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.