CAROTID SINUS REFLEX CHANGES PRODUCED BY DIGITALIS

¹ Department of Pharmacology, Georgetown University, Schools of Medicine & Dentistry, Washington, D. C.

The effect of ouabain and acetyistrophanthidin on the carotid sinus reflex mechanism was evaluated in decerebrate cats. Intracarotid injections of ouabain (10.0 and 20.0 µg) and acetylstrophanthidin (1.56, 3.12, 6.25, 12.5 and 25.0 µg) evoked dose-dependent decreases in contractile force and arterial pressure. No depression in these parameters occurred when these drugs were administered to animals with sectioned carotid sinus nerves. These same doses were found to greatly augment the spontaneous electrical firing of the carotid sinus nerve, and this neural activation was closely related in time to the observed cardiovascular effects. Intravenous administration of acetylstrophanthidin (12.5 and 25.0 µg/kg) was also found to activate the carotid sinus reflexes as an increase in sinus nerve activity occurred which coincided with cardiovascular effects, most notable of which was a decrease in contractile force. No depression in contractile force was noted when this agent was administered to animals with sectioned carotid thnus nerves. Instead, an increase in force as well as a marked pressor response were observed. These results demonstrate that the digitalis preparations studied can directly activate the carotid sinus baroreceptor mechanism and that this activation is a major determinant of their cardiovascular effects.

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