Changes In Serum Testosterone Concentrations Research Articles

Characterization of sperm motility and testosterone secretion in the taiep myelin mutant, a model of demyelination.

Presently, demyelinating diseases have been reported to affect the reproductive life of patients who suffer from them, but the progression of the alterations is unknown, especially in men. To better understand these effects, it is necessary to perform studies in animal models, such as the male taiep rat, which exhibits progressive demyelination of the central nervous system, altered kisspeptin expression at the hypothalamic level, and decreased luteinizing hormone, which could alter sperm quality and testicular diameter. Thus, the objective of the present study was to analyze the diameter of the seminiferous tubules, the sperm motility, and the testosterone levels of 90-day-old male taiep rats. The obtained results indicate that male taiep rats show an increase in testicular size accompanied by an increase in the diameter of the seminiferous tubules of the left testicle. There was also a decrease in progressive motility in sperm samples from the left epididymis of male taiep rats compared to the control group, with no changes in serum testosterone concentration. Therefore, we conclude that male taiep rats with central demyelination show altered testicular diameter and decreased motility in sperm from the left side. This type of studies serves as a basis for proposing possible reproductive strategies to improve the fertility and testicular function of men with demyelinating diseases of the central nervous system.

Dexamethasone mediated downregulation of PGC-1α and visfatin regulates testosterone synthesis and antioxidant system in mouse testis

Dexamethasone, a synthetic glucocorticoid has been used as an immunosuppressive and anti-inflammatory and affects reproduction. It has been suggested that testicular steroidogenesis involves PGC-1α and visfatin as key regulators. Previous studies have shown that dexamethasone down-regulates PGC-1α and visfatin expression in muscle and mammary epithelial cells respectively. However, the effect of dexamethasone on testicular visfatin and PGC-1α expressions has not been investigated. The aims of the present study were to investigate the effect of dexamethasone, on the expression of PGC-1α, visfatin and antioxidant enzymes activities in mouse testis. The results of the present study showed that dexamethasone treatment significantly decreased the expression of visfatin and PGC-1α in mice testis, along with significant decreased in testicular antioxidant enzymes activates. Further, dexamethasone treatment also significantly increased the testicular lipid peroxidation and decreased testosterone synthesis. The dexamethasone induced changes in PGC-1α and visfatin in the testis were significantly correlated with changes in serum testosterone concentrations and antioxidant enzymes activities. Thus, dexamethasone induced testicular toxicity may involve the PGC-1α and visfatin as important molecules to exhibit its effects.

Carnitine-mediated antioxidant enzyme activity and Bcl2 expression involves peroxisome proliferator-activated receptor-γ coactivator-1α in mouse testis.

The protective effects of carnitine have been attributed to inhibition of apoptosis, alleviating oxidative stress and DNA repair mechanism by decreasing oxidative radicles. Carnitine also increases mitochondrial biogenesis via peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). The role of carnitine in testicular PGC1α expression has not been documented. We hypothesised that the effects of carnitine as an antioxidant, inhibitor of apoptosis and controller of steroidogenesis in mouse testis may involve PGC1α as a regulator. The present study was designed to evaluate the localisation of PGC1α and the effects of carnitine treatment on the expression of PGC1α, Bcl2 and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx)) in mouse testis and serum testosterone concentrations. PGC1α was primarily immunolocalised to the Leydig cells and primary spermatocytes. Western blot analysis showed that carnitine (50mgkg-1 and 100mgkg-1 for 7 days) significantly increased PGC1α and Bcl2 expression in the testis in a dose-dependent manner. In addition, carnitine treatment significantly increased antioxidant enzyme (CAT, SOD and GPx) levels. The carnitine-induced changes in PGC1α in the testis were significantly correlated with changes in serum testosterone concentrations, as well as with changes in Bcl2 expression and antioxidant enzyme activity in the testis, as evaluated by electrophoresis. Therefore, the results of the present study suggest that carnitine treatment of mice increases PGC1α levels in the testis, which may, in turn, regulate steroidogenesis by increasing expression of Bcl2 and antioxidant enzymes.

Age and season affect serum testosterone concentrations in cryptorchid stallions

Cryptorchidism, characterised by inguinal and/or abdominal retention of one or both testes, is the most common developmental defect encountered in equine veterinary practice. Most cases present with stallion-like behaviour in...

Seasonal variation in serum testosterone, testicular volume and semen characteristics in coatis (Nasua nasua)

The objective was to characterize seasonal changes in serum testosterone concentration, testicular volume and sperm quantity and quality in captive coatis (Nasua nasua) from Pantanal, MT, Brazil. Sampling was done once monthly for 1 y. Mean (± SEM) serum testosterone concentrations (767.37 ± 216.2 ng/ml) and total and progressive sperm motility (79.6 ± 3.9%; 3.8 ± 0.3, on a scale of 0 to 5) peaked in July. The highest combined testis volume (10.3 ± 0.4 cm3) and sperm concentration (403 million ± 102 sperm/ml) occurred in August, at the peak of the winter breeding season. No seasonal effects on percentages of morphologically normal sperm, acrosome integrity, or live sperm were detected; however, the percentage of secondary sperm defects was higher in the winter. In conclusion, intricate relationships between testosterone concentration, testis volume, semen concentration and total and progressive sperm motility with high levels of breeding activity were observed during the dry season in the winter (June, July, August), followed by a subsequent decline in these activities during the wet season (i.e., summer: December, January, February). There was no seasonal pattern for production of functionally intact and morphologically normal sperm.

Seasonal variation in serum testosterone, testicular volume, and semen characteristics in the coyote (Canis latrans)

The coyote is a seasonally breeding mammal, with most copulations occurring between December and April (depending on location). The objective of this study was to characterize seasonal changes in serum testosterone concentrations, testicular volume, and ejaculate quantity and quality in captive male coyotes. There were seasonal differences in testicular volume, with the greatest volume (20.2+/-5.4cm2), mean+/-S.E.M.) in February, corresponding with peak breeding season. Circulating serum testosterone concentrations peaked (3.31+/-0.9 ng/mL) during January and were positively correlated (P< or =0.001, r=0.413) with testicular volume. Ejaculate volume (1.67+/-0.4 mL) and sperm concentration (549.2 x 10(6)+/-297.7 spermatozoa/mL) both peaked during January and February, consistent with the height of the breeding season. Ejaculate volume and sperm concentrations were positively correlated with testicular size (r=0.679, P< or =0.001 and r=0.499, P< or =0.001, respectively) and with serum testosterone concentrations (r=0.368, P< or =0.01 and r=0.208, P< or =0.05). Progressively motile, viable, and morphologically normal spermatozoa fluctuated seasonally, peaked (90.4+/-4.5, 84.8+/-4.1, and 87.9+/-2.9%) during the breeding season, and then subsequently declined (period of aspermatogenesis). All three of these end points were positively correlated with testicular size (r=0.589, P< or =0.001; r=0.586, P< or =0.001; and r=0.469; P< or =0.001) and serum testosterone (r=0.167, P< or =0.05; r=0.190, P< or =0.05; and r=0.221, P< or =0.01). In conclusion, there were intricate relationships among testosterone concentrations, testicular volume, and the production of both functionally intact and morphologically normal spermatozoa.

Duration of Testosterone Suppression after a 9.45 mg Implant of the GnRH-Analogue Buserelin in Patients with Localised Carcinoma of the Prostate: A 12-Month Follow-up Study

Objectives(1) To determine the duration of androgen deprivation after a single buserelin implant 9.45mg in the neoadjuvant setting in combination with curative radiation therapy of carcinoma of the prostate, and (2) to evaluate the time to recovery of gonadal function, and the incidence and duration of hypogonadal symptoms. MethodsWe prospectively evaluated 21 men with carcinoma of the prostate who received one implant of 9.45mg buserelin subcutaneously. Release of buserelin, changes in serum testosterone concentration, hot flushing and sexual function over a 12-month study period were recorded. ResultsTestosterone was suppressed below the castration limit (0.58ng/ml=2nmol/l) for 224 days (range, 139–309). The mean time to first return of testosterone above the castration limit was 246 days (range, 168–344); 50% of pre-treatment value was reached after 285 days (range, 218–370). The prevalence of hot flushing was 19 of 21 patients (90%) at 12 weeks. At the end of the study period, serum testosterone had reached 80% (range, 33%–166%) of pre-treatment concentration, sexual interest was present in 52%, erection was possible in 60%, and hot flushing remained in 24%. ConclusionA single injection of 3-month buserelin implant 9.45mg suppresses serum testosterone below the castration limit for at least 6 months. Testosterone secretion recovers by 8–12 months. Hypogonadal symptoms decreased with the restoration of serum testosterone secretion. These data are clinically relevant regarding the dose schedule for buserelin and the patient information provided.

Characterization of male killer whale ( Orcinus orca) sexual maturation and reproductive seasonality

Longitudinal serum testosterone concentrations ( n = 10 males) and semen production ( n = 2 males) in killer whales were evaluated to: (1) characterize fluctuations in serum testosterone concentrations with respect to reproductive maturity and season; (2) compare morphologic changes to estimated age of sexual maturity, based on changes in serum testosterone concentrations; and (3) evaluate seasonal changes in sperm production. Classification of reproductive status and age class was based on differences ( P < 0.05) in serum testosterone concentrations according to age; juvenile males ranged from 1 to 7 years (mean ± S.D. testosterone, 0.13 ± 0.20 ng/mL), pubertal males from 8 to 12 years (2.88 ± 3.20 ng/mL), and sexually mature animals were 13 years and older (5.57 ± 2.90 ng/mL). For captive-born males, serum testosterone concentrations, total body length and height to width ratio of the dorsal fin were 0.7 ± 0.7 ng/mL, 495.6 ± 17.5 cm and 1.14 ± 0.13 cm, respectively, at puberty; at sexual maturity, these end points were 6.0 ± 3.3 ng/mL, 548 ± 20 cm and 1.36 ± 0.1 cm. Serum testosterone concentrations were higher ( P < 0.05) from March to June than from December to February in pubertal animals (4.2 ± 3.4 ng/mL versus 1.4 ± 2.6 ng/mL) and than from September to December in sexually mature animals (7.2 ± 3.3 ng/mL versus 4.0 ± 2.0 ng/mL). Ejaculates ( n = 90) collected from two males had similar ( P > 0.05) sperm concentrations across all months. These data represent the first comprehensive study on male testosterone concentrations during and after sexual maturation, and on reproductive seasonality in the killer whale.

Aging and caloric restriction: Effects on Leydig cell steroidogenesis

We have shown previously that testosterone concentration in the blood serum of Brown Norway rat becomes reduced with aging, and that this results from reduced testosterone production by individual Leydig cells. Herein we examine the effects of caloric restriction (CR), an intervention shown to delay or inhibit age-associated pathologic and biologic changes in a number of systems and organisms, on Leydig cell steroidogenic function. CR (40%) was initiated in 4 month-old Brown Norway rats, and continued through age 34 months. Serum testosterone concentration in the ad libitum (AL)-fed controls was reduced by 30% from 5 to 13 months, by another 67% through 25 months, and then was sustained through 34 months. For the CR rats, the serum testosterone level was reduced to 45% of AL controls by 5 months, only 6 weeks after the initiation of the CR regimen. There was no further reduction through 25 months, at which time serum testosterone concentration in CR animals was significantly higher than in AL controls. By age 28–34 months, there was no significant difference between the two diets. The weights of prostate and seminal vesicle, two biomarkers of serum androgen levels, were consistent with the changes in serum testosterone concentration in both AL and CR animals. The ability of isolated Leydig cells to produce testosterone in vitro also paralleled the age- and CR-related changes in serum testosterone concentration. CR resulted in a rapid, 36% reduction in testosterone production from control by age 5 months. In contrast to cells from the AL rats, there were no further decreases in testosterone production through age 25 months. Indeed, Leydig cells from the 25 month-old CR rats produced significantly greater amounts of testosterone than cells from the 25 month-old AL rats. These results indicate that short-term CR results in the suppression of Leydig cell function and in reduction in serum testosterone levels. The significantly higher concentrations of serum testosterone concentration, and increased Leydig cell testosterone production, elicited by CR in 25 month-old rats compared to AL controls suggest that long-term CR can transiently suppress the reductions in steroidogenesis that are characteristic of aging.

Seasonal changes in testicular size and serum LH, prolactin and testosterone concentrations in male polar bears (Ursus maritimus).

Little is known about the reproductive endocrinology of the male polar bear, Ursus maritimus, except that serum testosterone concentrations are high in April and May during the mating season and are low from August to November during the non-mating season. The objective of this study was to describe the relationship between seasonal changes in testicular size and serum concentrations of testosterone, LH and prolactin. Blood samples and testicular measurements were obtained from free-ranging male polar bears in Canada in April (n = 5) and May (n = 15) near Resolute Bay, Northwest Territories and near Churchill, Manitoba in July (n = 15) and October (n = 22). Testis size was greater in May (39.4 +/- 3.5 cm(2)) than in October (27.3 +/- 2.0 cm(2)) (P = 0.002). Serum testosterone concentrations were approximately three-fold higher in April (5.8 +/- 0.8 ng ml(-1)) than in May (1.7 +/- 0.5 ng ml(-1)), July (0.6 +/- 0.2 ng ml(-1)) and October (1.1 +/- 0.2 ng ml(-1)). Similarly, serum LH concentrations were high in April (0.14 +/- 0.04 ng ml(-1)) and low in May (0.09 +/- 0.01 ng ml(-1)), July (0.10 +/- 0.02 ng ml(-1)) and October (0.08 +/- 0.00 ng ml(-1)). Serum prolactin concentrations were high in April (1.9 +/- 0.3 ng ml(-1)), highest in May (2.5 +/- 0.2 ng ml(-1)), lower in July (1.3 +/- 0.1 ng ml(-1)) and lowest in October (0.8 +/- 0.07 ng ml(-1)). The present study demonstrates a positive relationship between testicular size and serum concentrations of LH, prolactin and testosterone in the male polar bear and confirms the previously reported seasonal changes in serum testosterone concentrations. Data from the present study provide important baseline and comparative endocrine information that can be used to aid captive breeding programmes in zoos and to further ecological-behavioural studies of polar bears.

Expression and Regulation of Human Sex Hormone-Binding Globulin Transgenes in Mice during Development1

Human sex hormone-binding globulin (SHBG) is produced by hepatocytes and transports sex steroids in the blood. The rat gene encoding SHBG is expressed transiently in the liver during fetal life, but it is not expressed in the liver postnatally, and the small amounts of SHBG in rat blood are derived from gonadal sources. To study the biosynthesis and function of human SHBG in an in vivo context, we have produced several lines of transgenic mice that contain either 11 kb (shbg11) or 4.3 kb (shbg4) portions of the human shbg locus. The expression and regulation of these transgenes have now been studied during fetal and postnatal development. In situ hybridization of an shbg11 transgenic mouse fetus at 17.5 days postcoitus located human shbg transcripts only in duodenal epithelial cells and hepatocytes. Temporal differences in the hepatic expression of mouse shbg and human shbg transgenes during late fetal development were reflected in corresponding differences in mouse and human SHBG levels in fetal and neonatal mouse blood. Serum concentrations of human SHBG increased during the first weeks of life regardless of gender until about 20 days of age in shbg11 mice, but after this time they continued to increase only in the males. This sexual dimorphism was reflected in corresponding differences in human SHBG messenger RNA (mRNA) abundance in the livers of these animals. However, it was not observed in shbg4 mice, in which hepatic production of plasma SHBG continued to increase after puberty regardless of gender. Serum testosterone and SHBG levels correlated in all sexually mature shbg transgenic mice. Human shbg transcripts were detectable only in testes of shbg11 mice and increased progressively in abundance from 10 days of age until the animal reached sexual maturity at 30 days of age, with appreciable increases occurring well before any changes in serum testosterone concentration. In the kidney, SHBG mRNA levels accumulated earlier in shbg11 than in shbg4 mice, and the expression of both types of transgenes was sexually dimorphic, with much higher SHBG mRNA levels in the kidneys of male mice. As increases in SHBG mRNA in the male kidneys coincided with increases in serum testosterone during sexual maturation, we reasoned that shbg transgene expression is androgen dependent in the kidney. This was confirmed by demonstrating that a decrease in SHBG mRNA abundance in male mouse kidneys after castration could be reversed by 5alpha-dihydrotestosterone treatment. Moreover, exogenous androgen increased human SHBG mRNA levels in the kidneys of female mice. In summary, comparisons of how different human shbg transgenes are expressed in vivo provides information about the positions of potential regulatory sequences that may control the hormonal regulation and tissue-specific expression of this gene during development.

The relationship between testicular activity, accessory sex glands, and circulating steroid concentration during the reproductive cycle in a male Indian vespertilionid bat,Scotophilus heathi

The relationship between spermatogenesis, accessory sex glands, Leydig cell activity, and circulating concentrations of testosterone and androstenedione in male Scotophilus heathi, the greater yellow bat, was studied. Scotophilus heathi accumulated fat prior to winter dormancy at Varanasi, India. Spermatogenesis was seasonal and extended over the period November to March, with the testes becoming quiescent during winter. Monthly changes in testis and accessory sex gland masses showed two peaks, in November and January. Accessory gland secretory activity and fructose concentration showed only one peak, during January and February, which coincided with the mating period. The mass in the epididymides and their histological changes reflect the influence of testicular spermatogenesis. However, sperm were found in the cauda epididymidis during the spermatogenically quiescent period of winter dormancy. The Leydig cells showed intense side chain cleavage (SCC) enzyme activity from August to December. In late January and February, males had smaller Leydig cells and low SCC activity. Monthly changes in serum testosterone concentration included two peaks in November and January, coinciding with peak spermatogenic activity, whereas androstenedione showed only one peak, an unusually high concentration in November. The circulating serum androstenedione concentration may be responsible for the unique reproductive activity noted in this bat.

The relationship between endogenous testosterone and gonadotrophin secretion

The secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone in the adult male was studied by means of 48-hour profiles. The aim of the study was to examine the effects of the endogenous circadian variation in serum testosterone concentration on LH pulsatility, and to determine the temporal relationships between FSH and LH, and between LH and testosterone by cross-correlation, and the pulse frequency of these hormones by spectral analysis, as revealed by extended sampling periods. Hormone profiles were obtained by 20-minute sampling over 48 hours. Six healthy adult males, aged between 21 and 23 years. LH and FSH were measured using an immunoradiometric assay and testosterone with a solid-phase radioimmunoassay. The profiles showed pulsatile secretion of all three hormones, and a circadian rhythm with levels highest between 0200 and 0600 h. Cross-correlation analysis: There was a significant relationship between LH and FSH (r = 0.5; P = 0.001) at 0 minutes (i.e. no time lag). A pulse of testosterone followed on average 60 minutes after a pulse of LH (r = 0.26; P = 0.001). Fourier transformation: Spectral analysis showed the dominant period for LH and FSH pulsatility to be 200 minutes. The dominant period for testosterone pulsatility was 400 minutes. The effect of endogenous variations in serum testosterone concentrations: The LH profiles were divided into periods when the serum testosterone concentration was high or low, and Fourier transformation carried out on these shorter periods. These transforms showed that the dominant period during high serum testosterone concentration was 180 minutes, and during low serum testosterone was 120 minutes (P < or = 0.025). FSH and LH are co-secreted, and a pulse of testosterone follows a pulse of LH by 60 minutes. The physiological changes in serum testosterone concentration that occur during the day result in changes in the pulse frequency of LH. Testosterone concentrations thus have rapidly acting feedback activity at hypothalamic level.

A systems model of training responses and its relationship to hormonal responses in elite weight-lifters

A systems model, providing an estimation of fatigue and fitness levels was applied to a 1-year training period of six elite weight-lifters. The model parameters were individually determined by fitting the predicted performance (calculated as the difference between fitness and fatigue) to the actual one. The purpose of this study was to validate the systems model by comparing the estimated levels of fatigue and fitness with biological parameters external to the model calculation. The predicted and the actual performances were significantly correlated in each subject. The calculated fitness and fatigue levels were related to serum testosterone concentration, testosterone: cortisol and testosterone: sex hormone binding globulin ratios. The best results were obtained by the comparison between fitness and testosterone levels, which varied in parallel in each subject. In two subjects this correlation was significant (r = 0.91, P less than 0.05, and r = 0.92, P less than 0.01). The fitness changes calculated in each subject between the 15th and the 51st weeks of training were significantly correlated with the changes in serum testosterone concentration measured in the same period (r = 0.99, P less than 0.001). For the whole group testosterone and fitness variations were also significantly intercorrelated (r = 0.73, P less than 0.001). Correlations, less homogeneous and less significant, were calculated also for other hormones and ratios. These results suggest that (1) the relationships between training and performance can be described by the systems model, (2) the estimated index of fitness has a physiological meaning. The fatigue index remains to be clarified.

Effects of local heating of the testes on the concentration of testosterone in jugular and testicular venous blood of rats and on testosterone production in vitro.

Heating both testes of rats to between 39 degrees C and 41 degrees C for 30 min was apparently without effect 21 days later, but heating to between 41.5 degrees C and 43 degrees C for 30 min resulted in a significant drop in testis weight accompanied by significant rises in the serum levels of LH and FSH. There were no changes in serum testosterone concentration in the peripheral circulation although there were increases in the concentration in testicular venous blood. The ability of the heated testis to secrete testosterone in vivo in response to maximal stimulation by hCG was reduced, as judged by testosterone levels in peripheral blood, while there was a supranormal increase in testosterone levels in testicular venous blood. Maximally stimulated testosterone production in vitro by the heated testis was supranormal whereas the basal production of testosterone per testis was not different from control values. Therefore, it appears that the testosterone produced by Leydig cells from heated testes may not be secreted as effectively as in normal testes.

Cohabitation with a female activates testosterone-dependent social aggression in male rats independently of changes in serum testosterone concentration

Male hooded rats (350 to 450 g) were sham-castrated, castrated and implanted with testosterone-filled, or castrated and implanted with empty Silastic tubes. Twenty-four hours postoperatively the animals in each group were housed with a female or a male similar in size to the female. Beginning one week following surgery and continuing for three weeks thereafter, the female or male cagemate was removed once each week while a 15-min test of aggression toward an unfamiliar male intruder was conducted. During the aggression tests, lateral attacks, lunge attacks, bites, on-top, and piloerection were recorded. At the first aggression test, males housed with females were significantly more aggressive than their counterparts housed with males. In contrast, different testosterone regimes did not consistently influence the initial activation of intermale social aggression. At the second and third tests, males with testicular testosterone or a replacement were significantly more aggressive than their castrated controls on most measures but males housed with females continued to be more aggressive than the comparable group housed with males. These results suggest that normal fluctuations in serum testosterone concentration associated with sexual interaction are not necessary for the initial activation of intermale social aggression. Both repeated exposure to unfamiliar males as well as cohabitation with a female are effective stimuli for activation of testosterone-dependent social aggression.

Testosterone regulates the haemoglobin concentration in male puberty.

In a longitudinal study of male puberty 20 boys were examined every three months for at least two years. Haemoglobin concentration was determined and related to changes in serum testosterone concentrations. The data show a steep increase in serum testosterone during puberty (p less than 0.001) followed with a five months delay, by a significant increase in haemoglobin concentration (p less than 0.001). It is concluded that the steep increase in serum testosterone during puberty produces an acute stimulation of erythropoietin leading to an increase in erythrocyte production and thereby to a detectable increase in haemoglobin concentration a few months thereafter. The present study supports the idea that the selection of the relevant reference range for haemoglobin in boys should depend on the state of physical developments as expressed by serum testosterone.

Circannual Changes in Serum Testosterone Concentrations of Adult and Yearling Woodchucks (Marmota Monax)1

Testicular volumes and serum testosterone concentrations were determined biweekly in 5 adult and 4 yearling woodchucks maintained indoors from December through August. Food and water were provided ad libitum except for 2 mo beginning at the winter solstice when feeding and lighting (12L:12D) supplemental to available natural light were discontinued. Temperatures fluctuated with outdoor temperatures greater than 4 degrees C. No significant hibernation occurred. Testes in adults were small in December (0.3-1.8 cm3), largest in February and March (3.5-5.6 cm3), and smallest in late June (0.1-0.5 cm3). Testosterone was basal in December (less than 0.6 ng/ml), maximal (3.4-6.6 ng/ml) between early January and late March, and minimal from April through August (less than 0.8 ng/ml). In yearlings, maximum testes volumes (1.6 cm3) and serum testosterone (0.9 +/- 0.2 ng/ml) were less, and occurred later, than in adults. Testosterone levels and testis volumes measured in newly captured woodchucks in March and April and again 2-3 mo later were generally similar to those of their laboratory counterparts. Thus, in woodchucks: annual cycles of testosterone production and of testes recrudescence and regression parallel each other with maxima during the short, late-winter breeding season; those cycles are not altered significantly by the absence of hibernation or the present conditions of captivity; and yearling males apparently are not an important part of the breeding population.

Relationships between seasonal changes in serum testosterone concentrations, scrotal circumference and sperm morphology of male wapiti (Cervus elaphus).

One 2-year-old and 4 adult (greater than 3 years old) wapiti were studied throughout 1 year. Serum testosterone concentrations, scrotal circumference and % normal spermatozoa in the ejaculate peaked around September. Testosterone levels fell sharply by November, but scrotal circumference declined less sharply and normal sperm production occurred until March. There were indications of a secondary peak in these values around February-March.

Changes in serum testosterone concentrations in the male pig during development.

Serum testosterone concentrations were elevated between 40 and 60 days p.c. but were low between 60 and 100 days p.c. when the testis descends. Elevated concentrations occurred in the perinatal period and from the 18th week after birth. Between 60 days p.c. and 16 weeks after birth the changes in serum testosterone concentrations parallel those of testicular development, as determined by morphology and steroid histochemistry, and peripheral LH concentrations.