SPHINGOMYELINASE INHIBITS IN-VITRO LEYDIG-CELL FUNCTION

Activation of the immune system has profound effects on endocrine func tion which are mediated by cytokines including tumor necrosis factor-a lpha (TNF alpha). In vitro, TNF alpha has been shown to directly inhib it Leydig cell testosterone (T) production, but the mechanism of this effect is still unclear. Recent studies using cultured human fibroblas ts have shown that TNF alpha stimulates the activity of neutral sphing omyelinase (SMase) which hydrolyses sphingomyelin (SM) generating cera mide and changing membrane components including cholesterol. The cellu lar effects of increased SMase activity have been reproduced in vitro by the addition of exogenous SMase. III cultured fibroblasts, exogenou s SMase decreases cholesterol synthesis. These findings led us to hypo thesize that SMase might be important in the regulation of steroid hor mone synthesis. To our knowledge, no previous studies have investigate d this possibility. To test this hypothesis, rat Leydig cell enriched cultures were incubated in media containing SMase (0.1 to 100 mU/ml) o r in control media. SMase significantly decreased basal and human chor ionic gonadotropin (hCG) stimulated T production. SMase also decreased hCG binding and hCG stimulated adenosine 3':5'-cyclic monophosphate ( cAMP). N-acetyl-sphingosine (0.1 to 10 mu M), a water soluble ceramide , was used to determine whether or not the effects of SMase could be r eproduced by ceramide addition. N-acetyl-sphingosine had only slight e ffects an basal T and cAMP, and no effect on hCG binding or hCG stimul ated T or cAMP. These data suggest the metabolism of membrane sphingom yelin may be an important regulatory pathway in the control of Leydig cell function.