Agonist potencies of tryptamine derivatives at pre- and postjunctional receptors in canine saphenous vein.

Strips form canine saphenous veins were incubated with (3H)-noradrenaline and mounted for superfusion. 5-Hydroxytryptamine (5-HT inhibited the release of tritium caused by sustained electrical stimulation (2 Hz, 150 mA, 0.1 msec) being about 10 times more potent than noradrenaline. 5-HT inhibited contractions induced by intermittent electrical stimulation at 2 Hz but increased the tone of the preparations in the absence of stimulation. Agonist potencies of tryptamine derivatives at prejunctional 5-HT receptors were determined by calculating those concentrations which would reduce the contractile effect of 2 Hz to that of 1 Hz, agonist potencies at postjunctional 5-HT receptors were determined by estimating the concentration which produces 50% of maximum response (pD2 values). Comparison of the agonist potencies at pre- and postjunctional receptors of various tryptamine derivatives suggest that in canine saphenous vein the two types of 5-HT receptor are structurally similar.