α-Adrenergic and Serotonergic Receptors and Forearm Venous Compliance in Normal Human Subjects

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Abstract
Summary: The effect of α-adrenergic and serotonergic receptor agonists and antagonists on forearm venous capacitance and vascular resistance was studied in normal subjects. Venous volumes were significantly decreased by phenylephrine, an α1-adrenoceptor agonist, and norepinephrine, which stimulates both α1 and α2-adrenocep-tors, but not by the α2-adrenoceptor agonist clonidine. Vascular resistance was increased significantly by all three agonists. Both the α2-adrenoceptor antagonist yohimbine and the α1-adrenoceptor antagonist prazosin attenuated the venoconstrictor and vasoconstrictor response to norepinephrine, indicating that both adrenoceptors are present. 5-Hydroxytryptamine significantly decreased venous volumes, while vascular resistance was not affected. Ketanserin, a 5-HT2 and α1-adrenoceptor antagonist, attenuated the venous volume responses to 5-hydroxytryptamine and phenylephrine. It is concluded that there are α1- and α2-adrenoceptors and 5-HT2 receptors in the forearm venous system. However, vasoactive doses of clonidine are not venoconstricting. Forearm veins are sensitive to doses of 5-hydroxytryptamine, which do not change vascular resistance compared to α-adrenoceptor agonists, which affect both.

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