The conjugation of arylacetic acids in the pigeon compared with the hen.

In the domestic hen phenylacetic acid is excreted conjugated mainly with ornithine (Totani, 1910), but in the pigeon it is excreted conjugated with taurine and glycine (James et al., 1972). This difference between the hen and pigeon has now been further investigated with several arylacetic acids. The compounds used were 14C-carboxy-labelled phenylacetic acid, 4-chloroand 4-nitrophenylacetic acid, 1 -napthylacetic acid and diphenylacetic acid. They were administered as sodium salts in water by intraperitoneal injection into pigeons and hens. Each bird was kept separately in a cage mounted on a tray with a polythene lining on which a thin layer of sand (acid-purified sand, 30-90 mesh, 80g; Fisons Scientific Apparatus, Loughborough, Leics., U.K.) had been spread for the collection of excreta. The latter were absorbed into the sand, which could be scraped off the polythene lining completely. The sand containing theexcreta was suspended in water (100-150ml) and the suspension homogenized and then centrifuged. The sand residue contained only about 1 % of the 14C present in the original homogenate. The supernatant was subjected to paper and thin-layer chromatography and the chromatograms were scanned for I4C. The peaks containing 14C were identified by comparing RF values with those of authentic reference compounds and by appropriate colour reactions (see Idle et al., 1976). The results of these experiments are summarized in Table 1 which shows that the pattern of conjugation of arylacetic acids in the pigeon is quite different from that in the hen. For the first five compounds in Table 1 taurine conjugation is a major metabolic process in the pigeon, being as high as 70% of the 14C excreted in the case of l-napthylacetic acid. Glycine conjugation is also a significant mechanism in the pigeon, except for indolylacetic acid and diphenylacetic acid, which is discussed below. Ornithine conjugation does not occur in the pigeon with any of the six acids listed in Table l. In the hen taurine conjugation does occur, but to a lesser extent than in the pigeon. For 1-naphthylacetic acid, the taurine conjugate, which amounts to 23 % of the 14C excreted, is actually the major conjugate in the hen, but the hen excretes this acid mainly unchanged (64 % of the 14C excreted), whereas the pigeon excretes it almost entirelyconjugated. In contrast with the pigeon, glycine conjugation of the first four compounds is virtually absent from the hen, but ornithine conjugation, which does not occur in the pigeon, is a major process in the hen for phenyl-, khlorophenyland 4-nitrophenylacetic acid.