We investigated the role played by the exercise pressor reflex in sympathetic regulation of the renal circulation in rats. In mid-collicular decerebrate rats, mean arterial pressure (MAP), heart rate (HR), left renal cortical blood flow (RCBF) and left renal sympathetic nerve activity (RSNA) were recorded before and during 30 s of static contraction of the left triceps surae muscles evoked by electrical stimulation of the tibial nerve, which activates both metabo- and mechanosensitive muscle afferents, and during 30 s of passive stretch of the left Achilles tendon, which selectively activates mechanosensitive muscle afferents. Static contraction (n= 17, +344 ± 34 g developed tension) significantly (P < 0.05) increased MAP (+14 ± 3 mmHg), HR (+6 ± 1 beats min-1) and RSNA (n= 11, +19 ± 5%) and significantly decreased renal cortical vascular conductance (RCVC, n= 11, -11 ± 2%). Passive stretch (n= 20, +378 ± 11 g) also significantly increased MAP (+11 ± 2 mmHg), HR (+7 ± 2 beats min-1) and RSNA (n= 15, +14 ± 4%) and significantly decreased RCVC (n= 11, -12 ± 3%). RCBF showed no significant changes during static contraction or passive stretch. Renal denervation abolished the decrease in RCVC during contraction (n= 12) or stretch (n= 13). These data indicate that both the exercise pressor reflex and its mechanically sensitive component, the muscle mechanoreflex, induced renal cortical vasoconstriction through sympathetic activation in rats.
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