Catecholaminergic nerve fibers and β-adrenergic receptors in the human heart and coronary vessels

The relationship between catecholaminergic nerve fibers and beta-adrenergic receptors in the heart and in the coronary vessels was studied in humans. Only living tissues, harvested from brain-dead heart donors, were used in this experiment. Morphological observations and histochemical staining for norepinephrine and other catecholamines were carried out and beta-adrenergic receptors were stained by means of a beta-blocking fluorescent drug. All morphological data underwent quantitative analysis of images and statistical evaluation. This study provided direct evidence for the distribution of catecholaminergic nerve fibers and of beta-adrenergic receptors in the myocardium and in the coronary arteries. Catecholaminergic nerve fibers are located in the periadventitial tissue, in the adventitia and in the transitional zone between the intima and media. The beta-adrenergic receptors are mainly located in the more innervated part of the heart and coronary arteries but there is a major, although incomplete, overlap with related catecholaminergic nerve fibers. Moreover, using specific substrates and/or inhibitors, two types of beta-adrenergic receptors, beta(1) and beta(2) were demonstrated. Owing to the scarcity of available material (we used only four hearts), and objective difficulties in enrolling other patients, we are at this moment unable to draw general conclusions.