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Phenotypic characterization and functional correlation of alpha-MSH binding to pituitary cells
T Zheng1, C Villalobos, K D Nusser
1Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston 29425, USA.
The American Journal of Physiology
|February 1, 1997
Summary
Alpha-melanocyte-stimulating hormone (alpha-MSH) binds to specific pituitary cells, mammotropes, and activates a calcium signaling pathway. This hormone does not compete with dopamine for the same receptor site.
Area of Science:
- Endocrinology
- Neuroscience
- Cell Biology
Background:
- Alpha-melanocyte-stimulating hormone (alpha-MSH) from the pituitary neurointermediate lobe mediates suckling-induced prolactin release.
- The precise role and receptor interactions of alpha-MSH in this process require further elucidation.
Purpose of the Study:
- To determine if alpha-MSH reversibly binds to specific adenohypophyseal (AP) cells.
- To investigate whether alpha-MSH competes with dopamine for receptor binding.
- To identify a functional signaling pathway associated with alpha-MSH binding.
Main Methods:
- Alpha-MSH receptor autoradiography on pituitary cells from lactating rats.
- Adenohypophyseal (AP) hormone immunocytochemistry.
- Digital imaging fluorescence microscopy using fura 2 for calcium imaging.
Main Results:
- Alpha-MSH binding is exclusively localized to mammotropes.
- A subset of mammotropes expresses functional alpha-MSH receptors.
- These receptors are linked to a calcium (Ca2+) signaling pathway.
- Alpha-MSH does not compete with dopamine antagonists or agonists for receptor binding.
Conclusions:
- Alpha-MSH specifically targets mammotropes in the adenohypophysis.
- Functional alpha-MSH receptors on mammotropes modulate calcium signaling.
- The binding site for alpha-MSH is distinct from the dopamine receptor site.