Role of receptor elements in baroceptor resetting.

Spontaneously hypertensive rats (SHR), 4 wk of age, were treated with antihypertensive agents for 40 wk. The treatment was withdrawn for 2 wk so that the animals experienced hypertension for about 1 wk. The aortic arch was then perfused and aortic nerve activity was recorded. The threshold pressure was 140 mmHg in these SHR. This threshold pressure was less than that observed in age-matched untreated SHR (160--180 mmHg) but greater than that observed in age-matched Kyoto-Wistar rats (80--120 mmHg), indicating partial baroceptor resetting. No significant changes were observed in the vascular wall in these SHR, and partial baroceptor resetting was completely reversed when short duration of hypertension was reversed. On the other hand, baroceptor resetting in untreated SHR was always accompanied by significant changes in vascular wall, and reversal of baroceptor resetting was contingent upon regression of vascular wall hypertrophy. Partial baroceptor resetting in absence of significant changes in vascular wall may be explained by adaptation of baroceptors to persistent high blood pressure.