Using dispersed cultures of fetal rat hypothalami, we studied the effects of forskolin and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), activators of protein kinase A and C, respectively, upon vasopressin (VP) secretion, VP mRNA expression and VP mRNA poly(A) tail length. Forskolin stimulated the VP mRNA content and peptide secretion 2.6-fold and induced an increase in the poly(A) tail length of approximately 90 nucleotides. TPA induced an increase in VP mRNA size and stimulated 1.9-fold the secretion of VP without an increase in VP mRNA content. Depolarization with potassium induced an increase in the VP peptide secreted of 2.2-fold, with no effect on the VP mRNA content or size. Increased osmolality had no effect on either VP peptide or VP mRNA. We conclude that VP expression in cultured fetal rat hypothalamic cells is regulated via both protein kinase A and protein kinase C pathways.