Urinary excretion of purine derivatives as an index of microbial-nitrogen intake in growing rabbits

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1998Author
Ganuza, J. M.
Pérez, J. F.
Martin-Orúe, S. M.
González Ronquillo, Manuel
Suggested citation
Balcells Terés, Joaquim;
Ganuza, J. M.;
Pérez, J. F.;
Martin-Orúe, S. M.;
González Ronquillo, Manuel;
.
(1998)
.
Urinary excretion of purine derivatives as an index of microbial-nitrogen intake in growing rabbits.
British Journal of Nutrition, 1998, vol. 79, p. 373-380.
https://doi.org/10.1079/BJN19980062.
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Three experiments were carried out to establish a response model between intake and urinary
excretion of purine compounds. In Expt 1 the relationship between the intake of purine bases
(PB) and the excretion of total purine derivatives (PD) was determined in seven growing rabbits
with a mean initial live weight (LW) of 2.03 (SE 0.185) kg, aged 70 d, each fitted with a wooden
neck collar to prevent caecotrophagy. They were fed on five experimental diets formulated with
different levels of nucleic acids (0.00, 3.75, 730, 11.25, 15.00 g yeast-RNA/kg diet). The
relationship between intake of purine (x, pmol/kg W"'75) and total urinary PD excretion b,
pmol/kg WO"'), y = 0.56 + 0.67~(r 20 .86; RSD 0.338), indicated that about 70 % of duodenal
PB were recovered as urinary PD and that the endogenous contribution was constant and
independent of dietary PB supply. Endogenous excretion of PD (allantoin and uric acid) was
measured in a second experiment using six rabbits fed on a purine-free diet and fitted with neck
collars to avoid caecotrophagy. Basal daily urinary excretion values for allantoin and uric acid
were 532 (SE 33.9) and 55 (SE 7.3) pmol/kg W0'7' respectively; xanthine and hypoxanthine
were not found in urine samples and therefore the sum of allantoin and uric acid should
comprise the total excretion of PD (588 (SE 40.1) pmol/kg W0'75). The xanthine oxidase (EC
1.2.3.2) activity in plasma, liver, duodenum, jejunum and kidney was measured in a third
experiment. The activities of xanthine oxidase in duodenal and jejunal mucosa, liver and kidney
were: 0.61 (SE 0.095), 0.37 (SE 0.045), 0.035 (SE 0.001) and 0 units/g fresh tissue respectively
and in plasma 2.96 (SE 0.094) units/l. The results show that urinary excretion of PD may be a
useful tool to estimate duodenal PB input and microbial protein intake once the relationship
between PB and N has been established in caecal micro-organisms.