Abstract

The mesovarian suspensory ligament of the rat was used to compare the activities of beta adrenoceptor agonists and antagonists. The following beta adrenoceptor agonists, in descending order of potency, inhibited spontaneous activity in a dose-related manner: zinterol greater than isoproterenol much greater than dobutamine. Several noncardioselective, beta-2 adrenoceptor antagonists with intrinsic sympathomimetic activity (ISA) also inhibited the activity of the ligament: pindolol greater than alprenolol = bucindolol = oxprenolol greater than labetalol. Maximal relaxation induced by the antagonists was equivalent to that caused by the beta receptor agonists. Two cardioselective, beta adrenoceptor antagonists with ISA, acebutolol and practolol, did not inhibit the activity of the suspensory ligament but did increase the rate of the isolated right atrium of the rat. The maximal increases in atrial rate evoked by the antagonists were significantly less than those induced by the beta adrenoceptor agonists. Studies with ICI 118,551 or atenolol as beta-2 or beta-1 selective adrenoceptor blockers, respectively, suggest that the beta adrenoceptors of the suspensory ligament are predominantly of the beta-2 subtype. The possible relevance of these results to the induction of mesovarian leiomyomas in rats by noncardioselective beta adrenoceptor agonists and antagonists with ISA is discussed.