AJP - Endocrinology and Metabolism, Vol 268, Issue 1 E145-E152, Copyright © 1995 by American Physiological Society
Measurement of secretogranin II release from individual adenohypophysial gonadotropes
N. Wei, S. S. Kakar and J. D. Neill
Department of Physiology and Biophysics, University of Alabama at Birmingham 35294.
Secretogranin II (SG-II) is an acidic 86-kDa protein found in high
abundance in the anterior pituitary gland. In the present studies, we
investigated the secretion and the localization of SG-II using pituitary
cells from female rats at all stages of the estrous cycle. Double
immunofluorescence staining revealed that SG-II immunoreactivity was
localized in low abundance in about half of all pituitary cells and in high
abundance in all of the luteinizing hormone (LH)-immunoreactive cells
(which represent approximately 5% of all pituitary cells). Using a reverse
hemolytic plaque assay for measurement of SG-II release from individual
pituitary cells in culture, we found that SG-II secretion was strongly
stimulated by gonadotropin-releasing hormone in a dose-related fashion, and
the amount of SG-II secretion was also related to the stage of the estrous
cycle: it was highest at proestrus and lowest at estrus. SG-II plaque assay
followed by LH immunofluorescence staining further revealed that all the
SG-II-secreting cells contained LH immunoreactivity. At proestrus all the
LH-immunoreactive cells secreted SG-II, whereas another days of the estrous
cycle only a fraction of them did so. Thus our findings demonstrate a
striking resemblance between SG-II and LH with regard to cell localization
and secretory regulation.
