SOMATOTROPIN RESPONSE TO CORTICOSTERONE AND THE THYROID HORMONE T3 DURING CHICK EMBRYONIC DEVELOPMENT: INVOLVEMENT OF TYPE I AND TYPE II GLUCOCORTICOID RECEPTORS
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Corticosterone (CORT) can stimulate growth hormone (GH) cell (somatotroph) differentiation and GH secretion on embryonic day (e) 12 but not e20 in the chicken. GH induction involves both glucocorticoid receptors (GR) and mineralocorticoid receptors (MR); however, this finding has been characterized only on e12. To further define changes in somatotroph responsiveness to CORT, pituitary cells obtained on e12-e20 were cultured with CORT alone and in combination with T3. GH secretion increased over basal with CORT treatment on e12, e14, e16, and e18, but not e20. Contributions of GR and MR in CORT responses were evaluated using GR and MR antagonists. Blocking both receptors was required to abolish the CORT response by e12 cells. The same treatment on e20 decreased GH secretion relative to basal. We conclude that positive somatotroph responses to CORT are lost during embryonic development and that both GR and MR mediate CORT-induced GH secretion by cultured somatotrophs.