The hormonal regulation of premeiotic steps of spermatogenesis in the newborn rat

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.

Infancy is not a quiescent period of testicular development

Postnatal evolution of the testis in most laboratory animals is characterized by the close continuity between neonatal activation and pubertal development. In higher primates, infancy, a long period of variable duration, separates birth from the beginning of puberty. This period has been classically considered as a quiescent phase of testicular development, but is actually characterized by intense, yet inapparent activity. Testicular volume increases vigorously shortly after birth and in early infancy due to the growth in length of seminiferous cords. This longitudinal growth results from active proliferation of infantile Sertoli cells which otherwise display a unique array of functional capabilities (oestrogen and anti-müllerian hormone secretion, increase of FSH receptors and maximal response to FSH). Leydig cells also show recrudescence after birth, possibly determined by an active gonadotrophic-testicular axis which results in increased testosterone secretion of uncertain functional role. This postnatal activation slowly subsides during late infancy when periodic phases of activation of the hypothalamo-pituitary-testicular axis are paralleled by incomplete spermatogenic spurts. The beginning of puberty is marked by the simultaneous reawakening of Leydig cell function and succeeding phases of germ cell differentiation/degeneration which ultimately lead to final spermatogenic maturation. The marked testicular growth in this stage is due to progressive increase at seminiferous tubule diameter. Sertoli cells, which have reached mitotic arrest, develop and differentiate, establishing the seminiferous tubule barrier, fluid secretion and lumen formation, and acquiring cyclic morphological and metabolic variations characteristic of the mature stage. All of these modifications indicate that, far from being quiescent, the testis in primates experiences numerous changes during infancy, and that the potential for pubertal development and normal adult fertility depends on the successful completion of these changes.

Enhancement of A spermatogonial proliferation and differentiation in irradiated rats by gonadotropin-releasing hormone antagonist administration

The initial changes in the numbers, proliferation, and differentiation of A spermatogonia in irradiated rats after the administration of a GnRH antagonist, which is known to induce differentiation in this system, were investigated. LBNF1 rats were given 6 Gy of gamma-irradiation; some were treated with the GnRH antagonist Cetrorelix beginning 15 weeks after irradiation. Although the spermatogonia in the irradiated rats without hormone treatment continue to proliferate (labeling and mitotic indexes of 24% and 18%, respectively), they underwent apoptosis (apoptotic indexes of 21% by the terminal transferase-mediated end labeling assay and 9% by nuclear morphology), resulting in a constant number of A spermatogonia. Whole mount analysis of clones ofA spermatogonia revealed that larger clones were more likely to undergo apoptosis than mitosis. Hormone administration decreased the intratesticular testosterone concentration to 6% of the level in irradiated rats within 1 week. Concomitantly, there was a decrease in spermatogonial apoptotic indexes to 43% of levels in irradiated-only rats, leading to an increases in their numbers by 150%, their diameters by 11%, and their labeling indexes by 31%. The sizes of the mitotic clones gradually increased, and clones of more than eight cells appeared at week 3 of hormone treatment. A spermatogonial differentiation began at week 4, and by week 6.6, differentiation occurred in 30% of the tubules. Thus, suppression of intratesticular testosterone by the GnRH antagonist may be responsible for the immediate changes in spermatogonial numbers and kinetics, but several additional steps are required before differentiation begins, which did not occur until week 4.

Localization of follicle-stimulating hormone (FSH) immunoreactivity and hormone receptor mRNA in testicular tissue of infertile men

Testicular biopsies from 82 oligo- or azoo-spermic male patients were subjected to immunostaining using anti-human FSH antibodies. Histological evaluation showed normal spermatogenesis (nspg) in 7 (FSH: (2.7 +/- 0.7), mixed atrophy (ma) in 63 (FSH:L 5.3 +/- 0.5), and bilateral or unilateral Sertoli Cell Only syndrome (SCO) in 12 (FSH: 21.7 +/- 3.5) patients. For the relationship between FSH values and testicular histology, see Bergmann et al. (1994). FSH immunoreactivity was found exclusively in Sertoli cells and in some interstitial cells. Seminiferous epithelium showing normal or impaired spermatogenesis displayed only weak immunoreactivity compared to intense immunoreaction, i.e. large and numerous vesicles in Sertoli cells of SCO tubules in biopsies showing mixed atrophy or SCO. In addition, h-FSH receptor mRNA was demonstrated by in situ hybridization using biotinylated cDNA antisense oligonucleotides. Hybridization signals were found within the seminiferous epithelium exclusively in Sertoli cell cytoplasm associated with normal spermatogenesis and in epithelia showing different signs of impairment, including SCO. It is concluded that: (1) Sertoli cells are the only cells within the seminiferous epithelium expressing FSH receptors; (2) the accumulation of FSH immunoreactivity in Sertoli cells of SCO tubules appears to be a sign of impaired Sertoli cell function.

Age-dependent differences in the effects of 1,2-dibromo-3-chloropropane (DBCP) on fertility, sperm count, testicular histology and hormonal profile in rats

This study was set up to determine if there are any age-dependent differences in the adverse effects of DBCP on the reproductive system of male rats. Groups of male rats were injected at the ages of 7,30 or 90 days with a single (50 mg kg-1 body weight) or repeated (20 mg kg-1 body weight once a week for 3 weeks) dose of DBCP, dissolved in DMSO. Ninety days after the last injection the males' fertility was estimated and the animals were killed. Blood was collected for future hormone assays, organs were weighed, testes were then taken for histological studies and sperm counts. The results were compared with those of control peers. The results showed that animals injected at the ages of 7 or 90 days under both regimens of treatment were adversely affected. The damage was noted in their fertility rate, sperm production, testicular histology and hormonal profile. Those injected at the age of 30 days showed only an insignificant variation compared with controls.

Spermatogenic onset. II. FSH modulates mitotic activity of germ and Sertoli cells in immature rats

By using high doses of testosterone propionate (TP) endogenous FSH was lowered to non-detectable levels in immature rats of different ages. Combined administration of TP and human menopausal gonadotrophin (hMG) or purified human FSH (hFSH) restored circulating FSH to normal or supranormal levels. This experimental model was used to investigate the influences of hormones on the proliferation of Sertoli and germ cells. Mitoses in seminiferous tubules were counted after being blocked by administration of colchicine. The mitotic index so determined showed a reduction with FSH withdrawal and a significant increase when the hormone levels were restored. Testicular DNA content was determined in testicular homogenates and showed similar changes. Autoradiographs were prepared and 3H-thymidine incorporation into germ and Sertoli cells was quantified. It was found that hFSH induced a significant increase in the labelling indices of gonocytes, type A-spermatogonia and Sertoli cells. All of these changes were effective in rats younger than 10 days but no modifications in any of the parameters under study were observed after 20 days. It is concluded that FSH exerts a stimulatory effect on the proliferation of spermatogonia, Sertoli cells and testicular DNA content during the first 10 days of life.