Baroreceptor resetting during pressure recovery from hypotension.

In a previous study we showed that aortic baroreceptors of rat fully reset to hypotenslve levels 48 hours after a single injection of reserpine (2 mg/kg, i.p.). In the present experiments the reversibility of the resetting from hypotension during pressure recovery was analyzed in the same model. Direct mean arterial pressure (MAP) was measured daily in eight conscious unrestrained rats whose MAP varied from 71 to 84 mm Hg 24 to 48 hours after the reserpinization. In these animals the recovery of at least 20 mm Hg (96 to 117 mm Hg) from the lowest hypotensive level took 1 to 4 days. Electroneurographic analysis of the aortic baroreceptors was performed under pentobarbital anesthesia (30 mg/kg i.p.) in treated animals and in a group of 12 normotensive control rats. The anesthesia at the dose employed did not significantly alter the control pressure of conscious treated rats (105 ± 2 before and 92 ± 6 mm Hg after anesthesia). There was no lag between the firing range (threshold pressure of 107 ± 4/74 ± 4 mm Hg; "normal" firing of 131 ± 2/102 ± 3 mm Hg) and the exhibited control pressure (142 ± 2/106 ± 4 mm Hg) of the treated animals. A similar relationship was also observed for the control group (107 ± 4/74 ± 4 and 131 ± 2/102 ± 3 mm Hg, respectively, for the firing range indices and 142 ± 2/106 ± 4 mm Hg for the control pressure). The data showed that, even when the arterial pressure of treated rats had not completely reverted to normotension, the baroreceptor firing range had an upward displacement very close to that of blood pressure normalization, with no lag between these variables. This indicates that the process of baroreceptor resetting from hypotension is faster than baroreceptor resetting to hypotension, as shown previously for the resetting to and from chronic renal hypertension. (Hypertension 3 (suppl II): II-147-II-150, 1981)