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Receptor-Mediated Internalization of Fluorescent Gonadotropin-Releasing Hormone by Pituitary Gonadotropes

Eli Hazum, Pedro Cuatrecasas, Jan Marian and P. Michael Conn
Proceedings of the National Academy of Sciences of the United States of America
Vol. 77, No. 11, [Part 2: Biological Sciences] (Nov., 1980), pp. 6692-6695
Stable URL: http://www.jstor.org/stable/9625
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Receptor-Mediated Internalization of Fluorescent Gonadotropin-Releasing Hormone by Pituitary Gonadotropes
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Abstract

A bioactive, fluorescent derivative of gonadotropin-releasing hormone, $<$Glu-His-Trp-Ser-Tyr-D-Lys(Nε-tetramethylrhodamine)-Leu-Arg-Pro-Gly-NH2, was prepared. This peptide retained high-affinity binding (apparent dissociation constant, 3 nM) to the receptor for gonadotropin-releasing hormone and was utilized for microscopic visualization and localization of gonadotropin-releasing hormone receptors in cultured rat pituitary cells. The fluorescently labeled receptors were initially distributed uniformly on the cell surface and formed patches, which subsequently internalized (at 37 degrees C) into endocytic vesicles. These processes were dependent on specific binding sites for the rhodamine-labeled peptide to gonadotrope cells. Cluster formation and internalization were markedly reduced in the absence of Ca2+, which is required for gonadotropin secretion. It is possible that cluster formation, microaggregation, and internalization of gonadotropin-releasing hormone receptors may be important in eliciting biological effects or for the observed loss of tissue responsiveness after desensitization due to exposure to the homologous hormone.

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