Celiprolol, a potent cardioselective beta 1-adrenoceptor antagonist with mild alpha 2-adrenoceptor antagonist...

Celiprolol is a cardioselective beta-adrenoceptor antagonist, with interesting propranolol-insensitive cardiostimulatory, vasodilatory and bronchodilatory effects. Recent reports suggest that mild alpha 2-adrenoceptor antagonism may contribute to these effects. The present investigation further explored the alpha 2 effects of celiprolol. In isolated electrically-stimulated rat atria celiprolol (1.0 and 10 mumol/l) significantly increased the release of [3H]-norepinephrine, consistent with the blockade of pre-junctional alpha 2-adrenoceptors. Evidence for post-synaptic alpha 2-adrenoceptor antagonist activity was obtained in studies of the effects of celiprolol on the pressor response to clonidine and either phenylephrine or methoxamine in perfused hind-limbs of dogs (pretreated with mecamylamine and propranolol) and pithed rats. In the dog, celiprolol (10 mg/kg) significantly inhibited the vasoconstrictor response of clonidine while in the rat higher doses were required (> or = 12.5 mg/kg). Celiprolol did not affect the pressor response induced by alpha 1-agonists. We conclude that celiprolol possesses a mild alpha 2-adrenoceptor blocking action which may contribute to its unconventional profile.