[Intracerebroventricular administration of hypertonic saline inhibits the reabsorption of water and sodium in the proximal tubule]

Abstract

In anaesthetized rats with unilateral section of the renal nerve, the effect of intracerebroventricular (icv.) administration of hypertonic saline on the reabsorption of water and sodium in the proximal tubule was investigated, using the lithium clearance method. After icv. administration of hypertonic saline, the lithium clearance (CLi to glomerular filtration rate (GFR) ratio increased from 0.37 +/- 0.04 to 0.51 +/- 0.05 (P less than 0.01) in the denervated kidneys and from 0.26 +/- 0.03 to 0.31 +/- 0.04 (P less than 0.05) in the innervated kidneys, respectively. GFR, urine flow rate (V), urinary sodium excretion (UNaV) and urinary potassium excretion (UkV) increased in both innervated and denervated kidneys, the increments of V, UNaV and UkV being greater in the denervated kidneys than in the innervated kidneys. In micropuncture experiments, icv. administration of hypertonic saline caused an increase in proximal tubule flow rate, from 24.42 +/- 1.84 nl/min to 31.86 +/- 3.09 nl/min, without significant change in proximal tubule fluid osmolality in the innervated kidneys. These data support the notion that the diuresis and natriuresis induced by icv. administration of hypertonic saline in the anaesthetized rat result from an increase in GFR and a decrease in the reabsorption of water and sodium in the proximal tubule. Humoral factors are probably involved in these responses.