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Trh induced growth hormone release test of maturation of hypothalamo pituitary axis in post natal rat


, : Trh induced growth hormone release test of maturation of hypothalamo pituitary axis in post natal rat. Endocrinologia Experimentalis 15(4): 245-250

Small doses of TRH elicit GH[growth hormone] release from rat pituitary provided the pituitary lacks CNS influences (e.g. in vitro or in ectopic pituitaries). Hypothalamic regulation of TSH secretion matures between the 5th and 12th postnatal day. Therefore the possibility of TRH induced GH release was investigated in neonatal rats. GH concentration was measured by radioimunoassay at 10 min after s.c. TRH administration (4.1 pmol g-1 body wt) into female Wistar rats at the age 3, 9, 12, 15, 21, 30 and 100 days. Control animals were injected the same volume (1 .mu.l g-1 body wt) of saline. Serum GH in saline treated animals gradually decreased during postnatal ontogenesis. The TRH induced increase of serum GH level decreased during maturation: the most marked response was found at 3 days, it was somewhat lessened but still significant at 9 days and was absent in 12, 15, 30 days old and adult animals. Surprisingly, in 21 day old animals the increase of GH after TRH administration was again present. The ability of TRH to elicit GH release in newborn rats may depend on the maturity of the hypothalamo-pituitary axis. The effect of hypothalamic somatostatin is likely to inhibit such a response at the pituitary level in older rats.

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