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Departments of Clinical Biochemistry and Medicine, Cambridge Institute for Medical Research, Addenbrookes Hospital, Cambridge CB2 2XY, UK
1 Division of Endocrinology, Department of Internal Medicine I, University Hospital Würzburg 97080, Germany
2 Division of Endocrinology and Diabetes, Department of Internal Medicine II, Klinikum der Albert-Ludwigs-Universität Freiburg, Hugstetter Str. 55, D-79106 Freiburg, Germany
3 Department of Microbiology and Immunology, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva 84105, Israel
(Requests for offprints should be addressed to F Beuschlein; Email: beuschlein{at}medizin.ukl.uni-freiburg.de)
Pro-opiomelanocortin (POMC) is a polypeptide precursor that undergoes extensive processing to yield a range of peptides with biologically diverse functions. POMC-derived ACTH is vital for normal adrenal function and the melanocortin
-MSH plays a key role in appetite control and energy homeostasis. However, the roles of peptide fragments derived from the highly conserved N-terminal region of POMC are less well characterized. We have used mice with a null mutation in the Pomc gene (Pomc/) to determine the in vivo effects of synthetic N-terminal 128 POMC, which has been shown previously to possess adrenal mitogenic activity. 128 POMC (20 µg) given s.c. for 10 days had no effect on the adrenal cortex of Pomc/ mice, with resultant cortical morphology and plasma corticosterone levels being indistinguishable from sham treatment. Concurrent administration of 128 POMC and 124 ACTH (30 µg/day) resulted in changes identical to 124 ACTH treatment alone, which consisted of upregulation of steroidogenic enzymes, elevation of corticosterone levels, hypertrophy of the zona fasciculate, and regression of the X-zone. However, treatment of corticosterone-depleted Pomc/ mice with 128 POMC reduced cumulative food intake and total body weight. These anorexigenic effects were ameliorated when the peptide was administered to Pomc/ mice with circulating corticosterone restored either to a low physiological level by corticosterone-supplemented drinking water (CORT) or to a supraphysiological level by concurrent 124 ACTH administration. Further, i.c.v. administration of 128 POMC to CORT-treated Pomc/ mice had no effect on food intake or body weight. In wild-type mice, the effects of 128 POMC upon food intake and body weight were identical to sham treatment, but 128 POMC was able to ameliorate the hyperphagia induced by concurrent 124 ACTH treatment. In a mouse model which lacks all endogenous POMC peptides, s.c. treatment with synthetic 128 POMC alone can reduce food intake and body weight, but has no impact upon adrenal growth or steroidogenesis.
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