Hypoglycemia stimulates ACTH secretion through a direct effect on the basal hypothalamus

Area of Science:

• Neuroendocrinology
• Physiology

Background:

• Insulin-induced hypoglycemia is a known stimulus for adrenocorticotropic hormone (ACTH) secretion.
• The precise central nervous system (CNS) site mediating this response remains incompletely understood.

Purpose of the Study:

• To investigate the primary site of action of insulin hypoglycemia in stimulating ACTH secretion.
• To differentiate the roles of the medial basal hypothalamus versus extrahypothalamic CNS and the adenohypophysis.

Main Methods:

• Rats underwent medial basal hypothalamic ablation (MBHA) or deafferentation (MBHD), or received chlorpromazine-morphine-pentobarbital (C-M-P) anesthesia.
• Plasma corticosterone levels served as an indirect measure of ACTH secretion.
• Response to synthetic lysine-vasopressin was assessed to evaluate pituitary ACTH reserve.

Main Results:

• Hypoglycemia failed to stimulate ACTH secretion in MBHA and C-M-P treated rats.
• ACTH secretion in response to hypoglycemia was preserved in MBHD rats, similar to controls.
• Pituitary ACTH reserve was unaffected by MBHA, as shown by normal corticosterone response to vasopressin.

Conclusions:

• The medial basal hypothalamus is the primary site where hypoglycemia acts to stimulate ACTH secretion.
• Extrahypothalamic CNS and the adenohypophysis are not the primary mediators of this hypoglycemia-induced ACTH release.