Inhibition of Leydig Cell Steroidogenesis: Effect of Actinomycin D Before and After Preincubation of Leydig Cells In Vitro

The effect of preincubating purified Leydig cells in Eagle's medium and the subsequent effect of the mRNA synthesis inhibitor actinomycin D on LH-stimulated testosterone synthcsis has been investigated. The inhibitory effect obtained was found to decrease with the period of preincubation; with 0, 1, 2 and 3 h preincubation bcfore the addition of L H (100 ng/ml) 36.5 t 3.9, 31.2 k 2.5, 17.8 k 3.8 and 13.6 f 2.9 " i o inhibition occurred respectively when actinomycin D (6.4 PM) was added and the cells were incubated for 2 h (means k SCM, n = 5). During the first hour of incubation with L H and actinomycin D no inhibition occurred in cells that had been preincubatcd for 3 h. These results suggest that during preincubation and independently of LH, synthesis of intermediates (possibly mRNA(s)) required for stimulation of steroidogenesis may take place and that subsequent stimulation of steroidogenesis by I,H occurs without further de nono mRNA synthesis.