Urinary excretion of purine derivatives inBos indicus×Bos tauruscrossbred cattle

Abstract

Four experiments were performed to study the kinetics of purine metabolism and urinary excretion in Zebu crossbred cattle. Fasting excretion was established in Expt 1, using eighteen maleBos indicus×Bos tauruscrossbred cattle (261 (se 9·1) kg body weight), six of each of the following genotypes: 5/8Bos indicus, 1/2Bos indicusand 3/8Bos indicus. No significant differences were observed among genotypes in fasting purine derivative excretion (277·3 (se 35·43) μmol/metabolic body weight). In a second experiment we measured the xanthine oxidase activity, which was higher in liver than in duodenal mucosa (0·64 and 0·06 (se 0·12) units/g wet tissue per min respectively;P>0·05) being in plasma 0·60 (se 0·36) units/l per min. The kinetics of uric acid were measured by intravenous pulse dose of [1,3-¹⁵N]uric acid (Expt 3). The cumulative recovery of the isotope in urine was 82 (se 6·69) %, and uric acid plasma removal, pool size and mean retention time were 0·284 (se 0·051) per h, 5·45 (se 0·823) mmol and 3·52 (se 0·521) h, respectively. Allantoin was removed from plasma at an estimated fractional rate of 0·273 (se 0·081) per h and mean retention was 3·66 (se 1·08) h. In Expt 4, the relationship between urinary purine derivative excretion (Y; mmol/d) and digestible organic matter intake (X, kg/d) was defined by the equation:Y=7·69 (se 4·2)+5·69 (se 1·68)X;n16, Se 1·31,r0·67.