Detection of melanocortin-3 receptor mRNA in immature rat pituitary: functional relation to gamma3-MSH-induced changes in intracellular Ca2+ concentration?

We have previously shown that gamma3-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 gamma3-MSH, the present study explored whethe...

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Bibliographic Details
Published in:Journal of neuroendocrinology 1999-03, Vol.11 (3), p.171-179
Main Authors: Lorsignol, A, Vande Vijver, V, Ramaekers, D, Vankelecom, H, Denef, C
Format: Article
Language:English
Subjects:
Animals
Base Sequence
Calcium - metabolism
DNA Primers
Female
Melanocyte-Stimulating Hormones - metabolism
Melanocyte-Stimulating Hormones - pharmacology
Pituitary Gland - metabolism
Rats
Rats, Wistar
Receptor, Melanocortin, Type 3
Receptors, Corticotropin - antagonists & inhibitors
Receptors, Corticotropin - genetics
Reverse Transcriptase Polymerase Chain Reaction
RNA, Messenger - genetics
RNA, Messenger - metabolism
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Summary:We have previously shown that gamma3-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 gamma3-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 gamma3-MSH, and changes in intracellular free calcium levels ([Ca2+]i) were assessed by means of fluo-3 video imaging. Gamma3-MSH evoked a rapid and maintained oscillating [Ca2+]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]alpha-MSH-(4-10)-NH2 (SHU 9119) blocked the effect of gamma3-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, gamma3-MSH, on [Ca2+]i. Part of the effect of gamma3-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.
ISSN:0953-8194