DEVELOPMENT OF THE EMBRYO
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(142) ACTIVATION OF ADRENAL CORTICOSTERONE SECRETION IN THE CHICKEN EMBRYO AND ITS EFFECTS ON THE GROWTH HORMONE (GH)-INSULIN-LIKE GROWTH FACTOR (IGF) AXIS.
Jenkins, Sultan1, Richards, Mark2, Porter, Tom1, 1 Department of Animal and Avian Sciences, College Park, Maryland2 United States Department of Agriculture, Beltsville, Maryland
ABSTRACT- Adrenocorticotropic hormone (ACTH) is a peptide hormone that stimulates the adrenal cortex to secrete the glucocorticoid corticosterone. We have previously shown that injection of either corticosterone or ACTH into the albumen of fertile chicken eggs on embryonic day (e) 11 induces premature GH cell (somatotroph) differentiation on e14. The objective of the present study was to ascertain whether this premature induction of somatotrophs leads to an early activation of the GH-IGF axis. ACTH (0.1 ml; 6x10-5 M) was injected into eggs on e11. Plasma samples were collected 1, 3, 10, 16, 22, 28, 34, and 40 hours later. Plasma levels of corticosterone were assessed by radioimmunoassay. ACTH injection significantly elevated plasma corticosterone levels within 1 hour after injection, compared to water injected controls (P < 0.05; n = 4). ACTH, corticosterone (500 ng), and 0.1 ml of deionized water were injected into separate eggs on e11. On e14, e17, and e20 the embryonic livers were extracted, and total RNA was isolated. The RNA was subjected to reverse transcription - polymerase chain reaction (RT-PCR) to amplify cDNA for IGF-I and IGF-II. The cDNA was then quantified using capillary electrophoresis with laser induced fluorescence. Although ACTH treatment increased mean IGF-I gene expression on e17 two-fold compared to the water injected group, the results were not statistically different (P = 0.07; n = 4). Additional trials are planned to more clearly define effects on IGF-I mRNA levels. Injection of ACTH or corticosterone had no effect on IGF-II gene expression. The results indicate that the embryonic adrenal gland can produce sufficient corticosterone to play a role in regulating GH cell differentiation and that this premature induction of GH cells does not lead to increased IGF-I or IGF-II gene expression.
KEY WORDS: embryo, chicken, Adrenocorticotropic hormone, Corticosterone