THE EFFECTS OF SODIUM-NITROPRUSSIDE AND 8-BROMO-CYCLIC GMP ON ELECTRICAL AND MECHANICAL ACTIVITIES OF THE RAT TAIL ARTERY

1 The effects of sodium nitroprusside and 8-bromo-guanosine 3'':5''-cyclic monophosphate (8-bromocyclic GMP) on the electrical and mechanical activities of the rat tail artery were compared. 2 The inhibitory effects of sodium nitroprusside on the contractions induced by noradrenaline, phenylephrine, KCl and clonidine were mimicked by 8-bromo-cyclic GMP. 3 Sodium nitroprusside and 8-bromo-cyclic GMP increased the resting membrane potential only in preparations with low initial resting membrane potentials. 4 In tissues previously contracted and depolarized with noradrenaline, KCl and clonidine, both sodium nitroprusside and 8-bromo-cyclic GMP caused relaxation without significantly affecting the membrane potential. 5 Both sodium nitroprusside and 8-bromo-cyclic GMP abolished neurally-mediated contractions without any significant effect on the electrical responses. 6 These results suggest that the actions of sodium nitroprusside and 8-bromo-cyclic GMP are not related to membrane hyperpolarization or inhibition of membrane excitability.