Roles of FSH and testosterone in the initiation of spermatogenesis in prepubertal rats medically hypophysectomized by a GnRH antagonist

Effects of Osteocalcin on Synthesis of Testosterone and INSL3 during Adult Leydig Cell Differentiation

Proliferation and differentiation of adult Leydig cells are mainly completed in puberty. In many studies, apart from normal postnatal development process, it is widely indicated that, through administrating EDS, Leydig cell population is eliminated and regenerated. It is believed that osteocalcin released from osteoblasts, which is responsible for modulating bone metabolism, induces testosterone production in Leydig cells, independent of the HPG axis. In addition, INSL3 produced by Leydig cells, such as testosterone, plays a critical role in bone metabolism and is known to reflect the development process and functional capacities of Leydig cells. This study is aimed at investigating OC-mediated testosterone regulation and INSL3 synthesis during differentiation of adult Leydig cells that are independent of LH. For this purpose, male rats were divided into 2 groups: prepubertal normal rats and adult EDS-injected rats. Each group was divided into 4 subgroups in which GnRH antagonist or OC was applied. After adult Leydig cells completed their development, testicular tissue samples obtained from the sacrificed rats were examined by light-electron microscopic, immunohistochemical, and biochemical methods. Slight upregulation in 3βHSD, INSL3, and GPRC6A expressions along with the increase in serum testosterone levels was observed in groups treated with osteocalcin against GnRH antagonist. In addition, biochemical and microscopic findings in osteocalcin treated groups were similar to those in control groups. While there was no significant difference in the number of Leydig cells reported, the presence of a significant upregulation in INSL3 and GPRC6A expressions and the increase in serum testosterone and ucOC levels were observed. After evaluation of findings altogether, it is put forward that, for the first time in this study, although osteocalcin treatment made no significant difference in the number of Leydig cells, it increased the level of testosterone through improving the function of existing adult Leydig cells during normal postnatal development process and post-EDS regeneration. This positive correlation between osteocalcin-testosterone and osteocalcin-INSL3 is concluded to be independent of LH at in vivo conditions.

The hypogonadal (hpg) mouse as a model to investigate the estrogenic regulation of spermatogenesis

The hypogonadal (hpg) mouse is an excellent animal model in which to investigate the mechanism of action of estrogens on spermatogenesis because it has arrested reproductive development without the need for surgical, endocrine, pharmacological or immunological intervention. Hpg mice are hypogonadotrophic and fail to show normal postnatal testicular development due to the congenital inability to synthesize gonadotropin-releasing hormone in the hypothalamus. The hpg testis remains responsive to gonadotropins and androgens in that fertility can be induced by treatment with these hormones. Surprisingly, chronic treatment with low concentrations of estradiol alone induces qualitatively normal spermatogenesis. The induction of testicular development by estradiol in hpg mice is accompanied by a paradoxical increase in FSH production. The actions of estradiol in hpg mice appear to be via genomic estrogen receptors, as concurrent treatment with estrogen-receptor antagonist ICI182,780 completely blocks these pituitary and testis responses. Concurrent treatment with the androgen receptor antagonist bicalutamide does not affect the estradiol-induced increase in pituitary FSH content, but markedly attenuates the estradiol-induced increase in testicular weight. Western blot analyses and immunohistochemistry provide evidence for estrogen-receptor alpha and beta expression in both pituitary gland and testis of the hpg mouse. Estradiol may therefore exert direct actions within the testes and/or indirect neuroendocrine actions via the release of FSH or other hormones from the pituitary gland, but its actions are dependent upon the availability of low levels of androgen within the testis.

A Sertoli cell-selective knockout of the androgen receptor causes spermatogenic arrest in meiosis

Androgens control spermatogenesis, but germ cells themselves do not express a functional androgen receptor (AR). Androgen regulation is thought to be mediated by Sertoli and peritubular myoid cells, but their relative roles and the mechanisms involved remain largely unknown. Using Cre/loxP technology, we have generated mice with a ubiquitous knockout of the AR as well as mice with a selective AR knockout in Sertoli cells (SC) only. Mice with a floxed exon 2 of the AR gene were crossed with mice expressing Cre recombinase ubiquitously or selectively in SC (under control of the anti-Müllerian hormone gene promoter). AR knockout males displayed a complete androgen insensitivity phenotype. Testes were located abdominally, and germ cell development was severely disrupted. In contrast, SC AR knockout males showed normal testis descent and development of the male urogenital tract. Expression of the homeobox gene Pem, which is androgen-regulated in SC, was severely decreased. Testis weight was reduced to 28% of that in WT littermates. Stereological analysis indicated that the number of SC was unchanged, whereas numbers of spermatocytes, round spermatids, and elongated spermatids were reduced to 64%, 3%, and 0% respectively of WT. These changes were associated with increased germ cell apoptosis and grossly reduced expression of genes specific for late spermatocyte or spermatid development. It is concluded that cell-autonomous action of the AR in SC is an absolute requirement for androgen maintenance of complete spermatogenesis, and that spermatocyte/spermatid development/survival critically depends on androgens.

Precocious puberty secondary to topical testosterone exposure

We report a case of pronounced virilization, including marked penile and pubic hair growth, accelerated height velocity and skeletal maturation, and increased muscle mass in a 2.67 year-old boy resulting from presumed inadvertent, long-term exposure to a topical testosterone cream being used by his father.

Estradiol enhances the stimulatory effect of FSH on testicular maturation and contributes to precocious initiation of spermatogenesis

Male rats were daily injected with human FSH (hFSH) or estradiol benzoate (EB) or hFSH+EB between day 5 and 15 of life and autopsied on day 16. hFSH accelerated testicular growth, increased number of spermatogonia and serum level of testosterone. hFSH stimulated also spermatogonia differentiation, which resulted in 5-fold increase of the number of spermatocytes. EB given alone induced adverse, inhibitory effects on spermatogenesis and serum testosterone, did not influence serum FSH and LH but increased 14-fold the level of prolactin. Except from testosterone, EB given with hFSH not only overcame inhibitions, but multiplied hFSH stimulatory effects on spermatogenesis up to 30-times of control values. In addition, after FSH+EB premeiotic germ cell ratio reached adult type value precociously. Estradiol may play regulatory roles in testicular maturation (1) inhibitory, direct one or resulting from decrease in testosterone secretion; (2) stimulatory, by enhancement of FSH action, with a possible involvement of prolactin that may act in concert with FSH.