Several reports have been published on blood leptin concentrations in feral
animals, including members of the Carnivora, using a commercially available multi-species
radioimmunoassay (RIA) kit with anti-human leptin antibody. However, we observed weak
immunoreactivity between recombinant canine leptin and anti-human leptin antibody, suggesting
a limitation in the applicability of the RIA kit for leptin assays in Carnivora species. We tested the
applicability of RIA and sandwich enzyme-linked immunosorbent assay (ELISA) with anti-canine
leptin antibody to assay blood leptin in the dog (Canis familiaris) and the raccoon (Procyon lotor).
When RIA was used for recombinant canine leptin and dog sera, values were much lower than those
determined by ELISA at higher concentrations (410 ng/ml), while rather higher at lower
concentrations (o2 ng/ml). A similar discrepancy between the two methods was found for serum
leptin concentrations in raccoons. Clear seasonal variations were observed by ELISA, but not by
RIA, with high values in autumn (3.4670.45 ng/ml) and low values in spring and summer
(0.7170.07 ng/ml). Serum leptin concentrations in raccoons correlated positively with their body
weight (r50.753) and body mass index (r50.755), corroborating our previous findings of a strong
positive correlation between serum leptin concentrations and body fat content in dogs. Thus, the
canine leptin ELISA is useful for assays of dog and raccoon leptin, and blood leptin is a good marker
of nutritional condition in the species of Carnivora assayed in this study. J. Exp. Zool.
303A:527– 533, 2005. r 2005 Wiley-Liss, Inc.
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