Baroreceptor function in spontaneously hypertensive rats. Effect of preventing hypertension.

In the previous paper we showed that baroreceptor resetting in spontaneously hypertensive rats (SHR) resulted from an incomplete matching of increased receptor strain sensitivity with reduced vessel wall distensibility. Here SHR and Wister-Kyoto controls were treated with antihypertensive drugs in their drinking water (reserpine, hydrochlorothiazide, and hydralazine) from 5 weeks of age so that we might examine the role of blood pressure in the SHR vessel wall-receptor mismatch. Radius and receptor properties were measured using the in vitro aortic arch-aortic nerve preparation at 8, 14, 20, and 30 weeks. We found that baroreceptors from SHR with normal blood pressures had normal pressure thresholds and suprathreshold pressure sensitivities. However, the treated SHR receptors still had lower strain thresholds and the aortas still were less distensible than were the normal. Now, however, the increased receptor sensitivity was sufficient to normalize the relationship between baroreceptor function and arterial blood pressure. We conclude that, although blood pressure may be restored to normotensive levels by therapy, vascular abnormalities may continue to develop.