Pre- and postcapillary vascular responses to sympathetic nerve stimulation in DOCA-hypertensive dogs.

Measurements of precapillary resistance (Ra),postcapillary resistance (Rv), and mean capillary hydrostatic pressure (Pci) were made during sympathetic nerve stimulation (SNS) under constant-flow perfusion in isolated hindlimbs from deoxycorticosterone acetate (DOCA)-hypertensive dogs. We found that both pre- and postcapillary vascular responses to SNS were greater in the DOCA-hypertensive group when compared to the control group. Intraarterial injections of norepinephrine produced a dose-response curve for precapillary vessels in the hypertensive group that was asymmetrically shifted to the left (increased slope) and exhibited a significant decrease in vasoconstrictor threshold. these results, coupled with our earlier observations, suggest that the hyperresponsiveness of the precapillary segment in DOCA-hypertensive dogs could be attributed to both structural and intrinsic alterations of the resistance vessels. We present evidence that suggests, however, that the increased postcapillary resistance with SNS may be explained by a structural alteration causing a decrease in the diameter of existing postcapillary vessels, or may be due to a decrease in the actual number of postcapillary vessels, or both. It is concluded that in this model of hypertension, postcapillary vascular changes also contribute to the overall increase in total peripheral resistance.