Renal interstitial hydrostatic pressure and sodium excretion during acute volume expansion in diabetic rats

Experiments were performed to test the hypothesis that the renal interstitial hydrostatic pressure (RIHP) response to acute volume expansion is suppressed in diabetes mellitus. Sprague-Dawley rats received streptozotocin (STZ rats; 65 mg/kg ip) or vehicle (Sham rats). Two weeks later, RIHP and Na(+) excretion responses to acute graded volume expansion with isotonic saline were quantified under Inactin anesthesia (0.1 mg/kg ip). In Sham rats, acute graded volume expansion to 10% body wt produced increases in RIHP (Delta = 12.2 +/- 2.4 mmHg), urine flow (Delta = 54 +/- 8 microliter. min(-1). g(-1)), and Na(+) excretion (Delta = 11.5 +/- 1.9 mueq. min(-1). g(-1)). In STZ rats, these volume expansion-induced responses were significantly blunted (RIHP by 50%, urine flow by 81%, and Na(+) excretion by 76%). Renal decapsulation eliminated the differences between STZ and Sham rats with regard to volume expansion-induced increases in RIHP, urine flow, and Na(+) excretion. Renal denervation normalized the RIHP response to volume expansion and improved the diuretic and natriuretic responses in STZ rats. Moreover, diuretic and natriuretic responses to direct changes in RIHP (induced by renal interstitial volume expansion) were blunted in STZ rats. We conclude that diminished alterations in RIHP, as well as a reduced impact of RIHP on Na(+) excretion, contribute to the impaired diuretic and natriuretic responses to acute volume expansion during the early stage of diabetes.