COMPARATIVE EFFECTS OF ACTIVATION OF SOLUBLE AND PARTICULATE GUANYLYL CYCLASE ON CYCLIC-GMP ELEVATION AND RELAXATION OF BOVINE TRACHEAL SMOOTH-MUSCLE

1 The effects of nitric oxide-donating compounds and atrial natriuretic peptide on cyclic GMP accumulation and mechanical tone were compared with the effects of isoprenaline in bovine tracheal smooth muscle. 2 Sodium nitroprusside, glyceryl trinitrate, S-nitroso-N-acetylpenicillamine (SNAP), atrial!natriuretic peptide and isoprenaline each caused concentration-dependent inhibitions of histamine-maintained tone (EC(50) values 320 +/- 80, 150 +/- 45, 14,000 +/- 4,000, 2.8 +/- 0.8 and 6.6 +/- 4.3 nM respectively). 3 When compared with their effects on histamine-induced tone, sodium nitroprusside was equally potent and effective in causing relaxation of methacholine-supported tone (EC(50) 290 +/- 90 nM) while isoprenaline was as effective, but less potent (EC(50) 30 +/- 7 nM). SNAP was more potent and equi-effective as a relaxant of methacholine-supported tone (EC(50) 340 +/- 140 nM). At the maximum concentrations of glyceryl trinitrate and atrial natriuretic peptide tested against methacholine-supported tone, relaxations of 52% and 14% of the isoprenaline maximum were seen. 4 Sodium nitroprusside, glyceryl trinitrate and atrial natriuretic peptide each induced concentration-dependent increases in cyclic GMP accumulation. The time-courses of accumulation correlated closely with the relaxant actions of these compounds. 5 Pretreatment of tracheal smooth muscle with sodium nitroprusside or SNAP caused a rightward shift of the concentration-effect curve for histamine while reducing the maximum response. 6 LY 83583, a putative guanylyl cyclase inhibitor, caused a concentration-dependent reduction in basal cyclic GMP accumulation in tracheal smooth muscle and inhibited the effects of sodium nitroprusside on cyclic GMP accumulation. 7 LY 83583 also inhibited the relaxation of histamine-supported tone by glyceryl trinitrate, sodium nitroprusside, SNAP and atrial natriuretic peptide, and also sodium nitroprusside- and SNAP-induced relaxation of methacholine-supported tone. However, it had no significant effect on glyceryl trinitrate-induced relaxation of methacholine-supported tone. 8 It is concluded that the relaxant actions of sodiumnitroprusside, glyceryl trinitrate, SNAP and atrial natriuretic peptide follow as a result of their ability to activate either soluble or particulate guanylyl cyclase leading to cyclic GMP accumulation. Although there does not seem to be any functional difference in the relaxant response to cyclic GMP generated by the particulate as opposed to soluble form(s) of guanylyl cyclase, atrial natriuretic peptide receptor/guanylyl cyclase activation was much less effective in causing relaxation of methacholine-supported tone when compared to activators of soluble guanylyl cyclase.