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The pressor response to activation of mechanically and metabolically sensitive skeletal muscle afferent fibers is exaggerated in hypertension

Recent evidence suggests the exercise pressor reflex (EPR, a circulatory reflex originating from skeletal muscle) contributes significantly to the exaggerated blood pressure (BP) response to exercise in hypertension. However, the mechanism of this EPR overactivity is not clear. Activation of mechanically and metabolically sensitive afferent neurons in muscle contributes importantly to EPR activity. Therefore, we hypothesized the enhanced BP response to exercise mediated by the EPR in hypertension is due to functional alterations in the mechanically and metabolically sensitive components of the reflex. To test this hypothesis, mechanically and metabolically sensitive afferent fibers were selectively activated in normotensive male Wistar Kyoto (WKY; n=18) and spontaneously hypertensive (SHR; n=21) rats. Preferential activation of mechanically sensitive afferent fibers by passively stretching hindlimb skeletal muscle induced significantly larger increases in BP in SHR than WKY over a wide range of stimulus intensities. Likewise, preferential activation of metabolically sensitive afferent neurons by injecting capsaicin (0.01 to 1.00 μg / 100 μL) into the arterial supply of the hindlimb evoked significantly greater elevations in BP in SHR than WKY. In conclusion, these findings suggest that the EPR dysfunction manifest in hypertension is mediated by the overactivity of both the mechanically and metabolically sensitive components of the reflex.