SITE OF MACROPHAGE INHIBITION OF LUTEINIZING HORMONE-STIMULATED TESTOSTERONE PRODUCTION BY PURIFIED LEYDIG-CELLS

It has been observed that testicular macrophages and testicular macrop hage-conditioned medium reduce LH-stimulated, but not basal, testoster one production by purified Leydig cells in vitro. In order to determin e how this inhibition occurs, we have examined the effects of testicul ar macrophages and testicular macrophage-conditioned medium at discret e stages of the steroidogenic pathway. The lesion in steroidogenesis i s located at a step beyond cAMP formation, because the addition of dib utyryl cAMP or cholera toxin did not overcome the testicular macrophag e-conditioned medium inhibition of LH-stimulated steroidogenesis by Le ydig cells. This effect of testicular macrophage-conditioned medium on Leydig cell testosterone production is first observed at 18 h after i nitiation of culture. However, subsequent additions of 22R-hydroxychol esterol, pregnenolone, dehydroepiandrosterone, or androstenedione to t he Leydig cell cultures can overcome the inhibition so that, after a f urther G h of incubation, testosterone production is not significantly different from that of control Leydig cells cultured in the absence o f testicular macrophage-conditioned medium. These results suggest that the block in steroidogenesis is beyond cAMP production but prior to t he formation of pregnenolone, dehydroepiandrosterone, and androstenedi one. Since the medium for these cultures contained lipoprotein, it is possible that the testicular macrophage-conditioned medium metabolizes the lipoprotein, making it unavailable to the Leydig cells. However, our results show that preincubation of lipoprotein with testicular mac rophage-conditioned medium does not significantly alter testosterone p roduction by the Leydig cells in the culture. It is concluded that tes ticular macrophage-conditioned medium affects the transport or availab ility of cholesterol to mitochondria prior to further steps in the ste roidogenic pathway.