Systemic and coronary hemodynamic effects of prostacyclin and nitroprusside in conscious dogs

In order to simulate physiologic conditions and eliminate the influence of anesthesia on the cardiovascular responses to prostacyclin (PGI2) and nitroprusside, hemodynamic parameters were monitored in conscious dogs prior to and during infusion of the two agents at equally hypotensive concentrations. Heart rate was significantly increased with nitroprusside (p less than or equal to 0.05) and decreased with PGI2 (p less than or equal to 0.01), while mean ascending aortic blood flow or cardiac output increased (p less than or equal to 0.05) in response to both PGI2 and nitroprusside, more with nitroprusside than with PGI2 (p less than or equal to 0.05). Stroke volume increased with PGI2 only (p less than or equal to 0.05 vs. control, p less than or equal to 0.05 vs. nitroprusside). Both systemic and coronary (circumflex) vascular resistances decreased more with nitroprusside than with PGI2 (p less than or equal to 0.05); however, characteristic impedance (index of aortic elasticity) decreased similarly with PGI2 and nitroprusside. Circumflex coronary blood flow increased (p less than or equal to 0.05) only with nitroprusside. These results indicate that in conscious dogs (a) nitroprusside causes a greater decrease in vascular (systemic and coronary) resistance compared to PGI2, but the effects of the two vasodilators on arterial distensibility are similar; (b) nitroprusside, but not PGI2, causes a marked increase in coronary blood flow; and (c) the major distinguishing hemodynamic response to these vasodilators relates to marked bradycardia with PGI2 and tachycardia with nitroprusside, which may account for the observed differences in aortic blood flow and stroke volume.