Guanosine 3',5'-cyclic monophosphate (cGMP) accumulation in single and cocultures of calf pulmonary arterial endothelial (CPAE) and rabbit pulmonary arterial smooth muscle cells (RPASM) was investigated to discover whether endothelial cGMP is involved in the feedback regulation of basally released endothelium-derived relaxing factor (EDRF). Endothelial cell-induced increases in smooth muscle cGMP levels were inhibited by competitive inhibitors of endothelial nitric oxide synthesis, NG-monomethyl-L-arginine and N omega-nitro-L-arginine, in both long-term cocultures and short-term bioassay. Such treatment had no effect on endothelial content of cGMP. Coculture cGMP accumulation was stimulated (twofold increases) by endothelium-dependent vasodilators, bradykinin and acetylcholine. Bradykinin and acetylcholine did not elicit cGMP accumulation in single cultures of either smooth muscle or endothelial cells. To investigate the underlying mechanism(s) of dissociation in cGMP accumulation between cocultures and single endothelial cell cultures, the distribution profile of guanylate cyclase isoforms was determined by stimulating CPAE and RPASM cells with vasodilators activating selectively the soluble or particulate isoenzymes. Both nitrovasodilators, sodium nitroprusside and a putative EDRF, S-nitroso-L-cysteine, produced a 20-fold increase in cGMP content of RPASM cells only, having no effect on endothelial cells. Conversely, atriopeptin II caused 80-fold increases in endothelial cells. Exposure of the short-term bioassay system to 100 nM atriopeptin II, which caused 60-fold increases in CPAE cGMP levels, did not affect basal EDRF-induced smooth muscle cell cGMP accumulation, suggesting that a cGMP-mediated negative feedback mechanism does not appear to be involved in the regulation of basally released EDRF in culture.