Intermedin functions as a pituitary paracrine factor regulating prolactin release.
Calcitonin, alpha- and beta-calcitonin gene-related peptides, amylin, and adrenomedullin belong to a unique group of peptide hormones important for homeostasis maintenance. We recently identified intermedin (IMD) as a novel member of the calcitonin/calcitonin gene-related peptide family expressed in the pituitary, digestive tract, and other organs of vertebrates. Real-time PCR and immunohistochemical analysis of pituitaries from rats at different stages of development showed that IMD is expressed in the intermediate lobe and select adrenocorticotrophs in the anterior lobe, suggesting that IMD could function as a paracrine factor regulating anterior pituitary hormone secretion. In support of a paracrine role for IMD in the pituitary, quantitative and in situ hybridization analyses showed the expression of IMD receptor transcripts including the calcitonin receptor-like receptor and receptor activity-modifying proteins in the pituitary. Treatment with IMD leads to a dose-dependent increase of prolactin release in cultured rat pituitary cells. In contrast, IMD treatment has negligible effects on the release of GH, FSH, or ACTH. Likewise, in vivo treatment with IMD leads to an elevation of plasma prolactin levels in conscious rats. Based on these functional characteristics, we hypothesized that IMD could represent one of the intermediate lobe-derived prolactin-releasing factors important for prolactin regulation during reproduction. In support of this hypothesis, studies of IMD expression in lactating and ovariectomized rats showed that pituitary IMD transcripts in lactating animals increased to more than 2-fold over nonlactating controls whereas ovariectomy leads to a 90% reduction of IMD expression in the pituitary. Of importance, subsequent treatment with 17beta-estradiol or diethylstilbestrol increased pituitary IMD expression in ovariectomized rats. In addition, analysis of the proximate region of the IMD gene promoter showed that the IMD gene promoter contains consensus estrogen response element sequences, and estrogen treatments up-regulate the promoter reporter activity in transfected pituitary cells. Collectively, the present study indicates that IMD represents a novel estrogen-dependent intermediate lobe-derived prolactin-releasing factor and could play important roles in the regulation of prolactin release during reproduction in females.
Stanford University School of Medicine, Division of Reproductive Biology, Department of Obstetrics and Gynecology, Stanford, California 94305-5317, USA.
Chia
C
Lin Chang
Jaesook
J
Roh
Jae-Il
JI
Park
Cynthia
C
Klein
Nicole
N
Cushman
Rainer V
RV
Haberberger
Sheau Yu Teddy
SY
Hsu
D000324:Adrenocorticotropic Hormone / Q000032:analysis / Q000378:metabolism; D053607:Adrenomedullin; D000595:Amino Acid Sequence; D000818:Animals; D058286:Calcitonin Receptor-Like Protein; D002478:Cells, Cultured; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics; D007774:Lactation / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D019899:Paracrine Communication; D010903:Pituitary Gland, Anterior / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats; D058261:Receptor Activity-Modifying Proteins; D018003:Receptors, Calcitonin / Q000235:genetics; D014158:Transcription, Genetic
C499411:Adm2 protein, rat; D058286:Calcitonin Receptor-Like Protein; C545580:Calcrl protein, rat; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009479:Neuropeptides; D058261:Receptor Activity-Modifying Proteins; D018003:Receptors, Calcitonin; D053607:Adrenomedullin; D000324:Adrenocorticotropic Hormone; D011388:Prolactin