Myocardial blood flow after chronic cardiac decentralization in anesthetized dogs: effects of ACE-inhibition

Abstract

Coronary blood flow regulation was studied in dogs with an intact or chronically decentralized intrinsic cardiac nervous system. We also examined the effect of angiotensin-converting enzyme inhibition (ACEI) on coronary autoregulatory pressure–flow relations and distribution of blood flow since the renin–angiotensin system may play a critical role in vasoregulation. Myocardial oxygen demand was reduced in the chronic decentralized dogs compared to the control dogs. The lower pressure limit of the autoregulatory pressure–flow relation was similar for the control and chronic decentralized dogs (47±2 and 44±7 mm Hg, respectively; p=NS). After ACEI, the lower pressure limit shifted leftward to 40 mm Hg ( p=0.001) in both groups. Concomitant blockade of cyclooxygenase, bradykinin catabolism and nitric oxide synthase had no further effect on the lower pressure limit. Total myocardial blood flow was lower ( p=0.001) in the chronic decentralized dogs compared to the control dogs, while transmural distribution of blood flow was preserved in both groups. The results show that even though myocardial oxygen requirements are lower in the chronically decentralized heart compared to controls, coronary autoregulation is maintained at levels observed in normally innervated hearts. The present findings indicate that intrinsic cardiac neurons contribute to coronary autoregulatory control and myocardial blood flow distribution even in the absence of cardiac connections to the central nervous system. In addition, in the chronic decentralized dog, ACEI allows the heart to work at lower coronary perfusion pressures while myocardial blood flow distribution is preserved.