Role of FSH, numbers of FSH receptors and testosterone in the regulation of inhibin secretion during the seasonal testicular cycle of adult rams

Abstract

The regulation of inhibin secretion has not been elucidated fully in male ruminants. The aim of this study was to determine the relative importance of FSH and testosterone concentrations, and FSH receptors, in the control of secretion of immunoactive inhibin in rams. In Expt 1, temporal changes in hormone concentrations and testicular FSH binding were determined for two groups of rams (n = 4) kept under opposite, alternating 4 month periods of long (16 h light:8 h dark) and short (8 h light:16 h dark) days. Testicular biopsies (1-2 g) were collected when the testes were regressed, redeveloping, redeveloped and regressing. In Expt 2, separate groups of rams (n = 4) kept under natural photoperiod (latitude 45 degrees 48 minutes N) were designated as controls or passively immunized (for 3 weeks) with sufficient oestradiol antiserum to increase testosterone secretion without altering LH and FSH; this was done when the testes were regressed (non-breeding season) and redeveloped (breeding season). In both groups of rams (Expt 1), 'seasonal' increases in FSH concentrations began a few weeks earlier than did increases in inhibin concentrations. FSH reached maximum concentrations during testicular recrudescence, whereas numbers of FSH receptors in the testis and circulatory inhibin concentrations did not reach peak values until the testes were fully developed. Numbers of FSH receptors per testis, but not FSH concentration, were positively correlated (r = 0.65) with inhibin concentrations across the four stages of the testicular cycle. Near the end of testicular recrudescence early in the breeding season (Expt 2), relatively high FSH concentration was associated with increased abundance of FSH receptor mRNA (90%) and number of receptors (45%) in the testis and increased inhibin concentrations (50%), compared with when the testes were regressed. Moderate, physiological increases in testosterone secretion in immunized rams did not affect inhibin in either season. These results indicate that: (i) FSH stimulation of immunoactive inhibin secretion by Sertoli cells as testes recrudesce is via increases in secretion (early) and cognate receptors (late); (ii) FSH upregulates the synthesis of its own receptor late in recrudescence; and (iii) the positive correlation (r = 0.70) observed between circulatory testosterone and immunoactive inhibin does not reflect a causal relationship.

cGnRH II involvement in pyriform cell apoptosis

“…As previously demonstrated for several different hormones (Xiao and Goff 1999;Sanford et al 2002), GnRH-R in Podarcis is up-regulated by its ligand. Our in vitro experiments demonstrate that, following cGnRH II treatment, the number of pyriforms positive for the receptor antibody markedly increases.…”

Timing in the Testis

“…Not only the average serum concentrations of gonadotropins but also the frequency of LH pulses decline sharply as the testes regress (Sanford et al, 1974(Sanford et al, , 2002Fig. 4).…”

Possible Relationship Between Seminal Plasma Inhibin B and Spermatogenesis in Patients With Azoospermia

“…Carlsen et al (1999) found a significant diurnal variation in serum inhibin B levels in normal men, lacking evidence for a role of FSH. However, the covariation with serum concentrations of testosterone and estradiol suggested that these hormones might play a role in the diurnal rhythm of inhibin B, although some other common influences could not be excluded (Sanford et al, 2002). Comhaire et al (1995), using an alpha subunit assay, recorded a similar diurnal variability in serum inhibin, and so did Kamischke et al (2001).…”