THE ADRENERGIC‐NEURONE BLOCKING ACTION OF SOME COUMARAN COMPOUNDS

Ethyldimethyl(7‐methylcoumaran‐3‐yl)ammonium iodide (SK&F 90,109) and its guanidine analogue [N‐(7‐methylcoumaran‐3‐yl)guanidine nitrate] (SK&F 90,238) abolish the effects of adrenergic nerve stimulation in cats, as do xylocholine and bretylium. SK&F 90,109 has slight sympathomimetic actions; these are less marked than in SK&F 90,238. Large doses of SK&F 90,109 have an action, dependent on local noradrenaline stores, that delays the appearance of adrenergic‐neurone blockade in conscious cats. Responses to adrenaline are, in general, enhanced by each drug, but SK&F 90,238 transiently antagonizes tachycardia induced by adrenaline and isoprenaline. Both drugs inhibit the release of noradrenaline from the spleen during splenic nerve stimulation, but the release of catechol amines from the adrenal glands, in response to electrical or chemical stimulation, is unimpaired. In contrast to the prolonged adrenergic‐neurone blocking action, any inhibition of the effects of cholinergic nerve stimulation is transient. Large intravenous doses produce neuromuscular blockade. The compounds have a slight central depressant action. In contrast to reserpine and guanethidine the noradrenaline content of rat hearts is not appreciably lowered 24 hr after a single dose of either drug. Unlike xylocholine they are not local anaesthetics. Related compounds also block the effects of adrenergic‐nerve stimulation. The possible modes of action of these drugs are discussed.