Adrenergic and serotoninergic mechanisms in human hand arteries and veins studied by fluorescence histochemistry and in vitro pharmacology.

Isolated hand arteries and veins from healthy human subjects were tested in vitro for their contractile response to adrenergic agonists and 5-hydroxytryptamine (5-HT) under standardized conditions. This allowed for quantitative estimation of various receptor characteristics. The relative sympathomimetic potency suggested alpha-adrenergic receptors, which was confirmed in Schild plots following phentolamine antagonism of the response (pA2 for artery 7.57, for vein 7.75). 5-HT contracted with a relative potency approximately equal to noradrenaline and adrenaline in arteries, but only one fifth to one tenth of the catecholamine activity in veins. Ketanserin inhibited the 5-HT response in a competitive, probably also irreversible, manner in arteries (pA2 9.50, KA 8.90 X 10(-7) M). In the veins, ketanserin counteracted the 5-HT-induced contraction in a noncompetitive way.