Compartmental vascular changes in dogs after nephrectomy, DOCA, and saline: effect of nifedipine.

Hypertension (mean arterial pressure, (MAP) 131 +/- 3 mmHg) developed in 18 dogs 4 weeks after left nephrectomy, deoxycorticosterone acetate (DOCA), 5 mg/kg sc twice weekly), and 0.5% NaCl drinking solution. This can be compared with MAP (95 +/- 7 mmHg) of 13 dogs with nephrectomy alone and MAP (86 +/- 4 mmHg) of dogs without nephrectomy. The two-compartment model of the circulation revealed no differences in systemic vascular compliance, compartmental compliance, or flow distribution to the compartments. However, the time constant for venous return for the compartment with the rapid time constant was increased from 0.05 +/- 0.004 min in control animals to 0.07 +/- 0.006 min in the nephrectomy alone group and 0.09 +/- 0.008 min in the hypertensive group (p less than 0.001), as a result of an increase in venous resistance. Arteriolar resistance in this compartment was also increased in the hypertensive animals, as was the mean circulatory filling pressure and overall resistance to venous return. Nifedipine (0.025-0.05 mg/kg) reduced MAP by 15% in the nephrectomy alone group and by 22% in the hypertensive group, with reduction in arteriolar resistance only in the fast time constant compartment. In the slow time constant compartment, arteriolar resistance was increased by more than 100% and flow decreased by more than 50% after nifedipine. Unilateral nephrectomy, DOCA, plus NaCl resulted in hypertension by increasing arteriolar resistance in a vascular compartment with a fast time constant for venous return. Nifedipine countered this effect by inducing arteriolar vasodilation in this compartment. In addition, nifedipine reduced the mean circulatory filling pressure and overall resistance to venous return.