To determine whether the area postrema contributes to the development of hypertension in spontaneously hypertensive rats (SHR), sham or electrolytic lesions of the area postrema (AP) were made in 4-week-old SHR and Wistar-Kyoto (WKY) controls. From weeks 5 through 16, systolic pressure was measured via tail plethysmography. While blood pressure rose markedly in sham-operated SHR, increases in pressure were small in AP-ablated SHR and similar to those seen in all WKY. Subsequent direct measurements of mean arterial pressure in the same rats showed a significant correlation (r = 0.87, p less than 0.01) with the pressure data acquired via weekly tail-cuff measurement, thereby confirming that hypertension in AP-ablated SHR had indeed been attenuated. Analysis of several hundred computer-acquired measurements of mean arterial pressure from each rat showed that AP ablation shifted the distribution of mean arterial pressure to a lower range in SHR but not WKY. Ablation of the AP also decreased resting heart rate in SHR but not WKY. Suppression of heart rate in response to intravenous phenylephrine was equivalent in sham-operated and AP-ablated rats, suggesting that baroreflex-mediated slowing of heart rate was not impaired. In response to intravenous angiotensin II, suppression of heart rate was similar in sham and AP-ablated SHR, and actually was enhanced in AP-ablated WKY. Histological evaluation of the lesions indicated that visible damage to the adjacent nuclei of the solitary tracts was confined to a small portion of the commissural nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)