Biology of Reproduction, Vol 23, 1097-1108, Copyright © 1980 by Society for the Study of Reproduction

Correlative Study of Changes in the Morphology of the LH Gonadotroph and Anterior Pituitary Gland LH Secretion During the 4-Day Rat Estrous Cycle

¹ Department of Anatomy, University of Nebraska Medical Center, Omaha, Nebraska 68105

We have correlated changes in rat anterior pituitary gland LH secretion with morphological changes in LH gonadotrophs at different times during the 4-day estrous cycle. We kept rats for 4 or more weeks in a room with the lights on from 0500 to 1900 h and decapitated three or four rats at each of the following times: 1400, 1800, or 2200 h proestrus (P); 0200, 0600, or 1000 h estrus (E); or 1100 h diestrous Day 1 (DI). Luteinizing hormone concentration was determined in one half of each anterior pituitary gland while LH cells in the other half were stained immunocytochemically using rabbit anti-rat LH sera and examined at the ultrastructural level. Shortly prior to the onset of the preovulatory surge of LH in serum at 1400 h P, the shape of the basic LH cell was usually polygonal. The typical cell had a homogeneous cytoplasm, a single population of granules often aggregated but scattered throughout the cytoplasm, a near ovoid-shaped nucleus with a reasonably smooth outline of the nuclear membrane, a nucleolus and Golgi which were infrequently observed, nonprominent endoplasmic reticulum (ER), no light-dense bodies, no large granules (300 mm diameter), no lysosomes, and a portion of its cell membrane located adjacent to a blood vessel. At 1800 h P, serum LH concentration was elevated more than 32-fold, but anterior pituitary gland LH concentration was not significantly changed. Serum LH concentration decreased after 1800 h P to approach or reach basal levels by 2200 h P or 0200 h E. Anterior pituitary gland LH concentraion was low at 2200 h P and it did not rise significantly until 1100 h DI. The percentage of LH cells with an ovoid shape was higher at 1800 h P than during E and DI. Anterior pituitary gland LH concentration correlated positively with both the mean granule number per sectional profile of LH cells and the percentage of cells with an appreciable amount of clumped granules. Anterior pituitary gland LH concentration correlated negatively with the number of degranulated (<150 secretion granules per sectional profile) LH cells. Nonangular-shaped LH cells in which the secretion granules were virtually limited to the exterior of the cytoplasm so as to outline the cell were occasionally observed, but not at 1400 h P or 1100 h DI. The number of cells in which the ER was very prominent and the number of cells in which the nuclei had an irregular shape increased progressively from 1400 h P to 1000 h E. No changes occurred during the estrous cycle in type of cytoplasm, percentage of cells located adjacent to blood vessels, percentage of cells in which a Golgi or nucleolus was observed, number of cells in which any large granules (>300 nm) or any light-dense bodies and/or lysosomes were observed, and percentage of cells in which the nuclear membrane had an irregular outline. The results suggest that 1) only one basic cell type is involved in LH secretion during the rat estrous cycle; 2) anterior pituitary gland LH concentration is directly related to the number of LH secretion granules during the rat estrous cycle; 3) the LH cell may become more oval and less irregular in shape during the time of heightened LH secretion on P; 4) LH synthesis keeps pace with LH release during the early stages of the LH surge; 5) LH synthesis no longer keeps pace with LH release, and some LH cells are markedly degranulated during the latter portion of the LH surge; 6) nuclei become irregular in shape, and ER becomes more elaborated during the time of the LH surge and more dramatically thereafter during E, at least in some of the LH cells; 7) by DI the LH cell has replenished a substantial portion of its radioimmunoassayable LH stores, and the granulation of the cells is similar to that observed prior to the LH surge on P.

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ACKNOWLEDGMENTS I thank Dr. Albert F. Parlow, Dr. Leo Reichert, Jr., Dr. Gordon D. Niswender, and the Rat Pituitary Hormone Program of NIAMDD for their generous gifts of materials used for radioimmunoassay and staining of LH. The technical assistance of Dr. Oladapo Ashiru and Ms. Laura Garner is gratefully acknowledged.