Conctraction-mediating receptors in human peripheral vessels with special reference to veins and lymphatics

Sammanfattning: By means of a myograph, postjunctional alpha-adrenoceptors were characterized in human superficial epigastric arteries and veins obtained from health subjects. The rank order of potency of subtype selective agonists could not be used for receptor characterization in these vessels, whereas antagonists gave distinct results. It was found that the arteries were endowed mainly by alph1-adrenoceptors but in some patients alpha2-adrenoceptors could also be demonstrated. In the veins alpha2-adrenoceptors predominated, but a small population of alpha1-adrenoceptors was also present. Five different calcium antagonists were used to inhibit noradrenaline-induced contractions in the same type of vessels. The calcium antagonists had more pronounced effects in the arteries than in the veins. This does not support the view tha calcium antagonists are more effective inhibitors od alpha2- than alpha1-adrenoceptor-mediated contraction. The contractile effects of some alpha-adrenergic agonists were measured in vivo on the distal part of the human saphenous vein, and the dose-response curves were compared with concentration-response curves obtained in vitro on vessels taken from the same region. By comparing the relative potencies of the drugs it was shown that in vitro results are not directly applicable in vivo. Possible reasons for the discrepancies are discussed. Human lymphatics were extirpated from the groin and suspended in tissue baths. Contractions were induced by different agonists and concentration-response curves plotted. Noradrenaline had no effect whereas some prostanoids induced strong contractile responses. Competitive antagonism of prostaglandin endoperoxide analogue-induced contractions was obtained by two thromboxane antagonists. By lymphatic catheterization in healthy subjects it was found that exercise caused an increase in contraction frequency. Indomethacin given i.v. did not cause statistically significant changes in any of the measured parameters, however in two subjects the frequencies and amplitudes were §decreased with about 50% during standing, tip-toeing and running.