Prolonged exposure of canine coronary arteries to a nitric oxide donor desensitizes soluble guanylate cyclase

Background This study investigated the role of soluble guanylate cyclase desensitization in the development of tolerance to organic nitrates. Materials and methods In organ baths, canine coronary arteries were exposed to either sodium nitroprusside (SNP) (experimental group) or papaverine (control group) at various concentrations (10 −9 , 10 −7 , or 10 −5 M) for 3 h. Arteries were then compared for response to vascular agonists and for inducible cyclic guanine monophosphate (cGMP) formation. Results KCl (5 to 50 mM) and prostaglandin F 2α (10 −9 to 10 −5 M) induced similar vascular contractions ( n = 7, P > 0.05). Vascular relaxation in response to calcium ionophore A23187 (10 −9 to 10 −6 M) and to authentic nitric oxide (NO) (3 × 10 −9 to 10 −5 M) was attenuated in arteries exposed to SNP at 10 −7 and 10 −5 M concentrations but not at a 10 −9 M concentration ( n = 7 each, P versus the respective papaverine group). Pretreatment of arteries with methylene blue (10 −5 M) abolished the responses to authentic NO ( n = 4). In cGMP determinations, control arteries demonstrated an increase in cGMP from 364 ± 89 to 778 ± 175 pg/mg of protein with A23187 (3 × 10 −5 M) stimulation ( n = 5). Conversely, arteries exposed to SNP (10 −5 M) demonstrated similar levels of cGMP before (562 ± 126 pg/mg of protein) and after (641 ± 98 pg/mg of protein) A23187 stimulation. Conclusions Prolonged exposure of coronary arteries to SNP did not alter vascular smooth muscle function, but it markedly attenuated the relaxation in response to both A23187 and authentic NO at concentrations above 10 −9 M in a concentration-dependent fashion. The constant levels of cGMP in response to an NO donor suggest that the attenuation of relaxation is due to desensitization of soluble guanylate cyclase. Thus, this study supports the role of soluble guanylate cyclase desensitization in the development of tolerance to organic nitrates.