High dietary phosphate intake induces hypertension and augments exercise pressor reflex function in rats

5 An increasing number of studies have linked high dietary phosphate (Pi) intake to hypertension. It is well established that the rise in sympathetic nerve activity (SNA) and blood pressure (BP) during physical exertion is exaggerated in many forms of hypertension, which are primarily mediated by an overactive skeletal muscle exercise pressor reflex (EPR). However, it remains unknown whether high dietary Pi intake potentiates the EPR-mediated SNA and BP response to exercise. Accordingly, we measured renal SNA (RSNA) and mean BP (MBP) in normotensive Sprague-Dawley rats fed a normal Pi diet (0.6%, n = 13) or high Pi diet (1.2%, n = 13) for 3 mo. As previously reported, we found that resting BP was significantly increased by 1.2% Pi diet in both conscious and anesthetized animals. Activation of the EPR by electrically induced hindlimb contraction triggered greater increases in Delta RSNA and Delta MBP in the 1.2% compared with 0.6% Pi group (126 +/- 25 vs. 42 +/- 9%; 44 +/- 5 vs. 14 +/- 2 mmHg, respectively, P < 0.01). Activation of the muscle mechan-oreflex, a component of the EPR, by passively stretching hindlimb muscle also evoked greater increases in Delta RSNA and Delta MBP in the 1.2% compared with 0.6% Pi group (109 +/- 27 vs. 24 +/- 7%, 38 +/- 7 vs. 8 +/- 2 mmHg, respectively, P < 0.01). A similar response was produced by hindlimb intra-arterial capsaicin administration to stimulate the metaboreflex arm of the EPR. Thus, our data demonstrate a novel action of dietary Pi loading in augmenting EPR function through overactivation of both the muscle mechanoreflex and metaboreflex.