THE NICOTINIC EFFECTS OF CHOLINE ESTERS AND OF NICOTINE IN GUINEA PIG ATRIA

¹ Department of Pharmacology, State University of New York at Buffalo, Buffalo, New York

The concentration of atropine was found to be of critical importance in demonstrating the nicotinic effects of acetylcholine in guinea pig atria. Differences were found between the concentrations of atropine needed to unmask positive chronotropic effects and those needed to unmask positive inotropic effects. In the presence of various concentrations of atropine, carbamylcholine was found to have nicotinic effects in isolated guinea pig atria, while methachohine did not. Hexamethonium produced a combination of surmountable and nonsurmountable inhibition of the nicotinic effects of nicotine, while mecamylamine produced a purely nonsurmountable block. On the basis of experiments (reserpine pretreatments, 1.5 and 3.0 mg/kg) in isolated guinea pig atria with intact sympathetic nerves, the stores from which nicotinic agents release catecholamines appear to resemble the stores released by sympathetic nerve stimulation but to differ from those stores released by tyramine.