Kopp UC, Cicha MZ, Smith LA, Mulder J, Hö kfelt T. Renal sympathetic nerve activity modulates afferent renal nerve activity by PGE 2-dependent activation of ␣1-and ␣2-adrenoceptors on renal sensory nerve fibers. Am J Physiol Regul Integr Comp Physiol 293: R1561-R1572, 2007. First published August 15, 2007; doi:10.1152/ajpregu.00485.2007.-Increasing efferent renal sympathetic nerve activity (ERSNA) increases afferent renal nerve activity (ARNA). To test whether the ERSNA-induced increases in ARNA involved norepinephrine activating ␣-adrenoceptors on the renal sensory nerves, we examined the effects of renal pelvic administration of the ␣ 1-and ␣2-adrenoceptor antagonists prazosin and rauwolscine on the ARNA responses to reflex increases in ERSNA (placing the rat's tail in 49°C water) and renal pelvic perfusion with norepinephrine in anesthetized rats. Hot tail increased ERSNA and ARNA, 6,930 Ϯ 900 and 4,870 Ϯ 670% ⅐ s (area under the curve ARNA vs. time). Renal pelvic perfusion with norepinephrine increased ARNA 1,870 Ϯ 210% ⅐ s. Immunohistochemical studies showed that the sympathetic and sensory nerves were closely related in the pelvic wall. Renal pelvic perfusion with prazosin blocked and rauwolscine enhanced the ARNA responses to reflex increases in ERSNA and norepinephrine. Studies in a denervated renal pelvic wall preparation showed that norepinephrine increased substance P release, from 8 Ϯ 1 to 16 Ϯ 1 pg/min, and PGE 2 release, from 77 Ϯ 11 to 161 Ϯ 23 pg/min, suggesting a role for PGE 2 in the norepinephrineinduced activation of renal sensory nerves. Prazosin and indomethacin reduced and rauwolscine enhanced the norepinephrine-induced increases in substance P and PGE 2. PGE2 enhanced the norepinephrine-induced activation of renal sensory nerves by stimulation of EP4 receptors. Interaction between ERSNA and ARNA is modulated by norepinephrine, which increases and decreases the activation of the renal sensory nerves by stimulating ␣ 1-and ␣2-adrenoceptors, respectively, on the renal pelvic sensory nerve fibers. Norepinephrine-induced activation of the sensory nerves is dependent on renal pelvic synthesis/release of PGE 2. substance P; EP4 receptor; pelvis; prazosin; rauwolscine THERE IS CONSIDERABLE EVIDENCE for increased sympathetic nerve activation to further stimulate sensory nerve fibers following tissue injury (15). Studies on efferent renal sympathetic nerve activity (ERSNA) and afferent renal nerve activity (ARNA) suggest that such an interaction is not restricted to conditions of tissue injury but is an important mechanism regulating ERSNA during physiological conditions (30). The kidney has a rich supply of sympathetic nerves, which innervate all parts of the vasculature and the nephron (2). In contrast, the majority of the sensory nerve fibers are localized to the renal pelvic wall (25,26,32). There is anatomical support for an interaction between ERSNA and ARNA, as shown by the close relationship between unmyelinated sympathetic nerve fibers and myelinated afferent nerve fibers in renal tissue...
