Demonstration of alpha-adrenergic coronary control in different layers of canine myocardium by regional myocardial sympathectomy

Abstract

The direct effects of sympathetic coronary innervation in conscious dogs were analyzed by comparison of myocardial blood flow in a sympathectomized section of the left ventricle with blood flow in another section of the same ventricle with intact sympathetic innervation. Regional myocardial sympathectomy was accomplished by a protocol of intracoronary application of 6-hydroxydopamine (6-OHDA). Regional adrenergic nerve function was checked by studies on accumulation, retention and stimulus-induced release of labelled norepinephrine together with studies on regional ventricular contractility during stellate ganglion stimulation. These tests demonstrated complete sympathectomy in the 6-OHDA-treated section and an unimpaired adrenergic nerve function in the untreated control section. In these dogs at rest, myocardial blood flow (MBF) was 66±14 ml/min·100 g in the left ventricular control section and 108±16 ml/min·100 g in the 6-OHDA-treated section. Transmural distribution of MBF was similar in these two sections: subendocardial MBF/subepicardial MBF was 1.28±0.17 in the control section and 1.36±0.12 in the 6-OHDA-treated section. Application of 1.0 mg/kg propranolol i.v. did not modify MBF and its distribution in either section. Following 1.0 mg/kg phentolamine i.v., MBF in the control section approached that in the 6-OHDA-treated sympathectomized section. These results demonstrate that a substantial α-adrenergic constrictive coronary tone is operative in the ventricular control section in these conscious dogs at rest, which is of similar magnitude in different layers of the left ventricular wall.