A GHRH-like mRNA and peptide (t-GHRH) have been detected in rat and human testis. In rat, t-GHRH mRNA is localized to developing spermatogenic cells. We predicted that the most likely target cell of t-GHRH action would be the Sertoli cell. To test this prediction, we evaluated GHRH action on Sertoli cell function. Rat GHRH at a concentration of 10 nM or 100 nM stimulated cAMP production 2-fold over control levels after a 30 min incubation. This stimulation was obliterated by preincubation with a 10-fold excess of the GHRH antagonist (N-Ac-Tyr1, D-Arg2)-GRF(1-29)-NH2. The effect of treatment with [His1,Nle27]GHRH(1-32)-NH2, a GHRH analog, on Sertoli cell mRNAs was also assessed. Treatment with the analog significantly increased levels of c-fos and steel factor (the product of the Steel gene, also termed SCF) mRNAs above controls, but had no effect on sulfated glycoprotein-2 mRNA. We conclude that GHRH acts via adenylate cyclase to modulate specific Sertoli cell products, possibly as part of a network of local interacting factors controlling Sertoli and germ cell function.