The area postrema and control of arterial blood pressure; absence of hypertension after excision of the area postrema in rats.

Acute surgical excision of the area postrema (AP) in the rat failed to affect arterial blood pressure or heart rate. The was no effect on cardiovascular reflex responses during diving or on the heart rate responses to acute decreases or increases of blood pressure caused by bradykinin or angiotensin, respectively. Electrolytic lesions of the AP in acute experiments caused variable damage to the nucleus tractus solitarii (NTS). In these rats large variations in blood pressure occurred. Excision of the AP in a chronic experiment failed to change blood pressure, heart rate, water intake or plasma renin activity. In contrast, bilateral electrolytic lesions of the NTS at the level of the AP caused a severe acute hypertension and completely blocked cardiovascular reflex responses. Hypertension also existed in rats with NTS lesions studied for a longer period of time. There experiments failed to confirm the hypothesis that the AP exerts a tonic inhibitory control of basal blood pressure. Hypertension previously reported after ablation of the AP may be explained by damage to the NTS.