Renojejunal reflex controlling jejunal absorption of fluid and NaCl

The aim of this study was to elucidate renojejunal reflex controlling the net jejunal fluid, Na+, and Cl- absorption in response to an increased ureteropelvic pressure (UPP) in anesthetized dogs. Unilateral UPP was increased under hydrostatic pressure from 0 to 80 mmHg by a step of 20 mmHg in random order, while the contralateral UPP was maintained at around 0 mmHg. The net absorption of fluid, Na+, and Cl- decreased in proportion to increased UPP. At a UPP of 0 mmHg, the net jejunal fluid, Na+, and Cl- absorption were 11.1 +/- 0.4 ml, 2.48 +/- 0.07, and 1.98 +/- 0.05 mEq, and significantly decreased to 7.38 +/- 0.6 ml, 2.11 +/- 0.15, and 1.68 +/- 0.13 mEq by an increase of UPP to 40 mmHg, respectively. An increase of bilateral UPP up to 40 mmHg or more occlusively depressed the absorption. These responses were blocked by renal denervation and by administration of atropine but not by yohimbine. These results indicate that the increase of UPP decreases jejunal fluid, Na+, and Cl- absorption (renojejunal reflex), and that the afferent and efferent limbs of this reflex are the renal nerves and cholinergic fibers. This renojejunal reflex might play an important role in body fluid homeostasis under the pathological condition.