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Agouti-Related Protein Antagonizes Glucocorticoid Production Induced through Melanocortin 4 Receptor Activation in Bovine Adrenal Cells: A Possible Autocrine Control

Institut National de la Santé et de la Recherche Médicale Unité 418-Institut National de la Recherche Agronomique Unité Mixte de Recherche 1245 and Institut Fédératif de Recherche 62 Laënnec (M.D., A.B., M.-C.B., P.Du., D.N., M.B.), Hôpital Debrousse and Claude Bernard University, Lyon 69322 Cedex 05, France; and Institut Recherches Internationales Servier (P.De.), Courbevoie 92415 Cedex, France

Address all correspondence and requests for reprints to: Martine Bégeot, Institut National de la Santé et de la Recherche Médicale Unité 418-Institut National de la Recherche Agronomique Unité Mixte de Recherche 1245, Hôpital Debrousse, 29 rue Soeur Bouvier, 69322, Lyon Cedex 05, France. E-mail: begeot{at}lyon.inserm.fr.

Agouti-related protein (Agrp), primarily expressed in the hypothalamus, is an endogenous antagonist of MSH at the level of melanocortin 3 receptor (MC3-R) and MC4-R, but the adrenal gland represents the second major Agrp-expressing tissue. In adrenal fasciculata cells, the glucocorticoid secretion is under the control of ACTH, which binds specifically MC2-R, the only functional melanocortin receptor described in these cells to date. Nevertheless, using cultured bovine fasciculata adrenal cells, we report that Agrp has no antagonistic properties against ACTH at the level of MC2-R. In our studies, (Nle4, D-Phe7)-MSH (NDP-MSH) stimulated the production of cortisol in a dose-dependent manner, and these effects were abolished by Agrp or SHU9119, a synthetic antagonist of MC3-R and MC4-R. Using a more specific antagonist (JKC-363) and RT-PCR analysis, we can postulate that the effects of NDP-MSH were mediated via MC4-R. These results are suggestive that adrenal glucocorticoid production could be regulated through MC4-R that may have some relevance in the physiology of adrenal cells. Moreover, Agrp might exert an autocrine control on adrenal cells because a protein with biological Agrp-like activity is secreted by these cells. This peptide could then modulate locally the functions of some peripheral tissues such as adrenals.

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