EXPRESSION OF MELANOCORTIN-5 RECEPTOR IN SECRETORY EPITHELIA SUPPORTSA FUNCTIONAL-ROLE IN EXOCRINE AND ENDOCRINE GLANDS

Melanocortins (alpha MSH and ACTH-related peptides) influence the phys iological functions of certain peripheral organs, including exocrine a nd endocrine glands. This study was designed to determine the identity and anatomical localization of the melanocortin receptors (MC-R) expr essed in these organs in the rat. MC5-R messenger RNA was found in exo crine glands, including lacrimal, Harderian, preputial, and prostate g lands and pancreas, as well as in adrenal gland, esophagus, and thymus , as demonstrated by ribonuclease protection assays. In exocrine gland s, MC5-R messenger RNA expression was restricted to secretory epitheli a. MC-R protein tit-as likewise present in secretory epithelia of exoc rine glands, as determined by I-125-labeled [Nle(4),D-Phe(7)]alpha MSH ([I-125]NDP-MSH) binding and autoradiography in tissue sections. Spec ific [I-125]NDP-MSH binding was also observed in adrenal cortex, thymu s, spleen, and esophageal and trachealis muscle. MC receptors in these sites are accessible to circulating MC-R agonists in vivo, as specifi c binding of [[I-125]NDP-MSH was observed in exocrine and adrenal glan ds after systemic injection in vivo. Taken together, these findings sh ow that the MC5 receptor is commonly and selectively expressed in exoc rine glands and other peripheral organs. Based on these findings and c ompelling evidence from other studies, a functional coherence is sugge sted between central and peripheral actions of melanocortins and melan ocortin receptors in physiological functions, including thermoregulati on, immunomodulation, and sexual behavior.