Abstract
Circulating GH concentrations are high in the fetus and fall after birth. The high fetal GH levels have been postulated to reflect immaturity of hypothalamic control of GH secretion. GABA mediated regulation of GH release was studied in chronically catheterized ovine fetuses (term 147 days) and infant lambs. Muscimol (MUSC),a GABA agonist (300ug/kg) was given iv to 3 fetuses (108-137 days) and GH fell from 123.6 ± 53ng/ml to 64.7 ± 25.7ng/ml (p <0.05). In 2 younger fetuses (95,99days) no suppression was noted. Picrotoxin, (PIC),a GABA antagonist (500ug/kg) was given iv to 7 fetuses (80 - 140 days). Plasma GH rose from 76.3 ± 15.6ng/ml to 115.0 ± 8.5 ng/ml (p <0.05). The incremental GH response to PIC rose with gestational age (r=0.80, p <0.05). In 3 neonates, GH rose following PIC from 10.6 ± 8.5 ng/ml to 45.0 ± 13.9 ng/ml. Pretreatment with MUSC reduced the neonatal response to PIC (n=3) indicating that the action of PIC is mediated by GABA receptors. These data are evidence for GABA receptors in the fetal hypothalamic-pituitary unit. The GH response to PIC is evidence for tonic GABA mediated inhibition of fetal GH release in the late gestation fetus and neonate. This suggests that the high fetal GH levels do not represent entirely unrestrained activity of the hypothalamic-pituitary unit but that there is partial restraint of GH release mediated by GABA.
Supported by the Medical Research Council of New Zealand.
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Gluckman, P. 410 EVIDENCE FOR TONIC GAMMA-AMINOBUTYRIC ACID (GABA) MEDIATED INHIBITION OF GROWTH HORMONE (GH) SECRETION IN THE OVINE FETUS. Pediatr Res 15 (Suppl 4), 508 (1981). https://doi.org/10.1203/00006450-198104001-00421
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DOI: https://doi.org/10.1203/00006450-198104001-00421