The Effects Of Human Leptin On Food Intake In The African Clawed Frog Xenopus Laevis

Leptin is a polypeptide secreted by adipose and other tissues that has a dramatic inhibitory effect on appetite in mammals.  Recently, the structure of non-mammalian leptin peptides has been elucidated.  Despite having very little similarity based upon primary amino acid sequences, vertebrate leptins are surprisingly conserved based upon tertiary structure.  There is some evidence to suggest that human leptin may act on leptin receptors in other vertebrate species, but the data are based upon in-vitro heterologous expression assays.  In the present study we examined the ability of human recombinant leptin (hrLeptin) to modulate food intake in a model amphibian species, the South African clawed frog Xenopus laevis.  We hypothesized that hrLeptin will be effective in suppressing food intake in an amphibian species.  In our initial experiments juvenile frogs were injected via the dorsal lymph sac with one of five doses (0, 0.02, 0.2, 2, 20 ug) of leptin and food intake was assessed. hrLeptin had no effect on food intake in X. laevis after peripheral administration in two independent trials. Based upon qualitative reverse transcriptase PCR we detected mRNA for the leptin receptor in telencephalon and optic tectum of X. laevis. We are currently testing the effects of hrLeptin on food intake after intracerebroventricular administration in X. laevis.