α‐Adrenoceptors of aortae from genetically hypertensive rats: reaction with 2‐halogenoethylamines

The responses of aortic rings from adult spontaneously hypertensive and Carworth normotensive Wistar rats to noradrenaline were compared. The former developed slightly more tension at low, and markedly less tension at high concentrations (> 10⁻⁸m) of noradrenaline. The α‐adrenoceptors of these tissues were probed using 2‐halogenoethylamines to compare quantitatively α‐adrenoceptors in normotensive and hypertensive tissue. The kinetics of the recovery of response to noradrenaline from the short‐lived antagonism produced by NN‐dimethyl‐2‐bromo‐2‐phenylethylamine were identical in aortae from both strains of rat. The rate of recovery of response was the same as the rate of loss of tritium from the tissues, suggesting the absence of spare receptors in rat aorta. An estimation of the number of α‐adrenoceptors in aortic tissue did not show a difference between normotensive and hypertensive tissues. Evidence is presented that 2‐halogenoethylamines react at two kinetically distinguishable sites in rat aorta. The rates of return of response to noradrenaline after receptor blockade with N‐(2‐bromoethyl)‐N‐ethyl‐N‐1‐naphthylmethylamine (SY‐28) in tissues pretreated with NN‐dimethyl‐2‐bromo‐2‐phenylethylamine were the same in aortic smooth muscle from both strains of rat. No significant difference was found in the reactions of 2‐halogenoethylamine α‐adrenoceptor antagonists in aortic tissue from either strain of rat. 1972 Royal Pharmaceutical Society of Great Britain