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Detection of Melanocortin‐3 Receptor mRNA in Immature Rat Pituitary: FUnctional Relation to γ3‐MSH‐Induced Changes in Intracellular Ca 2+ Concentration?
Author(s) -
Anne Lorsignol,
Veerle Vande Vijver,
Dirk Ramaekers,
Hugo Vankelecom,
Carl Denef
Publication year - 1999
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.1999.00305.x
Subject(s) - medicine , endocrinology , receptor , melanocortin receptor , biology , pituitary gland , receptor antagonist , melanocortin 3 receptor , melanocortin , chemistry , antagonist , hormone
We have previously shown that γ 3‐MSH stimulates DNA replication in lactotrophs, somatotrophs and thyrotrophs of early postnatal rat pituitary in culture. Since the melanocortin‐3 (MC‐3) receptor is the only known receptor displaying high affinity for γ 3‐MSH, the present study explored whether mRNA of the latter receptor is present in the pituitary and whether the receptor is functional. RT‐PCR of RNA extracts from 14‐day‐old rat pituitary revealed the presence of MC‐3 receptor mRNA in both the anterior and the neurointermediate lobe. The identity of the amplified products was confirmed by sequence analysis. Dispersed cells of 14‐day‐old female rats (24 h in culture) were exposed to γ 3‐MSH, and changes in intracellular free calcium levels ([Ca 2+ ] i ) were assessed by means of fluo‐3 video imaging. γ 3‐MSH evoked a rapid and maintained oscillating [Ca 2+ ] i increase in 5%, 10% and 15% of the cells at a dose of 0.1, 1 and 10 nM, respectively. The MC‐3/MC‐4 receptor antagonist Ac‐Nle4‐c[Asp5,(D‐Nal(2)7,Lys10] α ‐MSH‐(4‐10)‐NH2 (SHU 9119) blocked the effect of γ 3‐MSH in about 50% of the responsive cells. The present data suggest that the MC‐3 receptor is expressed in the rat pituitary but that this receptor mediates only half of the effects of its putative ligand, γ 3‐MSH, on [Ca 2+ ] i . Part of the effect of γ 3‐MSH may be mediated by a MC‐3 receptor in a functional state different from the one studied previously in transfected cell lines or by a hitherto unidentified MC receptor.