Possible Mechanisms of Inhibitory Action of Sodium Nitroprusside on Histamine-Induced Contractile Responses in Isolated Rabbit Aorta Compared with Basilar Artery and Taenia Coli

Abstract

Possible mechanisms of the inhibitory actions of sodium nitroprusside (NaNP) on histamine-induced contractile responses of isolated rabbit aorta, basilar artery and taenia coli were studied. NaNP (3×10−5 M) reduced maximum contractile response to histamine in the aorta, whereas a concentration (10−4 M) of NaNP slightly shifted the concentration-response curve for histamine towards its higher concentrations, but did not influence the maximum response in the basilar artery and taenia coli. The reduction in the maximum response of the aorta by NaNP was reversed by removal of the endothelium, or treatment with indomethacm (5 × 10−6 M) or quinacrine (5×10−6 M), but not by nordihydroguaiaretic acid (NDGA) (5×10−5 M). Prostaglandin (PG) E1 PGE2 and PGI2 produced a relaxation in histamine-contracted basilar artery and taenia coli, whereas PGE1 and PGE2 produced a weak relaxation in histamine-contracted aorta. PGD2 relaxed taenia coli contracted by histamine, but had no influences in aorta and basilar artery. From these results, it is concluded that the inhibitory action of NaNP on histamine-induced contractile response in isolated rabbit aorta may be mediated at least partly by endothelium-derived arachidonic acid metabolite(s) via the cyclooxygenase pathway which must not involve PGI2. Furthermore, the difference in the inhibitory actions of NaNP between the tissues used in this study must be attributed to the absence of such mechanisms both in the basilar artery and taenia coli.