No abstract

In several biological systems, the inhibin A homodimer activin A is stimulated by, and in turn, inhibits the action of interleukin (IL)-1 (both IL-1 and IL-1 ) and IL-6. The possibility that a similar regulatory relationship operates within the testis was investigated. Sertoli cells from immature (20-day-old) rats were cultured with human IL-1 or IL-1 , human IL-6 and/or ovine FSH or dibutyryl cAMP. Activin A and the inhibin dimers, inhibin A and inhibin B, were measured by specific ELISA. Immunoreactive inhibin (ir-inhibin) was measured by RIA. Activin/inhibin subunit mRNA expression was measured by quantitative real-time PCR. Both IL-1 isoforms, but not IL-6, stimulated activin A secretion through increased synthesis of A -subunit mRNA. IL-1 also stimulated activin A secretion by testicular peritubular cells. In contrast to the effect on activin A, IL-1 suppressed inhibin B -subunit and, to a lesser extent, -subunit mRNA expression, thereby reducing basal and FSHstimulated inhibin B secretion by the Sertoli cells. Conversely, FSH inhibited basal activin A secretion and antagonised the stimulatory effects of IL-1. Dibutyryl cAMP partially inhibited the action of IL-1 on activin A secretion, but had no significant effect on basal activin A secretion. Secretion of inhibin A was low in all treatment groups. These data demonstrate that IL-1 and FSH/cAMP exert a reciprocal regulation of activin A and inhibin B synthesis and release by the Sertoli cell, and suggest a role for activin A as a potential feedback regulator of IL-1 and IL-6 activity in the testis during normal spermatogenesis and in inflammation.

The regulation of Sertoli cell activin A and inhibin B secretion during inflammation was investigated in vitro. Adult rat Sertoli cells were incubated with the inflammatory mediators, lipopolysaccharide (LPS), interleukin-1 (IL-1 ), IL-6 and the IL-1 receptor antagonist (IL-1ra) over 48 h in culture. Activin A, inhibin B and IL-1 were measured in the culture medium by specific two-site ELISAs. Both IL-1 -and LPS-stimulated activin A and inhibited inhibin B secretion. LPS also stimulated the production of IL-1 in the cultures. In contrast to IL-1 , IL-6 had no effect on activin A, although it did have a significant inhibitory effect on inhibin B secretion. Ovine follicle-stimulating hormone (FSH) and the cAMP analogue dibutyryl cAMP opposed the actions of IL-1 and LPS by suppressing activin A and IL-1 secretion and by stimulating inhibin B. Blocking IL-1 activity in the cultures by addition of an excess of IL-1ra completely prevented the response of activin A to exogenous IL-1 , and reduced the response to LPS by 50%. In the presence of IL-1ra, basal secretion of inhibin B was increased, but IL-1ra was unable to reverse the suppression of inhibin B by LPS. These data indicate the importance of both IL-1 isoforms in regulating secretion of activin A and inhibin B by mature Sertoli cells during inflammation. The data also establish that inflammation exerts its effects on activin A and inhibin B secretion via other pathways in addition to those mediated by IL-1, and that hormonal stimulation by FSH and cAMP moderates the Sertoli cell response to inflammation. Interference with the complex interactions between these cytokines and hormones may contribute to the disruption of reproductive function that can accompany infection and illness in men.

Production and regulation of activin A and inhibin B during the cycle of the seminiferous epithelium were investigated in adult rats. Immunohistochemistry localised the activin b Asubunit to the Sertoli cell cytoplasm, with much weaker expression in spermatocytes and spermatids. Both activin A and inhibin B, measured by ELISA were secreted by, seminiferous tubule fragments over 72 h in culture. Activin A was secreted in a cyclic manner with peak secretion from tubules isolated at stage VIII. Tubules collected during stage VI produced the least activin A. Inhibin B secretion was highest from stage IX-I tubules and lowest from stage VII tubules. Addition of interleukin-1b (IL-1b) had relatively little effect on activin A or inhibin B secretion in culture. In contrast, the peak secretion of activin A by stage VIII tubules was blocked by co-incubation with an excess of human recombinant IL-1 receptor antagonist, whereas inhibin B secretion increased slightly. Dibutyryl cAMP stimulated activin A secretion by late stage VII and VIII tubules and stimulated inhibin B across all stages. These data indicate that activin A and inhibin B are cyclically regulated within the seminiferous epithelium, with endogenous IL-1 (presumably IL-1a produced by the Sertoli cells), responsible for a peak of activin A production subsequent to sperm release at stage VIII. These data provide direct evidence that production of activin A and inhibin B by the Sertoli cell is locally modulated by IL-1a, in addition to FSH/cAMP, under the influence of the developing spermatogenic cells.