Effect of alpha 1-adrenoceptor blockade on blood pressure and iliac vascular resistance in normotensive and Goldblatt hypertensive dogs; influence of dietary salt and DOCA-salt.

Instrumented normotensive and two-kidney, one clip Goldblatt hypertensive dogs were placed on normal salt, high salt and DOCA-salt regimens and the effect on mean arterial blood pressure (MAP) and iliac vascular resistance (IVR) determined. High salt and DOCA-salt did not alter these variables in the Goldblatt hypertensive group. DOCA-salt increased MAP in the normotensives by 12 mmHg; however, IVR was not significantly increased by this treatment. In order to determine the degree of sympathetic tone in the iliac vascular bed, the change in IVR evoked by the alpha 1-adrenoceptor antagonists, urapidil and prazosin, was assessed. There were similar reductions in MAP and IVR after alpha 1-blockade in both groups of dogs, regardless of the salt regimen. However, urapidil caused a greater decrease in MAP in the normotensives than in the hypertensives. Captopril administration after alpha 1-blockade caused further reductions in MAP and IVR in the hypertensives, and in the MAP of the normotensive dogs on normal or high salt, indicating that the renin-angiotensin system maintained blood pressure in these groups. These results suggest that sympathetic tone is not increased by high salt- or DOCA-salt in normotensive or Goldblatt hypertensive dogs for the 8-11 day duration of these treatments.