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Plasma growth hormone releasing factor levels in children: physiological and pharmacologically induced variations
Insights
Plasma growth hormone releasing factor (GHRH) levels varied in children with short stature. L-Dopa stimulated GHRH release before growth hormone (GH) elevation, unlike other stimuli.
Area of Science:
- Pediatric Endocrinology
- Neuroendocrinology
- Growth Hormone Physiology
Background:
- Short stature in children is a common clinical concern.
- Growth hormone releasing factor (GHRH) is a key regulator of growth hormone (GH) secretion.
- Understanding GHRH dynamics is crucial for diagnosing growth disorders.
Purpose of the Study:
- To investigate the role of plasma GHRH in response to various stimuli in children with short stature.
- To determine if GHRH elevation precedes GH release under different stimulation tests.
- To explore the relationship between GHRH and GH secretion during sleep.
Main Methods:
- Plasma GHRH was measured using radioimmunoassay (RIA).
- 41 children with constitutionally short stature were studied.
- Stimuli included L-Dopa, amino acids, clonidine, and venous catheterization (stress).
- GH and GHRH levels were monitored over time.
Main Results:
- Basal plasma GHRH was 51 +/- 10 pg/ml.
- L-Dopa significantly increased plasma GHRH 30-45 minutes before GH elevation, with a positive correlation between peak GH and GHRH.
- Amino acid and clonidine-induced GH secretion were not preceded by GHRH elevation.
- Stress-induced GH release was preceded by a rise in plasma GHRH.
- No correlation between nocturnal GHRH and GH peaks was observed in sleeping adolescents.
Conclusions:
- Different stimuli elicit GH secretion through distinct mechanisms at the hypothalamo-pituitary level.
- L-Dopa and stress-induced GH release involve a preceding GHRH surge.
- Amino acid and clonidine tests may bypass or not rely on GHRH for GH release.
- Further research is needed to elucidate the complex regulation of GH secretion in short stature.
Abstract:
Plasma growth hormone releasing factor (GHRH) was measured by RIA in the plasma of 41 children with constitutionally short stature. Basal plasma GHRH was 51 +/- 10 pg/ml. L-Dopa induced a 2-fold increase in circulating GHRH 30-45 min before the elevation of GH. A positive correlation (p less than 0.005) was found between the peak of GH and GHRH during the dopaminergic stimulus. On the opposite, the secretion of GH induced by amino acids or clonidine is not preceded by an elevation of plasma GHRH. When a release of GH appeared after the insertion of the venous catheter alone, probably due to the stress, it was preceded by a rise of plasma GHRH. In four sleeping adolescents during the night no relationship was found between the peaks of plasma GHRH and the peaks of GH secretion. These results suggest that the various stimulations of GH secretion used for investigations of a short stature do not act in the same way at the hypothalamo-pituitary level.