Regulation of renal hemodynamics after protein feeding: effects of loop diuretics.

These studies were designed to test the hypothesis that the renal vasodilation and increased glomerular filtration rate (GFR) after a high-protein meal are mediated by the tubuloglomerular feedback (TGF) mechanism. In eight chronically instrumented conscious dogs, a meal of raw beef (10 g/kg) caused GFR to increase from 66 +/- 5 to 90 +/- 7 ml/min and effective renal plasma flow (ERPF) to increase from 191 +/- 25 to 281 +/- 24 ml/min, while plasma alpha-amino N levels rose from 4.0 +/- 0.1 to 7.3 +/- 0.6 mg/dl. On another day the dogs were given an infusion of furosemide to block TGF, and fluid and salt losses were continuously replaced. Furosemide alone caused GFR to increase in most animals, although the average change did not reach statistical significance, and ERPF increased by 31%. Sodium excretion rose from 15 +/- 5 to 2,390 +/- 280 mueq/min, and urine flow rose from 1.17 +/- 0.22 to 20.5 +/- 2.4 ml/min. Autoregulatory capability was also abolished (autoregulatory index = 0.87 +/- 0.09 compared with 0.19 +/- 0.05 before furosemide). However, there was no significant change in GFR and ERPF after a subsequent meat meal in dogs receiving furosemide. On another day, some of the dogs were given another loop diuretic, ethacrynic acid, which caused no change in GFR, whereas its effects on ERPF, sodium excretion, and urine output were similar to those of furosemide. There were also no changes in GFR or ERPF after a meat meal during ethacrynic acid administration, despite normal increases in plasma alpha-amino N.(ABSTRACT TRUNCATED AT 250 WORDS)