The characteristics and extent of rapid or acute resetting of the aortic baroreceptors were studied in long-term renal hypertensive rats during 30 minutes of sustained hypertension produced by phenylephrine infusion. The aortic baroreceptors of hypertensive rats exhibited complete resetting to hypertension because during the control period the systolic threshold pressure for activation of the baroreceptors was similar (137 +/- 5 vs. 142 +/- 4 mm Hg) to the control diastolic pressure. Five minutes after onset of hypertension, a resetting of 32% (percent change of mean pressure threshold divided by total change of mean pressure) was demonstrable. The extent of resetting was 39%, 38%, and 41% after 10, 20, and 30 minutes of hypertension, respectively. When the percent change of systolic threshold pressure divided by total change of control diastolic pressure was used to calculate the extent of resetting, similar results were obtained. The extent of displacement of the entire baroreceptor pressure-response curves was similar to that of pressure thresholds. Reversibility of the resetting process was not complete within 30 minutes of pressure normalization after the administration of phenylephrine was interrupted. These data indicate that the characteristics and extent of rapid resetting of the baroreceptors of renal hypertensive rats, which were reset to operate at hypertensive levels, are similar to those previously described in normotensive rats.