Area postrema-induced inhibition of the exercise pressor reflex

The exercise pressor reflex is opposed by the arterial baroreflex, and circulating peptides may act in the area postrema to enhance this inhibition. Therefore, we tested the hypothesis that the area postrema exerts an inhibitory effect on this reflex. Consequently, in six alpha-chloralose-anesthetized cats, blood pressure and heart rate responses to 30 s of electrically stimulated hindlimb contraction were compared before and after thermal coagulation of the area postrema. In six other cats, the same contraction-induced cardiovascular responses were assessed before and after chemical lesion of the area postrema using kainic acid (214 +/- 9 nl, 2.5-5 mM). Thermal lesion of the area postrema augmented blood pressure and heart rate responses to contraction from 29 +/- 5 to 47 +/- 7 mmHg (P < 0.05) and from 8 +/- 2 to 14 +/- 2 beats/min (P < 0.05), respectively. Chemical lesion of the area postrema enhanced contraction-evoked blood pressure (30 +/- 7 vs. 47 +/- 6 mmHg, P < 0.05) and heart rate (12 +/- 4 vs. 17 +/- 4 beats/min, P < 0.05) responses. These data suggest that the area postrema attenuates the exercise pressor reflex, possibly through the actions of circulating peptides on baroreflex function.