failed to suppress peripheral follicle-stimulating hormone (FSH) concentrations, although a significant increase was observed in both treatment groups after cessation of injections. Progesterone concentrations fell immediately after the second PG injection in all animals and remained below minimum detectable concentrations in all treated animals for the remainder of the experiment. In control animals, progesterone rose above minimum detectable concentrations by day 6 and continued to rise until the end of the experiment. Analysis of samples taken from treated animals several days after observed oestrus revealed that all had apparently ovulated. Mean daily luteinizing hormone (LH) concentrations did not differ between treatment groups before ovulation, but after ovulation, mean daily LH was significantly reduced in control animals as progesterone concentrations rose. Follicular development, as assessed by the mean antral diameter of the largest follicle on a pair of ovaries at ultrasound examination, was significantly suppressed in treated animals compared with controls (P < 0.01) and there was no significant difference (P = 0.397) between the two treatment groups. Control animals displayed oestrus 68 h (+/- 8 SEM) after the second PG injection, but oestrus was delayed in treated animals to 186h +/- 5 (FF group) and 191 h +/- 6 (-INH group).     

Control of FSH, follicular development and estrus synchronization in the mare with steroid-free follicular fluid

Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatments lasted for 10 days, at the end of which prostaglandin (PgF(2)alpha, 10 mg) was administered. Sexual behavior, follicular development and FSH concentrations were monitor daily. Concentrations of FSH in Group 2 mares, were not significantly different (P>0.05) from those of Group 1 until the mares in Group 2 were treated with follicular fluid (P<0.05). Concentrations of FSH in Group 3 mares, were significantly lower than those of Groups 1 and 2 (P<0.05) until the mares in Group 2 were treated with steroid-free follicular fluid. At this point there was no significant difference between groups 2 and 3 (P>0.05). Steroid-free follicular fluid appears to induce atresia in larger follicles (>11 mm), and the initiation of new follicular wave. The combination of progesterone and estradiol valerate appears to delay follicular growth and not to induce atresia, since larger follicles (>11 mm) continued to grow after treatment. Both treatments (groups 2 and 3) resulted in ovulations within 5 days period. The treatment in Group 1 did not have any effect on FSH or follicular development and ovulations were dispersed through a 9-day period. We concluded that steroid-free follicular fluid offers a new possibility to synchronize ovulation in the mare by controlling FSH and follicular development.     

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

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

Secretory patterns of LH and FSH during development and hypothalamic and hypophysial characteristics following development of steroid-induced ovarian follicular cysts in dairy cattle

Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17 beta (15 mg) and progesterone (37.5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2.0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development. In Exp. 1,22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2 alpha and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2 alpha injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 +/- 4 days (static phase). Then follicles developed which ovulated within 3-7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (+/- s.e.m.) concentrations of LH, FSH, oestradiol-17 beta and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P less than 0.1) in cows with cysts (2.9 +/- 0.2) than in cows without cysts (1.1 +/- 0.1) or control cows (1.4 +/- 0.2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P less than 0.1) in cows with cysts (3.6 +/- 0.3 and 2.2 +/- 0.3, respectively) than in non-cystic (2.3 +/- 0.2 and 1.0 +/- 0.2, respectively) and control (1.8 +/- 0.1 and 1.1 +/- 0.2, respectively) groups during the follicular phase. There were no differences in the FSH, oestradiol-17 beta or progesterone characteristics in cows of any of the 3 groups during the follicular phase.(ABSTRACT TRUNCATED AT 400 WORDS)     

FSH receptors in the bovine corpus luteum

Binding of follicle stimulating hormone (FSH) to a crude membrane fraction of bovine corpus luteum (CL) has been detected. This binding meets the usual criteria for a receptor based on specificity, time course of reaction and association constant (Ka = 8.5 x 10(10)M(-1)). Physiological studies with CL removed from heifers at specific times after estrus indicate that day-6 CL had the highest FSH binding. However, a correlation with physiological function was not obvious since some functional mid-cycle CL were high in progesterone and luteinizing hormone (LH) receptor but had nondetectable FSH receptor. Conversely, some late-cycle CL had low progesterone and LH receptor but significant quantities of FSH receptor.     

Relationship between the onset of oestrus, the preovulatory surge in luteinizing hormone and ovulation following oestrous synchronization and superovulation of farmed red deer (Cervus elaphus).

The timing of ovulation relative to the onset of oestrus and the preovulatory surge in luteinizing hormone (LH) was studied in red deer following treatments to synchronize oestrus and induce either a monovulatory or superovulatory response. Mature hinds (n = 36) were allocated randomly to two mating groups (n = 16 + 20), with respective treatments staggered by 4 weeks during the 1990 rut (March-April). Each hind was treated with an intravaginal controlled internal drug releasing (CIDR)-type S device for 14 days. Treatments to induce a monovulatory response included CIDR device alone (treatment A; n = 4 + 8) and additional injection of 200 iu pregnant mares' serum gonadotrophin (PMSG) at device removal (treatment B; n = 4 + 4). Treatments to induce a superovulatory response included injections of 200 iu PMSG and 0.5 units ovine follicle-stimulating hormone (FSH) at about time of removal of CIDR devices (treatment C; n = 4 + 4) and further treatment with gonadotrophin-releasing hormone (GnRH) analogue 18 h after removal of CIDR devices (treatment D; n = 4 + 4). The hinds were run with crayon-harnessed stags from insertion of CIDR devices (12 March or 9 April) and blood samples were taken every second day to determine plasma progesterone. Further blood samples were collected for determination of plasma LH and progesterone via indwelling jugular cannulae every 2 h for 72 h from removal of CIDR devices. Hinds were allocated randomly to an initial ovarian examination by laparoscopy at either 16 or 20 h (A and B), or 12 or 16 h (C and D) after the onset of oestrus, with laparoscopy repeated at intervals of 8 h until either ovulation was recorded (A and B), or for four successive occasions (C and D). All hinds received cloprostenol injections 15 days after device removal. A total of 28 hinds (78%) exhibited oestrus and a preovulatory LH surge, with mean (+/- SEM) times to onset of oestrus of 44.6 +/- 1.0 h (A; n = 7), 37.4 +/- 2.0 h (B; n = 7), 16.3 +/- 1.7 h (C; n = 6) or 14.0 +/- 1.7 h (D; n = 8). Failure to exhibit oestrus or LH surge was most prevalent among hinds in treatment A early in the rut.(ABSTRACT TRUNCATED AT 400 WORDS)     

Plasma follicle stimulating hormone,ovulation rate and fertility in Merino ewes treated with bovine follicular fluid

Charcoal-treated bovine follicular fluid (bFF) given as four 5-ml subcutaneous injections to 13 Merino-Border Leicester ewes around the time of natural luteolysis suppressed (P<0.01) plasma levels of follicle stimulating hormone (FSH) [from 1.08 ± 0.05 to 0.41 ± 0.03, mean ± s.e.m. of log_e (ng+ 1) /mlplasma]. This was followed (P < 0.01) by hypersecretion or a rebound of FSH (to 1.46 ± 0.11) lasting 32 h in 10 of the treated ewes, and then by a further fall (to 0.73 ± 0.03, P < 0.05) before the surge (1.21 ± 0.07, P < 0.05) associated with the preovulatory surge of luteinizing hormone (LH).Plasma FSH at 56–72 h before the LH surge (i.e., at the time of the FSH rebound) was correlated with the subsequent ovulation rate (n=13, r= + 0.73, P < 0.01). Fewer ewes treated with four injections of 2 or 5 ml of bFF than control ewes (injected with bovine plasma) became pregnant (28 of 41 vs. 38 of 41, χ² = 4.05, P < 0.05), although plasma progesterone was similar at Day 11 in treated and control ewes. It is concluded that plasma FSH during such a rebound influences the subsequent ovulation rate in sheep.     

Alterations in follicular fluid steroids and follicular hCG and FSH binding during atresia in hamster

Preovulatory follicles from hamsters treated on proestrus for 1-3 days with phenobarbital sodium exhibited early signs of atresia after 2-3 days of ovulatory delay. A significant increase in follicular fluid progesterone was evident by Day 1 of delay. Concentrations of androstenedione in follicular fluid were unaffected by ovulatory delay. Follicular fluid levels of estradiol in delayed follicles were either higher than proestrous values after 1 day of delay or lower after 2 and 3 days of delay. hCG binding was slightly higher than proestrous controls after ovulatory delay whereas FSH binding was significantly lower than controls after 2 and 3 days of ovulatory delay. These results indicate that in the barbiturate-treated hamster the elevated follicular fluid levels of progesterone precede by 1-2 days the previously reported increase in steroidogenic capability of delayed follicles to produce progesterone in vitro; this correlated with an increase in the ratio of hCG:FSH binding and this was mostly due to a decrease in FSH binding to whole follicles.     

Influence of dose and route of administration of bovine follicular fluid and the suppressive effect of purified bovine inhibin (Mr 31,000) on plasma FSH concentrations in ovariectomized ewes

Ovariectomized Merino ewes were used to develop an in-vivo bioassay for purified bovine inhibin of Mr 31,000. Various doses (0.25, 0.5, 1 or 2 ml) of bovine follicular fluid, given either by the intravenous (i.v.) or intracarotid route (i.c.) resulted in significant linear dose-related suppression of plasma FSH and interval to maximum suppression. Control ewes (1.0 ml steer plasma) showed no significant change in FSH over the same period. Doses of 470 and 2590 U of pure inhibin given i.v. caused a significant suppression of FSH in plasma in all ewes. The in-vivo potency estimate of the high dose (2760 U, 1420-4690 fiducial limits) agreed well with the in-vitro assay of potency. There were no significant changes observed in mean plasma LH after treatment with the higher dose of pure inhibin. There were no rebound effects of treatment with bovine follicular fluid or pure inhibin on FSH concentrations above that of controls. It is concluded that the form of bovine inhibin of Mr 31,000, which is believed to be the predominant circulating form, is biologically active when administered in vivo.     

Effects of oestradiol-17 beta, progesterone or bovine follicular fluid on the plasma concentrations of FSH and LH in ovariectomized Booroola ewes which were homozygous carriers or non-carriers of a fecundity gene

The plasma concentrations of FSH and LH were measured in ovariectomized Booroola FF and ++ ewes before and after treatment with subcutaneous implants of oestradiol-17 beta (0, 2 or 8 cm Silastic capsules; 5 ewes/genotype per dose) or progesterone (0, 1 or 3 Silastic envelopes; 5 ewes/genotype per dose) or subcutaneous injections of steroid-free bovine follicular fluid (bFF; 0, 0.5, 1.0, 2.5 or 5 ml; 4 ewes/genotype per dose). During the first 50 h after implantation of oestradiol or progesterone, or the first 24 h after bFF treatment, the FSH and LH concentrations in plasma were not different between the genotypes although there were significant effects of the steriods and bFF with respect to dose (P less than 0.05). At 6 days after steroid implantation, no gene-specific effects were noted for the plasma concentrations of FSH although significant effects of dose of oestradiol (P less than 0.01) but not progesterone were noted. Also at 6 days after steroid implantation, no gene-specific differences in the pulsatile patterns (i.e. peak frequency or amplitude) of plasma LH concentrations were noted although there were significant effects of steriod dose (P less than 0.05) on frequency and/or amplitude. It is concluded that the higher ovulation-rate in FF than ++ Booroola ewes is unlikely to be due to gene-specific differences in the sensitivity of the hypothalamic-pituitary axis to ovarian hormones.     

Direct effects of ovine follicular fluid on ovarian steroid secretion and expression of markers of cellular differentiation in sheep

The objective of this study was to assess the effect of ovine follicular fluid (FF) treatment (with or without FSH replacement) during the late follicular phase on plasma concentrations of gonadotrophins and the development of the ovulatory follicle. Ovarian steroid secretion and expression of mRNA encoding inhibin alpha and beta A, beta B subunits, P450 aromatase and P450 17 alpha-hydroxylase were used as endpoints. After induction of luteolysis by injection of 100 micrograms cloprostenol on days 10-12, Scottish Blackface ewes were allocated to one of three groups: (1) control (n = 7): no further treatment; (2) FF (n = 9): subcutaneous injections of 3 ml steroid-free ovine follicular fluid at 9 h intervals, 18 and 27 h after cloprostenol injection; (3) FF + FSH (n = 8): injections of follicular fluid as above plus subcutaneous injections of 0.36 iu ovine FSH at 6 h intervals, 18, 24, and 30 h after cloprostenol injection. Jugular venous blood samples were obtained via indwelling cannulae at 6 h intervals from 0 to 36 h after cloprostenol injection, and at 10 min intervals from 12 to 18 h (control phase) and from 30 to 36 h after cloprostenol injection (treatment phase). At laparotomy, 36 h after cloprostenol injection, ovarian venous blood was collected and ovaries were removed and processed for in situ hybridization. Plasma concentrations of FSH, luteinizing hormone (LH) and oestradiol were determined by radioimmunoassay. Follicular fluid treatment resulted in a decrease (P < 0.001) in FSH concentrations associated with an acute decrease in ovarian steroid secretion (P < 0.01) and a specific depression in P450 aromatase, (P < 0.001), inhibin-activin beta B subunit (P < 0.05) and thecal LH receptor (P < 0.001) expression. Follicular fluid treatment had no effect on inhibin-activin alpha and beta A, subunit or P450 17 alpha-hydroxylase expression. FSH co-treatment with follicular fluid restored circulating FSH concentrations to normal values and reversed some of the effects of follicular fluid (androstenedione, testosterone and progesterone secretion, and inhibin beta B and thecal LH receptor expression) but not oestradiol secretion or P450 aromatase expression. It was concluded that the actions of follicular fluid are mediated via both central effects on pituitary FSH secretion and by direct ovarian effects on granulosa cell aromatase activity. The results indicate that follicular fluid contains a factor that inhibits aromatase activity of granulosa cells directly and may play a role in the selection of the dominant follicle.