Concentrations of free testosterone, total testosterone, and androgen binding protein in the peripheral serum of male rats during sexual maturation

Testosterone Supplementation Induces Age-Dependent Augmentation of the Hypoxic Ventilatory Response in Male Rats With Contributions From the Carotid Bodies

Excessive carotid body responsiveness to O₂ and/or CO₂/H⁺ stimuli contributes to respiratory instability and apneas during sleep. In hypogonadal men, testosterone supplementation may increase the risk of sleep-disordered breathing; however, the site of action is unknown. The present study tested the hypothesis that testosterone supplementation potentiates carotid body responsiveness to hypoxia in adult male rats. Because testosterone levels decline with age, we also determined whether these effects were age-dependent. In situ hybridization determined that androgen receptor mRNA was present in the carotid bodies and caudal nucleus of the solitary tract of adult (69 days old) and aging (193–206 days old) male rats. In urethane-anesthetized rats injected with testosterone propionate (2 mg/kg; i.p.), peak breathing frequency measured during hypoxia (FiO₂ = 0.12) was 11% greater vs. the vehicle treatment group. Interestingly, response intensity following testosterone treatment was positively correlated with animal age. Exposing ex vivo carotid body preparations from young and aging rats to testosterone (5 nM, free testosterone) 90–120 min prior to testing showed that the carotid sinus nerve firing rate during hypoxia (5% CO₂ + 95% N₂; 15 min) was augmented in both age groups as compared to vehicle (<0.001% DMSO). Ventilatory measurements performed using whole body plethysmography revealed that testosterone supplementation (2 mg/kg; i.p.) 2 h prior reduced apnea frequency during sleep. We conclude that in healthy rats, age-dependent potentiation of the carotid body’s response to hypoxia by acute testosterone supplementation does not favor the occurrence of apneas but rather appears to stabilize breathing during sleep.

High-dose testosterone propionate treatment reverses the effects of endurance training on myocardial antioxidant defenses in adolescent male rats

This study was aimed at evaluation of changes in activities of selected antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) and contents of key nonenzymatic antioxidants (glutathione, protein thiol groups, and α- and γ-tocopherols) in the left heart ventricle of young male Wistar rats subjected to endurance training (treadmill running, 1 h daily, 5 days a week, for 6 weeks) or/and testosterone propionate treatment (8 or 80 mg/kg body weight, intramuscularly, once a week, for 6 weeks) during adolescence. The training alone increased the activities of key antioxidant enzymes, but lowered the pool of nonenzymatic antioxidants and enhanced myocardial oxidative stress as evidenced by elevation of the lipid peroxidation biomarker malondialdehyde. The lower-dose testosterone treatment showed mixed effects on the individual components of the antioxidant defense system, but markedly enhanced lipid peroxidation. The higher-dose testosterone treatment decreased the activities of the antioxidant enzymes, lowered the contents of the nonenzymatic antioxidants, except for that of γ-tocopherol, reversed the effect of endurance training on the antioxidant enzymes activities, and enhanced lipid peroxidation more than the lower-dose treatment. These data demonstrate the potential risk to cardiac health from exogenous androgen use, either alone or in combination with endurance training, in adolescents.

Effect of acrylamide on some hormones and endocrine tissues in male rats

Acrylamide is oxidized by cytochrome P450 2E1 (CYP2E1) to its epoxide form, glycidamide, which is believed to be responsible for the mutagenic and carcinogenic activities. This study was carried out to investigate the early changes that may be related to the carcinogenic activity of acrylamide in thyroid, adrenal glands and testis in male rats. Forty adult Sprague Dawley male rats were divided equally into four groups, rats of Group I served as control, and rats of Groups II, III and IV were treated orally with acrylamide with doses 5, 10, 15 mg/kg/day body weight for 8 weeks. The results indicated that the plasma carcino embryonic antigen (CEA) and malondialdehyde (MDA) levels are higher, but free and total testosterone, triiodothyronine (T3) and thyroxine, or 3,5,3′,5′-tetraiodothyronine (T4) and corticosterone levels are lower in rats treated with acrylamide than that in control rats. This study provides evidence of endocrine disturbance to the testis, thyroid and adrenal glands, which are also the organs in which acrylamide has been shown to cause tumors in experimental animals.

Proposed mechanism for sperm chromatin condensation/decondensation in the male rat

Condensation of sperm chromatin occurs after spermatozoa have left the caput epididymis and are in transit to the cauda epididymis, during which time large numbers of disulfide bonds are formed. The formation of these disulfide bonds requires the repeated oxidation of the cofactor, NAD(P)H. To date, the means by which this oxidation is achieved has yet to be elucidated. Spermatozoa lose the bulk of their cytoplasm prior to leaving the testis; and, as a result, any shuttle systems for removing and transferring reducing equivalents into the mitochondria are unlikely to be operational. In an apparent preparation for the loss of cytoplasm, however, the following events occur during spermatogenesis. First, androgen-binding protein (ABP) is produced by the Sertoli cells of the testis; second, high affinity binding sites for ABP are inserted into the membrane surrounding the nucleus; and third, a nuclear location is acquired for the enzyme, 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD). We propose that after the loss of cytoplasm, the nuclear region of spermatozoa is directly accessible to constituents contained in the lumen of the caput epididymis. As a consequence, luminal ABP attaches itself to the nuclear membrane via its binding sites, and is internalized. After internalization, ABP exerts its principle function, which is to bind to luminal 5alpha-dihydrotestosterone (5alpha-DHT), thereby ensuring its availability to the enzyme, 3alpha-HSD. In the conversion of 5alpha-DHT to 3alpha-androstanediol (3alpha-Diol), NAD(P)H is oxidized. Spermatozoa that reach the cauda epididymis have fully condensed chromatin. In addition, the nuclear region retains appreciable amounts of 5alpha-DHT and 3alpha-Diol, both bound to ABP. During fertilization, the bound 3alpha-Diol is converted back to 5alpha-DHT, reducing equivalents are transferred to NAD(P)+, and disulfide bonds are broken.IVF clinics report that spermatozoa with incompletely condensed chromatin have a low percentage of fertilization. If our proposed mechanism for chromatin condensation/decondensation is borne out by further research, IVF clinics might consider preincubating spermatozoa with 5alpha-DHT in order to increase the efficiency of fertilization.

Maternal hormonal manipulations in rats cause obesity and increase medial hypothalamic norepinephrine release in male offspring

In previous work it has been shown that adult male, but not female, offspring of rats that have either been injected with Protamine Zinc Insulin on days 15-20 gestation, or undernourished during the first 2 weeks of gestation, develop significant obesity commencing at about 50 days of age. The present experiment examines the question of whether rats with these two forms of obesity display neurochemical abnormalities in areas of the brain known to influence food intake and body weight. Twenty-one gauge stainless steel guide shafts were surgically implanted using standard stereotaxic procedures. One week later 26 ga microdialysis probes were lowered into the medial hypothalamus. Dialysates collected from male offspring in the two experimental conditions contain significantly higher norepinephrine (NE) levels than did controls. It would appear that in addition to sharing a similar time course of onset and a sex dependent expression of obesity, both of these models are also characterized by elevated medial hypothalamic NE. Since this obesity appears only in males, and at a time when testosterone levels are rapidly rising in males, and since testosterone has been shown to elevate food intake and body weights in rats, we also investigated whether gonadal weights or circulating testosterone levels were differentially elevated by our manipulations.

Effects of methanol vapors on testosterone production and testis morphology in rats

Potential toxic effects of methanol vapors on testicular production of testosterone and the morphology of testes were investigated using normal or methanol-sensitive folate-reduced rats. Methanol inhalation at the level of the current permissible exposure limit, 200 ppm, for up to six weeks (8 hours/day, 5 days/week), did not reduce serum testosterone levels in normal rats. Testes isolated from methanol-exposed (200 ppm) rats had the same capability as those from air-exposed rats in synthesizing testosterone whether testes were incubated in the absence or presence of hCG. The testes-to-body weight ratio of rats exposed up to 800 ppm methanol for up to 13 weeks (20 hours/day, 7 days/week) were not different from those of the air-exposed rats. Furthermore, methanol had no adverse effect on testicular morphology at the end of the 13 week exposure period at 800 ppm in either normal rats or folate-reduced methanol-sensitive rats when they were 10 months old at the time of examination. Thus, these data indicate that low level methanol may not cause an inhibitory effect on testosterone synthesis contrary to previous literature reports. However, a greater incidence of testicular degeneration was noticed in the 18 month old folate-reduced rats exposed to 800 ppm for 13 weeks (20 hours/day, 7 days/week), suggesting that methanol may have a potential to accelerate the age-related degeneration of the testes.

Androgen effects on Sertoli cells

Mature male rats, gamma-irradiated in utero, were hypophysectomized. In an effort to maintain the seminiferous epithelium, some animals were treated with exogenous androgen while in other animals the seminiferous epithelium was allowed to regress without hormonal treatment. These Sertoli cell-enriched (SCE) males were evaluated for 7 weeks following hypophysectomy. In SCE males the average initial weight of each testis was 300 mg which declined to 110 mg at 7 weeks post-hypophysectomy. Concomitantly, seminiferous tubule diameter decreased from 130 microns to approximately 89 microns. Numerous cells were detached from the lamina propria and were observed in the centre of the tubule. Two layers of Sertoli cell nuclei were frequently observed in the regressed seminiferous tubules. Many of these nuclei appeared to be less differentiated, i.e. the nuclei were smaller with smaller nucleoli and more heterochromatin. In contrast, hypophysectomized animals treated with testosterone propionate during the last 5 weeks of the 7 week observational period, retained a tissue weight of about 270 mg/testis (a 5-10% decline in weight compared with normal untreated controls). Also, these animals had seminiferous tubule diameters of 132 microns. Finally, the Sertoli cells which comprised primarily a single layer inside the seminiferous tubules had larger nuclei with finely granulated chromatin and large nucleoli. Protein changes in SCE testes, (+/-) androgen, following hypophysectomy were analysed using polyacrylamide gels containing SDS. Prominent changes in the protein profile as separated by molecular weight were observed and were attributable to androgen stimulation. These changes were probably occurring in Sertoli cells since the Sertoli cell represents about 70% of the total cell population in the gamma-irradiated model. It is concluded that testosterone is responsible for major changes in mature Sertoli cells, although potential contributions of other cell types such as myoid cells and Leydig cells are considered.

Changes in the secretion of ABP into testicular interstitial fluid with age and in situations of impaired spermatogenesis

Androgen-binding protein (ABP) was measured in serum and testicular interstitial fluid (IF) from rats during sexual maturation or in adult rats in which impairment of spermatogenesis had been induced by (i) testosterone withdrawal following Leydig cell destruction, (ii) local heating (43 degrees C) of the testes for 30 min or (iii) induction of unilateral cryptorchidism (UCD). The changes observed were related to the IF levels of testosterone and, in most instances, to the serum levels of FSH. The levels of ABP in serum and IF decreased together with age, being highest at 30 days, falling steeply by 40 days and then slowly but progressively up to 100 days of age. A similar pattern was observed for serum FSH, except that the initial fall occurred beyond 40 days of age. Treatment with EDS or exposure to local heating caused comparable reductions in testicular weight (25-30% by 7 days after treatment, 50% by 21-28 days) and raised the serum levels of FSH. In both groups the levels of ABP in IF were increased by two- to three-fold while the levels of testosterone were either reduced markedly (EDS-treatment) or remained unchanged (local heating). In rats made UCD for 60 days, the weight of the abdominal testis was reduced by 75%, compared with the contralateral scrotal testis, while the IF levels of ABP and testosterone were significantly increased (55%) and decreased (90%), respectively. Short-term (3 days) deprivation of testosterone in adult rats, following immunoneutralization of LH, was without significant effect on IF levels of ABP. It is concluded that ABP secretion into IF is increased in situations of subnormal (or sub-adult) numbers of germ cells and this is usually associated with high levels of FSH. Measurement of ABP levels in IF should prove of value for the monitoring of Sertoli cell function in vivo and may be of diagnostic use for the detection of changes in germ cell numbers.