| Abstract: | Summary Isolated perfused mesenteric artery preparations of genetic (Japanese strain), renal and DOCA/saline hypertensive rats showed a marked increase in reactivity to the vasoconstrictor effect of 5-hydroxytryptamine (5-HT) as compared with normotensive controls. In the arteries of the hypertensive animals, the threshold vasoconstrictor doses of 5-HT were lower, the 5-HT dose-response curves were steeper and their maxima were increased by a factor of 2.5–4.2. These observation only partially fit into the concept that increased vascular reactivity in hypertension is due to an increased wall/lumen ratio of the arterial blood vessels. Pressor responses to 5-HT were also higher in isolated perfused hindquarter and in pithed preparations from renal and DOCA/saline hypertensive rats but not in those from genetic hypertensive rats. In isolated perfused renal artery preparations, the reactivity to 5-HT was equal for normotensive and hypertensive (genetic and DOCA/saline) animals, indicating that not all arteries of hypertensive rats share the increased reactivity to 5-HT. Pretreatment with reserpine slightly reduced the reactivity to 5-HT in arteries from both hypertensive and normotensive rats. Non-vascular smooth muscle of DOCA/saline hypertensive rats, for which isolated gastric strips were used as an example, responded to 5-HT in the same way as that of normotensive rats. Methysergide blocked the pressor responses to 5-HT but did not influence the blood pressure of the hypertensive animals, thus questioning a causal relationship between the increased vascular reactivity to 5-HT and the maintenance of high blood pressure in these three types of experimental hypertension.Preliminary results have been presented at the 3rd Meeting of the Union of the Swiss Societies for Experimental Biology in Zurich (Haeusler and Finch, 1971). |
