Effect of renal nerve activity on tubular sodium and water reabsorption in dog kidneys as determined by the lithium clearance method.

The reliability of the lithium clearance method in studies of the effect of renal nerve activity upon tubular sodium and water handling in the dog kidney was investigated. Following unilateral acute surgical denervation of the kidney a significant increase in urinary flow rate (40 +/- 7%), sodium clearance (26 +/- 4%), lithium clearance (9 +/- 2%) and fractional lithium clearance (8 +/- 2%) was seen, as compared to the contralateral kidney with preserved innervation. Calculated absolute proximal reabsorption rate decreased significantly by 7 +/- 2%, while calculated absolute rates of distal reabsorption of sodium and water increased significantly by 9 +/- 2% and 8 +/- 2%. Low-frequency electrical stimulation of the distal nerve bundle of the denervated kidney caused a significant decrease in urine flow rate (37 +/- 6%), sodium clearance (31 +/- 4%), lithium clearance (17 +/- 5%) and in fractional lithium clearance (18 +/- 5%). Calculated absolute proximal reabsorption rate increased significantly by 17 +/- 3%, while calculated absolute rates of distal sodium and water reabsorption decreased significantly by 16 +/- 5% and 16 +/- 5%. These changes in tubular sodium and water reabsorption during alterations in renal nerve activity occurred without measurable changes in renal blood flow (RBF) and glomerular filtration rate (GFR). Administration of amiloride had no significant effect either on the lithium clearance, RBF or GFR, while the sodium excretion rate increased and potassium excretion rate decreased, supporting that significant distal lithium reabsorption did not occur under the present experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)