Compensation of endothelium-dependent responses in coronary circulation of eNOS-deficient mice

Nitric oxide plays a fundamental role in the regulation of blood flow. Here we analyzed compensatory mechanisms for the genetic eNOS deficiency in aorta and in coronary circulation. Vasodilation induced by acetylcholine, bradykinin, adenosine, and ADP as well as by S-nitroso-penicillamine (SNAP) was assessed in isolated aorta and in isolated mouse hearts from eNOS(-/-) and age-matched eNOS(+/+) mice. In aorta from eNOS(+/+) mice acetylcholineinduced vasodilation was entirely dependent on NO, and this response was absent in aorta from eNOS(-/-) mice. In eNOS(+/+) mouse hearts responses induced by bradykinin, adenosine and ADP were partially dependent on NO, but not on PGI(2), cytochrome P450-dependent metabolites, or H2O2. On the other hand, vasodilation induced by acetylcholine involved NO, but not PGI(2), in its immediate, short-lasting phase, whereas PGI(2) and NO mediated delayed, longerlasting phase of this response. In eNOS(-/-) mouse hearts coronary vasodilator function was compensated. Responses induced by acetylcholine and adenosine, but not by bradykinin or ADP, were in part compensated by NO, most likely derived from nNOS. However, the major mechanisms compensating for the loss of eNOS in the coronary circulation did not rely on NO, PGI(2), cytochrome P450-derived metabolites of arachidonic acid or on H2O2. Deficiency of eNOS is largely compensated in coronary circulation but not in aorta.