Related Experiment Videos
Variations of plasma growth hormone (GH)-releasing factor levels during GH stimulation tests in children
Insights
L-dopa stimulates growth hormone (GH) release by increasing growth hormone-releasing factor (GHRH) levels in short children. Ornithine, however, does not increase GHRH, suggesting different mechanisms for GH stimulation.
Area of Science:
- Pediatric Endocrinology
- Hormone Regulation
- Growth Hormone Secretion
Background:
- Growth hormone (GH) is crucial for childhood growth.
- Growth hormone-releasing factor (GHRH) is a primary regulator of GH secretion.
- Understanding stimuli that affect GHRH and GH is important for diagnosing and treating short stature.
Purpose of the Study:
- To investigate the differential effects of L-dopa and ornithine on plasma GHRH and GH levels in constitutionally short children.
- To explore the relationship between GH release and GHRH levels following these stimuli.
Main Methods:
- Plasma GHRH and GH levels were measured using radioimmunoassay (RIA).
- Twenty-two constitutionally short children received either an oral dose of L-dopa or an ornithine infusion.
- Measurements were taken after an overnight fast and rest period.
Main Results:
- L-dopa administration led to a significant increase in both GH and plasma GHRH levels in a subset of children, with a strong correlation between peak GH and GHRH concentrations.
- Ornithine infusion stimulated GH release but was followed by a decrease in plasma GHRH levels, not preceded by a rise.
- Some children did not respond to L-dopa with increased GH or GHRH.
Conclusions:
- L-dopa and ornithine stimulate GH release through distinct mechanisms.
- GH levels may play a role in the feedback regulation of GHRH secretion.
Abstract:
GH-releasing factor (GHRH) was measured by RIA in the plasma of 22 constitutionally short children given an ornithine infusion or an oral dose of L-dopa. After an overnight fast and 1 h of rest, plasma GHRH levels were 49.7 +/- 7.3 pg/ml (+/- SEM). In 5 children, L-dopa induced an increase in mean GH levels from 1.8 to 12 ng/ml at 60 min. Mean plasma GHRH levels increased from 47 pg/ml to a peak of 96 pg/ml at 15 min (P less than 0.02). In 4 other children, no increase in either GH or GHRH occurred after L-dopa treatment. In these 9 children, a significant correlation was found between the peak GH and GHRH concentrations (r = 0.841; P less than 0.001). On the contrary, ornithine-induced GH release was not preceded by a GHRH rise, but was followed by a GHRH decrease, from 51 to 27 pg/ml (P less than 0.02). We conclude that the 2 tests stimulate GH release in different ways, and that GH levels may be involved in the feedback control of GHRH secretion.