BETA-ADRENOCEPTOR DESENSITIZATION BY CLENBUTEROL IN RAT UTERUS

1. The relaxant response and cAMP production mediated by stimulation o f isoproterenol is reduced in uterine rings from clenbuterol treated r ats (0.25 mg kg-1 s.c. 24 hr before experiments) precontracted with 50 mM KCl. 2. Forskolin, in contrast, showed similar relaxant responses in untreated or clenbuterol treated rats. 3. Isoproterenol produces a biphasic response that is composed of a rapid relaxation followed by a slower regaining of tension, which is considered as desensitization. 4. The kinetic study demonstrates marked changes in the desensitizatio n process of beta-adrenoceptors after clenbuterol administration.