[Clinical studies of kidney function in sheep. I. Methods and reference values of healthy animals]

Investigations of renal function have been done on the basis of renal clearance (Clr) and excretion (E) of endogenous creatinine in health sheep of different body weight (89 female, 19 male). Creatinine-E was negatively correlated with body weight in female sheep, it can be calculated from body weight. The Creatinine-Clr in ewes ranged from 1.1 to 2.3 ml/min/kg and was highly correlated with inulin-Clr (r = 0.88, p < 0.001). Fractional excretion (FE) of creatinine, determined by inulin-Clr was 118%. That demonstrate a tubular secretion of 15% of the total excretion. Therefore the creatinine-Clr may be considered representative enough for the glomerular filtration rate (GFR). Urea-FE was 24-50%, and urea-Clr about 50% of the inulin-Clr, that points to a high tubular urea absorption (50-75%). For that reason urea is not appropriate for the characterization of kidney functions. Water, sodium, glucose, L-lactate and 3-OH-hydroxybutyrate were absorbed in the renal tubules nearly completely (FE < 2%). So they are suitable as endogenous markers for insufficient tubular absorption. Calcium, phosphate, magnesium and potassium are reabsorbed incompletely, depending on the supply of these substances (FE 0-15%, potassium 5-100%). A method for clinical determination of kidney function by measurement of concentrations of metabolites and electrolytes in blood plasma and spontaneous urine is described and evaluated. The method is based on the calculation of the creatinine-excretion, depending on sex and body weight, and especially allows the examination of male and sick animals without quantitative sampling of urine.(ABSTRACT TRUNCATED AT 250 WORDS)