THE AREA POSTREMA DOES NOT MODULATE THE LONG-TERM SALT SENSITIVITY OFARTERIAL-PRESSURE

The hindbrain circumventricular organ, the area postrema (AP), receive s multiple signals linked to body fluid homeostasis. In addition to ba roreceptor input, AP cells contain receptors for ANG II, vasopressin, and atrial natriuretic peptide. Hence, it has been proposed that the A P is critical in long-term adjustments in sympathetic outflow in respo nse to changes in dietary NaCl. The present study was designed to test the hypothesis that long-term control of arterial pressure over a ran ge of dietary NaCl requires an intact AP. Male Sprague-Dawley rats wer e randomly selected for lesion of the AP (APx) or sham lesion. Three m onths later, rats were instrumented with radiotelemetry transmitters f or continuous monitoring of mean arterial pressure (MAP) and heart rat e and were placed in individual metabolic cages. Rats were given 1 wk postoperative recovery. The dietary salt protocol consisted of a 7-day period of 1.0% NaCl (control), 14 days of 4.0% NaCl (high), 7 days of 1.0% NaCl, and finally 14 days of 0.1% NaCl (low). The results are re ported as the average arterial pressure observed on the last day of th e given dietary salt period: APx (n = 7) 114 +/- 2 (1.0%), 110 +/- 3 ( 4.0%), 110 1 3 (1.0%), and 114 +/- 4 (0.1%) mmHg; sham (n = 6) 115 +/- 2 (1.0%), 114 +/- 3 (4.0%), 111 +/- 3 (1.0%), and 113 +/-. 2 (0.1%) m mHg. Neither group of rats demonstrated significant changes in MAP thr oughout the entire dietary salt protocol. Furthermore, no significant differences in MAP were detected between groups throughout the protoco l. All lesions were histologically verified. These results suggest tha t the area postrema plays no role in long-term control of arterial pre ssure during chronic changes in dietary salt.