Renal clearance of plasma allantoin in sheep

Abstract

SUMMARYThe recovery in urine of an intrajugular infusion of physiological amounts of allantoin was measured in four sheep nourished by an intragastric infusion of volatile fatty acids and casein (to eliminate rumen fermentation). The recovery was 72 % (S.E.M. 7) and the remainder was presumed to have been lost by diffusion into the gut and degradation by gut microflora. Measured in two sheep, allantoin was removed from the blood at a fractional rate of 0 30 h-1, and excreted in urine at 0 23 h-. Calculation based on creatinine excretion showed glomerular filtration rate and tubular reabsorption of allantoin to be unchanged by the intravenous infusion. Maximal tubular reabsorption at 1-28 mmol day-' was saturated by the load of endogenous allantoin alone. In a second experiment with seven normally fed sheep (28-50 kg live weight, all given I kg feed), urinary excretion and plasma concentration of allantoin were linearly related. However, the errors were such that plasma allantoin concentration would be of little value as a predictor of urinary excretion. There was a nearly twofold range in allantoin excretion (the larger animals excreting less), which implied that the supply of microbial biomass to the host animal per unit of feed ingested could be profoundly affected by feeding level.

Microbial protein production determined by urinary allantoin and renal urea sparing in normal and low protein fed Corriedale sheep

“…limited and appears to be saturated by a tubular load equivalent to endogenous allantoin production [5]. This means that, at a constant glomerular filtration rate, any addition of allantoin to the blood, once filtered at the glomeruli, will be eliminated in the urine.…”

Estimation of microbial protein supply in ruminant animals based on renal and mammary purine metabolite excretion. A review

“…Further studies have established a PD clearance rate constant of approximately 33%/h in sheep (Chen et al, 1991) and cattle . Short term infusions of exogenous purines in sheep have established that purine metabolites are excreted in urine within 2-3 h after their appearance in plasma (Chen et al, 1997).…”

“…Despite recent observations in cattle that proportionately 0.86 of exogenous purines were recovered as PDs excreted in the urine , the validity of recently proposed models remains largely uncertain. Mean urinary recoveries of intravenous allantoin infusions of proportionately between 0.72-0.78 in sheep (Chen et al, 1991;Surra et al, 1997a) and 0.70 in cattle , tends to raise concerns over the accuracy of the coefficients used to describe the relationship between purine absorption and urinary PD excretion. Furthermore, Kahn and Nolan (1993) noted that the feedback control of de novo purine synthesis has not been experimentally verified, and questioned why mammals Purine absorption, mmol/d Figure 4.…”

“…Examination of the relationship between plasma purine metabolite concentrations and urinary PD excretion has indicated considerable between-animal variation in the GFR of PDs ranging between 137-145 (Chen et al, 1991) and 140-233 1/d (Chen et al, 1997) for sheep nourished by intra-gastric infusion, and between 65-158 1/d (Chen et al, 1991;Surra et al, 1997a) for conventionally fed animals. Studies in steers have also indicated large variations in the GFR of allantoin (range 847-1155 1/d) that were independent of a functional rumen , tentatively suggesting that renal clearances are unaffected by the supply of PDs entering the bloodstream.…”

Urinary excretion of purine derivatives as influenced by GFR and plasma retention of purines in cattle (<i>Bos indicus</i> × <i>Bos taurus</i>) and buffalo (<i>Bubalus bubalis</i>) bulls

“…Microbial protein forms the major portion of protein available at the duodenal level in ruminants that is consequently metabolized and excreted as PD in urine and milk, or retained in plasma. The plasma PD concentration is monitored by glomerular filtration rate (GFR) (Chen et al, 1991), whereas urinary PD may be of endogenous or exogenous origin . There is evidence suggesting that the urinary PD excretion rates of small ruminants as well as of zebu cattle and water buffaloes differ from those of European cattle (Thanh and Ørskov, 2006;Mota et al, 2008).…”