Regulation of Somatotroph Differentiation and Growth Hormone (GH) Secretion by Corticosterone and GH-Releasing Hormone during Embryonic Development

Abstract

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 (10−9m) and GH-releasing hormone (GHRH; 10−10-10−7m) 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.