The role of arterial baroreceptors in mediating the cardiovascular response to a cardiac glycoside in conscious dogs.

To determine the role of the arterial baroreceptor reflex in mediating the cardiovascular response to a cardiac glycoside, we examined the effects of ouabain (G-strophanthin), 17.5 mug/kg, iv, on direct and continuous measurements of left ventricular diameters, pressures, velocity of shortening, (dP/dt)/P, arterial pressure, cardiac output, and total peripheral resistance. These studies were conducted on healthy conscious dogs before and after total arterial baroreceptor denervation (TABD). Maximal pressor effects were observed in the first 3-5 minutes; mean arterial pressure increased by 11 +/- 1 mm Hg in normal dogs compared to 33 +/- 4 mm Hg in denervated dogs. In intact dogs at this time heart rate decreased by 18 +/- 2 beats/min and cardiac output fell by 18 +/- 3%; these values gradually returned toward control over 15-30 minutes. When heart rate was kept constant, cardiac output did not fall after injection of ouabain. In contrast, heart rate and cardiac output did not change significantly after ouabain in dogs with TABD. The maximal effects on the contractile state of the heart occurred between 15-30 minutes and were similar in both groups. Arterial baroreceptor reflexes appear to be responsible for the reduction in heart rate and cardiac output caused by administration of ouabain to the intact dog. They exert an important buffering action on the vasopressor effect but a less important action on the inotropic response.