In vitro and in vivo interactions of nitrovasodilators and zaprinast, a cGMP-selective phosphodiesterase inhibitor

Abstract We have examined the interaction of zaprinast, a selective inhibitor of cGMP phosphodiesterase, with guanylate cyclase activators on vascular smooth muscle relaxation in vitro and in vivo. Isolated porcine coronary arterial rings precontracted with prostaglandin F 2α (PGF 2α ) were relaxed dose dependently by the guanylate cyclase activators nitroglycerin and nitroprusside, the cGMP phosphodiesterase inhibitor zaprinast and the endothelium-dependent agent bradykinin. A 1 h pretreatment with 0.5 mM nitroglycerin shifted the dose-response curve to nitroglycerin to the right by a factor of 90, reflecting the development of tolerance. The dose-response curve to sodium nitroprusside was also affected, albeit to a much lesser degree (9-fold increase in IC 50 ). Both zaprinast and bradykinin remained unaffected by nitroglycerin pretreatment. A 30 min pretreatment of rings with zaprinast (1 μM) had no effect on nitroglycerin- or nitroprusside-induced relaxation in control rings, but enhanced vasorelaxation to both nitrovasolidators 7- and 2-fold, respectively, in tolerant rings. Similarly, a 30 min pretreatment of rings with (0.1 μM nitroprusside enhanced zaprinast-induced vasorelaxation 4- and 8-fold, respectively, in control and tolerant rings. Similar observations were made in vivo in anesthetized spontaneously hypertensive rats where zaprinast (0.1–3.0 mg/kg i.v.), caused dose-dependent reductions in mean arterial pressure. This effect was enhanced when rats had been pretreated with nitroprusside (1 μg/kg per min). In comparison, in zaprinast-pretreated rats the magnitude of depressor responses to nitroprusside (0.5–5.0 μg/kg) was not altered, but the duration of hypotensive response to the highest dose of nitroprusside was enhanced by zaprinast. These data demonstrate an enhanced vasodilatory response of nitrocompounds in combination with peak I-selective phosphodiesterase inhibitors.