Neural regulation of kidney function by the somatosensory system in normotensive and hypertensive rats

This investigation examined the renal sympathetic nerve and renal excretory responses to somatosensory stimulation in normotensive and stroke-prone spontaneously hypertensive rats (SHRSP). Somatosensory activation was achieved by either subcutaneous capsaicin administration or exposure of the airways tract to irritant fumes from acetic acid in chloralose-urethan-anesthetized animals. In Wistar rats, blood pressure increased between 10 and 20% (P < 0.001-0.01), renal perfusion pressure was maintained unchanged, renal hemodynamics were unaltered, and urine flow and sodium excretion were decreased by 25 to 50% (P < 0.001-0.05). In the SHRSP, the somatosensory-induced increases in blood pressure were slightly larger (approximately 15-20% P < 0.05) than those of the Wistar rats, whereas the excretory responses were one-half those of the normotensive animals (P < 0.05). The somatosensory challenges reflexly increased integrated renal sympathetic nerve activity in both normotensive and hypertensive rats. The power spectral analysis demonstrated that the increases in percentage power at heart rate frequency and total power were two to three times more (P < 0.05) in the Wistar rats compared with the SHRSP. The reduced ability of the SHRSP to modulate the energy in the renal sympathetic nerve signal at heart rate frequency might explain in part the attenuated functional responses to the somatosensory challenges.