Abstract
There are reports that cardiac glycosides potentiate responses of smooth muscle organs evoked by various stimulating agents as well as electrical stimulus. Brender and co-workers (1) reported that tension development and the contractile response of saphenous vein strip of dogs evoked by electrical stimulation were potentiated by acetylstrophanthidin (1 μg/ml). There is also evidence that digitoxin and ouabain potentiated the pressor actions of catecholamines in the dog (2, 3) and that ouabain potentiated the response of aortic strip of the rabbit to BaCl2 (4).
On the other hand, the authors synthesized several aminoguanidine analogues and examined pharmacological actions on autonomic nervous systems (5). Among them 3, 4-dihydroxy-5-methoxybenzoylaminoguanidine (AG-2H) had characteristic cardiac action as follows (6). Namely, AG-2H showed a fairly continuous positive inotropic action without a positive chronotropic action. This action was difficult to abolish using a adrenergic β-blocking agent. The positive inotropic action induced by noradrenaline was abolished by a high concentration of AG-2H. As to action potential of guinea-pig papillary muscle, the plateau phase was prolonged by AG-2H though the amplitude was little changed.
In the present study, effects of ouabain and AG-2H on the responses induced by various agents and electrical nerve stimulation on the blood pressure and the nictitating membrane of the cat were examined in paralel. Furthermore, using guinea-pig vas deferens as a typical adrenergically innervated organ, effects of both drugs on contractions induced by autonomic agents were investigated.
