Abstract
Neonatal rats exhibit a diminished pituitary and adrenal stress response during the first two weeks of life but the physiological bases for this phenomenon are still unclear as the pituitary and adrenals are functional at birtn and CRF can be released at early ages. Enhanced sensitivity to glucocorticoid feedback during this period appears to critically mediate the activation of the hypothalamus-pituitary adrenal axis following stress. Since thyroid hormones (TH) are known to impinge on brain maturation ana to influence corticosterone availability to target: cells, we investigated the effect of TH on development of the stress response. Daily T4 injections (100 ug/kg bw,sc) in normal rats from day 1 to 20 resulted in premature appearance of ACTH response to ether stress: 5 day-old rats exhibited a small increase (p 0.05) in ACTH secretion following stress while no response was observed in vehicle-treated rats. On days 10, 14 and 20, stress-induced ACTH levels were significantly higner than unstressed controls in both T4 and vehicle treated groups but no differences in ACTH response to stress were observed between the two groups. Additionally, T4 treatment produced marked signs of hyperthyroidism,, namely increased loomotor activity, pranature eye opening (3 days) and decreased pituitary (33%) and body (12%) weight. Other modifications of neonatal maturation like hypothyroidism are currently under study. In conclusion, T4 treatment is able to alter the developmental pattern of endocrine response to stress possibly through accelerated maturation of central afferents to hypothalamic CRF neurons (increased myelinization).
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Walker, CD., Sizoneko, P. & Aubert, M. EFFECTS OF THYROXINE ON THE DEVELOPMENT OF THE STRESS RESPONSE IN THE NEONATAL RAT. Pediatr Res 23, 106 (1988). https://doi.org/10.1203/00006450-198801000-00030
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DOI: https://doi.org/10.1203/00006450-198801000-00030