Role of 5-hydroxytryptamine in the vasoconstrictor action of compound 48/80 in the rat femoral vasculature.

1. The effect of compound 48/80 on the rat femoral vasculature was examined by means of a cross-circulation technique. 2. Intra-arterial injection of increasing doses (1.5 to 15 microgram) of compound 48/80 caused dose-dependent vasoconstriction preceded by transient vasodilatation. The vasoconstriction was significantly reduced in reserpine-treated preparations and converted to vasodilatation by methysergide. 3. When the vasoconstrictor response to a large dose (300 microgram) of adenosine was abolished by repeated administration, the response to compound 48/80 remained unaltered. 4. The present results indicate that the femoral arterial vasoconstriction by compound 48/80 in the rat is mediated by the release of 5-hydroxytryptamine (5-HT); this 5-HT may be liberated from a different storage site from that released by adenosine.