RELATIONSHIP BETWEEN CYCLIC GUANOSINE 3'-5'-MONOPHOSPHATE FORMATION AND RELAXATION OF CORONARY ARTERIAL SMOOTH-MUSCLE BY GLYCERYL TRINITRATE, NITROPRUSSIDE, NITRITE AND NITRIC-OXIDE - EFFECTS OF METHYLENE-BLUE AND METHEMOGLOBIN

Abstract

Time course relationships between cGMP accumulation and relaxation in bovine coronary artery were determined and the effects of recently identified inhibitors, methylene blue and methemoglobin, on these relationships were evaluated. Arterial strips were suspended in specially mounted tissue baths which permitted continuous recording of isometric tension until rapid freeze-clamping for subsequent determination of cGMP levels by radioimmunoassay. Relaxation and cGMP levels were measured in submaximally contracted strips at zero time (untreated) or 5-s to 5-min intervals after exposure to 0.5 .mu.l of nitric oxide, 1 .mu.M glyceryl trinitrate, 1 .mu.M sodium nitroprusside or 1 mM sodium nitrite in the absence or presence of 10 .mu.M methylene blue or 1 .mu.M methemoglobin. cGMP accumulation preceded onset of relaxation elicited by nitric oxide and glyceryl trinitrate and temporally correlated with relaxation induced by sodium nitroprusside and sodium nitrite. Methylene blue simultaneously inhibited cGMP accumulation and relaxation induced by all 4 relaxants. In contrast to methylene blue, methemoglobin abolished cGMP accumulation and relaxation elicited by nitric oxide without altering responses to glyceryl trinitrate, sodium nitroprusside and sodium nitrite. These findings are consistent with and strongly support an involvement of cGMP formation in vascular smooth muscle relaxation elicited by nitrogen oxide-containing vasodilators.