Renal haemodynamic and hormonal responses to a mixed high-protein meal in normal men

Studies in normal man have demonstrated an acute increase in glomerular filtration rate (GFR) and renal blood flow (RBF) after a mixed protein meal, but the hormonal mechanisms underlying this response are not well defined. Thirteen adult men were starved for 24 h, then fed a test meal containing 1.5 g/kg bodyweight of animal protein. Renal haemodynamics and plasma and urinary hormones were measured before and at 2 h and 4 h after the meal. GFR and RBF increased by 27% and 23% respectively at 2 h. Electrolyte excretion did not parallel and was independent of the haemodynamic changes. Plasma noradrenaline (median 350 versus 573 pg/ml), renin (0.64 versus 1.09 nmol AngI/l per h), and urinary prostaglandin E (PGE) (66.4 versus 238 pmol/min) were all significantly elevated at 2 h. In further experiments, nine of the subjects were given indomethacin 50 mg before and after the meal using the same protocol as before. In comparison with control data, GFR and RBF after indomethacin did not increase after the meal and plasma noradrenaline and renin and urinary PGE remained at baseline values. Electrolyte excretion was not affected. These results suggest that the renal response to protein feeding is partly mediated by intrarenal prostaglandins but is also part of a more complex interaction with the sympathetic nervous system.