The aims of the present study were to determine whether natriuretic peptide receptors coupled to guanylate cyclase are present in the neural lobe (NL) of the pituitary and eventually localized on pituicytes and/or on nerve fibers and whether cyclic GMP may be involved in the regulation of vasopressin secretion. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) enhanced cyclic GMP content of NLs in a dose-related fashion, with ED(50) values of about 5 x 10(-8)M, while CNP failed to significantly elevate guanylate cyclase activity. ANP stimulated cyclic GMP accumulation in NLs lacking functional nerve fibers, while it was without significant effect on isolated nerve terminals. In the brain, ANP-enhanced cyclic GMP production was similarly expressed in glial and not in neuronal cultures, although intracellular guanylate cyclase activity (stimulated by sodium nitroprusside) was present in both cell types. Finally, the cell permeant S-bromoguanosine 3':5'-monophosphate GMP failed to change either basal or isoproterenol-stimulated vasopressin secretion from incubated NLs. We conclude that in the NL, as well as in brain tissue cultures, the guanylate cyclase-NP receptor complex (most probably the ANP-A subtype) is localized on pituicytes/filial cells rather than on nerve fibers/cells and that cyclic GMP may not be directly involved in the regulation of vasopressin output from the NL.