THE INNERVATION OF GUINEA-PIG EPICARDIAL CORONARY VEINS - IMMUNOHISTOCHEMISTRY, ULTRASTRUCTURE AND VASOMOTILITY

The innervation and vasomotor responses to several vasoactive agents o f guinea pig epicardial coronary veins were investigated by means of i mmunohistochemical, histochemical, ultrastructural and in vitro pharma cological techniques. The use of an antiserum to the general neuronal marker protein gene product 9.5 revealed that coronary veins are suppl ied by a network of fine varicose nerve fibres in the adventitia. The majority of the nerve fibres possessed neuropeptide Y (NPY) and tyrosi ne hydroxylase immunoreactivity. Only a few nerve fibres displayed sub stance P, neuropeptide K (NK) and calcitonin gene-related peptide (CGR P) immunoreactivity. In double stained preparations substance P immuno reactivity was co-localized with NK and CGRP in the same nerve fibres. Nerve fibres containing vasoactive intestinal peptide (VIP) immunorea ctivity or acetylcholinesterase activity were not detected. Endothelin immunoreactivity was also found in the vein endothelial cells. Ultras tructural studies revealed the presence of axon varicosities at the ad ventitial-medial border. In vitro pharmacological studies showed that endothelin-1 and -2 elicited a significant contractile response of epi cardial vein segments. Noradrenaline, NPY, serotonin and uridine 5'-tr iphosphate induced only a relatively weak contractile response in the vein segments. Although vasodilatory responses were difficult to exami ne in these preparations, it was found that substance P, CGRP and VIP elicited a relaxation of the vein segments. These results indicate tha t guinea pig epicardial coronary veins are innervated by several nerve populations, however, the control of vasomotor tone of coronary veins appears to be predominantly regulated by 'non-neuronal' vasoactive ag ents such as endothelin and 5-HT.