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Cardiovascular and autonomic pharmacology of the macrolide antibiotic LY281389 in anesthetized beagles and in isolated smooth and cardiac muscles

As part of the preclinical safety evaluation process, an investigational macrolide antibiotic, LY281389, was examined for autonomic activity in isolated smooth and cardiac muscle preparations and for cardiovascular effects by intravenous infusion in anesthetized beagles. Concentration-dependent antagonism of acetylcholine and angiotensin I (guinea pig ileum), norepinephrine (rat vas deferens), and isoproterenol (guinea pig atria) was observed at LY281389 concentrations of greater than or equal to 10(-5) M. At LY281389 concentrations of greater than or equal to 10(-4) M, the response of the guinea pig ileum to electrical stimulation was also inhibited approximately 65 to 100%, indicative of potential anticholinergic or alpha-adrenergic activity. In anesthetized dogs, the predominant effect of LY281389 was an increase in heart rate at doses of greater than or equal to 200 micrograms/kg of body weight. LY281389 also produced slight increases in mean arterial pressure and shortening of the P-R interval of the electrocardiogram. In summary, LY281389 possesses nonselective receptor antagonist activity in vitro and produces cardiovascular stimulation in anesthetized dogs. These results indicate that, in addition to potent antimicrobial activity, the macrolide antibiotic LY281389 may exert unexpected actions on cardiovascular function.