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Faculties of Life Sciences and
¹ Medicine, Stopford Building, University of Manchester, Manchester M13 9PT, UK

(Requests for offprints should be addressed to A S I Loudon, Faculty of Life Sciences, 3.614 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK; Email: Andrew.Loudon{at}manchester.ac.uk)

(F R A Cagampang is now at Centre for Developmental Origins of Health and Disease, University of Southampton, Princess Anne Hospital (F-887), Coxford Road, Southampton SO16 5YA, UK)

Recent studies have suggested that the adipocyte-derived hormone, leptin, plays a role in the regulation of metabolism. Here, we tested this hypothesis in the seasonally breeding Siberian hamster, as this species exhibits profound seasonal changes in adiposity and circulating leptin concentrations driven by the annual photoperiodic cycle. Male hamsters were kept in either long (LD) or short (SD) photoperiods. Following exposure to short photoperiods for 8 weeks animals exhibited a significant weight-loss and a 16-fold reduction of serum leptin concentrations. At Week 9, animals in both photoperiods were infused with leptin or PBS via osmotic mini-pump for 14 days. Chronic leptin infusion mimicked LD-like concentrations in SD-housed animals and caused a further decline in body weight and adipose tissue. In LD-housed animals, leptin infusion resulted in a significant elevation of serum concentrations above natural LD-like levels, but had no discernable effect on body weight or overall adiposity. Both bending and compression characteristics and histomorphometric measurements of trabecular bone mass were unaltered by leptin treatment or photoperiod. Our data therefore show that despite a high natural amplitude cycle of leptin, this hormone has no apparent role in the regulation of bone metabolism, and therefore do not support recent propositions that this hormone is an important component in the metabolism of bone tissue.