Effects of ovine follicular fluid on plasma LH and FSH secretion in ovariectomized ewes to indicate the site of action of inhibin

Ovariectomized ewes were given 2 ml s.c. injections of ovine follicular fluid (oFF) (N = 3) or serum (N = 3) and blood samples were collected each day for 3 days. Follicular fluid caused a significant (P less than 0.005) reduction in FSH within 1 day, but did not affect mean LH values. Two groups of 3 ewes were treated as above but sampled intensively (each 10 min for 6 h) on Days 1 (before treatment) and 4; mean plasma FSH concentration and plasma LH pulse frequency and amplitude were ascertained. Significant (P less than 0.005) reduction of FSH concentration was seen in the oFF-treated ewes. A non-specific reduction in LH pulse amplitude, but not pulse frequency, was noted in the control ewes. This experiment was repeated with 2 groups of 4 ewes that were conditioned to the experimental environment and effects on LH secretion were not observed in the controls given serum. Treatment with oFF caused a 70% reduction (P less than 0.005) in plasma FSH and a small (30%) but significant (P less than 0.005) reduction in mean LH concentrations. The latter was probably associated with a reduction in LH pulse amplitude in 3/4 animals (N.S.) with no change in LH pulse frequency. Treatment with oFF, as in Exp. 1, caused a 95% reduction in FSH values and significant (P less than 0.01) reduction (32%) of LH pulse amplitude in ovariectomized ewes that had been subjected to hypothalamo-pituitary disconnection and in which gonadotrophin secretion was reinstated with pulses of 250 ng GnRH every 2 h. These results suggest that proteins from the sheep follicular fluid, including inhibin, act at the pituitary level to inhibit FSH secretion and may have some effects on LH pulse amplitude.     

Effects of bovine follicular fluid inhibin on serum gonadotrophin concentrations in ewes during oestrus

Experiments were conducted with ewes to investigate the effects of an enriched bovine follicular fluid inhibin preparation (INH) on gonadotrophin secretion after the onset of oestrus. Administration of INH (10 mg) 1 h after the onset of oestrus did not significantly alter the preovulatory FSH and LH surges or the second FSH peak. To determine the effects of INH on the second FSH surge, ewes were treated with saline (N = 7) or INH (N = 10) at 4 h (10 mg) and 24 h (5 mg) after the peak of the preovulatory LH surge. The second FSH surge was delayed about 24 h (P less than 0.05) in ewes treated with INH; however, the delay did not alter the interval to the next oestrus. In a third experiment, 16 ewes were assigned to 4 groups in a 2 x 2 factorial with the main effects being ovariectomy at 4 h and INH treatment (10 mg) at 4, 20 and 36 h after the peak of the LH surge. Controls received sham ovariectomy and saline injection as appropriate. Ovariectomy resulted in a rapid increase in serum FSH but not LH and this was delayed (P less than 0.05) by INH treatment. These results indicate that inhibin has a selective inhibitory action on FSH secretion in ewes and suggests that the second FSH surge results from increased basal FSH secretion due to decreased endogenous inhibin levels.     

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)     

The effect of dose and route of oestradiol benzoate administration on plasma concentrations of oestradiol and FSH in long-term ovariectomised heifers

Oestradiol (E(2)) suppresses FSH and affects follicle wave dynamics in cattle. However, neither the optimum dose of ODB required to suppress FSH nor the effect of route of ODB administration on blood concentrations of E(2) are known; hence, the aim of this experiment was to answer these questions. Ovariectomised heifers received Progesterone Releasing Intravaginal Device (PRID) for 7 days, and 4 days later heifers received one of eight ODB treatments at second PRID insertion as follows; (1) 0.0 mg (Control; n=3), (2) 0.5 mg (n=4), (3) 1.0 mg (n=4), (4) 2.5 mg (n=6), (5) 5.0 mg (n=4), (6) 10. 0 mg (n=4), (7) 5.0 mg (n=4), and (8) 10.0 mg (n=5). For treatments 2-6 inclusive, ODB was administered intramuscularly in oil, while for treatments 7 and 8, the ODB in powder form was administered topically in the vagina by gelatine capsule attached to the PRID. Blood samples were collected every 6 h for the first 48 h, every 12 h for the next 48 h, and twice daily for a further 6 days. The interval from ODB administration to peak E(2) concentration was similar (P0.05) for treatments 2-6 where ODB was administered intramuscularly (mean 13.4+/-1.24 h), and was longer (P<0.05) for the intravaginal capsule treatments (mean 25.5+/-2.84 h). Plasma concentrations of E(2) increased with increasing intramuscular dose of ODB injected, (plasma E(2)=-0.237+16.109 (dose)-0.74 (dose)(2), R(2)=0.75; P<0.05). Peak plasma concentrations of E(2) following the 5- and 10-mg capsules were similar to each other and to those following the 0.5-mg injection (P0.05), but were lower than concentrations obtained following injection of 1.0-5.0 mg (P<0.05). Across all treatments, both the maximum percentage decline in FSH and the interval to FSH nadir were related to the peak plasma concentrations of E(2) (maximum % decline in FSH=11.17+1.564 (peak E(2))-0.009 (peak E(2))(2), R(2)=0.75; P<0.01), (hours to FSH nadir=10.628+1.486(hours to peak E(2))-0.0282(hours to peak E(2))(2), R(2)=0.22; P<0.05). Concentrations of FSH increased as E(2) declined from its peak value, irrespective of maximum value achieved. It was concluded that the intramuscular administration of ODB in oil to ovariectomised heifers given a PRID results in higher plasma concentrations of E(2) and causes a greater reduction in FSH than administration topically by intravaginal gelatine capsule. E(2) transiently suppresses FSH in ovariectomised heifers, and the magnitude of the suppression is dose-dependent; however FSH concentrations begin to increase 1-2 days after ODB administration while concentrations of E(2) were declining but still high.     

Differences in the plasma concentrations of FSH and LH in ovariectomized Booroola FF and ++ ewes

During 12 sampling days before ovariectomy the mean plasma FSH but not LH concentrations in FF ewes were higher (P less than 0.01) than those in ++ ewes (16 ewes/genotype). After ovariectomy increases in the concentrations of FSH and LH were noted for ewes of both genotypes within 3-4 h and the rates of increase of FSH and LH were 0.18 ng ml-1 h-1 and 0.09 ng ml-1 h-1 respectively for the first 15 h. From Days 1 to 12 after ovariectomy, the overall mean +/- s.e.m. concentrations for FSH in the FF and ++ ewes were 8.1 +/- 0.6 and 7.1 +/- 0.4 ng/ml respectively and for LH they were 2.7 +/- 0.3 and 2.1 +/- 0.2 ng/ml: these differences were not statistically significant (P = 0.09 for both FSH and LH; Student's t test). However, when the frequencies of high FSH or LH values after ovariectomy were compared with respect to genotype over time, significant F gene-specific differences were noted (P less than 0.01 for both FSH and LH; median test). In Exp. 2 another 21 ewes/genotype were blood sampled every 2nd day from Days 2 to 60 after ovariectomy and the plasma concentrations of FSH and LH were more frequently higher in FF than in ++ ewes (P less than 0.01 for FSH and LH). The F gene-specific differences in LH concentration, observed at 21-36 days after ovariectomy were due to higher mean LH amplitudes (P less than 0.025) but not LH peak frequency in FF than in ++ ewes.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Effects of weaning on concentrations of inhibin in follicular fluid and plasma of sows.

Changes in plasma and follicular fluid concentrations of inhibin were examined in sows after weaning at 28-32 days post partum. From 0 to 48 h after weaning, inhibin concentrations were 200-300 times higher in follicular fluid from small (less than 4 mm) and medium-large (greater than or equal to 4 mm) follicles than in ovarian venous plasma. Inhibin concentrations increased in follicular fluid from medium-large follicles at 24 and 48 h after weaning; concentrations in ovarian venous plasma were positively correlated with the number of medium-large follicles (r = 0.40) and with ovarian venous plasma concentrations of oestradiol (r = 0.61). Blood samples were collected for 30 days from sows (n = 6) that exhibited oestrus within 5 days after weaning and from sows (n = 5) that remained anoestrous for 11 days after weaning. Plasma inhibin concentrations rose in oestrous and anoestrous sows by 12 h and continued to rise for 60 h after weaning. Plasma inhibin concentrations rose further and were higher at 3.5-4.5 days after weaning in oestrous sows than in sows that remained anoestrous. After oestrus, plasma inhibin concentrations declined. At weaning, plasma concentrations of follicle-stimulating hormone (FSH) were higher in sows that subsequently exhibited oestrus than in sows that remained anoestrous. After weaning, plasma concentrations of FSH declined in both groups, reached a nadir at 2.5 days, and increased gradually in anoestrous sows; oestrous sows exhibited an FSH surge at oestrus. Plasma FSH returned to preweaning concentrations in both groups of sows at Days 7-8.(ABSTRACT TRUNCATED AT 250 WORDS)     

Measurement of inhibin A and follicular status predict the response of ewes to superovulatory FSH treatments

Variability in superovulatory response to FSH stimulation is common to most mammals and imposes practical problems for assisted reproduction. In sheep, we have studied if this response is related to the ovarian follicular population and activity before the stimulation. During the breeding season, 30 ewes were treated with 40 mg FGA sponges for 14 days and 125 microg cloprostenol injection on Day 12, considering Day 0 as the day of progestagen insertion. Superovulatory response was induced with two different FSH regimes using the same total dose (8.8 mg), administered twice daily from 60 h before to 24 h after progestagen withdrawal. At the first FSH injection, all follicles > or = 2 mm were observed by transrectal ultrasonography and plasma FSH and inhibin A levels were determined. The number of corpora lutea and the number of and viability of recovered embryos in response to the treatment were determined on Day 7 after sponge withdrawal. No significant differences were found between treatments. The total mean number of corpora lutea (11.5 +/- 1.2) and recovered embryos (7.9 +/- 1.1) were positively correlated (P < 0.05 and <0.01, respectively) with the number of small antral follicles (2-3 mm: 9.2 +/- 0.7) and inhibin A concentration (240 +/- 18 pg/ml; P < 0.05 for corpora lutea and P < 0.005 for recovered embryos) observed at the onset of the superovulatory treatment, which was also positively correlated with the number of viable embryos (5.8 +/- 0.9, P < 0.005). In 18 ewes with follicles > or = 6 mm prior to FSH treatment, the ovulation rate was unaffected but the number of embryos (6.1 +/- 0.9 versus 11.6 +/- 2; P < 0.05) and their viability (4.5 +/- 0.8 versus 8.5 +/- 2; P < 0.05) was reduced. The lower number of embryos produced when a large follicle is present suggest that a proportion of the smaller follicles are in early stages of atresia and the developmental competence of their oocyte is compromised.     

Increase in ovulation rate after immunization of Merino ewes with a fraction of bovine follicular fluid containing inhibin activity

Affinity chromatography of bovine follicular fluid using Matrix gel Red A resulted in a 20-fold increase in inhibin-like specific activity assessed in a mouse ovulation inhibition test system. When this material was emulsified with Freund's adjuvant and injected into adult Merino ewes their mean ovulation rate was increased from 1.2 to 2.3 (P less than 0.01). Follicles of diameter greater than or equal to 3.5 mm and 2-3.4 mm were also increased (4.33 vs 2.25 and 5.39 vs 2.44 per ewe respectively). The ovulation rate response was variable and transient. Length of oestrous cycles, number of granulosa cells per follicle and seasonal oestrous patterns were not affected. Plasma from the immunized ewes contained antibodies to the immunogen and reversed the ovulation-inhibiting effects of bovine follicular fluid in mice.     

Associations between emergence of follicular waves and fluctuations in FSH concentrations during the estrous cycle in ewes

Folliculogenesis was studied daily in 16 interovulatory intervals in 5 Polypay ewes from mid February through April using transrectal ultrasonic imaging. The 3-mm follicles attaining > or = 5 mm on Days--1 (ovulation=Day 0) to 11 showed significant peak numbers on Days 0, 5 and 10. The number of 3- and 4-mm follicles that did not reach > 4 mm was not significant, indicating that these follicles did not manifest a wave pattern. A follicular wave was defined as one or more follicles growing to > or = 5 mm; the day the follicles were 3 mm was the day of wave emergence, and the first wave after ovulation was Wave 1. Waves 1, 2 and 3 emerged on Days -1 to 2,4 to 7 and 8 to 10, respectively. Four interovulatory intervals in April were short (9 to 14 d), indicating the end of the ovulatory season. In the remaining 12 intervals, the ovulatory wave was Wave 3 in one interval, Wave 4 in 8 intervals, and Wave 5 or 6 in 3 intervals. The ovulatory wave followed the rhythmic pattern of Waves 1 to 3 by emerging on Days 11 to 14 in 50% of the intervals. In the remaining intervals, either the ovulatory wave was Wave 4 but did not emerge until Day 16 or other waves intervened between Wave 3 and the ovulatory wave. The longest intervals (22, 24 and 24 d) had >4 waves. Based on a cycle-detection program, peak values of FSH fluctuations were temporally associated with the emergence of waves as indicated by the following: 1) tendency (P < 0.08) for an increase in FSH concentrations between 3 and 2 days before emergence of a wave; 2) close agreement between mean number of waves per interval (mean +/- SEM, 4.1 +/- 0.3) and mean number of identified FSH fluctuations (4.5 +/- 0.3); 3) close agreement in length of interwave intervals (4.0 +/- 0.3) and interpeak (FSH) intervals (3.6 +/- 0.2); 4) positive correlation (r(2)=0.8) for number of the 2 events (follicular waves and FSH fluctuations) within intervals; and 5) a closer (P < 0.01) temporal relationship between the 2 events than would have been expected if the events were independent. The results support a relationship between transient increases in FSH concentrations and emergence of follicular waves throughout the interovulatory interval in Polypay ewes, with the 2 events occurring approximately every 4 d.     

Effect of immunizing prepuberal lambs of low and high ovulation rate genotypes with inhibin partially purified from bovine follicular fluid

Active immunization of prepuberal lambs with a partially purified inhibin preparation, isolated from bovine follicular fluid, increased the ovulation rate. In ewe lambs of a low fecundity breed (Suffolk x Galway), the ovulation rate rose from 1.15 to 1.95 (P<0.05) compared with that of the controls. An ovulation rate of 3.38 was recorded for immunized ewe lambs of a high fecundity breed (Finn x Dorset Horn), while the rate for mature ewes from the same flock was 2.29. Immunization did not affect the time of onset of puberty or estrous cycle length. Following immunization, antibodies were produced that bound to a pure preparation of 68kDa bovine inhibin. This report demonstrates the production of antibody to a 68kDa preparation of inhibin following active immunization of sheep using a partially purified preparation. It was concluded that the increased ovulation rate was due to the production of antibodies to inhibin, which may have reduced its negative feedback effect of FSH secretion.     

Effects of oestradiol on LH, FSH and prolactin in ovariectomized ewes

This study was conducted to test the hypothesis that the rate (dose/time) at which oestradiol-17 beta (oestradiol) is presented to the hypothalamo-pituitary axis influences secretion of LH, FSH and prolactin. A computer-controlled infusion system was used to produce linearly increasing serum concentrations of oestradiol in ovariectomized ewes over a period of 60 h. Serum samples were collected from ewes every 2 h from 8 h before to 92 h after start of infusion, and assayed for oestradiol, LH, FSH and prolactin. Rates of oestradiol increase were categorized into high (0.61-1.78 pg/h), medium (0.13-0.60 pg/h) and low (0.01-0.12 pg/h). Ewes receiving high rates of oestradiol (N = 11) responded with a surge of LH 12.7 +/- 2.0 h after oestradiol began to increase, whereas ewes receiving medium (N = 15) and low (N = 11) rates of oestradiol responded with a surge of LH at 19.4 +/- 1.7 and 30.9 +/- 2.0 h, respectively. None of the surges of LH was accompanied by a surge of FSH. Serum concentrations of FSH decreased and prolactin increased in ewes receiving high and medium rates of oestradiol, when compared to saline-infused ewes (N = 8; P less than 0.05). We conclude that rate of increase in serum concentrations of oestradiol controls the time of the surge of LH and secretion of prolactin and FSH in ovariectomized ewes. We also suggest that the mechanism by which oestradiol induces a surge of LH may be different from the mechanism by which oestradiol induces a surge of FSH.     

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).     

Effects of oestradiol-17 beta on peripheral plasma concentrations of LH and FSH in ovariectomized tammars (Macropus eugenii)

Two experiments, each using 8 animals, were conducted in the non-breeding and breeding seasons, respectively, and each animal was injected with 4 different doses of oestradiol benzoate over 4 trials. The resulting physiological concentrations of plasma oestradiol caused depression of both LH and FSH values. The highest dose elicited a biphasic response in LH with a pulse-like surge at 24 h after injection. There was no significant difference between the response of either hormone at the two times of the year and it is concluded that, in tammars, there is no seasonal difference in the responsiveness of the hypothalamus/pituitary to the negative feedback effect of oestradiol.     

Use of fast protein liquid chromatography in the purification of inhibin from bovine follicular fluid

Inhibin from bovine follicular fluid was partly purified using affinity chromatography on immobilized Procion Red 3B, gel filtration on Sephadex G-25 and ion-exchange chromatography on the fast protein liquid chromatography system. Inhibin was subsequently characterized using preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis and electroelution. Biological activity was associated with a protein with an apparent molecular weight of approximately 65 kD.     

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)     

Inhibition and subsequent rebound of FSH secretion following treatment with bovine follicular fluid in the ewe

Plasma concentrations of gonadotropins were examined after treatment of ewes with bovine follicular fluid (FF) in four experiments. Mean concentrations of FSH were significantly decreased by FF treatment. The FSH depression appeared to continue throughout the length of treatment when the duration of treatment was 2-4 days. However, in an experiment in which the treatment period was 8 days, mean concentrations of FSH initially declined and then returned to control levels during the last 4 days of treatment. In all experiments, a rebound in FSH concentrations was found 24-36 h after cessation of FF treatment. The magnitude of this rebound appeared to be proportional to the degree of FSH suppression during FF treatment.     

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.     

Effects of FSH commercial preparation and follicular status on follicular growth and superovulatory response in Spanish Merino ewes

Ovarian follicular development was characterized in 24 Spanish Merino ewes to study effects of the follicular status and the FSH commercial product used on follicular growth and subsequent superovulatory response. Estrus was synchronized using 40 mg fluorogestone acetate sponges. The superovulatory treatment consisted in 2 daily i.m. injections of FSH from 48 h before to 12 h after sponge removal. Sheep were assigned randomly to 2 groups treated with 6 decreasing doses (4, 4, 3, 3, 2, 2 mg) of FSH-P or with 6 doses of 1.25 mL of OVAGEN. Growth and regression of all follicles > or = 2 mm were observed by transrectal ultrasonography, and recorded daily from Day 6 before sponge insertion to the first FSH injection, and then twice daily until estrus was detected with vasectomized rams. Differences were detected in follicular development from the first FSH injection to detection of estrus (-48 to 36 h from sponge removal) between groups. Administration of FSH-P increased the appearance of new follicles with respect to OVAGEN (6.3 +/- 0.7 vs 4.8 +/- 0.4; P < 0.05), and the mean number of medium (4 to 5 mm) follicles (8.9 +/- 1.2 vs 6.6 +/- 0.9; P < 0.05). However, the mean number of follicles that regressed in size after sponge removal (5.9 +/- 0.4 vs 3.3 +/- 0.4) and the number of preovulatory sized follicles that did not ovulate (60 vs 42.4%) were also higher in FSH-P treated ewes (P < 0.05). So, finally, there were no differences in ovulation rate, as determined by laparoscopy on Day 7 after sponge removal, between ewes treated with FSH-P or OVAGEN (6.3 +/- 1.9 vs 7.0 +/- 1.7 CL). In all the ewes, the ovulatory response was related (P < 0.05) both to the number of small follicles (2 to 3 mm in diameter) present in the ovaries at the start of treatment with exogenous FSH and to the number of follicles that reached > or = 4 mm in size at estrus, despite differences in the pattern of follicular development when using different commercial products.