Growth hormone in obesity.

Area of Science:

• Endocrinology
• Metabolic Disorders

Background:

• Obesity is characterized by blunted growth hormone (GH) secretion, affecting its half-life, episodic release, and daily production.
• Impaired GH response is observed with various stimuli, including hypothalamic and direct somatotrope stimulation, in obese individuals.

Purpose of the Study:

• To investigate the multifaceted causes of impaired GH secretion in obesity.
• To explore the role of hypothalamic, pituitary, and peripheral factors in GH hyposecretion.
• To assess the impact of metabolic factors and potential therapeutic interventions.

Main Methods:

• Evaluation of GH secretion in response to pharmacological stimuli (e.g., GHRH, GHRPs, insulin-induced hypoglycemia).
• Analysis of peripheral markers including IGF-I, IGFBPs, GHBP, and leptin.
• Assessment of metabolic factors like free fatty acids and the effects of caloric restriction and weight loss.

Main Results:

• Obese subjects show reduced GH responses to GHRH and GHRPs, even with combined administration.
• Peripheral factors like high free IGF-I and low IGFBP-1/2 are noted in obesity.
• Weight loss normalizes GH secretion, indicating an adaptive nature of the defect.

Conclusions:

• GH hyposecretion in obesity involves hypothalamic, pituitary, and peripheral mechanisms, potentially including somatostatin excess or GHRH deficiency.
• Elevated free fatty acids and free IGF-I may contribute significantly to impaired GH secretion.
• GH therapy may offer benefits for body composition and metabolic efficiency in obese patients during severe caloric restriction.