Urinary excretion of allantoin and allantoin precursors by sheep after different rates of purine infusion into the duodenum

Abstract

S U M M A R YTwo experiments were carried out to determine endogenous losses and the response of urinary purine derivatives to increased duodenal inputs of purine bases. Four ewes each fitted with a re-entrant cannula at the proximal duodenum, and conventionally fed, were subjected to full replacement of duodenal digesta followed by the administration of a solution either free of purines (Expt 1) or enriched with increasing amounts of purines, to supply 0-48-21-27 mmol/animal per day (Expt 2). Basal daily urinary excretions of allantoin, uric acid, hypoxanthine and xanthine were 11-5 + 0-94, 9-9 ±0-67, 6-9 ±0-46 and 1-2 ±016 mg/kg W 075 . Allantoin was the only purine derivative which increased in response to incremental inputs of duodenal purines. The relationship between allantoin excretion and infused purines showed a urinary recovery of 0-8 for purines infused at > 220 umol/kg W 076 . Lower rates of infusion did not alter allantoin excretion. The results show urinary allantoin to be a useful index to estimate duodenal input of purines when animals are fed close to or above their energy maintenance requirements.

Modelling purine derivative excretion in dairy goats: endogenous excretion and the relationship between duodenal input and urinary output

“…Endogenous contribution to urinary PD The isotopic ( 15 N) dilution of urinary PD in relation to duodenal PB confirmed an endogenous fraction in the urinary excretion (Table 4), which has been observed in non-isotopic studies of goats (Lindberg, 1989;Belenguer et al, 2002), other ruminants (Balcells et al, 1991;Orellana-Boero et al, 2001;Guerouali et al, 2004) and non-ruminant species (Martín Orú e et al, 1995;Balcells et al, 1998). Differences in estimates of the endogenous fraction may partly reflect the different experimental techniques adopted.…”

“…Initially proposed to be applied in sheep (Pé rez et al, 1998), the method based on the urinary dilution of labelled exogenous purines allows determination of the endogenous component of the urinary PD without having any adverse physiological effect on the animals. Using that method in sheep, the above authors obtained an endogenous excretion of 115.2 mmol/kg LW 0.75 , which was in the range (92 to 150 mmol/kg LW 0.75 ) reported by non-isotopic studies based on intragastric or digesta draining methods (Ørskov et al, 1979;Giesecke et al, 1984;Chen et al, 1990;Balcells et al, 1991). Furthermore, the technique has been used in lactating cows , showing that recycling of exogenous PB into the tissues by the salvage mechanism was negligible .…”

“…Lindberg (1991) estimated the endogenous fraction in milk-fed goat kids (242 mmol/kg LW 0.75 ), and Belenguer et al (2002) did so by using fasted goats (202.2 mmol/kg LW 0.75 ). However, those and other procedures, such as intragastric nutrition (Ørskov et al, 1979) or duodenal digesta draining (Balcells et al, 1991), are too aggressive to use with lactating animals. Initially proposed to be applied in sheep (Pé rez et al, 1998), the method based on the urinary dilution of labelled exogenous purines allows determination of the endogenous component of the urinary PD without having any adverse physiological effect on the animals.…”

“…That salvage pathway implies isotope enrichment of tissue PD, which might have affected our results, but it should be a time-dependent function. We felt that 48 h were needed to obtain a homogeneous distribution of the isotope in the rumen (Broderick and Merchen, 1992) and that an additional 24 h had to elapse before the 15 N enrichment in urinary PD reached a plateau following duodenal absorption Balcells et al, 1991). Therefore, 72 h should be sufficient to reach the isotope equilibrium without significant labelling of endogenous purines .…”

“…The excretion of purine derivatives (PD: allantoin, uric acid, xanthine and hypoxanthine) in urine reflects the duodenal flow of their precursors, purine bases (PB: adenine and guanine) Balcells et al, 1991). Furthermore, in ruminants, the PB in duodenal digesta are mostly of microbial origin (McAllan and Smith, 1973) and, thus, urinary PD excretion has been used to predict microbial mass flowing out of the rumen (Balcells et al, 1993;Pé rez et al, 1996).…”