Controlled beta-receptor blockade with flestolol: a novel ultrashort-acting beta-blocker

The pharmacological properties of an ultrashort-acting beta-receptor blocking agent, flestolol, were evaluated in rabbits. Infusion of graded doses (1-100 micrograms/kg/min, i.v.) into conscious rabbits produced dose-dependent bradycardia without any significant effect on mean arterial pressure. A desired level of heart rate could be obtained by either increasing or decreasing the dose infused. Such titration could be done by changing the dose of flestolol at 20-min intervals. Infusion of 31 micrograms/kg/min of flestolol into reserpinized, conscious rabbits had no effect on mean arterial pressure or heart rate but produced significant inhibition of isoproterenol-induced hypotension and tachycardia. This dose had no effect on the chronotropic and vascular effects of norepinephrine (NE), angiotensin II, adenosine, or acetylcholine. In these rabbits, flestolol was greater than 10-fold as active as esmolol, another ultrashort-acting beta-blocking agent, in inhibiting the responses to isoproterenol. In rabbits under pentobarbital anesthesia, infusion of flestolol (3.1, 10, and 31 micrograms/kg/min) produced dose-dependent beta-receptor blockade. On termination of a 70-min infusion, recovery of the responses to isoproterenol occurred within 30 min. In a separate series of experiments, the effects of infusion of flestolol (10 micrograms/kg/min) into the portal vein were compared with the effects of infusion of the same dose of flestolol into the femoral vein of anesthetized rabbits. Infusion into the femoral vein produced bradycardia and inhibited the hypotensive as well as cardioaccelerator effects of isoproterenol. Infusion into the portal vein was devoid of either effect, suggesting extensive inactivation by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)