Potentiation of adrenergic venomotor responses in dogs by cardiac glycosides.

Acetylstrophanthidin, 0.3 to 10 /xg/ml, caused contraction of helical strips of the dog cutaneous vein in an organ bath at 37°C. A latent period of 12 to 60 minutes preceded the contraction. During this time, the vein exhibited a progressive increase in response to transmural electric stimulation and added norepinephrine. As the dose of acetylstrophanthidin was increased, the latent period shortened and the increased response during the latent period was potentiated. When the contraction caused by 10 /xg/ml was maximal, no additional contraction occurred with electric stimulation; the response to electric stimulation was only partially restored by the repeated washing out of the drug, despite relaxation of the strip to almost base-line tension. Since transmural electric stimulation causes contraction by release of tissue catecholamines, these experiments demonstrate that digitalis glycosides sensitize the cutaneous veins of the dog to adrenergic stimulation. This was confirmed in dogs anesthetized with pentobarbital. Intravenous injections of acetylstrophanthidin and digoxin, in doses too small (12.5 to 15.5 /xg/kg) to cause direct constriction of the lateral saphenous vein, potentiated the constriction of this vein caused by electric stimulation of the lumbar sympathetic chain. ADDITIONAL