REAPPRAISAL OF THE ROLE OF INSULIN ON SODIUM HANDLING BY THE KIDNEY - EFFECT OF INTRARENAL INSULIN INFUSION IN THE DOG

Since several studies suggest that increased insulin levels may induce antinatriuresis, the present work was undertaken to determine whether a physiological increase in insulin levels in blood perfusing the kidney may exert direct effect on kidney function, and more specifically on sodium reabsorption. To this end, insulin was infused directly into one renal artery of 10 anaesthetized dogs at the rate of 4 mU min-1 for a period of 90 min. The contralateral kidney was infused with saline alone, to provide reference values. Insulin level in the renal vein of the insulin-infused kidney went up from 1.4 +/- 0.9 before to 30.6 +/- 7.1-mu-U ml-1 after 90 min of insulin perfusion. There was no significant effect on renal plasma flow, glomerular filtration rate and renal uptake of substrates or oxygen between ipsi- and contralateral kidney. The fractional excretion of sodium was likewise unaffected, since it averaged at the end of insulin infusion 0.41 +/- 0.11% vs. 0.50 +/- 0.14% for the contralateral saline infused kidney. Even if one may assume that the baseline low insulin concentrations promote tubular sodium reabsorption, the results of the present study suggest that a moderate hyperinsulinaemia is without any additional effect on renal sodium handling.