Area postrema and cardiovascular regulation in rats.

The area postrema (AP) of the dog mediates pressor responses to angiotensin II and plays a role in the maintenance of normal arterial pressure. Ablation of the AP (APX) in the rat has been reported to have little or no effect on cardiovascular regulation. In the present study, computer data acquisition techniques were used to investigate this question. APX in the rat significantly lowered resting mean arterial pressure within 1 h (P less than 0.005) and lowered heart rate within 1 day (P less than 0.05) following the lesion. Increases in heart rate following atropine injections were significantly greater (P less than 0.05) in AP relative to sham lesion rats, suggesting higher vagal tone in the AP lesion rats. In addition, APX significantly enhanced the baroreflex control of heart rate in response to intravenous phenylephrine (P less than 0.05). Lability of pressure was not affected by the lesion. The hypotension and bradycardia produced by APX were still present 1 wk after APX. These AP lesions apparently did not produce significant damage to the function of the nearby NTS, since 1) histological analysis revealed minimal NTS damage, 2) arterial pressure lability was not increased, and 3) APX enhanced rather than impaired baroreflex control of heart rate. We conclude that the AP may have a role in the maintenance of resting arterial pressure and heart rate in the rat.