Peripheral Testosterone Concentrations Research Articles

Infertility in a cryptorchid bull: A case report

A unilateral cryptorchid bull stationed in an AI center for 3.5 yr was studied to determine if maintaining such a bull could be justified. The following parameters were determined: quantity and quality of the ejaculates, basal and stimulated plasma testosterone concentrations, and the histology and testosterone concentrations of the testicles. The bull produced 232 ejaculates of which 125 (53.8%) were immediately discarded; the rest (107 ejaculations) were processed into pellets. Two of the 107 frozen ejaculates (2%) were found to be of excellent quality, 37 were (34.5%) of good quality, 45 were (42%) of satisfactory quality and 23 were (21.5%) of poor quality. Treatment of the calf with GnRH and hCG at 4 and 5 mo of age did not initiate the descent of the retained testicle. Testosterone concentrations measured at 14 mo, after hCG stimulus, indicated that the bull had impaired steroidogenesis when compared with 2 control bull calves. Post mortem examination revealed a small left testicle in the inguinal canal and a normal right testicle as well as normal secondary sex glands. During the breeding period at the AI center, the bull's peripheral testosterone concentrations decreased from 2.2 to 0.95 ng/ml Testosterone concentrations in the parenchymal tissue of the scrotal testicle were higher than in the parenchyma of the retained testicle (98.2 vs 53.9 ng/g). In contrast, the epididymis of the scrotal testicle had a lower testosterone concentration than the epididymis of the retained testicle (10.8 vs 33. 0 ng/g). On histological examination no spermatozoa were found in the retained testicle, the Sertoli cells showed fat degeneration, and fibrotic tissue surrounded the tubuli seminiferi. No pathological changes were found in the normal scrotal testicle. In conclusion, no justification was found for maintaining such a bull in the AI center for breeding purposes.

The effect of nutrition on testicular growth in mature Merino rams involves mechanisms that are independent of changes in GnRH pulse frequency.

In mature Merino rams, changes in diet to below or above the requirements for maintenance of body weight lead to changes in gonadotrophin secretion and testicular growth. However, the effects on testicular growth persist for much longer than those on LH and FSH secretion so that the gonadal and gonadotrophin responses are poorly correlated over time. This suggests that the gonadal effects may be partly independent of changes in the hypothalamic secretion of GnRH, an hypothesis tested in this study. In a short-term experiment (November, late spring, non-breeding season), we tested whether a high frequency of exogenous GnRH pulses could override the endogenous system and mimic the change in gonadotrophins seen in rams fed a high plane of nutrition. Mature Merino rams (scrotal circumference (mean +/- S.E.M.) 33.6 +/- 0.5 cm, body weight (mean +/- S.E.M.) 59.0 +/- 0.9 kg) were fed 900 g chaff + 1.6 kg lupin grain (High diet) or 360 g chaff + 60 g lupin grain (Low diet) and infused with 8 pulses of GnRH or saline daily for 5 weeks (n = 5/group). Blood was sampled every 20 min for 12 h on days-1 and 14 relative to the start of treatments. Relative to pre-treatment levels, LH pulse frequency and FSH concentrations were decreased on day 14 in saline-infused rams fed the Low diet and increased in saline-infused rams fed the High diet (P < 0.001). In GnRH-infused rams, gonadotrophin secretion was not affected by diet and the patterns of secretion of LH and FSH were similar to those in saline-infused rams fed the High diet. This model was used for a more complete endocrine analysis in a longer experiment designed to test the hypothesis that the effect of nutrition on testicular growth is partly independent of changes in the secretion of GnRH. The same treatments were imposed for 35 days on a different group of similar rams in March (autumn, mid-breeding season). Body weight and scrotal circumference were measured weekly and blood was sampled on days -1 and 14. On days -1 and 35, testosterone secretion in response to LH was tested by injecting exogenous ovine LH (NIADDK-oLH-25; 200 ng/kg body weight) to all rams. Body weight increased in rams fed the High diet and decreased in those fed the Low diet (P < 0.001) and was not affected by treatments as in experiment 1.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of prostaglandin F 2α and oxytocin release after inhibition of testosterone synthesis in the goat

Increased peripheral plasma concentrations of testosterone were detected in goats on days 13 and 14 of the oestrous cycle (oestrus = day 0), at the onset of luteolysis. Subcutaneous administration of spironolactone (10 mg kg −1 day −1) on days 10 to 19 inhibited the increases in testosterone, delayed luteolysis and suppressed plasma concentrations of 13,14-dihydro-15-ketoprostaglandin F 2α and oxytocin. These results suggest that testosterone of follicular or luteal origin, possibly via aromatisation to oestrogens, is needed to expedite luteolysis and induce oestrus in the goat.

Role of gonadal negative feedback on the gonadotrophin responses to gonadotrophin-releasing hormone (GnRH) in ram lambs from two lines of sheep selected for their luteinizing hormone response to GnRH

Divergent selection has resulted in two lines of lambs (high and low) that have a 5-fold difference in their ability to release luteinizing hormone (LH) in response to 5 micrograms of gonadotrophin-releasing hormone (GnRH). Baseline gonadotrophin concentrations, the gonadotrophin responses to a GnRH challenge and the concentrations of testosterone and oestradiol were compared in lambs which were castrated at birth and intact lambs from both selection lines at 2, 6, 10 and 20 weeks of age. The pattern of LH and follicle-stimulating hormone (FSH) secretion was similar in the two lines, but differed between the intact and the castrated lambs. Basal LH and FSH secretion were significantly higher in the castrates than in the intact lambs from both selection lines. The high-line lambs had significantly higher basal FSH concentrations at all ages tested and significantly higher basal LH concentrations during the early postnatal period. The magnitude of the gonadotrophin responses to GnRH differed significantly between the intact and the castrated lambs within each line, the amount of gonadotrophins secreted by the castrated lambs being significantly greater. The removal of gonadal negative feedback by castration did not alter the between-line difference in either LH or the FSH response to the GnRH challenge. Throughout the experimental period, the concentration of testosterone in the intact lambs was significantly greater than in the castrated lambs in both selection lines, but no significant difference was seen in the concentrations of oestradiol. No significant between-line differences were found in the peripheral concentrations of testosterone or oestradiol in the intact lambs from the two selection lines. Therefore, despite similar amounts of gonadal negative feedback in the selection lines, there were significant between-line differences in basal gonadotrophin concentrations, at 2 and 6 weeks of age, and in the LH and FSH responses to an exogenous GnRH challenge, at all ages tested. Removal of gonadal negative feedback did not affect the magnitude of the between-line difference in the response of the lines to GnRH stimulation. The results indicate that the effects of selection on gonadotrophin secretion are primarily at the level of the hypothalamo-pituitary complex.

Changes in the behaviour and androgen levels during pubertal development of the buffalo bull

Sexual behaviour and peripheral testosterone concentrations were studied longitudinally in a group of ten buffalo bulls of Nili-Ravi breed raised from birth under similar feeding and management conditions. Changes in sexual behaviour of these animals in response to a teaser bull were observed at weekly intervals from 15 months of age to attainment of puberty (mean age at puberty, 23.6 ± 0.9 months). Sexual behaviour of individual bulls was scored by a procedure based on an assessment of behavioural events and expressed as a percentage of the maximal points. These events ranged from reaction of the bull during approach towards the teaser to intromission and ejaculation in an artificial vagina. Serum testosterone was determined by radioimmunoassay in blood samples obtained at monthly intervals, from each bull. Analysis of behavioural data indicated a significant increase in sexual behaviour score (from 5 ± 2% to 40 ± 7%) 4–5 months prior to the attainment of puberty. Following a transitory decline, the sexual behaviour score reached a maximum (69 ± 5%) during the month in which first ejaculation with motile sperm was achieved. Behavioural profiles of individual bulls indicate that the period of prepubertal increase in sexual activity corresponded to the physiological puberty rather than to the chronological age of the bulls. The prepubertal as well as pubertal increase in sexual behaviour score was invariably preceded by a significant ( P < 0.05) elevation of serum testosterone concentrations. The data suggests that the prepubertal increase in sexual activity in the buffalo bull may serve as a criterion of onset of puberty and may be helpful in the selection of sires at a stage prior to sexual maturation.

Effects of pretreatment with adrenocorticotropin on endocrine and behavioral responses of bulls to sexual activity

Peripheral concentrations of cortisol, growth hormone and testosterone were determined in two experiments which examined the endocrine and behavioral responses of sexually mature Angus bulls to an estrous female (Experiment 1) and to female exposure 5 hours following an adrenocorticotropin (ACTH) injection (Experiment 2). Sexual activity of bulls in Experiment 1 significantly increased levels of cortisol when compared with concentrations before exposure to a female. Administration of ACTH in Experiment 2 consistently elevated levels of cortisol by 30-fold (P<0.01) when compared with pre-ACTH concentrations. This heightened level of cortisol persisted throughout the period of exposure to an estrous cow, although a gradual decline in cortisol concentrations occurred over time (P<0.05). In Experiment 1, growth hormone profiles tended to increase in response to sexual activity (P<0.10), whereas in Experiment 2, growth hormone increased in response to ACTH administration (P<0.01) and to female exposure (P<0.01). Concentrations of testosterone were unaffected (P>0.10) by mating activity in Experiment 1. In Experiment 2, acute suppression (P<0.01) in testosterone concentrations 5 hours after ACTH administration coincided with the exposure period to the estrous female. Frequencies of mounting behavious (penis extension, mounting, intromission and ejaculation) exhibited by ACTH-treated bulls were significantly lower compared with the frequencies two days earlier. Exogenous ACTH administration suppressed reproductive behaviors of bulls and altered secretion of cortisol, growth hormone and testosterone. Furthermore, these data provide evidence that specific mating behaviors of the bull can be influenced by circulating steroids.

Androgen production by epithelial ovarian tumours in post-menopausal women

Peripheral serum concentrations of androstenedione (A) and testosterone (T) were measured in 31 post-menopausal women with epithelial ovarian tumours (12 cancer, 5 borderline malignant and 14 benign tumours), and in 20 post-menopausal women who were free from ovarian neoplasms. The levels of these androgens were also measured in ovarian venous blood in 17 women with ovarian tumours. No significant differences were found between the mean serum androgen levels in patients with malignant, borderline malignant or benign ovarian tumours or the control group. The measured levels of A and T in peripheral and ovarian venous blood were highest in women with mucinous ovarian tumours. Histopathological examinations of the ovarian tumours showed hyperplasia or luteinization in ovarian tumour stroma in 5 out of 17 cases (3 mucinous tumours, I endometrioid adenocarcinoma and I serous adenocarcinoma). The results indicate that of all epithelial tumours mucinous ovarian tumours most often demonstrate hormonal activity and that malignancy has no effect on hormonal activity.

Stimulatory Effects ofα-hANP on Testosterone Secretion in Man

Several recent observations suggest that atrial natriuretic peptides (ANP) can modulate steroidogenesis in isolated rat Leydig cells. At present, it is unknown whether ANP influence human testicular steroidogenesis. We therefore evaluated the effects of alpha-human ANP (hANP) administration on testosterone plasma levels in peripheral and internal spermatic venous blood of young men (catheterized for contrast study of varicocele). Six subjects were injected with 100 micrograms alpha-hANP in the cubital vein. Six different patients similarly received 50 micrograms LHRH. Three controls received 2 ml saline. Plasma LH, FSH, and testosterone were then determined 15 min before, at time of injection, and 15, 30, 45, and 60 min thereafter in spermatic vein and peripheral venous blood, as well as at 120 min in peripheral blood. LHRH--induced LH increase was followed by a marked increase of spermatic vein testosterone concentrations, but the peripheral testosterone concentration did not increase. Similarly, alpha-hANP administration did not affect peripheral testosterone and LH concentrations, but significantly increased spermatic vein testosterone levels (P less than 0.01). Our findings demonstrate that alpha-hANP exerts its stimulatory effect on testicular steroidogenesis in man without modifying gonadotropin secretion, suggesting that alpha-hANP may directly influence Leydig cell function.

Cortisol, growth hormone, and testosterone concentrations during mating behavior in the bull and boar.

Two experiments were conducted to evaluate peripheral concentrations of cortisol (C), growth hormone (GH), and testosterone (T) in bulls and boars during mating and to correlate mating behaviors with endocrine secretion in the presence of an estrous female. In Exp. 1, six sexually inexperienced mature bulls were bled every 15 min for 2 h before and 2 h after a 30-min exposure to a single, restrained, estrous cow; sampling occurred every 5 min during exposure. In Exp. 2, six sexually experienced boars were bled similarly before and after exposure to a sow and every 5 min during a 15-min exposure to a freely moving, estrous sow. Behavioral events recorded during exposure to a female included the following: flehmen responses (bulls only), mounts, penis extensions, intromissions, ejaculations, and time to first mount and first ejaculation. Of the six bulls, four completed at least one service (intromission + ejaculation), and three of six mounted the estrous cow eight or more times. Completion of one or more services resulted in significant elevations in serum C and GH concentrations, but not T concentrations, during the exposure period. Bulls mounting eight or more times also experienced significant elevations in C concentrations during exposure. Three of six boars completed at least one service. Servicing and mounting the sow fewer than five times were both associated with significant elevations in serum C concentrations. Serum concentrations of T were also elevated as a result of exposure to an estrous sow. Collectively, these data support the suggestion that specific events during natural mating activity can alter endocrine secretions of C and GH in bulls and C and T in boars.

Testosterone secretion during early pregnancy in the goat

Increased peripheral concentrations of testosterone were detected on Days 12 and 13 of the estrous cycle (estrus = Day 0), at the onset of luteolysis in goats. In pregnant goats no increases in testosterone occurred between Days 10 and 18 after mating, and luteal regression was inhibited. It is suggested that testosterone is required for luteolysis in goats, and that the absence of any increase in testosterone concentrations is another manifestation of the mechanisms involved in the maternal recognition of pregnancy.

The effect of inhibition of aromatase enzyme activity on Leydig cell number and ultrastructure in beagles.

We have shown previously that administration of an orally active competitive aromatase inhibitor 4-(5,6,7,8-tetrahydroimidazo [1,5a] pyridin-5-yl) benzonitrile monohydrochloride to adult male beagles increases peripheral blood LH and testosterone concentrations, and that testes from treated dogs produce more testosterone when perfused in vitro than age-matched controls. In the present study we posed the question of whether the increased testosterone secretion by testes from these same aromatase-treated dogs was due to Leydig cell hypertrophy or hyperplasia, and if the latter, whether cytoplasmic organelles are increased. Beagles were treated with the inhibitor at a dosage of 2.5 mg/kg.day for 25 weeks and were euthanized by an overdose of iv sodium pentobarbital; testes were perfusion-fixed, embedded, and sectioned for stereological analysis. There were no significant differences in testis volume and absolute volumes of seminiferous tubules, blood vessels, lymphatic space, macrophage cells, and mesenchymal cells between the control and treated dogs. In contrast absolute interstitium volume and the absolute volume of Leydig cells per testis were significantly increased (P less than 0.05) in treated dogs. This increased Leydig cell volume per testis was due to increased volume of individual Leydig cells rather than to increases in Leydig cell number per testis. Additional studies showed that the surface area per Leydig cell of smooth endoplasmic reticulum, outer and inner mitochondrial membranes, and membranes of lipid droplets per testis were significantly higher (P less than 0.05) in the treated dogs as compared to the controls. In summary, the results of this study lead us to conclude that aromatase inhibition in the mature dog causes Leydig cell hypertrophy rather than hyperplasia and increased surface area per Leydig cell of subcellular organelles that contain enzymes involved in steroid biosynthesis.

A possible role for testosterone during luteolysis in the ewe

Increased peripheral plasma concentrations of testosterone were detected at the commencement of luteolysis and at oestrus in sheep. Daily subcutaneous administration of spironolactone (10 mg kg-1) between days 10 and 16 of the oestrous cycle suppressed testosterone secretion and delayed luteolysis and oestrus. In pregnant ewes no increases in testosterone concentrations occurred between days 10 to 16 after mating and luteal regression, monitored by peripheral progesterone concentrations, was inhibited. It is suggested that aromatisation of testosterone to oestrogens is needed for luteolysis in sheep.

Plasma concentrations of progesterone, oestrogens, testosterone and LH-like activity during the oestrous cycle of the camel (Camelus dromedarius)

Peripheral plasma concentrations of progesterone, total oestrogens and testosterone (measured by RIAs) and LH (monitored by the mouse Leydig cell bio-assay) were measured in 8 female camels for a complete oestrous cycle (23.1 +/- 1.2 days). The absence of an LH surge and a low concentration of progesterone (less than 1 ng/ml) during oestrus (5 days) and throughout the cycle indicated a failure of spontaneous ovulation and absence of a subsequent luteal phase in this species. High concentrations of testosterone and oestrogens indicated that the oestrous cycle in the camel is mostly follicular and that the increasing values of the two hormones during follicular development (5 days) is probably the stimulus to behavioural oestrus.

Secretion of androgens and estrogens by normal and neoplastic ovaries in postmenopausal women

Peripheral and ovarian venous concentrations of testosterone, androstenedione, estradiol-17 beta, and estrone were measured in 30 postmenopausal women. Ovarian venous concentrations of testosterone and estradiol-17 beta were 5.6 and 4.3 times the peripheral concentrations of women with normal ovaries. This suggests that the ovaries of postmenopausal women continue to secrete these two steroids. Mean peripheral testosterone concentrations in 14 postmenopausal women with a nonfunctional or functional ovarian tumor were increased significantly. Ovarian venous concentrations of these four steroids from the side draining the tumor-bearing ovary were increased in 40 to 80% of the women. The venous concentrations from the normal ovary were also increased in 22% or more of the women with an ovarian tumor. Any ovarian neoplasm in postmenopausal women may be associated with increased ovarian sex-steroid secretion.

Age-associated increases in serum follicle-stimulating hormone levels on estrus are accompanied by a reduction in the ovarian secretion of inhibin.

In light of recent data demonstrating age-related alterations in the secretion and production of follicle-stimulating hormone (FSH) during the secondary FSH surge on estrus, the following study was conducted to determine the effects of age on periovulatory inhibin secretion. Ovarian venous blood was collected from groups of ether-anesthetized 3- and 7-month-old rats exhibiting 4-day estrous cycles at the following times: 1200 and 2400 h on proestrus and 1600 h on estrus. Following a 10-min collection period, a terminal blood sample was obtained from the abdominal aorta. Peripheral serum concentrations of luteinizing hormone (LH), FSH, estradiol-17 beta (E2), progesterone (P) and testosterone (T) were measured by RIA. Inhibin activity in ovarian venous serum (OVS) was assessed by the ability of OVS to suppress basal FSH secretion from dispersed pituitary cells during a 24-hour culture period. At 1200 h on proestrus, serum FSH (and LH) levels were higher in 7-month-old rats than in younger rats while the FSH-suppressing activity of OVS did not differ between age groups at this time. Bioassayable inhibin activity substantially declined between 1200 and 2400 h on proestrus in both groups. By 1600 h on estrus, serum FSH levels and inhibin secretion were higher and lower, respectively, in the older age group compared to 3-month-old rats. Significant increases in inhibin secretion between 2400 h on proestrus and 1600 h on estrus were observed only in younger rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral and ovarian venous concentrations of steroid and gonadotropin hormones in postmenopausal women with epithelial ovarian tumors

Peripheral serum concentrations of estrone (E 1), estradiol (E 2), testosterone, androstenedione, dehydroepiandrosterone sulfate (DHEAS), cortisol, prolactin, LH, and FSH were measured in 28 postmenopausal women with epithelial ovarian tumors (12 ovarian cancer, 5 borderline malignant, 11 benign neoplasms) and in 15 controls before bilateral salpingo-oophorectomy and 1 and 8 weeks postoperatively. The levels of these hormones were also measured in ovarian venous blood of 15 patients with ovarian tumors. E 2 was significantly higher in the tumor group than in controls preoperatively and the levels of E 1 and E 2 decreased after radical operation. Hormone levels were similar in the benign and malignant tumor groups. Only DHEAS levels in peripheral serum were significantly lower in ovarian cancer patients than in the group with benign neoplasm. This was not the case in testosterone and androstenedione measurements. The measured levels of the hormones in ovarian venous blood were highest in mucinous ovarian tumors. E 2 and testosterone levels were higher in mucinous ovarian tumors than in others. LH(hCG)-receptor levels were measured in 24 specimens and none of these showed detectable concentrations of LH(hCG) receptor. The results indicate that of all epithelial tumors mucinous ovarian tumors had hormonal activity most often, and malignancy had no effect on hormonal activity.

Estrogen regulates placental androstenedione production during rat pregnancy.

During rat pregnancy the placenta appears to provide androgens, particularly androstenedione (delta 4A) as a source of precursor for estradiol (E2) formation by the ovary. The present study determined if the ovary and, specifically, estrogen have roles in regulating placental delta 4A production during the second half of rat pregnancy. Pregnant rats were ovariectomized (OVX) on day 9 of gestation, treated daily with 4 mg progesterone (P4) to maintain pregnancy, and received a Silastic capsule containing either E2 or oil on day 10 of gestation only. Placental steroidogenesis was then determined in vitro on day 14 by the ability of this tissue to convert [3H]pregnenolone ([3H]P5) substrate to the intermediate [3H]P4 and product [3H]delta 4A. Mean (+/- SE) placental formation of delta 4A from P5 increased (P less than 0.01) from 6.3 +/- 0.5% in control animals to 10.7 +/- 1.6% in OVX P4-treated rats. In contrast, placentae from OVX animals treated with P4 and E2 exhibited a decline in delta 4A formation (2.5 +/- 0.3%) compared to that in both control (P less than 0.01) and OVX P4-treated (P less than 0.001) animals. The amount of P5 converted to P4 and thus not further metabolized to delta 4A decreased (P less than 0.05) from 64.0 +/- 3.1% in control animals to 49.0 +/- 4.7% in OVX rats treated with P4 alone. However, OVX animals treated with P4 and E2 exhibited an increase in placental conversion of P5 to P4 (80.3 +/- 4.7%) compared to values in both control (P less than 0.05) and OVX P4-treated (P less than 0.001) animals. The peripheral serum concentrations of delta 4A and testosterone (T) were 3- and 2-fold greater (P less than 0.01), respectively, in OVX P4-treated animals compared to concentrations in the untreated controls. Rats that had been OVX and treated with both P4 and E2 had peripheral serum delta 4A and T concentrations that were approximately 10-15% (P less than 0.001) of the concentrations in OVX P4-treated animals. In conclusion, ovariectomy or ovariectomy and estrogen supplementation resulted in comparable alterations in the formation of delta 4A within the placenta and the concentrations of this steroid in the peripheral circulation. Thus, ovariectomy caused an elevation in and ovariectomy with E2 treatment caused a decline in both placental delta 4A formation and peripheral serum androgen concentrations. We suggest, therefore, that ovarian estrogen may feed back to inhibit placental delta 4A and T production, thereby regulating its substrate availability during the second half of rat pregnancy.

Androgen and estrogen secretion by normal and neoplastic ovaries in premenopausal women.

Peripheral and ovarian venous concentrations of estradiol-17 beta, estrone, testosterone, and androstenedione were measured in 47 premenopausal women at the time of laparotomy. Ovarian histology was normal in 32 women, and 15 women had a unilateral (N = 13) or bilateral (N = 2) ovarian neoplasm. That the concentrations of these steroids in women with normal ovaries were comparable to values reported by others suggests that surgical stress did not affect the results. The concentration of both estrogens in the vein draining a nonfunctional neoplasm were significantly less than estrogen concentrations in the vein draining the ovary with the dominant follicle or corpus luteum. Peripheral venous estrogen, as well as androgen concentrations were normal in women with a nonfunctional neoplasm. Peripheral concentrations and concentrations of both androgens in the vein draining the ovary with a functional neoplasm were increased significantly. In 21 to 33% of all women with a neoplasm, the ovarian venous concentration of one or both androgens was increased significantly. No woman with an ovarian neoplasm had a significant increase in ovarian venous estrogen concentration. Although we did not define the mechanism for a selective increase in ovarian androgen secretion in a fraction of women, we conclude that any ovarian neoplasm may be associated with abnormal ovarian secretion of sex steroids.

Peripheral androgen levels in peripuberal rams infected with Fasciola hepatica

Three-month-old, Polled Dorset rams infected with Fasciola hepatica and uninfected control rams were monitored throughout the peripuberal phase for peripheral concentrations of testosterone and for body weight. No differences between groups occurred in these measurements from early spring to mid-autumn. However, the infected postpuberal rams demonstrated a reduced ability to remove exogenous testosterone from the circulation. Liver damage induced by moderate infections of flukes apparently impairs hepatic catabolism of this steroid but compensatory mechanisms appear to maintain circulating levels comparable to those of uninfected rams.

Reproduction in the vervet monkey (Cercopithecus aethiops): I. Testicular volume, testosterone, and seasonality.

To test whether the male could contribute to the birth peak seen in both wild and captive vervets, testicular volume and peripheral testosterone concentration were measured monthly in nine adults throughout a 14-month period. Volume was an average of 15% greater during the months of June to September, the period of natural breeding activity in the wild, than at other times of the year. Testosterone concentration rose throughout the time period but did not correlate with testicular volume. Quarterly biopsies of the right testis in animals either used for or withheld from breeding revealed the presence of spermatozoa and the existence of spermatogenesis throughout the year. There was no correlation of testicular volume with breeding status or biopsy. If these results from individually caged animals are representative of group-caged and wild animals, then such small seasonal changes are unlikely to affect year-round breeding. Therefore, a physiological contribution by the male to natural birth peaks seen in the wild and captivity is not readily apparent.