INTERLEUKIN-1-ALPHA AS A POTENT INHIBITOR OF GONADOTROPIN ACTION IN PORCINE LEYDIG-CELLS - SITE(S) OF ACTION

The effects of interleukin on testicular steroidogenesis have been studied in several laboratories, most often by using cultured rat Leydig cells. Several reports have indicated that interleukin-1-beta (IL-1-beta), but not interleukin-1-alpha (IL-1-alpha), exert a potent effect on gonadotropin action in rat Leydig cells. By using cultured porcine Leydig cells as a model, we found that IL-1-alpha (and to a lesser extent IL-1-beta), contrary to previous reports, is a potent inhibitor of LH/hCG steroidogenic action; and we further localized the steroidogenic biochemical step(s) affected by IL-1-alpha. IL-1-alpha inhibited hCG-induced testosterone secretion (about 67%) in a dose- and time-dependent manner. Half maximal and maximal effects were obtained with 4 U/ml (approximately 0.4 ng/ml, 0.3 x 10(-10) M) and 20 U/ml (approximately 2 ng/ml, 1.4 x 10(-10) M) of IL-1-alpha, respectively. The inhibitory effect of IL-1-alpha on gonadotropin action was detected at 6 h and was maximal after 24 h of treatment with the cytokine. The IL-1-alpha inhibitory effect was more potent than that of IL-1-beta: the maximal inhibitory effect of IL-1-beta was obtained with 400 U/ml. Subsequent investigations indicated that IL-1-alpha inhibited different biochemical steps involved in gonadotropin-induced testicular steroidogenesis. In this context, although IL-1-alpha appears to inhibit Leydig cell membrane functions (through a decrease in LH/hCG binding and gonadotropin-induced cAMP production), the antigonadotropin action of the cytokine is probably exerted predominantly at a step(s) located beyond cAMP formation. Indeed, the cytokine exerted its potent and significant (p < 0.001) inhibitory effect on testosterone formation in a similar manner when Leydig cells were stimulated with hCG (3 ng/ml, 3 h) or with 8-bromo-cAMP (3 x 10(-3) M, 3 h). The inhibitory effect of the cytokine on testosterone secretion was not observed when Leydig cells were incubated with 22R-hydroxycholesterol (5-mu-g/ml, 2 h) or other steroid intermediates. Together, the present findings suggest that the antigonadotropin action of IL-1-alpha is predominantly exerted through a decrease in the availability of cholesterol substrate in the mitochondria for steroid hormone formation.