Preovulatory Follicle-stimulating Hormone Research Articles

Effects of unilaterally microinjecting ethanol in the preoptic-anterior hypothalamic areas of rats on ovulation.

Intragastric or intraperitoneal ethanol (EtOH) treatment inhibits reproductive functions in females and male rats. The area of the hypothalamus where these effects take place is unknown. As the participations of the preoptic-anterior hypothalamic area (POA-AHA) in regulating ovulation is asymmetric, this study aims to analyze the effects on 17β-estradiol(E2 ), progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) serum levels, the messenger ribonucleic acid (mRNA) expression of estrogen receptor alpha (ERα) and beta (ERβ), and ovulation resulting from unilaterally microinjecting water or an EtOH solution into either side of the POA-AHA. The treatment consisted of microinjecting a 8.6 μM EtOH solution into either side of the POA-AHA. The study was performed on groups of adult cyclic rats at 09.00 hours on diestrus-1, and sacrificed on diestrus-2 at 13.00, on proestrus at 09.00 or 17.00 or on estrus at 09.00 hours. Ovulation rates were assessed in rats sacrificed on estrus. Hormonal serum levels were measured using radioimmunoassay, and as a function of ERα and ERβ mRNA expression in each side of the POA-AHA by reverse transcriptase polymerase chain reaction. EtOH treatment blocked ovulation and the preovulatory release of LH, and lowered E2 levels. Irrespective of the treated POA-AHA side, ERα mRNA expression was consistently lower in the left POA-AHA and higher on the right. EtOH treatment in the left POA-AHA decreased FSH serum levels and lowered ERβ mRNA expression. In turn, EtOH treatment on the right POA-AHA resulted in higher FSH levels and ERβ mRNA expression. The present results show that EtOH blocks the preovulatory surge of LH on the POA-AHA. The effects of EtOH treatment of preovulatory FSH surge on the POA-AHA are asymmetric (stimulative on the right and inhibiting in the left). The effects of EtOH treatment on preovulatory LH and FSH surge could be explained by the inhibition of ERα and ERβ mRNA expression, respectively.

Gonadotropin-Releasing Hormone, Estradiol, and Inhibin Regulation of Follicle-Stimulating Hormone and Luteinizing Hormone Surges: Implications for Follicle Emergence and Selection in Heifers

Mechanisms regulating gonadotropin surges and gonadotropin requirements for follicle emergence and selection were studied in heifers. Experiment 1 evaluated whether follicular inhibins regulate the preovulatory luteinizing hormone (LH)/follicle-stimulating hormone (FSH) surges elicited by gonadotropin-releasing hormone (GnRH) injection (Hour = 0) and the subsequent periovulatory FSH surge. Treatments included control (n = 6), steroid-depleted bovine follicular fluid (bFF) at Hour -4 (n = 6), and bFF at Hour 6 (n = 6). Gonadotropins in blood were assessed hourly from Hours -6 to 36, and follicle growth tracked by ultrasound. Consistent with inhibin independence, bFF at Hour -4 did not impact the GnRH-induced preovulatory FSH surge, whereas treatment at Hour 6 delayed onset of the periovulatory FSH surge and impeded growth of a new follicular wave. Experiment 2 examined GnRH and estradiol (E2) regulation of the periovulatory FSH surge. Treatment groups were control (n = 8), GnRH-receptor antagonist (GnRHr-ant, n = 8), and E2 + GnRHr-ant (n = 4). GnRHr-ant (acyline) did not reduce the concentrations of FSH during the periovulatory surge and early follicle development (<7.0 mm) was unaffected, although subsequent growth of a dominant follicle (>8.0 mm) was prevented by GnRHr-ant. Addition of E2 delayed both the onset of the periovulatory FSH surge and emergence of a follicular wave. Failure to select a dominant follicle in the GnRHr-ant group was associated with reduced concentrations of LH but not FSH. Maximum diameter of F1 in controls (13.3 ± 0.5 mm) was greater than in both GnRHr-ant (7.7 ± 0.3 mm) and E2 + GnRHr-ant (6.7 ± 0.8 mm) groups. Results indicated that the periovulatory FSH surge stems from removal of negative stimuli (follicular E2 and inhibin), but is independent of GnRH stimulation. Emergence and early growth of follicles (until about 8 mm) requires the periovulatory FSH surge but not LH pulses. However, follicular deviation and late-stage growth of a single dominant follicle requires GnRH-dependent LH pulses.

Expression of estrogen receptors in the hypothalamo-pituitary-ovarian axis in middle-aged rats after re-instatement of estrus cyclicity

During reproductive aging female rats enter an anovulatory state of persistent estrus (PE). In an animal model of re-instatement of estrus cyclicity in middle-aged PE rats we injected the animals with progesterone (0.5 mg progesterone/kg body weight) at 12:00 for 4 days whereas control animals received corn oil injections. After the last injection animals were analyzed at 13:00 and 17:00. Young regular cycling rats served as positive controls and were assessed at 13:00 and 17:00 on proestrus. Progesterone treatment of middle-aged PE rats led to occurrence of luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin surges in a subset of animals that were denoted as responders. Responding middle-aged rats displayed a reduction of ER-β mRNA in the preoptic area which was similar to the effect in young rats. Within the mediobasal hypothalamus, only young rats showed a decline of ER-α mRNA expression. A decrease of ER-α mRNA levels in the pituitary was observed in progesterone-responsive rats and in young animals. ER-β mRNA expression was reduced in young regular cycling rats. ER-β mRNA levels in the ovary were reduced following progesterone treatment in PE rats and in young rats. Taken together our data show that cyclic administration of progesterone reinstates ovulatory cycles in intact aging females which have already lost their ability to display spontaneous cyclicity. This treatment leads to the occurrence of preovulatory LH, FSH and prolactin surges which are accompanied by differential modulation of ERs in the hypothalamus, the pituitary and the ovary.

Differential regulation of the secretion of luteinizing hormone and follicle-stimulating hormone around the time of ovulation in the bitch

Plasma concentrations of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined 3–6 times daily in six Beagle bitches from the start of the follicular phase until 5 d after the estimated day of ovulation. The aim of the study was to gain more detailed information regarding the changes in and the temporal relation between these hormones around the time of ovulation. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. The mean duration of the pre-ovulatory FSH surge (110 ± 8 h) was significantly longer than that of the pre-ovulatory LH surge (36 ± 5 h). The FSH surge started concomitantly with the pre-ovulatory LH surge in four bitches, and 12 h before the start of the LH surge in the other two bitches. The pre-ovulatory LH surge had a bifurcated pattern in four bitches. The mean plasma LH concentration before (1.9 ± 0.4 μg/L) and after (1.9 ± 0.3 μg/L) the pre-ovulatory LH surge were similar. The mean plasma FSH concentration during the period 72–28 h before the pre-ovulatory LH surge (1.6 ± 0.3 U/L) was lower ( P < 0.001) than that during the period 100–144 h after the pre-ovulatory LH surge (3.1 ± 0.2 U/L). In conclusion, this study demonstrated concurrent pre-ovulatory surges of FSH and LH and provided more evidence for differential regulation of the secretion of FSH and LH.

Temporal relations between plasma concentrations of luteinizing hormone, follicle-stimulating hormone, estradiol-17β, progesterone, prolactin, and α-melanocyte-stimulating hormone during the follicular, ovulatory, and early luteal phase in the bitch

Compared with other domestic animals, relatively little is known about the changes in, and temporal relations between, reproductive hormones around the time of ovulation in the domestic bitch. Therefore, plasma concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17β, progesterone, prolactin (PRL), and α-melanocyte-stimulating hormone (α-MSH) were determined one to six times daily from the start of the follicular phase until 5 days after the estimated day of ovulation in six Beagle bitches. In all bitches, the pre-ovulatory LH surge was accompanied by a pre-ovulatory FSH surge. A pre-ovulatory PRL or α-MSH surge was not observed. The pre-ovulatory FSH and LH surges started concomitantly in four bitches, but in two bitches the FSH surge started 12 h earlier than the LH surge. The FSH surge (110 ± 8 h) lasted significantly longer than the LH surge (36 ± 5 h). In contrast with the pre-ovulatory FSH surge, the pre-ovulatory LH surge was bifurcated in four of six bitches. The mean plasma LH concentrations before (1.9 ± 0.4 μg/L) and after (1.9 ± 0.3 μg/L) the LH surge were similar, but the mean plasma FSH concentration before the FSH surge (1.6 ± 0.3 U/L) was significantly lower than that after the FSH surge (3.1 ± 0.2 U/L). In most bitches the highest plasma estradiol-17β concentration coincided with or followed the start of the pre-ovulatory LH surge. In five of the six bitches the plasma progesterone concentration started to rise just before or concurrently with the start of the LH surge. In conclusion, the results of this study provide evidence for the differential regulation of the secretion of LH and FSH in the bitch. In addition, the interrelationship of the plasma profiles of estradiol-17β and LH suggests a positive feedback effect of estradiol-17β on LH surge release. The start of the pre-ovulatory LH surge is associated with an increase in the plasma progesterone concentration in this species.

Variations in Plasma Levels of Substance P and Effects of a Specific Substance P Antagonist of the NK1 Receptor on Preovulatory LH and FSH Surges and Progesterone Secretion in the Cycling Cynomolgus Monkey

These studies investigated the role of substance P (SP) in the regulation of the hypothalamic-pituitary-ovarian axis in cynomolgus monkeys with normal menstrual cycles. Plasma concentrations of SP were determined in blood samples taken every morning in normally menstruating cynomolgus monkeys throughout the menstrual cycle. There was a significant decreasing linear trend of SP during the follicular phase (cycle day –13 to day 0) and a significant inverse relationship between SP plasma values and plasma 17β-estradiol (E₂) values from day –13 to day 0 of the adjusted cycle. Correspondingly, SP area under the curve was significantly greater during the follicular phase than the luteal phase. In a second experiment, plasma concentrations of E₂, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone and length of cycles were measured after five daily intragastric administrations (10 mg/kg) of an NK₁ receptor (SP receptor) antagonist (RPR 100893; 10 mg/kg) initiated after serum E₂ concentrations had exceeded 125 pg/ml. There was a statistically significant reduction in the amplitude (41% of control) and the area under the curve (37% of control) of the preovulatory LH surge. In addition, there was a reduction of the duration of the LH surge (3 ± 0.1 days in controls vs. 2.1 ± 0.2 days in treated animals). The present results show for the first time that there are significant variations in plasma levels of SP, with a strong negative correlation with serum levels of E₂ during the follicular phase of the cynomolgus monkey, and that endogenous SP has a potentiating role in the interactive hypothalamo-anterior-pituitary mechanisms which lead to the preovulatory LH and FSH surges during the menstrual cycle in the monkey.

Plasma Gonadotropin Concentrations in the Cyclic Female Brushtail Possum (Trichosurus vulpecula)

Changes in plasma concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and their relationship to antral follicle development and ovulation, were determined in female brushtail possums (Trichosurus vulpecula) in experiments in which pouch young were removed (RPY) from lactating females to promote ovarian activity. In Experiment 1 (n=8), the development of preovulatory follicles and ovulation was monitored by laparoscopy. In Experiment 2 (n=15) estrus and mating were monitored by cytology of urine. Ovulation occurred in 4/8 (Experiment 1) and 9/16 (Experiment 2) possums, and in these animals, plasma FSH concentrations fell progressively over the period of preovulatory follicle development and returned to pretreatment levels after ovulation. With the exception of samples taken at the time of the preovulatory gonadotropin surge, mean plasma LH levels remained basal. In those possums that failed to ovulate, plasma FSH concentrations were elevated while plasma LH concentrations were low; these patterns remained unchanged throughout the sampling period. It was not possible to distinguish between animals that would ovulate and those that would not ovulate after RPY on the basis of gonadotropin profiles at the time of RPY. A further group of possums (Experiment 3, n=10) were blood-sampled at hourly intervals for 48 h to characterize preovulatory gonadotropin surges, using laparoscopy to monitor preovulatory follicular development and predict ovulation. A preovulatory LH surge (max. conc. 10.2–43.5 ng/ml, duration 7–9 h) was recorded in 4 animals, with a coincident preovulatory FSH surge (max. conc. 1.4–21.4 ng/ml, duration 3–11 h) observed in 3 of these possums. The patterns of gonadotropin secretion in the cycling brushtail possum conform to those reported for eutherians that ovulate spontaneously and appear to be regulated by similar mechanisms.

Secretion of inhibin A, inhibin B and inhibin pro-alphaC during the oestrous cycle of the golden hamster (Mesocricetus auratus).

Plasma concentrations of inhibin pro-alphaC, inhibin A and inhibin B were determined by enzyme-linked immunosorbent assay at 6 h intervals throughout the 4-day oestrous cycle of the golden hamster. Plasma concentrations of follicle-stimulating hormone (FSH) and oestradiol-17beta were also measured by radioimmunoassay during the oestrous cycle. Plasma concentrations of inhibin A increased from the early morning of day 1 (day 1=day of ovulation) and reached plateau levels at 0500 h on day 2. An abrupt increase in plasma concentrations of inhibin A was found at 1700 h on day 4, when the preovulatory FSH surge was observed. An increase in plasma concentrations of inhibin B occurred on day 1 and reached plateau levels at 1700 h on day 1. The levels remained elevated until 0500 h on day 4 and declined gradually by 2300 h on day 4. Plasma concentrations of inhibin pro-alphaC gradually increased with some fluctuation from day 1 to 1700 h on day 4 and then declined. Significant negative relationships were noted between plasma FSH and both dimeric forms of inhibin from day 1 to day 3. Significant positive relationships were found between plasma oestradiol-17beta and inhibin A or inhibin pro-alphaC throughout the oestrous cycle. In contrast, no significant relationship was found between plasma oestradiol-17beta and inhibin B. These findings suggest that both dimeric forms of inhibin play a role in the regulation of FSH secretion during follicular development. These findings also suggest that inhibin pro-alphaC could be secreted primarily by large follicles, and early atretic follicles could also be responsible for inhibin pro-alphaC secretion. On the other hand, the secretory pattern of dimeric inhibins might shift from inhibin B to inhibin A with follicular development.

Role of corticosteroids in female reproduction.

Corticosteroids, ACTH, and stress can exert inhibitory and facilitory effects on reproduction. The purpose of this review is to reconcile the divergent effects of corticosteroids on gonadotropin secretion based on recent work in the area. Whether stimulation or inhibition of gonadotropin secretion is observed appears to depend on two important variables: 1) length of exposure, and 2) background of estrogen priming. The acute administration of ACTH and certain corticosteroids to estrogen-primed animals brings about the release of LH and FSH. Corticosteroids have also been shown by some investigators to cause selective release of follicle-stimulating hormone (FSH) both in vitro and in vivo. This selective facilitation of FSH release by corticosteroids may explain many deleterious effects on reproduction observed after adrenalectomy, and it may have relevance in explaining the beneficial effects of corticosteroids in inducing ovulation in anovulatory patients suffering from polycystic ovarian syndrome. Finally, evidence is presented which suggests that adrenal steroids may participate in initiation and synchronization of the preovulatory LH and FSH surge, as well as the secondary FSH surge seen on estrus in the rat.

Changes in peripheral levels of immunoreactive inhibin and gonadotropins in cattle induced to superovulate by porcine follicle-stimulating hormone.

Concentrations of inhibin in peripheral blood were determined in cattle treated with porcine follicle-stimulating hormone (FSH). Changes in plasma concentrations of FSH, luteinizing hormone (LH), estradiol and progesterone were also examined. These results were compared with hormonal profiles in the intact estrous cycle prior to FSH treatment of the same cows. Plasma levels of estradiol before ovulation and of progesterone after ovulation during the period of treatment with porcine FSH were much higher than those in the intact cycle. Concentrations of plasma inhibin rose promptly after injections of porcine FSH and maintained high levels for a longer period than estradiol after the LH surge. Changes in plasma concentrations of inhibin were not correlated to those of progesterone in superovulating cattle. In the superovulating animals, peaks of the preovulatory FSH surge were suppressed to 70.4% of the intact cycle, though LH peaks were not significantly suppressed. These results indicate that high levels of inhibin after treatment with porcine FSH may be involved in a partial suppression of the preovulatory surge of FSH in superovulating cattle. These findings also suggest that unovulated follicles maintain the ability to secrete inhibin and that the corpus luteum in superovulating cattle is not the active source of inhibin secretion.

Characterization of gonadotropic and ovarian steroid hormones during the periovulatory period in high ovulating select and control line gilts.

Cyclic gilts from Control (C, randomly selected, n = 11) and Relax Select (RS, nine generations of selection for increased ovulation rate followed by seven generations of relaxed or random selection, n = 9) lines of the University of Nebraska Gene Pool population (derived from 14 different breeds) were utilized to characterize differences in gonadotropic and ovarian steroid hormones during preovulatory and postovulatory phases of the estrous cycle. Blood samples were collected during four periods (0500, 1100, 1700 and 2300) daily beginning 2 d prior to anticipated estrus (d -2, d 18 of a 20-d estrous cycle), and continuing through d 4 postestrus (d 0 = 1st of standing estrus). Sampling within a period consisted of five blood samples at 15-min intervals. All plasma samples were analyzed for concentrations of follicle stimulating hormone (FSH) and luteinizing hormone (LH). Neither mean LH nor peak concentration of LH during the preovulatory surge differed between genetic lines (P greater than .10). Concentrations of FSH increased faster (line X period, P less than .05) and tended (P less than .1) to peak at a higher concentration in RS (.88 ng/ml) than in C (.54 ng/ml) gilts (P less than .05) during the 12 h preceding the FSH and LH preovulatory peaks. The second FSH surge began approximately 24 h after the preovulatory FSH peak. Peak FSH concentrations were observed at 42 h in both lines (1.46 vs 1.74 ng/ml for C and RS gilts, respectively). The higher FSH concentration in RS gilts established during the preovulatory surge was maintained through the second FSH surge (P less than .01). No line differences were detected in plasma concentrations of estradiol-17 beta and progesterone.

Pulsatile secretion of luteinizing hormone and follicle stimulating hormone and their relationship to secretion of estradiol and onset of estrus in weaned sows

The objective of this experiment was to characterise temporal changes in estradiol and pulsatile secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH) during the interval between weaning and estrus in the sow. Five multiparous sows were sampled at 10-min intervals for 3 h beginning 8 h after weaning and continuing every 12 h until estrus. Interval to estrus was 102 ± 2 h (range 96–108) after litters were weaned, and interval to preovulatory LH and FSH surges was 109 ± 5 h (range 92–116). With the exception of the period of the preovulatory surge, neither average nor basal concentrations of LH or FSH changed over time. Number of LH peaks per 3 h reached a maximum of 2.8 at 48 h before the preovulatory surge, then declined to 0.8 at 12 h before the surge. Peak amplitude for LH and peak frequency and amplitude for FSH also declined with time before preovulatory surges. Relative ranks were computed for individual sows based on the mean concentration of LH or FSH for each bleeding period. Rankings were consistent over the periods, but were not correlated with interval to estrus. Estradiol concentrations peaked (88 ± 7 pg/ml) at 36 h before preovulatory surges, coincident with the decline in peak frequency of LH. We conclude that pulsatile secretion of LH and FSH changes during the interval between weaning and estrus but secretion of these two hormones may be controlled by different mechanisms.

Dose-dependent inhibition of the preovulatory surges of gonadotropins and prolactin by the antiestrogen CI-628: possible sites of action.

The present series of experiments was conducted in an attempt to correlate previously reported dose-dependent and site-selective inhibitory effects of an antiestrogen, CI-628, on 17 beta-estradiol (E2)-receptor interactions in the anterior pituitary gland (AP) and hypothalamus with its effects on the preovulatory surges of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin. The effects of CI-628 on the response of the AP to luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH) also were examined. In the first study, rats exhibiting 4-day estrous cycles were injected with various doses (0.02, 0.20, 2.0, and 20 mg/kg) of CI-628 or vehicle at 0900 h on diestrus-2 and proestrus. The preovulatory LH surge and both preovulatory and secondary FSH surges were marginally affected by 0.02 mg/kg CI-628, but were completely abolished by higher doses. In contrast, a dose of 0.20 mg/kg only delayed the prolactin surge; however, higher doses were effective in extinguishing cyclic prolactin release. In a second experiment, CI-628 in rats treated on diestrus-2 and proestrus exerted a dose-dependent suppression of the AP LH response to an initial injection of LHRH on proestrous afternoon in rats whose endogenous LH surges were blocked by phenobarbital. However, AP LH responses to a second LHRH injection to assess the self-priming capacity of LHRH were attenuated only in rats given 0.20, 2.0, and 20 mg/kg CI-628. Contrastingly, the AP prolactin response to TRH was suppressed only in rats given 0.20 mg/kg CI-628.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma follicle stimulating hormone and luteinizing hormone patterns during the estrous cycle of ewes

Fifteen Suffolk ewes were used in three experiments to compare plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) patterns during the estrous cycle and to determine whether FSH levels undergo changes in pulse frequency. Luteinizing hormone changed inversely with progesterone levels whereas FSH and progesterone concentrations revealed no obvious relationship. Unlike LH, FSH levels did not pulsate during the follicular phase. Higher FSH levels were detected on days 1, 6 and 12 and lower levels on days 0, 4 and 16. Coincident preovulatory LH and FSH surges were observed and this was the only time FSH and LH levels appeared to be jointly controlled.

Biphasic effect of gonadotropin releasing hormone on progestin secretion by rat granulosa cells.

The effect of an agonistic gonadotropin releasing hormone (GnRH)-analog (D-Ala6, des-Gly10-NH2-GnRH-ethylamide, GnRHa) on granulosa cell steroidogenesis in the presence or absence of follicle-stimulating hormone (FSH) or luteinizing hormone (LH) was studied. Granulosa cells, isolated from preovulatory follicles of pregnant mare's serum gonadotropin (PMSG)-treated immature rats or from the less mature follicles of untreated immature rats, were cultured for a period of 72 h with daily changes of medium, and progesterone and its metabolite, 20 alpha-dihydro-progesterone (20 alpha-OHP), were assayed in the medium. In granulosa cells from preovulatory follicles, LH and FSH caused a much greater stimulation of steroidogenesis than did GnRHa. There appeared to be no interaction between GnRHa and FSH during the first 10 h, but at 24 h and later the presence of GnRHa clearly inhibited the steroidogenic response to LH and FSH. Steroidogenesis in granulosa cells from immature rats was considerably lower and the effects of GnRHa and FSH alone less pronounced. In these cells, FSH-stimulated progesterone secretion was inhibited by GnRHa only at 72 h. In contrast, 20 alpha-OHP secretion in the same cultures was potentiated by the combined presence of FSH and GnRHa. In conclusion, it seems as though the effects of GnRHa on granulosa cell steroidogenesis varies with exposure time, the initial response being stimulatory and the later inhibitory. Furthermore, the response is also to some extent determined by the maturational stage of the granulosa cells.

Serum luteinizing hormone, follicle stimulating hormone and prolactin response to photoperiod during the estrous cycle of Holstein heifers.

The objectives were to determine if photoperiods of 8 h light:16 h dark (8L:16D) and 16L:8D affect time of day when preovulatory surges of luteinizing hormone (LH) and follicle stimulating hormone (FSH) occur and if photoperiods affect diestrus and estrous concentrations of LH, FSH and prolactin (PRL). Postpubertal Holstein heifers were assigned to receive either 8L:16D (n - 9) or 16L:8D (n = 9) from September 21 through January 31. Hormone concentrations were determined in serum collected at 2-h intervals during diestrus and estrus of a single estrous cycle in autumn and again 4 mo later, during a single estrous cycle in winter. Neither photoperiod nor season affected time of day at which preovulatory LH and FSH surges occurred in heifers. The LH surges did not differ in amplitude and duration within and between photoperiods and within individual animals. In 29 of 33 surges, peak concentrations of FSH coincided with peaks of LH. Peak concentrations of FSH were greater during the winter than during autumn in heifers exposed to 8L:16D, but were not different between autumn and winter in heifers exposed to 16L:8D. Between autumn and winter, surges of FSH were similar in magnitude and duration within individual animals. In comparison with 8L:16D, PRL was increased in heifers that received 16L:8D in autumn, but photoperiod had no effect on PRL during winter. Concentrations of PRL were increased at estrus relative to diestrus in autumn and winter. It is concluded that photoperiods of 8 and 16 h do not affect the timing, amplitude or pattern of preovulatory surges of LH or FSH, the rise in PRL associated with estrus, or length of estrous cycles in postpubertal Holstein heifers.

Effect of immunoneutralization of luteinizing hormone releasing hormone on the estrogen-induced luteinizing hormone and follicle-stimulating hormone surges in the ewe.

The importance of luteinizing hormone releasing hormone (LHRH) in inducing the preovulatory luteinizing hormone (LH) surge in the ewe was investigated by administration of LHRH antiserum approximately 10 h before the expected onset of the rise in LH in the blood. Ten ewes with synchronized estrous cycles were studied. Luteolysis was induced by prostaglandin and 26 h later the ewes were injected with 50 �ig estradiol benzoate in arachis oil, and after a further 10 h, 5 control ewes received 100 ml ovine antiserum to bovine serum albumin (BSA) i.v., and 5 remaining animals 100 ml ovine antiserum to LHRH (LHRH antiserum). All 5 control ewes demonstrated the expected sharp rise in plasma LH concentrations, peak values occurring 26 ± 2 h (mean ± SEM) after estradiol benzoate administration. This rise was absent in the LHRH antiserum treated animals, who also failed to ovulate as judged from the absence of a rise in plasma progesterone concentrations during the following 16 days. Plasma LH concentrations remained low during the 16-day period in the treated animals. In the control ewes there was a clear surge of follicle-stimulating hormone (FSH) coincidently with the LH surge. This did not occur in the ewes treated with antibodies to LHRH. However, plasma FSH concentrations rose despite the presence of antibodies to LHRH and although a clear second FSH peak which occurred in the controls was not evident in the LHRH antibody treated animals, there was no significant difference in the amount of FSI-I released during this time period between the two groups. Also, plasma FSH concentrations during the remaining 16 days were unaltered by the LHRH antibodies. Thus in the ewe, the estrogen-primed hypothalamo-pituitary system cannot produce an LH surge if LHRH is neutralized by giving antiserum before the onset of the surge and basal LH output is also reduced. The major preovulatory FSH surge is also inhibited when LHRH is neutralized but basal secretion of the hormone remains unaltered.

The role of nest-building activity in gonadotropin secretions and the reproductive success of ring doves (Streptopelia risoria).

This study was undertaken to investigate the intricate relations between prelaying nest-building activity and preovulatory hormonal changes, and the effects of these events on breeding success. Pairs of ring doves were allowed to go through a complete breeding cycle under four conditions of nest-building opportunity. Nest were self-made, pre-made, pre-made and covered, or removed daily to generate various levels of building activity. Behavioral and hormonal changes were observed throughout the cycle. Blood levels of gonadotrophins were monitored by daily measurements with the method or radioimmunoassay. A depression of follicle-stimulating hormone (FSH) typically was associated with every preovulatory surge of luteinizing hormone (LH); an LH surge not accompanied by a FSH dip was not followed by ovulation. Moreover, the FSH depression was significantly correlated with the level of nest-building activity. These findings led to the proposal that nest-building activity stimulated preovulatory FSH change and, hence, ovulation. The constructed nest in turn appeared to promote incubation behavior. These results are discussed in the context of breeding success.

The Effect of a Synthetic Progestogen, Ethylnorgestrienone, on Hypothalamic-Pituitary-Ovarian Function, Cervical Mucus, Vaginal Cytology, and Endometrial Morphology

The antifertility mechanism of a new progestin preparation, ethylnorgestrienone (13 beta-ethyl-17 alpha-ethynyl-17-hydroxy-gona-4,9,11-triene-3-one) (R2323), was evaluated. The compound was administered orally in doses of 5 mg weekly to seven subjects for a total of nine treatment cycles. Each woman served as her own control and was studied during a normal menstrual cycle followed by a cycle in which she received R2323. Serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol, and progesterone, as well as cervical mucus properties, were studied serially during the control and treatment cycles. Results indicated that all control cycles were ovulatory. Ovulatory gonadotropin patterns were observed in four treated cycles, but preovulatory FSH and LH peaks and progesterone production during the luteal phase were suppressed significantly. Estradiol levels showed an early increase during the follicular phase and a significantly decreased preovulatory peak. Cervical mucus properties were altered and sperm penetration in cervical mucus was inhibited in all treatment cycles. These findings suggest that at least two different factors might be involved in the contraceptive mechanism of R2323: (1) alteration of the ovulatory process and progesterone production, and (2) cervical mucus changes leading to inhibition of sperm migration.

Follicle-stimulating hormone secretion in the female rat: cyclic release is dependent on circulating androgen.

In adult cyclic female rats, intravenous injections of an antiserum to testosterone prevented the continued increase in serum follicle-stimulating hormone (FSH) which normally occurs during the early morning hours of estrus. This treatment did not prevent the initial increases in serum FSH (and luteinizing hormone) which occur during the critical period (1400 to 2000 of proestrus), nor did it interfere with subsequent ovulation. These observations indicate the existence of two separate mechanisms for preovulatory FSH release in the rat and implicate circulating testosterone as the stimulus for continued secretion of FSH during estrus.