Seasonal variation in pituitary-gonadal function in free-ranging impala (Aepyceros melampus).

Blood, testicular biopsies and electroejaculates were collected from adult male impala, free-ranging in the Kruger National Park (Republic of South Africa), during the breeding (rut; April-May) and nonbreeding (September-October) seasons. Blood samples were collected at 5-min intervals for 120 min from anaesthetized males (n = 7 impala/group) treated intravenously with saline, gonadotrophin-releasing hormone (GnRH: 1 microgram/kg body weight) or human chorionic gonadotrophin (hCG: 10 or 30 iu/kg). Semen was collected from six more animals during the breeding season and 12 animals during the nonbreeding season using a standardized electroejaculation protocol. Ejaculates obtained during the nonbreeding season were of inferior quality to those collected during the breeding season, and were characterized by lower sperm concentrations, poorer sperm motility and more morphologically abnormal sperm forms. Within season, there were no differences in testosterone secretion between the two hCG doses, and these responses were similar to those observed after GnRH, but during the rut, testosterone secretion stimulated by both GnRH and hCG was approximately nine times greater than during the nonbreeding season. This seasonal increase in testosterone production was associated with a doubling in testicular volume and concentrations of luteinizing hormone (LH) receptors. Although concentrations of testicular follicle-stimulating hormone (FSH) receptors were similar between seasons, receptor content increased during rut as a result of increased testicular volume. In contrast to testosterone secretion, basal LH and FSH secretions were unaffected by season and GnRH-induced gonadotrophin secretion was reduced during rut.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunoreactive inhibin levels in peripheral blood during the breeding season in the female Japanese monkey

Serum levels of immunoreactive inhibin as well as FSH, LH, estradiol-17 beta, and progesterone were measured by RIA in four mature female Japanese monkeys (Macaca fuscata fuscata) during the breeding season and subsequent transition into the nonbreeding season. During the breeding season, each monkey showed 2-6 ovulations, which were inferred from underlying endocrine events. The concentrations of serum inhibin increased during the luteal phase, but were low during the follicular phase. Such changes in serum inhibin levels correlated positively with those in serum progesterone levels. Basal levels of serum inhibin also increased during the breeding season, decreased during transition from the breeding season, and were low during the nonbreeding season. The parallel change in serum levels of inhibin and progesterone together with the increased basal levels of serum inhibin during this period suggests that both the CL and antral follicles are sources of circulating inhibin. Decreases in serum FSH levels during the luteal phase suggest that secretion of FSH is controlled by an inhibitory action of ovarian inhibin in addition to steroid hormones.     

Seasonal changes in plasma testosterone and ejaculatory capacity in squirrel monkeys (Saimiri sciureus)

Seasonal changes in body weight, plasma testosterone and ejaculatory capacity were observed in five intact and two testosterone-implanted castrated squirrel monkeys for a total of 13 months. Electroejaculation was employed for obtaining data concerning ejaculation. In the intact animals, there were significant increases in body weight, ejaculate volume and plasma testosterone during the breeding season. With the exception of one animal, there was also a decrease in ejaculation latency during the season. Seasonal differences in the sperm count and sperm motility were not observed. Testosterone-implanted castrates showed changes in both ejaculate volume and ejaculation latency similar to those seen in intact monkeys during the breeding season. The body weight and plasma testosterone of the castrates remained quite constant throughout the year. Supported by NIH grants HD 00778, MH 21178 and MH 23645.     

Seasonally and experimentally induced changes in testicular function of the Australian bush rat (Rattus fuscipes)

Serum concentrations of LH, FSH and testosterone were measured monthly throughout the year in male bush rats. Testicular size and ultrastructure, LH/hCG, FSH and oestradiol receptors and the response of the pituitary to LHRH were also recorded. LH and FSH rose in parallel with an increase in testicular size after the winter solstice with peak gonadotrophin levels in the spring (September). The subsequent fall in LH and FSH levels was associated with a rise in serum testosterone which reached peak levels during summer (December and January). In February serum testosterone levels and testicular size declined in parallel, while the pituitary response to an LHRH injection was maximal during late summer. The number of LH/hCG, FSH and oestradiol receptors per testis were all greatly reduced in the regressed testes when compared to active testes. In a controlled environment of decreased lighting (shortened photoperiod), temperature and food quality, the testes of sexually active adult males regressed at any time of the year, the resultant testicular morphology and endocrine status being identical to that of wild rats in the non-breeding season. Full testicular regression was achieved only when the photoperiod, temperature and food quality were changed: experiments in which only one or two of these factors were altered failed to produce complete sexual regression.     

Studies of pituitary-adrenal-testis interaction in sheep. II. The effects of repeated injections of adrenocorticotrophic hormone outside the breeding season

The administration of 0.5 mg of long-acting adrenocorticotrophic hormone (ACTH, Synacthen-Depot) twice daily for 5.5 d to four rams outside the breeding season caused marked rises in plasma cortisol without any evidence of adrenal depletion. This treatment also caused marked rises in basal plasma follicle stimulating hormone (FSH) concentrations which remained high even after cessation of treatment. Plasma FSH responses to 5 ug of gonadotrophin releasing hormone (GnRH) were consistently observed and ACTH treatment increased the FSH response to GnRH. In contrast, spontaneous fluctuations in the plasma luteinizing hormone (LH) and testosterone concentrations were abolished by ACTH treatment. The quantity of testosterone released after GnRH (estimated by the maximum values reached and by the area under the response curve) was also suppressed while that of LH was only slightly lower. A comparison of the results of this experiment with those obtained in rams during the breeding season showed that the effects of ACTH on LH and testosterone were more marked during the breeding season. In contrast, the effect of ACTH on FSH is to increase the latter during the nonbreeding season, whereas no effect was observed during the breeding season.     

Changes in circulating inhibin levels during pregnancy and early lactation in the Japanese monkey

Changes in immunoreactive (ir-) inhibin concentrations in serum throughout pregnancy and early lactation up to one month after parturition were characterized in 6 Japanese monkeys (Macaca fuscata fuscata) by a heterologous radioimmunoassay (RIA) based on a bovine RIA. Serum levels of FSH, LH/monkey chorionic gonadotropin (mCG), estradiol-17 beta, and progesterone were also monitored for the entire period. Ir-inhibin levels in the serum were low (under 0.5 ng/ml) before conception. Three marked increases in serum ir-inhibin levels were found during pregnancy. The first increase was noted during early pregnancy, with a peak (2.2 +/- 0.2 ng/ml) at Day 22 of pregnancy (Day 0 = day of LH surge). The second increase was noted after Day 38 until Day 72 of pregnancy, when a peak value was noted (19.0 +/- 1.4 pg/ml). Plateau levels were maintained until late pregnancy, and a final rise was evident near the term with a peak (36.7 +/- 3.8 ng/ml) at Day 158 of pregnancy, 5 days before parturition. After parturition, ir-inhibin levels in the serum plummeted to nonpregnant levels within one day, and were maintained during early lactation. The first rise in serum inhibin during pregnancy was parallel to the rise of mCG and estradiol-17 beta, and the second and third rise were well correlated with serum estradiol-17 beta. Serum FSH was maintained at low levels throughout pregnancy, followed by a slight increase after parturition when serum inhibin decreased abruptly. Both bioactivity and immunoreactivity of inhibin were detected in the placental homogenates obtained at 120 days of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variations in seminal parameters over a 12-month period in captive bonnet monkeys

Semen samples were collected from adult fertile bonnet monkeys twice a month by penile electroejaculation for twelve consecutive months. Various parameters like semen volume, weight of ejaculate and coagulum, sperm count, sperm motility, sperm morphology, and functional parameters e.g. plasma membrane integrity,in vitro nuclear chromatin decondensation and acrosomal status were evaluated to assess within and between animal variations. Effects of seasonality, if any, on quantity and quality of semen were also studied. Considerable intra- and inter-individual variations in the geometric mean values were observed for semen volume, weights of ejaculate and coagulum, and sperm counts during the study period. On the other hand, sperm motility, morphology, and functional parameters showed less within and between animal variations. Results on motility, morphology, and functional parameters indicated that good semen quality was maintained throughout the year. Various routine and functional parameters did not show any annual variations. The diurnal rhythmicity in circulatory testosterone levels was observed throughout the year. The study shows lack of seasonality in exocrine and endocrine testicular functions and further suggests that motility, morphology, and functional parameters are better indicators of semen quality in captive bonnet monkeys.     

Age-related and seasonal variation in the Sertoli cell population, daily sperm production and serum concentrations of follicle-stimulating hormone, luteinizing hormone and testosterone in stallions

Testes and blood samples were obtained from 201 stallions aged 6 months to 20 years in either December-January (nonbreeding season) or June-July (breeding season) to study the effect of age and season on reproductive parameters. Seasonal differences in the Sertoli cell population of adult (4-20 years old) horses were characterized by a 36% larger number of Sertoli cells in the breeding season than in the nonbreeding season. Seasonal elevation in the Sertoli cell population was associated with an increase in testicular weight and daily sperm production per testis (DSP/testis). Concentrations of luteinizing hormone (LH) and testosterone in serum varied with season. Although follicle-stimulating hormone (FSH) concentrations also tended to be higher in the breeding season, this trend was not statistically significant (P less than 0.08). Sertoli cell numbers averaged over both seasons, like testicular weights, increased with age until 4-5 years of age, but were stabilized thereafter. This age-related difference was also associated with increased concentrations of FSH, LH and testosterone, and with increased DSP/testis. The Sertoli cell population was capable of increasing in the adult horse by fluctuating its size with season. The number of elongated spermatids per Sertoli cell over both seasons increased with age up to 4-5 years of age and was stabilized thereafter. Thus, seasonal and/or age-related differences in DSP/testis were associated with significant elevations in serum concentrations of FSH, LH and testosterone, testicular weights, numbers of elongated spermatids per Sertoli cell and elevation of the Sertoli cell population.     

Seasonality of LH,testosterone and sperm parameters in spider monkey males (Ateles geoffroyi)

There are no reported data on hormonal fluctuations in black‐handed spider monkey males. On previous research about the reproductive physiology of this monkey we have found that during the dry season females show ovulatory estrogen peaks and males present the best quality semen. As part of an ongoing research, in this study we assessed seasonal variations in the concentration of serum luteinizing hormone (LH) and testosterone (T) in three adult spider monkey males to corroborate the seasonal reproductive synchrony. At the same time sperm count and motility were evaluated to search for any correlation between those sperm parameters and hormonal concentrations. We took blood and semen samples (by electroejaculation) of anesthetized males throughout the rainy (June–September) and dry (October–May) months. Our results revealed that T and LH were higher throughout the dry season and there was a significant correlation between T concentration and sperm count. Although higher during the dry season, sperm motility tended to correlate with testosterone and LH levels. These results demonstrated that black‐handed spider monkeys have a tendency to show a seasonal pattern of reproduction being the dry season the most likely time to achieve fertilization. Am. J. Primatol. 71:427–431, 2009. © 2009 Wiley‐Liss, Inc.     

Effect of an LHRH agonist on pituitary and testicular function in rhesus monkeys

Male rhesus monkeys were given 100 micrograms [(imBzl)-D-His6,Pro9-NEt]-LHRH (LHRH-A), a potent LHRH agonist, s.c. daily for 40 weeks. The first dose of LHRH-A caused acute increases (2-4 h after injection) in serum LH (50-fold), FSH (2 X 5-fold) and testosterone (15-fold) concentrations. Chronic treatment led to a 95% decrease in LH and FSH responses. In spite of a marked decrease in LH response the effect on testosterone response was less evident. Administration of 50 i.u. hCG to control and LHRH-A-treated animals showed that the testicular steroidogenic response was unimpaired by the chronic treatment. Evaluation of the electroejaculated semen at regular intervals showed that there was no consistent reduction in the sperm count of LHRH-A-treated monkeys. Testicular biopsies showed that normal spermatogenesis was occurring in all treated animals, but testicular volume was significantly decreased. These results suggest that, in rhesus monkeys, the pituitary is more susceptible to desensitization by chronic LHRH agonist treatment than are the testes, and that LHRH agonists do not have direct antitesticular effect in rhesus monkeys.     

Sperm production, testicular size, serum gonadotropins and testosterone levels in Merino and Corriedale breeds

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 13 rams (four Corriedale, nine Australian Merino) during the late spring and autumn. Rams were weighed and testis size was estimated by orchimetry at each time period. Sperm production was estimated during a 2-week period, 2 months before blood collection and during each week following every blood collection. There was no relationship between testicular size and sperm production measured at the same time, nor between live weight and sperm production. In contrast, testicular volume during the late spring was correlated with sperm production in the autumn (r = 0.65; P = 0.02). The autumn serum LH was higher in Corriedale than in Merino rams. LH pulsatility was unaffected by season, but LH pulse frequency tended to be higher in Corriedale than in Merino rams, particularly in the late spring (2.37 versus 1.56 pulses/6 h; P = 0.08). Serum testosterone concentration was similar in both breeds and seasons. FSH levels were higher in the late spring than in the autumn in both breeds (Corriedale: 2.83 +/- 0.48 versus 2.17 +/- 0.24 ng x mL(-1); Merino: 2.23 +/- 0.24 versus 1.88 +/- 0.17 ng x mL(-1)). FSH and testosterone concentrations during the late spring were positively correlated with autumn sperm production (P = 0.07 and P = 0.03, respectively). In conclusion, the present experiment suggests that LH secretion is not a good parameter for the prediction of sperm production. In contrast, in our conditions (breeds and native pastures) testicular size and testosterone or FSH concentrations from the late spring may be used to predict sperm production in the autumn.     

Seasonal variation in reproductive physiological status in the Iberian ibex (Capra pyrenaica) and its relationship with sperm freezability

The present work examines the relationship between seasonal changes in testicular function, accessory gland size, and horn growth in Iberian ibexes, as well as the relationship between these changes and the resistance of ibex spermatozoa to freezing-thawing. The size of the bulbourethral glands and seminal vesicles showed pronounced monthly variation (P < 0.001), which was correlated positively with the plasma testosterone concentration (P < 0.001) and scrotal circumference (P < 0.001). The size of the accessory sex glands peaked during the autumn. Overall, semen quality was markedly improved during autumn and winter. When horn growth was at a minimum during autumn and winter, semen quality and accessory gland size were all increased compared to in spring and summer. However, increased plasma testosterone levels in the autumn were strongly associated with reduced sperm freezability; thus, the cryosurvival of spermatozoa collected during the autumn was poorer than at other times of the year. In winter, however, when the plasma testosterone concentration fell to baseline, the negative effects of cryopreservation on the percentage of motile spermatozoa and on the integrity of the plasma membrane of frozen-thawed sperm cells were significantly less intense (P < 0.05). These findings show a clear relationship between the functional and morphological status of the different parts of the reproductive tract that optimises reproductive function during the breeding season in the ibex male. They also show that winter is the most suitable season for the collection and cryopreservation of ibex spermatozoa.     

Seasonal variation in reproductive physiological status in the Iberian ibex (Capra pyrenaica) and its relationship with sperm freezability

The present work examines the relationship between seasonal changes in testicular function, accessory gland size, and horn growth in Iberian ibexes, as well as the relationship between these changes and the resistance of ibex spermatozoa to freezing-thawing. The size of the bulbourethral glands and seminal vesicles showed pronounced monthly variation (P < 0.001), which was correlated positively with the plasma testosterone concentration (P < 0.001) and scrotal circumference (P < 0.001). The size of the accessory sex glands peaked during the autumn. Overall, semen quality was markedly improved during autumn and winter. When horn growth was at a minimum during autumn and winter, semen quality and accessory gland size were all increased compared to in spring and summer. However, increased plasma testosterone levels in the autumn were strongly associated with reduced sperm freezability; thus, the cryosurvival of spermatozoa collected during the autumn was poorer than at other times of the year. In winter, however, when the plasma testosterone concentration fell to baseline, the negative effects of cryopreservation on the percentage of motile spermatozoa and on the integrity of the plasma membrane of frozen-thawed sperm cells were significantly less intense (P < 0.05). These findings show a clear relationship between the functional and morphological status of the different parts of the reproductive tract that optimises reproductive function during the breeding season in the ibex male. They also show that winter is the most suitable season for the collection and cryopreservation of ibex spermatozoa.     

Testicular function and Scrotal coloration in patas monkeys

Patas monkeys ( Erythrocebus patas ) have aquamarine-coloured scrota, but data are unavailable regarding the potential connection between changes in scrotal coloration and testicular function. In the rhesus monkey ( Macaca mulatta ), seasonality of mating is accompanied by an intensification of red colour of the scrotum and a doubling of testicle size. A one-year study of male patas monkeys was undertaken in order to examine potential seasonal correlates of testicular function and scrotal colour. Increases in testosterone concentrations and testicular volume occurred during the mating season in adult males, but scrotal colour was fairly uniform throughout the year. Neither age, body weight, nor health influenced scrotal colour. These findings contradict the suggestion that the sex skin of seasonally breeding primates will become more intense during the mating season as a result of elevations in steroid hormone levels. Evidence from field studies in Africa suggest that the colour is part of a constellation of traits involved in male competition for mates.     

Aging-related reproductive decline in the male spider monkey (Ateles geoffroyi)

Background It is unknown whether male black‐handed spider monkeys (Ateles geoffroyi) undergo a reproductive decline as they age. The purpose of this work was investigating whether serum testosterone and semen quality decrease with age in these primates as occur in other species. Methods In this study, we assessed age variations in the concentration of serum testosterone, sperm counts, and motility in nine males. We took serum blood samples and semen samples by electroejaculation of anesthetized males throughout the fertile season. Results We found that testosterone levels and total sperm concentration, motile, progressive, fast linearly moving, medium linearly moving, slow linearly moving and immotile sperm significantly decreased with age. Conclusions Our results show that a reproductive decline occurs in male spider monkeys because of a decrease in sperm counts. These results are similar to those of rhesus monkeys and men, despite the phylogenetic distance between New and Old World primates.     

Effects of season on the secretion of LH and testosterone in intact and castrated red deer stags (Cervus elaphus).

At 2--4 monthly intervals during the year blood samples were collected every 15 min for 6 h from 2 intact and 3 castrated red deer stags to study the relationship between season and the secretion of LH and testosterone. In the intact stags plasma LH and testosterone concentrations changed during the year; the LH levels were maximal in August during the phase of testicular redevelopment, while the testosterone levels were maximal from September to November coinciding with the time of peak testicular activity and the mating season. The castrated stags had higher plasma levels of LH than the intact stags at all times of the year, and there was no clear seasonal cycle in LH levels in these animals.     

Effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion in rats

The effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion and their relationships to gonadotropins were studied in rats. Mature Wistar male rats weighing approximately 300 g were made either uni- or bilaterally cryptorchid. Testicular inhibin and testosterone content and plasma levels of LH and FSH were examined 2 weeks later. A similar remarkable decrease in testicular inhibin content was found in uni- and bilaterally cryptorchid testes. On the other hand, the testicular testosterone content was significantly decreased only in unilaterally cryptorchid testis with an inverse increase in the contralateral testis. Plasma testosterone levels were normal and plasma LH and FSH increased significantly in both of the cryptorchid groups. These results showed that cryptorchidism impairs both Sertoli and Leydig cell functions. While testosterone production was compensated by increased LH for 2 weeks, neither inhibin secretion nor storage changed in cryptorchid or contralateral testes during the same period.     

Seasonal changes in the reproductive organs and plasma and pituitary hormone content of the male Bennett's wallaby (Macropus rufogriseus vufogriseus)

In a number of species of seasonally breeding marsupial, the male is fertile throughout the year but there is a marked seasonal change in weight of the accessory sexual glands. In this study, body weight, prostate, epididymis and testis weights and plasma concentrations of testosterone, LH and prolactin and pituitary content of LH and prolactin were determined in male Bennett's wallabies shot at 1–2 month intervals over a period of 17 months. There was a highly significant increase in prostate weight which was coincident with the breeding season for this species. A small but significant increase in testis weight was also observed but epididymis weight remained unchanged. Plasma testosterone concentrations were significantly increased at a time coincident with the increase in prostate weight. Plasma prolactin and LH concentrations were low in most animals and remained unchanged during the study. In contrast, pituitary prolactin and LH contents showed highly significant changes, with increasing and peak hormone content preceding maximum prostate weight and plasma testosterone concentrations by several months. While these latter results suggest a role for prolactin and LH in the seasonal control of the reproductive organs in the male wallaby, a more intensive study of the pattern of secretion of these hormones and possibly more sensitive hormone assays are required to understand their relative roles in regulating the annual cycle of prostate growth.     

Gonadal function in young adults after surgical treatment of cryptorchidism.

In a follow-up study of 48 young men who had been surgically treated for cryptorchidism before puberty testicular function was assessed by examining the genitalia, testicular volume, secondary sex characteristics, semen, plasma luteinising hormone (LH) and follicle-stimulating hormone (FSH) concentrations after luteinising hormone-releasing hormone stimulation, and plasma testosterone concentrations. Clinical androgen effects were normal. The mean testicular volume of both testes was in the low normal range in those who had had unilateral cryptorchidism and below normal in those who had had bilateral cryptorchidism. Of 37 patients whose sperm counts were recorded (14 bilateral) six showed azoospermia (all bilateral), five had severe oligospermia (four bilateral), and 10 had moderate oligospermia (one bilateral). In nearly all those who had had bilateral cryptorchidism and most of those who had had unilateral cryptorchidism plasma gonadotrophin levels were increased. Four cases of possible partial LH deficiency were identified. Plasma testosterone concentrations were normal in all except two patients.     

Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R2 = 0.77; FSH, R2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 +/- 0.04). Maximal concentrations of LH (20.58 +/- 1.97 ng/mL, Day 34.8 +/- 3.2) were attained approximately 2 wk before the peak in FSH (16.99 +/- 1.97 ng/mL, Day 49.7 +/- 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.