Effect of Digitalis on Carotid Sinus Baroreceptor Activity

The effect of intracarotid injections of ouabain (25.0 ng) or acetylstrophanthidin (1.56 tig) on feline carotid sinus baroreceptors was evaluated using an isolated perfused carotid sinus preparation. The effects of the drugs on baroreceptor activity were determined by monitoring carotid sinus nerve activity and systemic arterial blood pressure. Administration of either drug to the isolated carotid sinus region altered the relationship between the change in carotid sinus pressure and the fall in systemic arterial blood pressure. Raising the carotid sinus pressure produced a greater depressor response when digitalis was present (-29.6 ± 3.8 mm Hg) than it did when digitalis was absent (-15.3 ± 2.6 mm Hg). Digitalis administration also resulted in a greater increase in carotid sinus nerve discharge when carotid sinus pressure was increased. At a constant carotid sinus pressure, digitalis increased the spontaneous firing of the carotid sinus nerve; the drug-induced augmentation in nerve firing was identical to that produced by raising carotid sinus pressure. These changes in baroreceptor activity in the presence of digitalis occurred without drug-induced changes in the pressure in the isolated carotid sinus region. The results demonstrate that the digitalis preparations studied can directly alter the sensitivity of baroreceptors and produce significant changes in carotid sinus nerve activity and cardiovascular function.