Population dynamics in the gonadotrope population

Studies in G.V. Childs' lab
University of Arkansas for Medical Sciences, Little Rock, AR

Are small gonadotropes precursor cells?

This figure shows a typical small gonadotrope. The cell has been labeled for LH with immunoperoxidase techniques (label is on the round-ovoid black granules) The cell is difficult to distinguish from small thyrotropes or corticotropes. It resembles gonadotropic cells from neonatal rats.

Small gonadotropes are prominent early in the cycle and express abundant mRNA during peak transcription periods. The cells contain few small storage granules usually at the cell periphery. Over 80% of these small cells store only one of the gonadotropins. However, more of them store both hormones after a 4 h stimulation with GnRH. This suggests that the cells may serve as precursors for the bihormonal gonadotropes.

However, there is no evidence that large gonadotropes appear at the expense of the smallest cells. In fact, just before ovulation the small cells increase in number and help augment the gonadotrope population. Thus they may serve unique functions in the cell population. In the coming years, we hope to learn if we can drive the population to look and act like their larger counterparts. We also hope to learn if they respond to unique sets of hormones or growth factors that regulate the reproductive system.

Medium-sized gonadotropes may be responsible for surge secretion.

Many of these cells contain densely packed granules, often of homogeneous size and density. This figure shows a medium sized gonadotrope immunolabeled with peroxidase techniques for LH antigens. Other cells like the one in this figure contain scattered granules. The granules may contain one or both gonadotropins. About 50-60% of medium-sized gonadotropes are bihormonal (contain both gonadotropins). This and the number of secretory granules distinguishes them from the small gonadotrope population.

In medium-sized gonadotropes, rough endoplasmic reticulum is often in isolated sheets or dilated sacs scattered among the granules. The cells are angular-ovoid and may extend long processes to blood vessels during times of peak secretion.

During the stages leading up to ovulation, medium sized gonadotropes increase in number, resulting in an overall 4-fold increase in gonadotropes. After peak secretion before and during ovulation, the medium-sized cells appear to be reduced in number. This apparent reduction may be the result of loss of hormone stores during the active secretory activity.

Studies of gonadotropin secretion from these cells show that they outsecrete their counterparts in the larger cell fractions, especially during stages of peak secretion. Thus, these cells may be primed to support the surge secretory activity. They may serve as a unique secretory subset. If so, they should express receptors for GnRH before ovulation. Future studies will test this hypothesis. We will also test if estrogens or other regulatory peptides will upregulate expression of GnRH receptors in this subset.

The largest gonadotropes may maintain and regulate the system.

In the early 1980's we discovered that large gonadotropes enriched a cell population that could be separated by centrifugal elutriation. It contained 60% gonadotropes and thus provided a good model for physiological and biochemical studies. Our morphological studies show that the largest cells look like medium-sized cells (see figure on first page) only they may be larger and have more dilated rough endoplasmic reticulum. They mostly contain both LH and FSH in the same cell. However, the two hormones may be stored in either the same or in different storage granules in that bihormonal cell. For illustrations, see figures in Web page describing gonadotropin storage

Large gonadotropes exhibit two major morphological subtypes. In the figure on the first page The cell on the left has large and small granules scattered among dilated sacs of rough endoplasmic reticulum. The other cell has clusters of granules that are homogeneous in size. They may pack more densely in the cytoplasm.

The largest cells secrete well except just before ovulation. They do not secrete as well as the medium-sized cells at that time. They may require other factors to elicit secretion. Alternatively, they may serve another function. Perhaps they are cells that maintain ovarian function during most stages of the cycle. Our future studies will test effects of other stimulatory agents on their functions.

We now have developed a technique that uses centrifugal elutriation to separate gonadotropes that are enlarged by GnRH stimulation.  This will be published in Feb, 2001, Endocrinology.

Our publications on small, medium and large subsets of gonadotropes during the past 12 years

Hyde, C.L., Childs, G.V., Wahl, L.M., Naor, Z. and Catt, K.J. Preparation of gonadotropin-enriched cell populations from adult rat anterior pituitary cells by centrifugal elutriation. Endocrinology 111:1421-1423, 1982.

Childs, G.V., Hyde, C., Naor, Z. and Catt, K. Heterogeneous LH and FSH storage patterns in subtypes of gonadotropes separated by centrifugal elutriation. Endocrinology 113:2120-2128, 1983. Note: This paper has been reprinted twice in the "Survey of Obstetrics and Gynecology" with a review by the editors discussing the significance of the work (see issues published in October, 1984 and January, 1985).

Lloyd, J.M. and Childs, G.V. Differential storage and release of LH and FSH from individual gonadotropes separated by centrifugal elutriation. Endocrinology 122:1282-1290, 1988.

Childs, G.V., Unabia, G., Lloyd, J. Recruitment and maturation of small subsets of luteinizing hormone (LH) gonadotropes during the estrous cycle, Endocrinology, 130:335-345 1992.

Childs, G.V., Unabia, G., Lee, B.L., Rougeau, D. Heightened secretion by small and medium-sized luteinizing hormone (LH) gonadotropes late in the cycle suggests contributions to the LH surge or possible paracrine interactions, Endocrinology, 130: 345-352 1992.

Lee, B.L., Unabia, G., Childs, G. Expression of follistatin mRNA in somatotropes and mammotropes early in the estrous cycle J. Histochem. Cytochem, 41: 955-960, 1993.

Childs, G.V. , Unabia G., Rougeau D. Cells that Express Luteinizing Hormone (LH) and Follicle Stimulating Hormone (FSH) Beta ( ) Subunit mRNAs during the Estrous Cycle: The major contributors contain LH , FSH and/or Growth Hormone, Endocrinology, 134: 990-997 1994.

Childs, G.V., Geda Unabia, and Brian T. Miller, Cytochemical detection of GnRH binding sites on rat pituitary cells with LH, FSH and GH antigens during diestrous upregulation. Endocrinology 134: 1943-1951, 1994.

Childs, G.V. Division of Labor among Gonadotropes, Vitamins and Hormones, 50: 217-283, 1995.

Childs, GV. Cytochemical studies of multifunctional gonadotropes. Microscopy Research and Techniques, in press, 1997.

Ghosh, BR, J.C., Wu, G.V. Childs, and W.L. Miller, Inhibin and Estradiol Alter Gonadotropes Differentially in Ovine Pituitary Cultures: Changing Gonadotrope numbers and Calcium Responses to Gonadotropin-Releasing Hormone, Endocrinology, 137: 5144-5154, 1996.

Childs, GV. Simultaneous identification of a specific gene protein product and transcript using combined immunocytochemistry and In Situ Hybridization with non-radioactive probes. Scanning Microscopy Supplement 10, 17-26, 1997.

Childs, GV, Miller B, and Miller, W. Differential effects of inhibin on gonadotropin stores and gonadotropin releasing hormone binding to pituitary cells from cycling female rats. Endocrinology, 138:1577-1584, 1997.

Armstrong, J and Childs, GV. Changes in expression of epidermal growth factor receptors by anterior pituitary cells during the estrous cycle. Cyclic expression by gonadotropes. Endocrinology, 138:1903-1908, 1997.

Armstrong, J and Childs, GV. Differential Expression of c-fos in vitro by all anterior pituitary
cell types during the estrous cycle: enhanced expression by luteinizing hormone but not follicle stimulating hormone cells. J Histochem Cytochem, 45(6): 785-794, 1997.

Armstrong J and Childs GV. Regulation of expression of epidermal growth factor receptor in
gonadotropes by epidermal growth factor and estradiol: Studies in cycling female rats.   Endocrinology, 138: 1577-1584 1997.

Childs GV and Unabia G. Cytochemical studies of the effects of activin on gonadotropin releasing hormone (GnRH) binding by pituitary gonadotropes and growth hormone cells. J Histochem Cytochem, 45: 1603-1610, 1997.

Protocols and related web pages:

| Affinity Cytochemistry | In situ hybridization Histochemistry | Go to Childs Home Page |

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