Binding of [3H]-5-hydroxytryptamine to human coronary artery and bypass graft vessels

5-Hydroxytryptamine (5-HT) has a wide range of vascular effects mediated via specific receptors and it has been suggested to be a mediator in ischemic heart disease. The aim of the present study was to localise the 5-HT receptors within the vessel wall.

Epicardial coronary arteries obtained from patients undergoing cardiac transplantation, internal mammary arteries from heart donors and saphenous veins from patients undergoing coronary bypass surgery, were sectioned and incubated with [3H]-5-HT for in vitro receptor autoradiography.

Microscopic analysis of high resolution autoradiographic images revealed a similar pattern of [3H]-5-HT binding in epicardial coronary and internal mammary artery, where it predominated in the lamina muscularis. In the saphenous vein, binding increased towards the adventitia which showed dense, displaceable binding to the vasa vasorum as well as to nerve-like structures, from which binding was only partially displaced. Computer-assisted densitometric analysis of low resolution autoradiographs revealed a high degree of specific binding to all vessels examined.

The distribution of the [3H]-5-HT binding is different in the saphenous vein compared to epicardial coronary and internal mammary artery. The dense binding to vasa vasorum in the saphenous vein suggests a role for 5-HT in closure of these nutrient vessels, which could contribute to the formation of atherosclerotic changes in saphenous vein grafts.