Contractile effects of noradrenaline and 5-hydroxytryptamine in human hand veins: a pharmacological receptor characterization.
The postjunctional receptors mediating contractile responses to noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were characterized in ring segments of human hand veins by using subtype selective agonists and antagonists. The mechanical characteristics of the preparations were also examined by length-tension measurements. The length-active wall tension curve was bell-shaped and reached a maximum at a length corresponding to a passive distending pressure of approximately 14 mmHg. (-)-Phenylephrine consistently contracted the veins and was 24 times less potent than (+/-)-NA whereas clonidine produced a contraction in only two out of 11 vessel segments. Neither prazosin nor rauwolscine competitively inhibited the contractile response to NA, and large inter-individual differences were found in the degree of inhibition produced by the antagonists. However, application of both prazosin and rauwolscine almost abolished the NA-induced contraction. Ketanserin and methergoline inhibited the contractile response to 5-HT; the former in an apparently competitive manner with a pA2 value of 8.94, whereas the latter substantially reduced the maximum 5-HT response. It is suggested that NA elicits contraction in human hand veins by acting at a mixed population of alpha 1- and alpha 2-adrenoreceptors. The contractile response to 5-HT, on the other hand, appears to be mediated predominantly by 5-HT2 receptors.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D006225:Hand / Q000098:blood supply*; D006801:Humans; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D010656:Phenylephrine / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects; D011985:Receptors, Serotonin / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects; D014680:Veins / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011941:Receptors, Adrenergic; D011985:Receptors, Serotonin; D010656:Phenylephrine; D012701:Serotonin; D009638:Norepinephrine