23 September 2008
Receptor affinity for agonist and antagonist, Hand arteries and veins, Fluorescence microscopy, Noradrenaline concentration, In vitro pharmacology, Adrenaline, Isoprenaline, 5-Hydroxytryptamine, Phentolamine, Methysergide, Ketanserin
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 α-adrenergic receptors, which was confirmed in Schild plots following phentolamine antagonism of the response (pA<sub>2</sub> 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 (pA<sub>2</sub> 9.50, K<sub>A </sub>8.90 × 10<sup>–7</sup> M). In the veins, ketanserin counteracted the 5-HT-induced contraction in a noncompetitive way.