Testosterone

About: Testosterone is a research topic. Over the lifetime, 23258 publications have been published within this topic receiving 808079 citations. The topic is also known as: 4-androsten-17beta-ol-3-one & 4-Androsten-3-one-17b-ol.

Variation in the end products of androgen biosynthesis and metabolism during postnatal differentiation of rat Leydig cells

Abstract: The amount of testosterone (T) secreted by Leydig cells is determined by a balance between T biosynthetic and metabolizing enzyme activities. It has been established that 5alpha-androstan-3alpha,17beta-diol (3alpha-DIOL) is the predominant androgen secreted by the testes of immature rats during days 20-40 postpartum, whereas T is the major androgen by day 56. However, the underlying changes in T biosynthetic and metabolizing enzymes during Leydig cell development and their magnitudes have remained unclear. The aim of the present study was to define the developmental trends for T biosynthetic and metabolizing enzymes in Leydig cells at three distinct stages of pubertal differentiation: mesenchymal-like progenitors on day 21, immature Leydig cells on day 35, and adult Leydig cells on day 90. Production rates for precursor androgen (androstenedione), T, and 5alpha-reduced androgens [androsterone (AO) and 3alpha-DIOL] were measured in progenitor, immature, and adult Leydig cells in spent medium after 3 h in vitro. Steady state messenger RNA (mRNA) levels and enzyme activities of biosynthetic and metabolizing enzymes were measured in fractions of freshly isolated cells at each of the three stages. Unexpectedly, progenitor cells produced significant amounts of androgen, with basal levels of total androgens (androstenedione, AO, T, and 3alpha-DIOL) 14 times higher than those of T alone. However, compared with immature and adult Leydig cells, the capacity for steroidogenesis was lower in progenitor cells, with a LH-stimulated production rate for total androgens of 84.33 +/- 8.74 ng/10(6) cells x 3 h (mean +/- SE) vs. 330.13 +/- 44.19 in immature Leydig cells and 523.23 +/- 67.29 in adult Leydig cells. The predominant androgen produced by progenitor, immature, and adult Leydig cells differed, with AO being released by progenitor cells (72.08 +/- 9.02% of total androgens), 3alpha-DIOL by immature Leydig cells (73.33 +/- 14.52%), and T by adult Leydig cells (74.38 +/- 14.73%). Further examination indicated that changes in the predominant androgen resulted from differential gene expression of T biosynthetic and metabolizing enzymes. Low levels of type III 17beta-hydroxysteroid dehydrogenase (17betaHSD) mRNA and enzyme activity were present in progenitor cells compared with immature and adult Leydig cells. In contrast, levels of type I 5alpha-reductase (5alphaR) and 3alpha-hydroxysteroid dehydrogenase (3alphaHSD) mRNA and enzyme activities were dramatically lower in adult Leydig cells compared with those in progenitor and immature Leydig cells. Several T biosynthetic enzymes attained equivalent levels in immature and adult Leydig cells, but T was rapidly metabolized in the former to 3alpha-DIOL by high 5alphaR and 3alphaHSD activities, which were greatly reduced in the latter. Therefore, declines in 5alphaR and 3alphaHSD activities are hypothesized to be a major cause of the ascendancy of T as the predominant androgen end product produced by adult Leydig cells. These results indicate that steroidogenic enzyme gene expression is not induced simultaneously, but through sequential changes in T biosynthetic and metabolizing enzyme activities, resulting in different androgen end products being secreted by Leydig cells during pubertal development.

Aromatization and 5α-Reduction of Androgens in Discrete Hypothalamic and Limbic Regions of the Male and Female Rat1

Abstract: The in vitro aromatization and 5alpha-reduction of androgens to estrogens and dihydrotestosterone (DHT) were determined in incubations of microdissected brain regions of male and female gonadectomized, adrenalectomized rats. Metabolites formed from [1alpha,2alpha-3H]androstenedione or [1alpha,2alpha-3H]testosterone were purified by celite liquid-liquid partition chromatography, silica gel chromatography and recrystallization to stable 3H/14C ratios. The medial preoptic nucleus-anterior hypothalamic nucleus exhibited the highest aromatase activity and the second highest conversion to DHT. The lateral preoptic and lateral hypothalamic nuclei showed little aromatase activity yet exhibited high rates of formation of DHT. The medial basal hypothalamus showed the second highest level of aromatase activity but consistently formed the lowest amount of DHT. The discrect anatomical localization of these enzymatic conversions is suggestive of their being involved in the physiological actions of androgens.

An orally active selective androgen receptor modulator is efficacious on bone, muscle, and sex function with reduced impact on prostate.

Abstract: A number of conditions, including osteoporosis, frailty, and sexual dysfunction in both men and women have been improved using androgens. However, androgens are not widely used for these indications because of the side effects associated with these drugs. We describe an androgen receptor (AR) ligand that maintains expected anabolic activities with substantially diminished activity in the prostate. LGD2226 is a nonsteroidal, nonaromatizable, highly selective ligand for the AR, exhibiting virtually no affinity for the other intracellular receptors. We determined that AR bound to LGD2226 exhibits a unique pattern of protein-protein interactions compared with testosterone, fluoxymesterone (an orally available steroidal androgen), and other steroids, suggesting that LGD2226 alters the conformation of the ligand-binding domain. We demonstrated that LGD2226 is fully active in cell-based models of bone and muscle. LGD2226 exhibited anabolic activity on muscle and bone with reduced impact on prostate growth in rodent models. Biomechanical testing of bones from animals treated with LGD2226 showed strong enhancement of bone strength above sham levels. LGD2226 was also efficacious in a sex-behavior model in male rats measuring mounts, intromissions, ejaculations, and copulation efficiency. These results with an orally available, nonaromatizable androgen demonstrate the important role of the AR and androgens in mediating a number of beneficial effects in bone, muscle, and sexual function independent from the conversion of androgens into estrogenic ligands. Taken together, these results suggest that orally active, nonsteroidal selective androgen receptor modulators may be useful therapeutics for enhancing muscle, bone, and sexual function.

Role of estrogen receptors and g protein-coupled estrogen receptor in regulation of hypothalamus-pituitary-testis axis and spermatogenesis.

Abstract: Male reproductive function is under the control of both gonadotropins and androgens through a negative feedback loop that involves the hypothalamus, pituitary and testis known as hypothalamus-pituitary-gonadal axis (HPG). Indeed, also estrogens play an important role in regulating HPG axis but the relative contribution to the inhibition of gonadotropins secretion exerted by the amount of estrogens produced within the hypothalamus and/or the pituitary or by the amount of circulating estrogens are still ongoing. Moreover, it is known that maintenance of spermatogenesis is controlled by gonadotrophins and testosterone, the effects of which are modulated by a complex network of locally produced factors, including estrogens. Physiological effects of estrogens are mediated by the classical nuclear estrogen receptor alpha (ESR1) and estrogen receptor beta (ESR2), which mediate both genomic and rapid signaling events. In addition, estrogens induce rapid non-genomic responses through a membrane-associated G protein-coupled receptor (GPER). Ours and other studies reported that, in the testis, GPER is expressed in both normal germ cells and somatic cells and it is involved in mediating the estrogen action in spermatogenesis controlling proliferative and/or apoptotic events. Interestingly, GPER expression has been revealed also in hypothalamus and in pituitary. However, its role in mediating estrogen rapid actions in this context is under investigation. Recent studies indicate that GPER is involved in modulating GnRH release as well as gonadotropins secretion. In this review, we will summarize the current knowledge concerning the role of estrogen/estrogen receptors (ERs) molecular pathways in regulating GnRH, FSH and LH release at hypothalamic and pituitary level in male as well as in controlling specific testicular functions such as spermatogenesis, focusing our attention mainly on estrogen signaling mediated by GPER.

Low levels of estradiol are associated with vertebral fractures in older men, but not women: the Rancho Bernardo Study.

Abstract: This longitudinal study included 288 postmenopausal women without estrogen use (median age, 72 yr) and 352 men (median age, 66 yr). All were community-dwelling, ambulatory, and Caucasian. Blood for hormone assays (total and bioavailable estradiol and testosterone, estrone, androstenedione, dihydrotestosterone, dehydroepiandrosterone, and dehydroepiandrosterone sulfate) was obtained in 1984–1987, and vertebral fractures were diagnosed from lateral spine radiographs obtained in 1992–1996. At least one vertebral fracture was found in 21% of women and 8% of men. Among men, age-adjusted hormone levels differed by fracture status only for total (64.1 vs. 75.4 pmol/L, P = 0.012) and bioavailable (43.0 vs. 51.4 pmol/L, P = 0.008) estradiol. There was a graded association between higher concentrations of total and bioavailable estradiol and lower fracture prevalence (trend P < 0.01 for both hormones). Men with total testosterone levels compatible with hypogonadism (<7 nmol/L) were not more likely to have vertebral...