Exposure of pig epidermal sheets to the protein kinase C (PKC) activator, phorbol 12-myristate, 13-acetate (PMA) resulted in an increase in forskolin-induced cyclic AMP accumulation in the epidermis. Cholera toxin-induced cyclic AMP accumulation was moderately increased by PMA treatment, but this was not statistically significant. On the other hand, receptor-mediated adenylate cyclase responses (beta-adrenergic-, prostaglandin E-, adenosine-, and histamine (H2)-adenylate cyclase responses) were significantly decreased. These PMA-induced effects on the epidermal adenylate cyclase system were mimicked by 1-oleoyl-2-acetyl-glycerol, a membrane-permeable synthetic diacylglycerol, and by the non-phorbol PKC activator, mezerein. 4-O-methyl PMA, a very weak PKC activator, had no effect on adenylate cyclase responses of the epidermis. The addition of the PKC inhibitor, H-7 (1-(5-isoquinoline-sulfonyl)-2-methyl piperazine dihydrochloride), to the incubation medium significantly inhibited the effect of PMA on forskolin-induced cyclic AMP accumulation. Furthermore, following H-7 treatment, the epidermal receptor-adenylate cyclase responses were significantly increased. These results indicate that PKC modulates epidermal adenylate cyclase responses resulting in an increase in forskolin-induced cyclic AMP accumulation and a decrease in receptor-adenylate cyclase responses of the epidermis.