Kinetics of allantoin metabolism in sheep

Abstract

The kinetics of allantoin metabolism were studied in rumen-cannulated sheep by means of a single intravenous injection of [4,5-14C]allantoin. The decline in the specific radioactivity of allantoin in plasma following the injection of tracer was best described by a double exponential function, indicating that allantoin moves in and out of two or more kinetically distinct compartments. Sequestering of tracer in secondary or tertiary compartments in the body water appears likely to have resulted in overestimation of net flux of allantoin through the blood in the present study. In future studies, sampling of blood for several days after administration of tracer should alleviate this problem. About 80 % of the [14C]allantoin injected was recovered as [14C]allantoin in urine during the 12 h after tracer injection, increasing to 94 % after 4 d. Allantoin-C also passed through the blood bicarbonate pool, suggesting that allantoin is degraded in the gastrointestinal tract. A small amount of allantoin-C (4 % of the net flux of allantoin through the blood pool) was apparently degraded to form bicarbonate-C in the rumen and postruminally, and subsequently appeared in blood bicarbonate-C. Transfer of allantoin-C into the rumen via saliva was insignificant. In view of these findings, the net flux of allantoin through the blood should be a better predictor of rumen microbial outflow than urinary allantoin excretion, because urinary excretion of purine derivatives must be adjusted for conversion of allantoin-C to blood bicarbonate when used to predict the flow of microbial protein from the rumen.

Urinary purine derivates excretion as an indicator of in vivo microbial N flow in cattle: A review

“…In further work, Surra et al (1997) estimated that the salivary secretion was only 0.003 of urinary PD excretion. In agreement, only 0.015 (Prasitkusol et al, 2002), and less than 0.01 (Kahn and Nolan, 2000) of intravenously administered 14 C-allantoin entered the rumen via saliva. Therefore, the recycling of PD through saliva does not explain the incomplete recovery of PD in urine.…”

“…With 14 C-allantoin intravenously infused in sheep, these proportions may depend on glomerular filtration rate, but were found to be unpredictable between and within animals (Prasitkusol et al, 2002). Moreover, Prasitkusol et al (2002) found a large between-animal variation in the recovery of 14 C-allantoin ranging from 0.66 to 0.95 with 8 animals, whereas Kahn and Nolan (2000) reported a similar recovery of 0.94 with two animals. In the experiments in Table 2, the relationships are determined with only 2 to 5 animals.…”

“…Allantoin and uric acid can not be utilised by tissue, and are excreted mainly in urine, but also secreted in saliva and milk. The renal clearance rate of PD is high, and N80% of intravenously administered 14 C-allantoin appeared in urine within 12 h (Kahn and Nolan, 2000). Plasma PD concentration and urinary excretion responded rapidly to a change in duodenal infused purine nucleosides with a lag time of 2-3 h (Chen et al, 1997).…”

“…Therefore, the recycling of PD through saliva does not explain the incomplete recovery of PD in urine. Kahn and Nolan (2000) further estimated that in total 0.04 of the intravenously administered 14 C-allantoin was degraded to bicarbonate in the gastro-intestinal tract, mostly postrumen. In conclusion, only a small amount of PD is recycled to and extensively degraded in the gut, and therefore only has a small effect on urinary PD excretion to predict microbial protein synthesis.…”

Antihypertensive Action of Allantoin in Animals

“…[17] 30 minutes before injection of allantoin; and (IV) the allantoin treated SHRs group ( n = 8) treated by intravenous injection of allantoin at various dose for desired time. Because allantoin has been documented to be easily degraded in intestinal tract [19] for resulting in a marked loss of activity after oral administration [20, 21], we administered it using intravenous injection in the present study.…”