Renal urea handling in goats fed high and low protein diets

Four female goats first were fed a high protein diet and later a low protein diet. Renal urea handling was studied during feeding of both diets. Glomerular filtration rate was measured with [hydroxymethyl-carbon-14] inulin. Glomerular filtration rate dropped about 60% when nitrogen intake was restricted. Urea concentration of plasma fell from 6 mM on high protein diet to .6mM on low protein diet. On low protein diet the rate of urea filtration at the glomeruli was only 4% of that on high protein diet, 22 versus 519 mumol/min. In addition, tubular urea reabsorption in percentage of filtered urea rose up to 92% on low protein diet. As a result of all these renal changes following dietary nitrogen restriction, urinary urea excretion was only .6% of urinary urea excretion on high protein diet. In goats as in other ruminants, renal mechanisms effectively contribute to urea conservation during protein deprivation.