Effects of ouabain and catecholamines on the refractory periods and contractions of isolated atria.

Effects of ouabain and catecholamines_ and their modifications_ by propranolol were investigat ed on the functional refractory period ( FRP ), contractile force and heart rate in isolated atria of guinea-pigs_ and rats.. Catecholamines produced a transient decrease in the FRP of guinea-pig atria, while ouabain caused a continual increase after a latent period of 5 to 10 minutes. The FRP in rat atria was_ increased by either ouabain or catecholamines.. Pretreament with propranolol, which by itself produced a moderate increase in the FRP, completely blocked the effects. of catecholamines_, but did not prevent those of ouabain in both atria. It seems from these data on the FRP changes_ that no evidence was_ obtained for a ouabain-catecholamine r elationship. However, from the observation on the spontaneously beating atria that the toxic effects of ouabain on contractility and rhythmicity were markedly reduced by propranolol it would be suggested that catecholamines_ might be related to the action of ouabain in its. toxic stage.