Interpretation of the discrepancy observed between plasma free and salivary testosterone levels in man

The differences observed between plasma free and saliva testosterone levels do not result from methodological artefacts. We postulate that androgens metabolism in salivary glands modulates saliva testosterone levels both in men and women. In women, the "excess" of saliva testosterone (compared to the calculated free testosterone concentration), could be due to conversion of androstenedione in the salivary glands. The rate of this transformation is exaggerated in hirsute patients resulting in a significantly higher excess of saliva testosterone. In men, on the contrary, a "deficit" in saliva testosterone is observed suggesting testosterone transformation in salivary glands. This deficit is more marked in impotent men and appears to be reversed by testosterone administration. Saliva testosterone levels do not merely reflect plasma free hormone concentrations but also afford potentially useful information on androgens metabolism.     

Development of a highly sensitive and specific new testosterone time-resolved fluoroimmunoassay in human serum

A new time-resolved fluoroimmunoassay (TR-FIA) of testosterone in serum is described, using a biotinylated testosterone tracer, with a long spacer arm between biotin and testosterone, coupled to the C3 of the testosterone: a biotinylaminodecane carboxymethyloxime testosterone. This tracer affords a great sensitivity of the standard curve, because a amount of 0.3 pg of testosterone can be significantly measured on the testosterone standard curve. The "functional" sensitivity is at least equal to 21 pg/ml of serum. The specificity of the assay is insured by a celite chromatographic step on new minicolumns before immunoassay. The variation coefficient of inter-series reproducibility measured on low and normal testosterone levels in untreated and testosterone treated hypogonadal men were between 2.17 and 5.07%. The accuracy test, (overload and dilution tests) gave satisfying results. Moreover, in a comparison with GCMS, it appeared that the correlation coefficient was 0.992 and no significant difference could be exhibited between the two methods. Consequently, this specific, sensitive reproducible and easy to use method is well suited to the measurement of testosterone in clinical and pharmacological conditions.     

Interaction of BDNF and testosterone in the regulation of adult perineal motoneurons

In androgen-sensitive motoneurons of the spinal nucleus of the bulbocavernosus (SNB), we investigated the interaction of BDNF (brain-derived neurotrophic factor) and testosterone to understand whether each factor gates the ability of the other to regulate androgen receptor expression and soma size, and whether each factor requires the presence of the other for its action. We axotomized SNB motoneurons and applied BDNF or PBS (phosphate-buffered saline) to the cut ends of the axons in rats that were castrated and treated with either testosterone or placebo. Control groups were either not castrated or not axotomized, or had intact SNB axons and were castrated and treated with testosterone or placebo. We found that testosterone determined the expression of nuclear androgen receptor, and this effect was enhanced by both BDNF and contact with the target muscles. The effect of BDNF on androgen receptor expression was seen only when testosterone was present. In the regulation of soma size, BDNF dominated. The application of BDNF completely compensated for the loss of testosterone in castrated males so that the testosterone effect on soma size was seen only in intact SNB motoneurons and in axotomized motoneurons treated with PBS. Moreover, testosterone increased androgen receptor and soma size in axotomized SNB motoneurons, indicating that testosterone can act on sites other than the target muscles of the SNB to regulate each of these. These results indicate that the regulation of androgen receptor by testosterone does not require BDNF, but the regulation of androgen receptor by BDNF does require testosterone. The regulation of soma size by BDNF does not require high expression of nuclear androgen receptor.     

睾酮对鸟类繁殖影响研究进展

类固醇激素睾酮是影响鸟类繁殖最重要的性激素之一,与鸟类的繁殖行为的各个方面息息相关。睾酮通过影响鸟类的羽色、鸣声等来影响鸟类的配偶选择,同时睾酮可以调节配偶选择和繁殖投入之间的平衡。睾酮水平影响出雏数、出飞数、孵化率成功率等繁殖成效。睾酮还对个体的免疫活性和个体的存活率等产生影响。目前关于睾酮对鸟类繁殖影响的研究大多是通过外源性植入睾酮的方式来改变个体睾酮的浓度,其研究结果也常出现相互矛盾之处,对于自然状态下影响睾酮水平变化的因素尚缺乏了解,睾酮对雌雄鸟在繁殖过程中的影响也不尽相同,有必要继续深入研究。     

Sex and testosterone effects on growth, immunity and melanin coloration of nestling Eurasian kestrels

1. Sex differences in testosterone levels and sex-biased sensitivity to testosterone are the basis of some ideas postulated to account for sex-linked environmental vulnerability during early life. However, sex variation in circulating testosterone levels has been scarcely explored and never manipulated at post-natal stages of birds in the wild. 2. We measured and experimentally increased circulating testosterone levels in nestling Eurasian kestrels Falco tinnunculus. We investigated, possible sexual differences in testosterone levels and the effect of this hormone on growth (body mass and tarsus length) and cell-mediated immunity in males and females. We also explored testosterone effects on rump coloration, a highly variable melanin-based trait in male nestlings. We analysed data on circulating testosterone levels of nestlings in 15 additional bird species. 3. Increased levels of testosterone tended to negatively affect body condition, reduced cell-mediated immune responses in male and female nestlings and also diminished the expression of grey rump coloration in male nestlings. No sex differences were observed in testosterone levels in either control or increased testosterone group nestlings, and no interactions were found between sex and treatment. However, male nestlings showed a lower cell-mediated immune response than females in both groups. 4. Our results indicate first, that a high level of testosterone in all nestlings in a brood entails costs, at least in terms of immunity, coloration and probably growth. Secondly, sex differences in post-natal cell-mediated immunity, and consequently in the capacity to prevent diseases, cannot be explained by sex differences in circulating testosterone levels. Finally, by comparing published data at an interspecific level, contradictory sex patterns in circulating testosterone levels have been found, supporting the idea that circulating testosterone might not be a proximate factor causing sex-dependent vulnerability in bird species.     

Effect of intratesticular administration of TRH or anti-TRH antiserum on function of rat testis

The effect of intratesticular administration of thyrotropin-releasing hormone (TRH) and anti-TRH antiserum on steroidogenesis was studied in immature and adult rats. In 9-day-old animals local administration of the neuropeptide resulted in an increase in basal testosterone secretion in vitro. Similar treatment of 15-day-old rats suppressed hCG-stimulated testosterone secretion with no change in basal testosterone production. In both immature groups the treatment did not affect serum testosterone concentration. By contrast, in adults TRH decreased serum testosterone level, but did not influence basal and hCG-stimulated testosterone secretion. Both in immature and adult rats, the changes in steroidogenesis were evident 1 hour posttreatment. Five days after the administration of anti-TRH antiserum into the remaining testis of immature rats subjected to hemicastration just prior to the antiserum treatment, the alterations in steroidogenesis were opposite to those detected after treatment with TRH. In 9-day-old rats the antiserum suppressed steroidogenesis, while in 15-day-old animals it stimulated testosterone secretion. The results suggest that testicular TRH might exert a local action on testicular steroidogenesis, and the effect is age-dependent.     

Passage of testosterone,testosterone propionate and testosterone enanthate from silastic implants and the retention of testosterone once it enters the blood of ewes

Two studies were conducted to determine the passage of testosterone, testosterone propionate and testosterone enanthate through silastic implants and to determine the retention of the three hormones once they enter the blood. In the first experimental, ovariectomized ewes with implants containing testosterone propionate and ewes with implants containing testosterone enanthate had higher levels of plasma testosterone than ewes with implants containing testosterone. Testosterone enanthate implants released more hormone during the 13-day period than the testosterone propionate and testosterone implants and testosterone propionate implants released more hormone than testosterone implants. In the second experiment, concentrations of plasma testosterone were elevated longer for ovariectomized ewes intravenously administered testosterone propionate, than ewes receiving testosterone or testosterone enanthate intravenously.     

17alpha-methyl testosterone is a competitive inhibitor of aromatase activity in Jar choriocarcinoma cells and macrophage-like THP-1 cells in culture

17alpha-methyl testosterone is a synthetic androgen with affinity for the androgen receptor. 17alpha-methyl testosterone is used widely as a component of hormone replacement therapy. Previous reports have indicated that contrary to testosterone, 17alpha-methyl testosterone is not aromatized. However, 17alpha-methyl testosterone still could affect local estrogen formation by regulating aromatase expression or by inhibiting aromatase action. Both possibilities have important clinical implications. To evaluate the effect of 17alpha-methyl testosterone on the expression and activity of aromatase, we tested the choriocarcinoma Jar cell line, a cell line that express high levels of P450 aromatase, and the macrophage-like THP-1 cells, which express aromatase only after undergoing differentiation. We found that in both cell lines, 17alpha-methyl testosterone inhibits aromatase activity in a dose-related manner. The curve of inhibition parallels that of letrozole and gives complete inhibition at 10(-4) M 17alpha-methyl testosterone, determined by the tritium release assay. 17alpha-methyl testosterone does not have detectable effects on aromatase RNA and protein expression by Jar cells. Undifferentiated THP-1 cells had no aromatase activity and showed no effect of 17alpha-methyl testosterone, but differentiated THP-1 (macrophage-like) cells had a similar inhibition of aromatase activity by 17alpha-methyl testosterone to that seen in Jar cells. The Lineweaver-Burke plot shows 17alpha-methyl testosterone to be a competitive aromatase inhibitor. Our results show for the first time that 17alpha-methyl testosterone acts as an aromatase inhibitor. These findings are relevant for understanding the effects of 17alpha-methyl testosterone as a component of hormone replacement therapy. 17alpha-methyl testosterone may, as a functional androgen and orally active steroidal inhibitor of endogenous estrogen production, also offer special possibilities for the prevention/treatment of hormone-sensitive cancers.     

Acute effects of testosterone on serum PGE2 levels in male dogs

Serum prostaglandin levels are influenced by testosterone. To test the hypothesis that the effect of testosterone is mediated through the prostate gland, testosterone was given acutely to intact and to prostatectomized male dogs. Intact dogs responded to testosterone with an abrupt, transient rise in plasma PGE2 levels; prostatectomized dogs did not respond. We conclude that testosterone has an acute effect on the prostate gland which results in release of PGE2 into the blood stream.     

Testosterone in tropical birds: effects of environmental and social factors

Previous investigations suggest that male tropical birds have lower plasma testosterone concentrations than northern latitude species. To test whether this generalization is valid, we analyzed all currently available plasma testosterone data of tropical birds. We focused on peak breeding testosterone levels using phylogenetic and conventional statistics. Explanatory variables considered were social mating system, type of territoriality, breeding season length, and altitude. On average, tropical birds had lower mean peak testosterone levels than northern temperate birds. However, in several tropical species, testosterone levels were well within the range of northern latitude birds. Without controlling for phylogeny, breeding season length, type of territoriality, and altitude explained a significant proportion of the variance in testosterone levels. The shorter the breeding season, the higher the testosterone levels. Tropical birds that defend a breeding season territory had higher testosterone levels than birds that were year-round territorial or colonial, and testosterone levels were positively correlated with altitude. When controlling for phylogeny, only breeding season length predicted testosterone levels. In conclusion, we propose to refine previous notions of low plasma testosterone levels in tropical birds: short breeding seasons and perhaps environmental conditions at high altitudes precipitate conditions under which high testosterone levels are beneficial in the tropics.     

Territorial aggression does not feed back on testosterone in a multiple-brooded songbird species with breeding and non-breeding season territoriality,the European stonechat

Testosterone mediates reproductive behaviours in male vertebrates. For example, breeding season territoriality depends on testosterone in many species of birds and in some, territorial interactions feed back on testosterone concentrations. However, the degree to which territorial behaviour and testosterone are associated differs even between species with seemingly similar life histories, especially between species that also defend territories outside the breeding season. Here, we investigate the link between territorial behaviour and testosterone in European stonechats. Previous studies found that territorial aggression in stonechats depends on testosterone in a breeding, but not in a non-breeding context. We investigated whether stonechats show a rise in testosterone during simulated territorial intrusions (STI) during the breeding season. Post-capture testosterone concentrations of males caught after an STI were not higher than those of males caught in a control situation regardless of breeding stage. However, most of the males would have been able to mount a testosterone response because the same individuals that did not increase testosterone during the STI showed a substantial increase in testosterone after injections of gonadotropin-releasing hormone (GnRH). GnRH-induced and post-capture testosterone concentrations were positively correlated and both decreased with successive breeding stages. Further, territory owners with a short latency to attack the decoy expressed higher post-capture testosterone concentrations than males with a longer latency to attack the decoy. Thus, there is no evidence for behavioural feedback on testosterone concentrations during male-male interactions in stonechats. In combination with previous studies our data suggest that testosterone functions as an on/off switch of high intensity territorial aggression during the breeding season in stonechats. The among-species variation in the androgen control of territorial behaviour may be only partly a result of environmental differences. Instead, potential differences in how territoriality evolved in different species may have influenced whether and how a reproductive hormone such as testosterone was co-opted into the mechanistic control of territorial behaviour.     

Correlation between serum zinc and testosterone: A systematic review

Zinc is a vital trace element for normal function of the living system. In male, zinc is involved in various biological processes, an important function of which is as a balancer of hormones such as testosterone. For this purpose, studies related to the influence of zinc on serum testosterone were selected and summarized, including the effect of dietary zinc deficiency and zinc supplementation on testosterone concentrations. After preliminary searching of papers on databases, 38 papers including 8 clinical and 30 animal studies were included in this review. We concluded that zinc deficiency reduces testosterone levels and zinc supplementation improves testosterone levels. Furthermore, the effect degree of zinc on serum testosterone may vary depending on basal zinc and testosterone levels, zinc dosage form, elementary zinc dose, and duration. In conclusion, serum zinc was positively correlated with total testosterone, and moderate supplementation plays an important role in improving androgen.     

Effects of testosterone on spatial learning and memory in adult male rats

A male advantage over females for spatial tasks has been well documented in both humans and rodents, but it remains unclear how the activational effects of testosterone influence spatial ability in males. In a series of experiments, we tested how injections of testosterone influenced the spatial working and reference memory of castrated male rats. In the eight-arm radial maze, testosterone injections (0.500 mg/rat) reduced the number of working memory errors during the early blocks of testing but had no effect on the number of reference memory errors relative to the castrated control group. In a reference memory version of the Morris water maze, injections of a wide range of testosterone doses (0.0625-1.000 mg/rat) reduced path lengths to the hidden platform, indicative of improved spatial learning. This improved learning was independent of testosterone dose, with all treatment groups showing better performance than the castrated control males. Furthermore, this effect was only observed when rats were given testosterone injections starting 7 days prior to water maze testing and not when injections were given only on the testing days. We also observed that certain doses of testosterone (0.250 and 1.000 mg/rat) increased perseverative behavior in a reversal-learning task. Finally, testosterone did not have a clear effect on spatial working memory in the Morris water maze, although intermediate doses seemed to optimize performance. Overall, the results indicate that testosterone can have positive activational effects on spatial learning and memory, but the duration of testosterone replacement and the nature of the spatial task modify these effects.     

Fundamental aspects of hypogonadism in the aging male

With aging in men, serum testosterone levels decline progressively and the prevalence of hypogonadism increases; these changes are associated with alterations in androgen-regulated physiological functions. In young hypogonadal men, similar alterations improve with testosterone replacement. In older men, short-term testosterone treatment trials suggest benefits (eg, on body composition and bone mineral density), without significant adverse effects. Therefore, androgen deficiency may contribute to physiological decline with aging, and testosterone therapy is reasonable for older men with clinical manifestations of androgen deficiency and low testosterone levels. However, the long-term benefits and potential risks (eg, for prostate disease) of testosterone treatment in older men are unknown.     

Regulation of thyroid hormones on the production of testosterone in rats

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)-stimulated secretion of testosterone and the production of adenosine 3',5'-cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin-releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH-stimulated LH release as well as hCG-stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17beta-HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats.     

Modulation of Leishmania donovani infection and cell viability by testosterone in bone marrow-derived macrophages: signaling via surface binding sites

Androgens can increase susceptibility toward numerous parasitic infections as well as modulate apoptosis of immune cells. According to the current view, androgens mediate immune cell activities not only through classical intracellular androgen receptors (AR), but also through membrane receptors on the cell surface. Here, using murine bone marrow-derived macrophages (BMMs), we examined the influence of testosterone on Leishmania donovani infection and cell viability in vitro as well as the possible mechanisms. Our data demonstrated that testosterone directly increased intramacrophage infection by L. donovani. In addition, testosterone decreased cell viability by way of apoptosis, accompanied by increased Fas, FasL, and Caspase-8 expression. However, these effects of testosterone could not be associated with the classical AR in BMMs since AR was not detectable using different experimental techniques. Instead, it was found that testosterone could bind to the surface of BMMs by the use of an impermeable testosterone-BSA-FITC in confocal laser scanning microscopy and flow cytometry. Collectively, our data indicated that the influence of testosterone on L. donovani infection and viability of BMMs was mediated through the binding sites of testosterone on cell surfaces, which provided a novel mode of direct action of testosterone on AR-free BMMs.     

The dynamics of the testosterone response of perifused mouse Leydig cells to hCG and arginine vasopressin

The effect of hCG and Arginine-Vasopressin (AVP) on testosterone production by purified mouse Leydig cells was examined under dynamic conditions in a perifusion system. A rapid and dose-dependent increase in testosterone release was induced by a 5 min exposure of the cells to increasing concentrations of hCG (0.01 to 1 ng/ml). The testosterone response to hCG was Gaussian in distribution with a peak value by 100 min. A 12 h pretreatment of Leydig cells with 10(-5) M AVP enhanced testosterone accumulation in the perfusate under basal conditions, but markedly reduced the hCG-stimulated testosterone production. The basal and hCG-stimulated testosterone secretion profiles by freshly isolated Leydig cells were, however, unaffected by the continuous presence of the same dose of AVP. These results support the finding that AVP acts directly on Leydig cells. They support the hypothesis of a possible role of neurohypophysial peptides on reproductive functions in the mouse by modulating steroidogenesis at the testicular level.     

Acute suppression of endogenous testosterone levels by exogenous testosterone in normal men

The effect of exogenous testosterone on endogenous plasma testosterone was studied in normal men. Intramuscularly administered testosterone-19,19,19-d3 rapidly appeared in the systemic circulation in large amounts. Endogenous plasma testosterone was suppressed to near-castrate levels. The suppressed level began to rise between 6 and 10 h, and reached a preinjection level at 24 h after the injection. Plasma LH decreased with a concomitant decrease in endogenous testosterone and began to rise as soon as plasma total testosterone returned to physiological levels.     

催乳素对培养的绵羊睾丸间质细胞睾酮分泌的影响

在绵羊睾丸间质细胞体外无血清长期培养的条件下,研究了催乳素对睾丸间质细胞睾酮分泌的调节作用。实验结果表明,催乳素可增强细胞对人绒毛膜促性腺激素(hCG)刺激的反应。催乳素的这种作用呈双相调节。睾酮分泌量显著高于hCG和催乳素单独作用时的总和。在hCG存在下,不同的底物转化为睾酮的量不同。其中雄烯二酮和孕酮转化为睾酮的方式存在着双相性。脱氢表雄酮转为睾酮的量少,不存在双相性,而与其剂量成正比。催乳素在hCG存在下可调节底物转化为睾酮。低剂量的催乳素(1ng/ml)可使一定剂量的孕酮(10～30ng/ml)转化为睾酮的量明显增加,而高剂量的催乳素(>10ng/ml)却明显地抑制孕酮转化为睾酮。催乳素可明显地抑制雄烯二酮转化为睾酮,与剂量无关。可见催乳素对于孕酮和雄烯二酮这两个关键底物转化为睾酮的调节是不同的。催乳素增强hCG刺激睾酮分泌的作用可能部分是通过其促进孕酮转化为睾酮来实现的。     

Effects of testosterone and 5alpha-dihydrotestosterone on luteal lifespan in dairy heifers

Endogenous concentrations of testosterone increase approximately 7 d prior to estrus in cattle and goats. Inhibition of testosterone synthesis results in a delay of luteal regression in both species. The purpose of this experiment was to determine if treatment with testosterone or 5alpha-dihydrotestosterone (DHT), 2 to 6 d prior to the endogenous rise in testosterone, would result in premature luteal regression. Sixteen heifers were randomly assigned to one of three treatment groups: 1) Control (n = 6); 2) testosterone (100 mug, n = 5); or 3) DHT (100 mug, n = 5). Each heifer received a single injection of the appropriate steriod on Day 8, 9, 10, 11 or 12 post estrus. Jugular venous blood samples were collected at frequent intervals for 24 h to quantify testosterone, and then daily for 14 d to quantify progesterone. Concentrations of testosterone increased within 15 min of injection of testosterone, and reached a maximum at 30 min. Concentrations were maintained at > 2 ng/ml throughout the first 24 h after injection. Based on concentrations of progesterone, neither androgen had any effect on the lifespan of the corpus luteum or the level of luteal function.