Serum profiles of androstenedione, testosterone and LH from birth through puberty in buffalo bull calves

Blood samples were taken once per week for 4-7 weeks from 59 buffalo calves in 14 age groups, 1-2 months apart. Hormones were quantified by validated radioimmunoassays. Values of androstenedione and testosterone were low at birth (141.3 +/- 33.5 pg/ml and 18.0 +/- 2.9 pg/ml, respectively; mean +/- s.d.). Serum androstenedione concentrations gradually increased from birth until 8 months of age and declined (P less than 0.05) thereafter, whereas mean testosterone values were low up to 8 months and then significantly (P less than 0.05) increased as age advanced. LH concentrations averaged 2.12 +/- 0.47 ng/ml at birth. Thereafter, a decline in LH values was followed by an increase between 6 and 15 months of age. We conclude that, in buffalo bull calves, the pubertal period occurs from about 8 to 15 months of age. For pubertal buffalo bulls 15-17 months of age, serum concentrations of androstenedione, testosterone and LH were 156.9 +/- 54.6 pg/ml, 208.4 +/- 93.8 pg/ml and 2.10 +/- 0.70 ng/ml, respectively.     

Oestradiol-17beta, progesterone, FSH and LH in prepubertal calves induced to superovulate

Fluorogestone acetate (vaginal sponge for 4 days) and PMSG (i.m. injection at the time of sponge insertion) treatment was administered to seven 3-month-old calves to induce superovulation. Samples of peripheral plasma were taken every 4 h during treatment (4 days) and then every 2 h for 7 days. FSH, LH, oestradiol and progesterone were measured by radioimmunoassays. In all calves oestradiol concentrations increased 24 h after PMSG injection and reached the highest levels (41-502 pg/ml) during the preovulatory surge of both gonadotropins. The surge of LH and FSH occurred from 12 to 22 h after cessation of treatment. The maximum levels of LH and FSH were 11-72 ng/ml and 23-40 ng/ml respectively and occurred within 4 h of each other. Between 40 and 68 h after the LH peak the concentrations of progesterone began to increase from basal values, reaching 24.0-101.7 ng/ml when the animals were killed. A quantitative relationship was found between plasma oestradiol concentration and the numbers of ovulating follicles. Progesterone levels seemed to be related to the numbers of corpora lutea and also to the numbers of unovulated follicles. Gonadotrophin output was not quantitatively related to ovarian activity or to steroid secretion.     

Pituitary response of prepuberal lambs to oestradiol-17 beta.

In two experiments 48 prepuberal Merino ewe lambs were injected with oestradiol-17 beta (E2) or saline to study the effect of E2 on their plasma LH levels and on oestrus and ovulation. In the three groups which received 30 (experiment I), 50 and 30 (experiment II) microgram E2 respectively, 27 out of 28 lambs showed an LH response, the corresponding mean LH peaks being 64.3 +/0 22.5, 153.6 +/-33.4 and 91.7 +/- 16.9 ng/ml at mean intervals of 11.1, 11.2 and 10.5 h, respectively, after injection. None of the 20 lambs in the control groups had an LH level higher than 18 ng/ml 12 h after injection. In the three E2 groups, 41.7, 62.5 and 37.5% of animals showed oestrus within 26 h of injection while in the control groups only one animal showed oestrus. Of 13 animals showing oestrus in the E2 groups, 11 failed to ovulate. The mean pre-injection plasma FSH level in experiment I was 102.7 ng/ml, and in four 5--7-month-old lambs over several weeks uas 155.3 ng/ml. Despite these high pre-injection levels of FSH, it appears that the follicles were unable to respond to the LH peak which followed the E2 injection.     

Changes in circulating levels of immunoreactive follicle stimulating hormone, luteinizing hormone, and testosterone during sexual development in the rhesus monkey, Macaca mulatta

Basal serum levels of follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) and the responsiveness of these hormones to a challenge dose of luteinizing hormone releasing hormone (LHRH), were determined in juvenile, pubertal, and adult rhesus monkeys. The monkey gonadotrophins were analyzed using RIA reagents supplied by the World Health Organization (WHO) Special Programme of Human Reproduction. The FSH levels which were near the assay sensitivity in immature monkeys (2.4 +/- 0.8 ng/ml) showed a discernible increase in pubertal animals (6.4 +/- 1.8 ng/ml). Compared to other two age groups, the serum FSH concentration was markedly higher (16.1 +/- 1.8 ng/ml) in adults. Serum LH levels were below the detectable limits of the assay in juvenile monkeys but rose to 16.2 +/- 3.1 ng/ml in pubertal animals. When compared to pubertal animals, a two-fold increase in LH levels paralleled changes in serum LH during the three developmental stages. Response of serum gonadotrophins and T levels to a challenge dose of LHRH (2.5 micrograms; i.v.) was variable in the different age groups. The present data suggest: an asynchronous rise of FSH and LH during the pubertal period and a temporal correlation between the testicular size and FSH concentrations; the challenge dose of LHRH, which induces a significant rise in serum LH and T levels, fails to elicit an FSH response in all the three age groups; and the pubertal as compared to adult monkeys release significantly larger quantities of LH in response to exogenous LHRH.     

Ability of cortisol and progesterone to mediate the stimulatory effect of adrenocorticotropic hormone upon testosterone production by the porcine testis

The influence of corticosteroids and progesterone upon porcine testicular testosterone production was investigated by administration of exogenous adrenocorticotropic hormone (ACTH), cortisol and progesterone, and by applying a specific stressor. Synthetic ACTH (10 micrograms/kg BW) increased (P less than 0.01) peripheral concentrations of testosterone to peak levels of 5.58 +/- 0.74 ng/ml by 90 min but had no effect upon levels of luteinizing hormone (LH). Concentrations of corticosteroids and progesterone also increased (P less than 0.01) to peak levels of 162.26 +/- 25.61 and 8.49 +/- 1.00 ng/ml by 135 and 90 min, respectively. Exogenous cortisol (1.5 mg X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although peripheral concentrations of corticosteroids were elevated (P less than 0.01) to peak levels of 263.57 +/- 35.03 ng/ml by 10 min after first injection. Exogenous progesterone (50 micrograms X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although concentrations of progesterone were elevated (P less than 0.01) to peak levels of 17.17 +/- 1.5 ng/ml by 15 min after first injection. Application of an acute stressor for 5 min increased (P less than 0.05) concentrations of corticosteroids and progesterone to peak levels of 121.32 +/- 12.63 and 1.87 +/- 0.29 ng/ml by 10 and 15 min, respectively. However, concentrations of testosterone were not significantly affected (P greater than 0.10). These results indicate that the increase in testicular testosterone production which occurs in boars following ACTH administration is not mediated by either cortisol or progesterone.     

Maturation of the pituitary-gonadal system in the male rat

Serum FSH and testosterone concentrations reached maximum levels between 35 and 45 days of age, which coincided with the appearance of mature spermatozoa in the majority of seminiferous tubules. Spermatozoa were not observed in sections of the urethra until the age of 46 days. Serum LH concentrations were low (5-6 ng/ml) before Day 25, became highly variable (12-57 ng/ml) between Days 25 and 53 and remained consistently above 35 ng/ml thereafter. Serum prolactin levels rose significantly between 30 and 43 days of age. Maximum prolactin levels coincided with the start of accelerated growth in the prostate and seminal vesicle glands. Testicular weights relative to body weight reached a plateau by 35 days of age, while relative pituitary and adrenal weights decreased throughout the study period. It is suggested that spermatogenesis is not complete until FSH and testosterone reach maximum levels, while prolactin may be involved in the stimulation of accessory sex organ growth. The pronounced variation in serum LH concentrations during the maturation period may reflect a progressive change in the sensitivity of the hypothalamic-pituitary axis to the negative feedback of gonadal steroids.     

Plasma progesterone, FSH and LH levels associated with implantation in the mouse

Measurement of plasma progesterone, LH and FSH were made every 6 h during the first 6 days of pregnancy in the mouse. Plasma progesterone and LH were low on day 1, minimum values being recorded at 24 h post coitus. Concentrations of both these hormones started rising during the second half on day 2 with the rise continuing during day 3 to a progesterone peak of 25 ng/ml early on day 4 and an LH peak of 37 ng/ml late on day 4. Levels of progesterone fell during day 4 and LH during day 5 to approximately half their respective peak values and then remained relatively constant over the remainder of the measurement period. Levels of FSH, which were high early on day 1 (180 ng/ml), fell sharply by midday with a small rise late in the day followed by a decline during day 2 to a minimum level of 2 ng/ml at 48 h post coitus. Early on day 3 FSH values rose to 120 ng/ml then fell to 50-60 ng/ml during the next 6 h and remained relatively stable at this level during days 4 and 5. It is suggested that LH is concerned with progesterone production and maintenance of the corpus luteum whilst FSH is concerned with the production of oestrogen required for implantation in this species.     

Seasonal levels of LH, FSH, testosterone and prolactin in adult male pudu (Pudu puda)

Seasonal levels of LH, FSH, testosterone (T) and prolactin (PRL) were determined in plasma of six captive adult male pudu (Pudu puda) kept in Concepcion, Chile. Average PRL levels exhibited one peak (28 ng/ml) in December (summer); minimal levels (3 to 6 ng/ml) were detected between April and July. FSH concentrations remained at peak levels (54–63 ng/ml) from December until March; minimal values (25–33 ng/ml) were detected from April until October. T levels exhibited two, almost equal peaks; the first peak (2.8 ng/ml) was detected in March (rut) and the second one (2.7 ng/ml) in October (spring). Both T peaks were preceded by an earlier elevation of LH in February and July (both around 1.3 ng/ml). During the fall, only the alpha male exhibited a sharp peak of T (8.4 ng/ml), whereas in the spring five out of six bucks demonstrated an increase of T levels. Two peaks of LH and T and the 4 months of elevated FSH may be related to a long period of spermatogenesis observed in this species.     

Effects of gonadotropin-releasing hormone pulse-frequency modulation on luteinizing hormone, follicle-stimulating hormone and testosterone secretion in hypothalamo/pituitary-disconnected rams

The effects of changes in pulse frequency of exogenously infused gonadotropin-releasing hormone (GnRH) were investigated in 6 adult surgically hypothalamo/pituitary-disconnected (HPD) gonadal-intact rams. Ten-minute sampling in 16 normal animals prior to HPD showed endogenous luteinizing hormone (LH) pulses occurring every 2.3 h with a mean pulse amplitude of 1.11 +/- 0.06 (SEM) ng/ml. Mean testosterone and follicle-stimulating hormone (FSH) concentrations were 3.0 +/- 0.14 ng/ml and 0.85 +/- 0.10 ng/ml, respectively. Before HPD, increasing single doses of GnRH (50-500 ng) elicited a dose-dependent rise of LH, 50 ng producing a response of similar amplitude to those of spontaneous LH pulses. The effects of varying the pulse frequency of a 100-ng GnRH dose weekly was investigated in 6 HPD animals; the pulse intervals explored were those at 1, 2, and 4 h. The pulsatile GnRH treatment was commenced 2-6 days after HPD when plasma testosterone concentrations were in the castrate range (less than 0.5 ng/ml) in all animals. Pulsatile LH and testosterone secretion was reestablished in all animals in the first 7 days by 2-h GnRH pulses, but the maximal pulse amplitudes of both hormones were only 50 and 62%, respectively, of endogenous pulses in the pre-HPD state. The plasma FSH pattern was nonpulsatile and FSH concentrations gradually increased in the first 7 days, although not to the pre-HPD range. Increasing GnRH pulse frequency from 2- to 1-hour immediately increased the LH baseline and pulse amplitude. As testosterone concentrations increased, the LH responses declined in a reciprocal fashion between Days 2 and 7. FSH concentration decreased gradually over the 7 days at the 1-h pulse frequency. Slowing the GnRH pulse to a 4-h frequency produced a progressive fall in testosterone concentrations, even though LH baselines were unchanged and LH pulse amplitudes increased transiently. FSH concentrations were unaltered during the 4-h regime. These results show that 1) the pulsatile pattern of LH and testosterone secretion in HPD rams can be reestablished by exogenous GnRH, 2) the magnitude of LH, FSH, and testosterone secretion were not fully restored to pre-HPD levels by the GnRH dose of 100 ng per pulse, and 3) changes in GnRH pulse frequency alone can influence both gonadotropin and testosterone secretion in the HPD model.     

Effects of hemicastration at various ages and of oestradiol-17 beta on plasma concentrations of gonadotrophins and androgens, testicular growth and interstitial cell responses in prepubertal lambs

The effect of the removal of one testis from cross-bred lambs at 1, 4, 8 or 12 weeks of age on plasma FSH, LH and testosterone was studied until 16 weeks of age. Hemicastration at all ages elicited a significant increase in plasma FSH compared to controls without a corresponding change in plasma LH or testosterone. The raised FSH after hemicastration at 1 or 4 weeks of age was suppressed to control levels between weeks 7 and 8; such a suppression was not observed in the 4 weeks following hemicastration at 8 or 12 weeks of age. The weight of the remaining testis had increased compared with the control by 12 weeks of age after hemicastration at 1 week (+ 69%), 4 weeks (+ 13%) and 8 weeks (+ 40%); hemicastration at 12 weeks of age also resulted in growth of the remaining testis at 16 weeks (+ 82%). The total androgen production of interstitial cells in response to ovine LH stimulation in vitro did not differ significantly between lambs of 1 and 12 weeks of age, or in animals of 4, 8 and 12 weeks of age after hemicastration at 1 week of age. Subdermal implantation of oestradiol-17 beta into 1-week hemicastrated lambs at the time of operation or at 6 weeks of age increased plasma oestradiol concentrations by approximately 2-4-fold, prevented the FSH and testicular growth responses to hemicastration and suppressed plasma LH and testosterone to levels lower than those in control lambs. The total androgen response of interstitial cells from the remaining testis of oestradiol-implanted lambs at 12 weeks of age was significantly reduced. We suggest that the pituitary-testis axis varies in sensitivity during the prepubertal period although the interstitial cellular response of the testis to LH stimulation remains constant.     

Induction of estrus and ovulation in non-cyclic buffalo (Bubalusbubalis) heifers with progesterone-releasing intravaginal device and pregnant mare serum gonadotrophin and their gonadotrophin profile

A study was undertaken to induce estrus among 15 non-cyclic Murrah buffalo heifers at a relatively early age of 2.5 to 3 yr by progesterone releasing intravaginal device (PRID) application. On Day 13, the PRID was removed and the animals were divided into two groups (A and B). Group B received 1000 IU of pregnant mare serum gonadotrophin (PMSG) intramuscularly (i.m.) immediately after removal of the PRID, whereas Group A was given no further treatment. Circulating gonadotrophin profiles (luteinizing hormone (LH) and follicle stimulating hormone (FSH) were quantified during and after the PRID treatment, as well as during the induced estrous cycle. LH and FSH levels before, during, and after PRID treatment were in the range of 0.5 to 3.0 ng/ml and 10 to 45 ng/ml, respectively, and could be considered basal levels. The peak FSH levels of Group B (PRID + PMSG) during estrus ranged from 69.44 to 337.06 ng/ml, much higher than the levels recorded in Group A (PRID). None of the animals in Group A showed peak LH levels during estrus, whereas two animals in Group B had peak LH levels of 15.84 and 16.93 ng/ml at 0 h and 12 h after detection of estrus. The higher LH and FSH levels obtained in Group B animals compared with Group A animals was possibly due to the superimposed effect of PMSG over PRID. All of the 14 animals exhibited estrus. None of the animals in Group A conceived whereas three out of seven animals in Group B conceived, indicating that PMSG following PRID resulted in ovulatory estrus.     

Relationship between follicle growth and circulating gonadotrophin levels during postnatal development of sheep

This study investigates the number and size of ovarian antral follicles in relation to plasma follicle stimulating hormones (FSH) and luteinizing hormone (LH) concentrations from birth to 26 weeks of age in ewe lambs of the Ouled Djellel breed, a non-seasonal breed of sheep. Plasma was collected from 10 ewe lambs at 14 sampling times (Week 0, i.e. <24h, Week 1 and every two weeks from Week 4 to Week 26, inclusive). At each of these stages, four ewe lambs were slaughtered, the ovaries recovered and weighed, and the number and size of the follicles determined from histological examination. The pattern for plasma FSH showed a peak at Week 10, a smaller peak at Week 18 and a very small peak at Week 24. The pattern for LH was similar until Week 24 when the largest peak occurred. Paired ovarian weight increased rapidly from birth to four weeks and then more slowly to 10 weeks, followed by a decline at 12 weeks and a gradual increase from 14 to 24 weeks of age. The number and total diameter of follicles > or =3 mm in diameter showed similar patterns of development--rising gradually from birth to Week 14, falling to Week 16 and then rising more rapidly to a peak at Week 24. Maximum follicle diameter declined from birth to Week 1, then rose rapidly to Week 4, followed by a more gradual rise to Week 14 and, thereafter, a more rapid increase to a peak of 7.23+/-0.16 mm at 24 weeks old. The number of follicles (<3 mm diameter) increased rapidly from birth to Week 10 and then declined to values similar to those at Weeks 1 and 4. First behavioural oestrus was observed at Week 24 and a corpus luteum was present on the ovary of one lamb at Week 24 and two lambs at Week 26. It was concluded that two or three peaks in plasma FSH and LH levels precede puberty and first ovulation in Ouled Djellel ewe lambs, and first ovulation occurred at 24-26 weeks of age. The increase in follicle number and size generally reflected the pattern of plasma FSH and LH levels.     

Changes in gonadotrope responsivity to gonadotropin releasing hormone during development of the rhesus monkey

To assess the changing responsiveness of pituitary gonadotropes to gonadotropin releasing hormone (GnRH) during development, 5 male and 5 female rhesus monkeys were studied. Three monkeys of each sex were tested periodically with a subcutaneous injection of 500 micrograms of GnRH dissolved in 50% polyvinylpyrrolidone (PVP) beginning at 2 to 4 weeks of age and continuing into young adulthood. The remaining 4 monkeys received injections of the vehicle (PVP) alone and served as controls. Serum concentrations of bioactive luteinizing hormone (LH) were determined by an interstitial cell testosterone bioassay, and follicle-stimulating hormone (FSH) levels were measured by radioimmunoassay. Baseline FSH levels in the 5 female neonatal monkeys were higher than those of the 5 male neonatal monkeys during the first 2 months of life. In both sexes, FSH concentrations decreased with age, and FSH was barely detectable by 6 months. Baseline LH values in the 5 female monkeys declined during the first 6 months of the study and were undetectable (less than 0.5 micrograms/ml) at 6 months of age. Baseline LH levels in 4 of the 5 neonatal males also declined to undetectable concentrations by 6 months of age. During the first 3 months of life, there was a striking increase in the serum concentrations of both LH and FSH following GnRH. Although the LH responses to GnRH (delta LH) were similar in males and females of comparable ages, the FSH responses (delta FSH) were considerably greater in the female monkeys. In the males, the delta LH exceeded the delta FSH, whereas in the females, the delta FSH were greater than the delta FSH. In both sexes, the delta LH and delta FSH generally were greatest in the youngest monkeys and decreased gradually with increasing age. By 6 months, the gonadotropin responses to GnRH either were undetectable (males) or very small (females). After 6 months there was no longer an increase in serum gonadotropins after GnRH in either sex until 1.5-4 years (females) or 3 years (males) of age. The delta LH in response to GnRH in the male monkeys 3-5 years of age were comparable to the responses during the first month after birth. Serum concentrations of FSH in the adult males, however, did not increase after GnRH. In the female monkeys, serum levels of LH and FSH increased after GnRH at 1.5 years (1 monkey) and 4 years (2 monkeys) of age. The delta LH were similar to those of the 1- to 2-month-old female monkeys. The delta FSH, however, were variable and were approximately 20% of the neonatal response. In these young adult female monkeys the delta LH exceeded the delta FSH.(ABSTRACT TRUNCATED AT 400 WORDS)     

Serum follicle stimulating hormone, luteinizing hormone, and testosterone in sexually stimulated intact and unilaterally castrated rams

Ten two-year-old intact (IN) and unilaterally castrated (UC) Targhee rams were exposed to an estrogenized ewe each week from June to October. Each week the rams were subjectively evaluated for libido (10 for high interest and 1 for no interest). Semen was collected from all cooperating rams and evaluated for volume, concentration, and motility. Every 2 wk, blood samples were obtained at -30 and 0 min before and 30 and 60 min after ewe access. Serum was harvested; follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone concentrations were quantified by radioimmunoassay (RIA). Week 5 of ewe access was assigned as Week 1. Libido scores rose from a low on Week 1, with eight rams ejaculating, to a high on Week 12, with all rams ejaculating (Week 1, 5.0 +/- 1.0; Week 12, 10.0 +/- 0.0). The product of testis length and width was significantly greater in UC compared with IN rams (88.4 +/- 1.4 versus 73.2 +/- 1.0 cm(2), respectively). Serum FSH concentrations (ng/ml) were greater (P < 0.05) in UC than IN rams and dropped over the experimental period. Serum LH concentrations (ng/ml) were significantly greater in UC compared with IN rams. This difference was more pronounced in Weeks 1 and 3 compared with Weeks 11 and 13. Serum testosterone concentrations (ng/ml) were similar in UC and IN rams throughout the experiment. In conclusion, serum testosterone was not altered in UC rams; however, serum FSH and LH concentrations were increased in UC rams. Unilateral castration did not enhance the normal changes in semen quantity and quality in the rams from July to October.     

Circadian and pulsatile variations in plasma levels of inhibin, FSH, LH and testosterone in adult Murrah buffalo bulls

The present study investigated pulsatile and circadian variations in the circulatory levels of inhibin, gonadotrophins and testosterone. Six adult buffalo bulls (6 to 7 yr of age) were fitted with indwelling jugular vein catheters, and blood samples were collected at 2-h intervals for a period of 24 h and then at 15-min interval for 5 h. Plasma concentrations of inhibin, FSH, LH and testosterone were determined by specific radioimmunoassays. Plasma inhibin levels in Murrah buffalo bulls ranged between 0.201 to 0.429 ng/mL, with a mean of 0.278 +/- 0.023 ng/mL. No inhibin pulses could be detected during the 15-min sampling interval. Plasma FSH levels ranged between 0.95 to 3.61 ng/mL, the mean concentration of FSH over 24 h was 1.66 +/- 0.25 ng/mL. A single FSH pulse was detected in 2 of 6 bulls. The LH levels in peripheral circulation ranged between 0.92 to 9.91 ng/mL, with a mean concentration of 3.33 +/- 1.02 ng/mL. Pulsatility was detected in LH secretion with an average of 0.6 pulses/h. Plasma testosterone levels in 4 buffalo bulls ranged from 0.19 to 2.99 ng/mL, the mean level over 24 h were 1.34 +/- 0.52 ng/mL. Testosterone levels in peripheral circulation followed the LH secretory pattern, with an average of 0.32 pulses/h. The results indicate parallelism in inhibin, FSH and LH, and testosterone secretory pattern. Divergence in LH and FSH secretory patterns in adult buffalo bulls might be due to the presence of appreciable amounts of peripheral inhibin.     

Seasonal variation in the feedback of sex steroid hormones on serum LH concentrations in the male horse

The possibility of seasonal variation in the feedback effect of testosterone or oestradiol was investigated by giving replacement treatment to geldings for 2-3 weeks during breeding and non-breeding seasons. In the non-breeding season, testosterone suppressed LH values (mean +/- s.e.m., ng/ml) in all geldings (before treatment, 7.5 +/- 2.3; final treatment week, 1.8 +/- 0.2; P less than 0.05), whereas early in the breeding season, testosterone caused a prolonged rise in LH (before, 6.8 +/- 2.3; final week, 18.9 +/- 6.4; P less than 0.05). In all testosterone experiments, LH returned to pretreatment levels within 2 weeks after treatment. Oestradiol treatment caused a prolonged increase (P less than 0.05) in LH concentrations (mean +/- s.e.m., ng/ml) in both seasons (breeding: before 5.2 +/- 1.1; final week, 16.2 +/- 4.8; non-breeding before, 10.9, 20.1 +/- 5.2). We conclude that in geldings the feedback effect of testosterone varies with season and, further, that testosterone replacement may be able to restore to geldings the stallion's seasonal pattern of LH secretion. The results suggest that, in male horses, testosterone and possibly oestradiol, are important components in the neuroendocrine pathway controlling seasonal breeding and, moreover, are essential for the generation of a positive signal for LH secretion in the breeding season.     

The Sulawesi Crested Black Macaque (Macaca nigra) menstrual cycle: changes in perineal tumescence and serum estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone levels.

Events in the normal menstrual cycle of the endangered Sulawesi Crested Black Macaque (Macaca nigra) were characterized. Daily blood samples were obtained during 10 menstrual cycles from five M. nigra demonstrating regular cycles. The amount of perineal tumescence was scored daily. Serum levels of estradiol and progesterone were determined by RIA, serum LH levels were determined by the mouse Leydig cell bioassay, and serum FSH levels were determined by the rat granulosa cell aromatase bioassay. Cycle length was 39.8 +/- 1.0 days (mean +/- SEM) with an LH surge occurring 25 +/- 1.5 days from the onset of menses. After menses, both LH and estradiol were initially depressed, with estradiol first exceeding 50 pg/ml 8 days before the LH surge. In five cycles, peak estradiol levels (340 +/- 44 pg/ml) occurred on the day of the LH surge (637 +/- 58 ng/ml) and in the other five cycles, on the day before the LH surge. There was a broad increase of FSH in midcycle without a well-defined surge corresponding to the LH surge. Progesterone began increasing on the day of the LH surge and reached peak levels (6.8 +/- 0.96 ng/ml) 8 days later. Maximal perineal tumescence was generally associated with the time of the LH surge, but variation between animals made it impossible to predict accurately the day of the LH surge by perineal tumescence scores alone.     

The relationship between secretory patterns of gonadotrophic hormones and the attainment of puberty in bull and heifer calves born early or late during the spring calving season

It was suggested that an early increase in gonadotrophin secretion in calves aged between 6 and 24 weeks might be critical for initiating developmental changes culminating in puberty. An early rise in luteinizing hormone (LH) release appears to be caused by an increase in LH pulse frequency in bull calves and by an increase in LH pulse amplitude in heifer calves. Previously we have found differences in the characteristics of the LH rise between prepubertal beef calves born in spring or fall; however, age at puberty was not affected by season of birth. Here we report the LH/FSH secretory patterns in prepubertal bull and heifer calves (Hereford x Charolais), born in March or April, respectively (i.e., early or late during the spring calving season; six animals of each sex born at each time). The bull calves of both groups reached puberty (defined as an attainment of scrotal circumference of >or=28 cm) at 43.2+/-1.3 weeks of age (P>0.05). Age at puberty for March- and April-born heifer calves (defined as the age at which serum progesterone concentrations first exceeded 0.4 ng/ml) averaged 56.0+/-1.4 weeks (P>0.05). Based on blood samples taken weekly from birth to 26 weeks of age, and then every other week until puberty, bull calves born in March exceeded April-born bull calves in mean serum LH concentrations at 6, 10 and 12 weeks of age (P<0.05). Mean FSH concentrations were greater (P<0.05) in March-born compared to April-born bull calves from 34 to 32 weeks before puberty. Mean serum LH (at 40, 42 and 56 weeks) and FSH concentrations (at 2, 10, 20, 22-26, 30 and 56 weeks of age) were greater (P<0.05) in heifer calves born in April than March. On the basis of frequent blood sampling (every 12 min for 10 h), heifer calves born in April exceeded March-born animals in mean LH and FSH concentrations, at 5 and 25 weeks, and LH pulse frequency, at 5, 10 and 25 weeks of age (P<0.05). None of the parameters of LH secretion (i.e., mean concentrations of LH, LH pulse frequency and amplitude based on frequent blood collection) differed between March- and April-born bull calves in this study (P>0.05). In summary, March-born bull calves had greater mean serum LH and FSH concentrations prior to 24 weeks of age than April-born calves. April-born heifer calves had greater mean serum concentrations of LH and FSH but this difference was not confined to the early postnatal period. Although there were significant differences in absolute amounts of LH secreted, there were no differences in the frequency of LH secretory pulses amongst March- and April-born bull calves and no differences in LH pulse amplitude in heifer calves born in March or April. As these particular parameters of LH secretion, as well as age at puberty, are not affected by the time or season of birth, they may be primary hormonal cues governing sexual development in bulls and heifers, respectively.     

Effect of melatonin on pulsatile release of luteinizing hormone in female lambs.

This study investigated the effect of melatonin treatment of ewe lambs on LH pulsatility in an attempt to examine the mechanism whereby melatonin advances the onset of puberty. Six ewe lambs were given intravaginal melatonin implants at 12.8 weeks of age. Another six lambs received empty implants. All lambs were serially blood sampled every 15 minutes for six hours on several occasions prior to the onset of puberty. One week after implantation LH pulse frequency and mean LH levels were higher in treated lambs than the control lambs (pulse frequency 0.13/h vs 0.03/h; mean LH levels 2.0 +/- 0.2 ng/ml vs 1.3 +/- 0.1 ng/ml; p less than 0.05). Melatonin treatment failed to alter pulse frequency after the initial increase. Puberty was advanced by 3 weeks in the treated group. In the second experiment six lambs received melatonin implants at 13 weeks of age and another six lambs served as control. In this experiment blood samples were taken intensively during the first few weeks after treatment. Results of this study show that mean plasma LH levels and LH pulse frequency were again higher during the first week after implantation. This transient increase in LH release may be part of the mechanism initiating the eventual advancement of puberty although the significance of this increase is questionable. In both experiments the LH response to estradiol injection was monitored at various times after treatment, but no effects of melatonin were found, although the magnitude of the response increased with age.     

Luteinizing hormone, oestrogen and progesterone levels in peripheral serum of anoestrous and cyclic ewes as determined by radioimmunoassay.

Jugular vein blood was collected daily from four mature ewes throughout anoestrus and the first oestrous cycle of the breeding season until 4 days after the second oestrus. The levels of oestrogen, progesterone and LH were determined by radioimmunoassay. There were fluctuations in the LH level throughout most of the observed anoestrous period with a mean plus or minus S.E. value of 2-3 plus or minus 0-9 ng/ml. High LH values of 20-0, 41-2 and 137-5 ng/ml were observed in three ewes on Day - 24 of anoestrus. A brief minor rise in progesterone level was also observed around this period. Progesterone levels were consistently low (0.11 plus or minus 0-01 ng/ml) before Day - 25 of anoestrus. A major rise occurred on Day - 12 of anoestrous and this was followed by patterns similar to those that have been previously reported for the oestrous cycle of the ewe. Random fluctuations of oestrogens deviating from a mean level of 4-40 plus or minus 0-1 pg/ml were observed during anoestrus and the mean level during the period from the first to the second oestrus was 5-2 plus or minus 0-3 pg/ml. A well-defined peak of 13-3 plus or minus 0-7 pg/ml was seen in all ewes on the day of the second oestrus. Results of the present study suggest that episodic releases of LH occur during anoestrus and periods of low luteal activity. The fluctuations in LH levels, as observed during the period of low luteal activity, i.e. before Day - 25 of anoestrus, were less pronounced during the periods of high luteal activity. The view that luteal activity precedes the first behavioural oestrus of the breeding season is supported.