Phenotypic characterization and functional correlation of alpha-MSH binding to pituitary cells.
It is clear that alpha-melanocyte-stimulating hormone (alpha-MSH), released by the hypophysial neurointermediate lobe, is a mediator of suckling-induced prolactin release, but several questions surrounding its role remain unresolved. Accordingly, the objectives of the present study were 1) to establish whether alpha-MSH could bind in a reversible manner to a specific secretory type cell within the adenohypophysis (AP), 2) to resolve the issue of whether the peptide could compete with dopamine for the same receptor binding site, and 3) to seek a functional signaling correlate for alpha-MSH binding. In pursuit of these objectives, we subjected pituitary cells from lactating rats to alpha-MSH receptor autoradiography, AP hormone immunocytochemistry, or digital imaging fluorescence microscopy with fura 2 as a calcium-sensitive probe. Our results show that alpha-MSH binding is restricted to mammotropes and that a specific subpopulation of these express functional alpha-MSH receptors that are coupled to a Ca2+ signaling pathway. Moreover, alpha-MSH does not compete with dopamine antagonists/agonists for the same binding site.
Zheng
T
T
Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA.
Villalobos
C
C
Nusser
K D
KD
Gettys
T W
TW
Faught
W J
WJ
Castaño
J P
JP
Frawley
L S
LS
D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D006462:Hemolytic Plaque Technique; D007150:Immunohistochemistry; D010641:Phenotype; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D000521:alpha-MSH / Q000031:analogs & derivatives / Q000378:metabolism*
D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D000521:alpha-MSH; D013973:Thyrotropin-Releasing Hormone; C027756:MSH, 4-Nle-7-Phe-alpha-; D002118:Calcium