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Department of Poultry Science, Texas A&M University (C.E.D.), College Station, Texas 77843; and the Department of Animal and Avian Sciences, University of Maryland (T.E.P.), College Park, Maryland 20742
Address all correspondence and requests for reprints to: Dr. Tom E. Porter, Department of Animal and Avian Sciences, University of Maryland, College Park, Maryland 20742. E-mail: tp44{at}umail.umd.edu
The role of extracellular factors in the regulation of anterior pituitary cell differentiation and GH secretion during embryonic development was investigated. Previously, we reported that somatotrophs become a significant population by embryonic day (e-) 16 of the chick and that corticosterone is the active compound responsible for the observed GH cell-differentiating activity of e-16 serum. More recently, the influence of hormone interactions on somatotroph differentiation and GH secretion during mid- to late embryogenesis was evaluated. Anterior pituitary cells from e-12, -14, and -17 chicks were cultured for 2, 3, and 6 days with corticosterone (10-9 M) and GH-releasing hormone (GHRH; 10-10-10-7 M) alone and in combination. Medium samples were analyzed for GH concentrations, and recovered cells were subjected to GH reverse hemolytic plaque assay for determination of somatotroph percentages and the relative amount of GH secretion from individual somatotrophs. GHRH significantly (P < 0.05) increased GH secretion from e-17, but not e-12 and e-14, pituitary cells during 2 and 3 days of culture. Corticosterone alone failed to increase GH secretion from e-12, -14, and -17 pituitary cells; however, corticosterone in combination with GHRH increased GH secretion from cells of all three ages. Culture with GHRH decreased percentages of e-17 GH-secreting cells in a concentration-dependent manner (from basal levels of 12.3 ± 2.4% to 3.2 ± 0.7% by 2 days), but did not affect percentages of e-12 and e-14 somatotrophs. Conversely, corticosterone increased percentages of e-12 and e-14 GH-secreting cells (by as much as 14- and 3-fold above basal levels, respectively), but did not alter the proportions of e-17 GH cells. Corticosterone in combination with GHRH was more effective than either hormone alone for increasing percentages of e-12 GH-secreting cells (from 9.6 ± 0.8% with corticosterone to 15.9 ± 1.5% with corticosterone plus GHRH), but this synergistic effect was not apparent until after 3 days of culture. Exposure to corticosterone in culture for 2, 3, and 6 days increased subsequent GH release from e-12 and e-14 pituitary cells during reverse hemolytic plaque assay. Combined treatment with corticosterone and GHRH further increased subsequent GH release from e-12 and e-14 cells. We conclude that glucocorticoids induce GH cell differentiation and that corticosterone and GHRH can interact at specific stages of embryonic development to regulate somatotroph differentiation and GH secretion.
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 C Mogi, H Goda, K Mogi, A Takaki, K Yokoyama, M Tomida, and K Inoue Multistep differentiation of GH-producing cells from their immature cells J. Endocrinol., January 1, 2005; 184(1): 41 - 50. [Abstract] [Full Text] [PDF]
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H. Ozawa, F. Han, and M. Kawata Exocytosis sensitivity to growth hormone-releasing hormone in subsets of GH cells in rats under different corticosterone conditions. Ultrastructural study using microwave irradiation for fixation and immunocytochemistry J. Endocrinol., December 1, 2004; 183(3): 507 - 515. [Abstract] [Full Text] [PDF]
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X. Fu, S. Nishimura, and T. E Porter Evidence that lactotrophs do not differentiate directly from somatotrophs during chick embryonic development J. Endocrinol., November 1, 2004; 183(2): 417 - 425. [Abstract] [Full Text] [PDF]
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X. Fu and T. E. Porter Glucocorticoid Induction of Lactotrophs and Prolactin Gene Expression in Chicken Embryonic Pituitary Cells: A Delayed Response Relative to Stimulated Growth Hormone Production Endocrinology, March 1, 2004; 145(3): 1322 - 1330. [Abstract] [Full Text] [PDF]
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L. Liu, C. E. Dean, and T. E. Porter Thyroid Hormones Interact with Glucocorticoids to Affect Somatotroph Abundance in Chicken Embryonic Pituitary Cells in Vitro Endocrinology, September 1, 2003; 144(9): 3836 - 3841. [Abstract] [Full Text] [PDF]
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C. Boisvert, C. Pare, C. Veyrat-Durebex, A. Robert, S. Dubuisson, G. Morel, and P. Gaudreau Localization and Regulation of a Functional GHRH Receptor in the Rat Renal Medulla Endocrinology, April 1, 2002; 143(4): 1475 - 1484. [Abstract] [Full Text] [PDF]
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I. Bossis and T. E. Porter Ontogeny of Corticosterone-Inducible Growth Hormone-Secreting Cells during Chick Embryonic Development Endocrinology, July 1, 2000; 141(7): 2683 - 2690. [Abstract] [Full Text] [PDF]
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