Follicle-stimulating Hormone Pulse Frequency Research Articles

Pulsatile Luteinizing Hormone and Follicle-Stimulating Hormone Secretion and Gonadotropin Subunit mRNA Levels in the Ovariectomized GPR-4 Transgenic Rat

Genetic targeting of the cAMP-specific phosphodiesterase 4D1 (PDE4D1) to gonadotropin-releasing hormone (GnRH) neurons in the GPR-4 transgenic rat resulted in decreased luteinizing hormone (LH) pulse frequency in castrated female and male rats. A similar decrease in the intrinsic GnRH pulse frequency was observed in GT1 GnRH cells expressing the PDE4D1 phosphodiesterase. We have extended these findings in ovariectomized (OVX) GPR-4 rats by asking what effect transgene expression had on pulsatile LH and follicle-stimulating hormone (FSH) secretion, plasma and pituitary levels of LH and FSH, and levels of the α-glycoprotein hormone subunit (α-GSU), LH-β and FSH-β subunit mRNAs. In OVX GPR-4 rats the LH pulse frequency but not pulse amplitude was decreased by 50% compared to wild-type littermate controls. Assaying the same samples for FSH, the FSH pulse frequency and amplitude were unchanged. The plasma and anterior pituitary levels of LH in the GPR-4 rats were significantly decreased by approximately 45%, while the plasma but not anterior pituitary level of FSH was significantly decreased by 25%. As measured by real-time RT-PCR, the mRNA levels for the α-GSU in the GPR-4 rats were significantly decreased by 41%, the LH-β subunit by 38% and the FSH-β subunit by 28%. We conclude that in the castrated female GPR-4 rats the decreased GnRH pulse frequency results in decreased levels of LH and FSH and in the α- and β-subunit mRNA levels.

Influence of dose, frequency, and duration of infused gonadotropin-releasing hormone on secretion of luteinizing hormone and follicle-stimulating hormone in nutritionally anestrous beef cows

Nutritionally induced anovulatory cows were ovariectomized and used to determine the relationships between dose, frequency, and duration of exogenous gonadotropin-releasing hormone (GnRH) pulses and amplitude, frequency, and concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum. In Experiment 1, cows were given pulses of saline (control) or 2 μg of GnRH infused iv during a 0.1-, 1.25-, 5-, 10-, or 20-min period. Concentrations of LH and FSH during 35 min after GnRH infusion were greater than in control cows (P < 0.01), and FSH concentrations were greater when GnRH infusions were for 10 min or less compared with 20 min. In Experiment 2, the effect of GnRH pulse frequency and dose on LH and FSH concentrations, pulse frequency, and pulse amplitude were determined. Exogenous GnRH (0, 2, or 4 μg) was infused in 5 min at frequencies of once every hour or once every 4th hr for 3 d. There was a dose of GnRH × frequency × day effect on LH and FSH concentrations (P < 0.01), indicating that gonadotropes are sensitive to changes in pulse frequency, dose, and time of exposure to GnRH. There were more LH pulses when GnRH was infused every hour, compared with an infusion every 4th hr (P < 0.04). Amplitudes of LH pulses were greater with increased GnRH dose (P < 0.05), and there was a frequency × dose × day effect on FSH pulse amplitude (P < 0.0006). We conclude that LH and FSH secretion in the bovine is differentially regulated by frequency and dose of GnRH infusions.

Depression of FSH and LH secretion following pulsatile GnRH administration in ovariectomized women.

To investigate the mechanism by which pulsatile administration of gonadotrophin-releasing hormone (GnRH) modifies secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), we studied three groups of five women who had been ovariectomized for non-malignant gynaecological conditions at least 6 months previously, none of whom had received substitutional hormone therapy. Before and after 15 day treatment with subcutaneous pulsatile GnRH (one 20 microg dose every 90 min in group A, one 10 microg dose every 90 min in group B and one 20 microg dose every 120 min in group C), pulsatile secretion of LH and FSH was characterized by determining these hormones in 4 ml blood samples taken every 10 min for 8 h (9.00 a.m. to 5.00 p.m.). For both LH and FSH, mean serum concentration and pulse amplitude were lower after GnRH treatment than before (and in the case of LH the decrease depended upon both the size and frequency of exogenous GnRH pulses) but in no group was there a significant change in LH or FSH pulse frequency. We conclude that exogenous pulsatile GnRH probably acts by partially desensitizing the pituitary rather than by depressing endogenous GnRH secretion. Such partial desensitization would explain reports that exogenous pulsatile GnRH improves ovulation by women with polycystic ovary syndrome.

Endocrinology: Evidence suggesting an additional control mechanism regulating episodic secretion of luteinzing hormone and follicle stimulating hormone in pre-pubertal children and post-menopausal women

The possible differential regulation of pulsatile follicle stimulating hormone (FSH) and luteinizing hormone (LH) secretion in pre-pubertal children and in post-menopausal women was investigated. Children were studied for 4 h and post-menopausal women for 6 h; blood samples were taken every 10 min. Post-menopausal women were studied before and 21 days after administration of a single i.m. dose of gonadotrophin-releasing hormone (GnRH) analogue. Eight post-menopausal women and 18 children (nine boys and nine girls) were enrolled. The children were divided into two groups: A, at Tanner stages 0-1 (four boys and three girls); B, at Tanner stage 2-3 (five boys and six girls). Plasma LH and FSH concentrations were determined using an immunofluorimetric assay. Time series were analysed and the specific concordance (SC) index was computed to determine the degree of concordance between episodes of LH and FSH secretion. While children of group A had LH concentrations below the minimal detectable dose of 0.1 IU/l, group B showed measurable LH plasma concentrations (1.4 +/- 0.3 IU/l, mean +/- SEM). Plasma FSH concentrations were detectable in both groups. Group A showed FSH plasma concentrations significantly lower than those of group B (0.75 +/- 0.2 and 1.95 +/- 0.4 IU/l respectively; P < 0.05), but FSH pulse frequency was higher in group A (P < 0.05). Children of group B showed significant concomitance of LH and FSH secretory events at time 0 (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated inhibin concentration in the follicular fluid of dairy cows with chronic cystic ovarian disease

This study compared serum and follicular fluid inhibin and gonadotropin profiles between chronic cystic ovarian diseased (CCOD) and normal cyclic dairy cows. Blood samples and follicular fluid were collected from CCOD cows (n=15) and cyclic cows in the follicular phase of the estrous cycle (control, n=6) and analyzed for inhibin, follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations. There was a significant increase in inhibin and a decrease in FSH and LH concentrations in the follicular fluid of CCOD cows compared with those of cyclic cows (P < 0.05). Mean serum inhibin, FSH and LH concentrations between CCOD and cyclic cows were not differnt (P > 0.05), however, there was a tendency for serum inhibin to be higher and FSH to be lower in CCOD cows compared to cyclic animals (P < 0.1). The FSH pulse frequency also was lower in CCOD cows than in cyclic cows (P < 0.05). These data suggest that increased production of inhibin from cystic follicles of CCOD cows alters pituitary FSH secretion and subsequently reduces the concentration of FSH in follicular fluid. As a result, decreased FSH stimulation at the ovarian level could ultimately lead to the reduction in follicular LH and FSH receptor concentrations, resulting in abnormal follicular steroidogenesis in CCOD dairy cows.

The effect of danazol on pulsatile gonadotropin secretion in women with endometriosis

To determine whether the effect of danazol on gonadotropin pulsatility was due to a direct effect of the drug or the suppression in the estradiol (E2) levels. Prospective analysis of serial blood samples at 10-minute intervals for 5 hours on days 3, 4, or 5 of the control cycle and 2 months after the start of danazol treatment. Tertiary institutional outpatient care. Six eugonadal women with minimal endometriosis. Oral administration of danazol, 200 mg three times daily. Gonadotropin mean levels, pulse frequency, and amplitude. The mean level of E2 was the same in the control cycle as that during danazol treatment (170 pmol/L). Danazol administration resulted in a 16% increase in the mean luteinizing hormone (LH) pulse amplitude (95% confidence interval [CI] 6% to 26%, P less than 0.01), associated with a 20% decrease in LH pulse frequency (95% CI -71% to +31%, P = 0.37). There was a nonsignificant increase in follicle-stimulating hormone (FSH) pulse amplitude (2%, 95% CI -9% to +14%, P = 0.68) and in FSH pulse frequency (27%, 95% CI -4% to +58%, P = 0.08). The 22% decrease in the mean LH level (95% CI -85% to +12%, P = 0.13) and the 20% decrease in the mean FSH level (95% CI -53% to +37%, P = 0.33) were also not significant. The increase in LH pulse amplitude represents a direct effect of danazol on the hypothalamic-pituitary axis.

Specific regulatory actions of dihydrotestosterone and estradiol on the dynamics of FSH secretion and clearance in humans.

The authors investigated immunoactive and bioactive follicle-stimulating hormone (FSH) secretion and clearance in six healthy young men during steady-state infusions of vehicle (basal, B, 28 hours), dihydrotestosterone (DHT, 4.5 days), or estradiol (4.5 days) accompanied by blood sampling at 10-minute intervals for 28 hours. Serum FSH concentrations were assayed by a two-site immunoradiometric assay (IRMA) and two separate in vitro bioassays (rat granulosa and Sertoli cell systems). FSH measurements included: 24-hour mean serum concentrations (IRMA and bioassay), multiple-parameter deconvolution of 24-hour pulsatile FSH time series and FSH release in response to exogenous gonadotropin-releasing hormone (GnRH) boluses (IRMA) to assess secretion and clearance, and circadian serum FSH concentration rhythms by cosinor analysis (IRMA). We found: 1) a significant decrease in 24-hour mean IRMA FSH concentrations during DHT infusion while both in vitro estimates of FSH bioactivity were unchanged; 2) significant decreases in the mass of IRMA FSH secreted per 24 hours during DHT infusion; 3) significant decreases in the IRMA FSH half-life during estradiol infusion without any change in FSH interpulse interval; 4) no steroidal effects on FSH secretory responses to exogenous GnRH; and 5) abolition of basal circadian FSH rhythms during sex-steroid infusions. Based on these findings, we conclude that steady-state sex-steroid hormone infusions selectively alter IRMA FSH secretion and clearance without affecting IRMA FSH pulse frequency or mean concentrations of bioactive FSH.

Pulsatile release of gonadotropins in young pony stallions

Basal concentrations and pulsatile-release patterns of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were characterized in five pony stallions, aged 2 to 4 yr. Jugular blood was collected from each pony at 20-min intervals for 24 h. Plasma was separated and frozen until quantification of LH and FSH by RIA. Hormonal data were subjected to a computerized cycle-detection program for estimating frequency and amplitude of regular and irregular episodic fluctuations in gonadotropin concentrations in the presence of high levels of random measurement errors. Ponies were castrated, testes were weighed, and parenchymal sections were procured for determination of daily spermatozoal production per gram of testicular parenchyma (DSP/gm) and daily spermatozoal production per pony (DSP). Values (mean ± SD) for basal concentration of LH (basal LH), LH pulse amplitude (amp LH), duration of LH pulse (dur LH), LH pulse frequency (freq LH), basal concentration of FSH (basal FSH), FSH pulse amplitude (amp FSH), duration of FSH pulse (dur FSH), and FSH pulse frequency (freq FSH) were 4.80 ± 2.39 ng/ml, 3.13 ± 1.16 ng/ml, 46.4 ± 3.6 min, 0.869 ± 0.04 pulses/h, 7.34 ± 6.33 ng/ml, 6.50 ± 7.60 ng/ml, 43.9 ± 11.7 min, and 0.868 ± 0.14 pulses/h, respectively. Regression analyses revealed significant (P<0.05) linear relationships between freq LH and DSP/gm (r=0.97), basal LH and DSP/gm (r=0.89), amp LH and DSP (r=0.99), freq LH and DSP (r=0.97), and basal LH and DSP (r=0.92). A significant quadratic relationship existed between amp LH and DSP/gm (r=0.99). Both amp LH and freq LH were more highly correlated with DSP/gm and DSP than was basal LH. Basal concentrations and pulsatile release characteristics of LH were not related to testes weight (TW) (P>0.05). Morever, basal concentrations and pulsatile release characteristics of FSH were not related to TW, DSP/gm or DSP (P>0.05). Cross-correlations between LH and FSH were not observed (P>0.05).

Alcohol effects on LH and FSH in ovariectomized female monkeys

The acute effects of alcohol (2.5, 3.0, 3.5 g/kg) and sucrose control solution on basal levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were compared in recently and chronically ovariectomized female rhesus monkeys. Integrated plasma samples were collected at 20 min intervals for 3 hr before and 6 hr after nasogastric intubation of alcohol or isocaloric sucrose control solution. Baseline levels of LH and FSH were significantly higher in recently than in chronically ovariectomized females ( p<0.001). Baseline LH pulse frequency was also significantly higher ( p<0.001) in the recently ovariectomized group than in the chronically ovariectomized group (0.704±0.03 vs. 0.379±0.10 pulses/hr). FSH pulse frequency was equivalent in both groups (0.444±0.06 to 0.360±0.06 pulses/hr). After 2.5 g/kg of alcohol, peak blood alcohol levels were 243 to 256 mg/dl and LH decreased significantly ( p<0.01) in both groups. After 3.0 g/kg alcohol, peak blood alcohol levels were 237 to 289 mg/dl, and basal LH levels ( p<0.05) and LH pulse frequency ( p<0.05) decreased significantly only in the recently ovariectomized group. After 3.5 g/kg of alcohol, peak blood alcohol levels exceeded 320 mg/dl, and LH did not change significantly in either group. Administration of 3.5 g/kg alcohol was associated with increased LH pulse amplitude in some individuals. Since lower alcohol doses (2.5 and 3.0 g/kg) and sucrose control administration were followed by a significant decline in LH ( p<0.05−0.01) and the highest alcohol dose (3.5 g/kg) was not, these data suggest the possible influence of nonspecific “stress” on modulation of LH secretory activity. FSH did not change after sucrose administration in recently ovariectomized monkeys, but was significantly suppressed after 2.5 and 3.5 g/kg alcohol ( p<0.05). In the chronically ovariectomized monkeys, FSH decreased significantly after administration of sucrose and all alcohol doses. LH suppression was not consistently associated with changes in FSH in either group—a finding consonant with the hypothesis that LH and FSH may be controlled by different hypothalamic regulatory factors.

Ovarian inhibition of peripheral plasma concentration of follicle stimulating hormone in prepuberal holstein heifers

The objective of this study was to determine effects of age and castration on follicle stimulating hormone (FSH) secretion in prepuberal heifers. In experiment 1, twelve heifers were bilaterally ovariectomized at 3, 6, or 9 months of age (n = 4/group). Blood was collected at 10 min intervals for 8 hr at 1 week before ovariectomy and 1 and 4 weeks after ovariectomy. Frequency, amplitude and duration of FSH pulses were calculated. Mean plasma concentration of FSH (ng/ml), and frequency (pulses/8 hr), amplitude (ng/ml), and duration (min/pulse) of FSH pulses were not altered by age. Mean concentration of FSH increased (P<.01) from 1 week before to 1 week and 4 weeks after ovariectomy, respectively, in all age groups. Pulse frequency increased (P<.05) from 1 week before ovariectomy to 4 weeks after ovariectomy in 3 month old heifers. Pulse amplitude of FSH increased (P<.01) from 1 week before to 1 week after ovariectomy in 3 month old heifers, from 1 week before to 4 weeks after ovariectomy in 6 month old heifers, and from 1 week before to 1 week and 4 weeks after ovariectomy in 9 month old heifers. In experiment 2, twelve heifers were bilaterally ovariectomized at 3, 6 or 9 weeks of age (n = 4/group). Sample collection and measurement of mean concentration of FSH were the same as in experiment 1. Mean concentration of FSH increased (P<.01) from 1 week before to 1 and 4 weeks after ovariectomy in heifers ovariectomized at 6 and 9 weeks of age. Mean concentration of FSH increased (P<.01) from 1 week before to 4 weeks after ovariectomy in heifers ovariectomized at 3 weeks of age and was increasingly higher (P<.05) in heifers ovariectomized at 3 to 6 to 9 weeks of age. Thus, ovarian inhibition of FSH secretion is established in Holstein heifers ovariectomized at 9 weeks of age and maintained through 9 months of age.

Pulsatile patterns of gonadotropins and ovarian steroids during estrus and pseudopregnancy in the rabbit.

Consecutive daily plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17 beta (E2), progesterone (P4) and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP) were monitored in estrous rabbits and in these same doses during pseudopregnancy (PSP); these daily hormone levels, as well as the immediate post-coital changes in gonadotropin secretion, were similar to those in previous reports. To examine the pulsatile patterns of the gonadotropins and ovarian steroids, sequential, 10-min plasma samples were collected for 6 h from estrous does and on Days 3, 10, and 17 of PSP. All five hormones were measured in the serial samples from estrous and PSP Day 10 does; LH and FSH only were assayed in the remaining sequential samples. The amplitude and frequency of FSH pulses did not differ between any of these stages. In marked contrast, LH pulse amplitudes, and even pulse frequencies in Day 17 does, were profoundly increased during PSP above those in estrous does. Progestin secretions, both P4 and 20 alpha-OHP, also were sharply elevated in PSP Day 10 does as compared with those in estrous rabbits; the pulse amplitudes of both progestins were severalfold higher during PSP. P4 pulse frequencies were also increased at this time. Conversely, the parameters of E2 secretion did not differ between estrous and PSP Day 10 animals. In PSP Day 10 does, high amplitude pulses of both P4 and 20 alpha-OHP occurred simultaneously with high amplitude LH pulses. Simultaneous E2 and P4 pulses were evident in these same sequential plasma samples, and this E2-P4 pulse association was greater than that of 20 alpha-OHP pulses with E2 pulses. Our findings failed to identify conclusively the trophic stimulus for the progestin pulse patterns, but the mechanism may involve the coordinated action of LH and E2. The results do demonstrate that each gonadotropin and ovarian steroid is secreted in a pulsatile manner in both estrous and pseudopregnant rabbits. There are altered profiles in LH and progestin pulses, without major changes in FSH and E2 patterns, between the stages of estrus and PSP. The causes and consequences of these divergent endocrine shifts cannot be deduced from these data.

Follicular phase gonadotropin secretion in cyclic postpartum beef cows with phlorizin-induced hypoglycemia.

Twenty mature, lactating Hereford-cross cows were used to determine the effect of phlorizin-induced hypoglycemia on gonadotropin secretion following prostaglandin-induced luteolysis. Cows were 43 to 108 d postpartum and had a functional corpus luteum (CL) at the start of infusion treatment (d 1). Infusions consisted of either saline (control) or 3 g/d of phlorizin infused continuously from the time of prostaglandin injection at 1000 on d 1 until 0800 on d 5. Blood samples were collected for determination of plasma concentrations of insulin, glucose and free fatty acids (FFA) and for serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone. Plasma concentrations of insulin (P less than .05) and glucose (P less than .05) were lower, whereas FFA concentrations increased (day X treatment, P less than .05) over the infusion period in phlorizin-treated cows compared with saline-infused controls. Mean serum concentrations of LH (1.17 +/- .10 vs 1.53 +/- .20 ng/ml; P less than .05) and LH pulse amplitude (1.69 +/- .14 vs 2.47 +/- .37 ng/ml; P less than .10) were lower in phlorizin-infused compared with saline-infused cows during the 0 to 24-h period immediately preceding the ovulatory gonadotropin surge. The FSH pulse frequency increased (.33 +/- .11 to .55 +/- .12 pulses/h) in saline-infused cows, but decreased (.61 +/- .10 to .41 +/- .11 pulses/h) in phlorizin-infused cows before the gonadotropin surge. Other characteristics of gonadotropin secretion were similar among phlorizin-infused and saline-infused cows. All but one phlorizin-infused cow ovulated and formed functional CL similar to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of exogenous melatonin administration on gonadotropin and prolactin patterns in ovariectomized estradiol-treated heifers exposed to increasing photoperiod

Eight nulliparous Angus and Angus crossbred heifers, which had been ovariectomized and treated with estradiol-17β (E 2) S.Q. implants for 6 months, were used to determine the effects of exogenous melatonin on serum gonadotropin and prolactin concentrations. Melatonin (15 mg) or corn oil (vehicle) was administered as a single i.m. injection at 1600 h daily for 12 weeks (March 19 to June 4, 1982). Blood samples taken weekly via jugular venipuncture at approximately 1100 h were assayed for luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin and E 2. At 4-week intervals, animals were fitted with indwelling jugular cannulae at 1100 h and samples were taken for 4 h at 15-min intervals. These samples were used to estimate pulsatile patterns of LH, FSH and prolactin. On the day of the first 15-min sampling, additional blood samples were collected at 30 min intervals from 1500 to 2200 h to determine the acute effect of melatonin injection on concentrations of LH, FSH and prolactin. Melatonin did not affect concentrations of FSH collected at weekly intervals (P=0.03) but tended to inhibit the decrease in concentrations of LH seen in the heifers treated with vehicle (P=0.12). There was a melatonin × time interaction for FSH (P=0.04) and a tendency for this interaction for LH (P=0.11). Circulating concentrations of prolactin were not different between treatment groups (P=0.83) nor was there a melatonin × time interaction (P=0.03). Estradiol was higher in the melatonin treated group (P=0.03) (15.58 ± 4.17 versus 8.25 ± 1.25 pg/ml) (X ± SEM) and the melatonin × time interaction was significant (P=0.001). There was a tendency for a melatonin × time interaction for FSH pulse frequency (P=0.10). Prolactin pulse duration tended to decrease in response to melatonin treatment (P=0.14) (15.92 ± 9.29 versus 11.04 ± 4.57 min). These data do not support the hypothesis that melatonin decreases prolactin concentrations in cattle and indicates that other factors must mediate photoperiod regulation of this hormone. However, the interpretation of these data is less clear concerning the hypothesis that melatonin may maintain elevated concentrations of gonadotropins in the presence of increasing photoperiod. Concentrations of FSH appeared to be more affected by melatonin than LH; consistent with previous observations that FSH may be more affected than LH by changes in photoperiod (2). But neither LH or FSH concentrations were clearly shown to be consistantly elevated in the melatonin treatment group.

Effects of intermittent injections of LHRH on secretory patterns of LH and FSH and ovarian follicular growth during postpartum anovulation in suckled beef cows.

Changes in numbers of ovarian follicles and coincident secretion of pituitary gonadotropins were characterized in suckled, anovulatory beef cows injected iv with 500 ng of luteinizing hormone-releasing hormone (LHRH) every 2 h for 48 or 96 h, starting 21.4 +/- .4 d after parturition. Two hours after the last injection, all cows were ovariectomized. Compared with saline-injected controls, LHRH had no effect on baseline or overall concentrations of luteinizing hormone (LH) in serum (P greater than .10), but increased (P less than .05) frequency and decreased (P less than .05) amplitude of LH pulses. Luteinizing hormone-releasing hormone increased (P less than .05) baseline concentration of follicle stimulating hormone (FSH) in serum and frequency of FSH pulses, but decreased (P less than .05) pulse amplitude. Overall concentrations of FSH increased 20% (P less than .10). Exogenous LHRH did not affect diameter of the two largest follicles or numbers of follicles 1.0 to 3.9 mm, 4.0 to 7.9 mm or greater than or equal to 8.0 mm in diameter. These data suggest that increasing the frequency of episodic LH and FSH pulses in postpartum cattle by intermittent administration of LHRH did not increase mean circulating levels of LH, or alter size and numbers of ovarian follicles within the 96-h period of injections. Thus, induction of ovulation in anovulatory cows treated with low-dose injections of LHRH cannot be explained on the basis of an increase in mean concentrations of LH or numbers of antral follicles within 96 h after initiation of injections.

Selective inhibition of follicle-stimulating hormone by porcine follicular fluid extracts in the monkey: effects on midcycle surges and pulsatile secretion

Nonsteroidal factor(s) in porcine follicular fluid (pFF) can selectively suppress tonic follicle-stimulating hormone (FSH) concentrations when administered in the follicular phase to monkeys. Here it is demonstrated that when administered in either the early follicular phase or in the midst of the spontaneous preovulatory estradiol (E2) surge (E2 greater than or equal to 200 pg/ml), pFF preferentially inhibits FSH or blocks the FSH surge, respectively, whereas immunoassayable and bioassayable luteinizing hormone (LH) surges persist. Delay in the timing of ovulation uniformly follows follicular phase pFF administration, and corpus luteal insufficiency is often seen. The inhibitions of FSH in circulation were achieved by a decrease in amplitude and frequency of FSH pulses. No discernible effect on LH pulsatility was observed.

Pituitary and ovarian function in postpartum beef cows. III. Induction of estrus, ovulation and luteal function with intermittent small-dose injections of GnRH.

The effects of intermittent small-dose injections of gonadotropin-releasing hormone (GnRH) and/or exogenous estradiol-17p (E2) on estrus, ovulation and luteal function were examined. Fifty-five anestrous postpartum beef cows were allotted at random to 1 of 5 treatment groups (11 cows/group). The groups were designated: suckled control (SC, no GnRH or E3); GnRH; E2; GnRH + E2; and weaned control (WC, no GnRH or E2, calves weaned on Day 20 ± 2 postpartum). E2 implants and/or injections of GnRH (500 ng/injection every 2 h) were given for 4 days starting on Day 20 ± 2 postpartum. The intermittent injections of GnRH induced pulses of luteinizing hormone (LH) (2.8-3.3 ng/ml) and follicle-stimulating hormone (FSH) (57.3-65.4 ng/ml) that were greater (P 0,10) on the frequency of FSH pulses. The magnitude of the LH and FSH pulses was similar (P>0.10) between the 5 treatment groups Serum E3 concentrations were increased (P<O.01) in cows treated with GnRH and/or exogenous E3. Also, WC cows had higher (P<0.01) E2 concentrations than SC cows. Cows in the GnRH, GnRH + E2 and WC groups had shorter (P<O.01) postpartum intervals than cows in the SC and E2 groups since more (P<0.01) of these cows had exhibited estrus and ovulated by 8 days posttreatment. Cows in the E2 group had postpartum intervals that were 10 days longer than cows in the SC group, indicating that reduction of pulsatile LH release can prolong the postpartum interval. All cows that ovulated in response to either the GnRH injections or weaning continued to cycle. However, a large percentage of GnRH and WC cows had short (<17 days) first estrous cycles. Exogenous E3 appeared to overcome this problem since almost all of the cows in the GnRH + E2 group normal length first estrous cycles. It is concluded from the indirect evidence obtained from these data that suckling prolongs the postpartum interval of the beef cow by reducing the frequency of pulsatile GnRH release from the hypothalamus.