Hypothalamic targets for growth hormone secretagogues

Area of Science:

• Endocrinology
• Neuroscience

Background:

• Novel growth hormone (GH) secretagogues stimulate GH release from the pituitary through a pathway independent of GH-releasing hormone (GHRH).
• These secretagogues also exert central effects, activating hypothalamic neurons and requiring an intact GHRH system for significant in vivo activity.

Purpose of the Study:

• To investigate the central actions and in vivo activity of GH secretagogues.
• To explore the implications of the cloned endogenous receptor for GH secretagogues.

Main Methods:

• Studies were conducted using normal and transgenic growth-retarded (Tgr) rats.
• GH release and activation of the adrenocorticotrophin-adrenal axis were monitored in response to GH secretagogues.
• The pattern of secretagogue administration was varied to assess its effect on GH release.

Main Results:

• Both normal and Tgr rats released GH in response to GH secretagogues, with responses dependent on administration patterns.
• GH secretagogues were not fully specific, also activating the adrenocorticotrophin-adrenal axis, indicating additional central effects.
• The cloning of an endogenous receptor for GH secretagogues provides a tool to identify central targets.

Conclusions:

• GH secretagogues have complex central actions beyond direct GH release.
• The identification of an endogenous receptor suggests an endogenous ligand, though its origin and physiological role require further investigation.
• Understanding these central mechanisms is crucial for optimizing therapeutic applications of GH secretagogues.