Celiprolol: a positive inotropic beta-adrenoceptor blocking agent in conscious dogs.

1. beta-Adrenoceptor blocking agents are used to manage various cardiovascular disorders. A limiting factor in their use is the suppression of the cardiac contractile state. In our study, we examined the cardiac effects of celiprolol, a new beta-adrenoceptor blocking agent with reported positive inotropic effects. 2. Dogs were instrumented by use of sterile surgical techniques for the study of myocardial inotropic state, heart rate and internal left ventricular dimensions. Following complete recovery from surgery, experiments were conducted in the conscious state. 3. Intravenous injection of celiprolol (3 mg kg-1) in nine dogs, increased LV dP/dt by 13 +/- 2.6%, velocity of shortening (LV dD/dt) by 9.2 +/- 3.4%, and heart rate by 19 +/- 4.6% and decreased LV end-diastolic diameter by 1.8 +/- 0.8%, all significantly (P less than 0.05). Celiprolol blocked the inotropic actions of isoprenaline (0.5 micrograms kg-1) but only partially reduced its hypotensive effects. Propranolol, in contrast, reduced LV dP/dt by 17 +/- 3.3% and heart rate by 8.1 +/- 2.7% (P less than 0.05) while totally abolishing the hypotension, tachycardia and increase in LV dP/dt caused by isoprenaline. Following beta-adrenoceptor blockade with propranolol and with heart rate held constant by electrical pacing, celiprolol increased LV dP/dt by 16 +/- 4.0%, LV dD/dt by 12 +/- 3.0% and reduced LV end-diastolic diameter by 3.5 +/- 0.5% (P less than 0.05). 4. Thus, in conscious dogs, celiprolol increases inotropic state and reduces preload independently of beta 1-adrenoceptor mechanisms and the Bowditch phenomenon, while effectively blocking beta 1-receptors in the heart. These properties would make celiprolol useful in patients where a conventional beta-adrenoceptor blocking agent might lead to pump failure.