The aim was to investigate the presence and activity of cGMP hydrolysing phosphodiesterases in guinea pig basilar arteries and the effect of selective and non-selective phosphodiesterase inhibitors on cerebral artery dilatation involving the nitric oxide (NO)-guanosine cyclic 3'5-monophosphate (cGMP) pathway. Immunoreactivity to phosphodiesterases 1A, 1B and 5, but not phosphodiesterase 1C was found in fractions of homogenised cerebral arteries eluted by high-pressure liquid chromatography (HPLC). Both the phosphodiesterase 1 inhibitor 8-methoxymethyl-1-methyl-3-(2methylpropyl)-xanthine (8-MM-IBMX) and the phosphodiesterase 5 inhibitors zaprinast and dipyridamole induced dilatation of cerebral arteries. The dilatory response to 8-MM-IBMX was reduced by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 microM) and endothelial removal and restored by sodium nitroprusside (0.1 microM) pretreatment, indicating a close relation to the nitric oxide-cGMP pathway. The responses to zaprinast and dipyridamole, however, were not only moderately affected, but also restored by sodium nitroprusside (0.1 microM) pretreatment. At high concentrations, the dilatory effects of zaprinast and dipyridamole were partly caused by cGMP-independent mechanisms. Targeting the phosphodiesterases present in cerebral arteries, with selective inhibitors or activators of phosphodiesterase, may be a possible new way of treating cerebrovascular disease.