Effects of Pyridostigmine, Corticotropin-Releasing Hormone and Growth Hormone-Releasing Hormone on the Pituitary-Adrenal Axis and on Growth Hormone Secretion in Dementia

Alterations of neuroendocrinological indices determined by the impaired regulating effects of cholinergic neurotransmission have been described in primary dementia. In this study we have evaluated the effects of acetylcholines-terase inhibition by pyridostigmine on growth hormone (GH), adrenocorticotropic hormone (ACTH) and cortisol secretion and on their responses to GH-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) in 7 patients with primary degenerative dementia and in 8 sex- and age-matched controls. Demented subjects showed higher cortisol basal levels and lower ACTH levels than controls. Pyridostigmine increased the GH response to GHRH in both groups, the effect being significantly enhanced in patients. An increase of ACTH and cortisol levels was found in both groups after pyridostigmine and CRH administration. Pyridostigmine pretreatment significantly increased the ACTH response to CRH in controls but not in patients. The obtained data may indicate that a muscarinic receptor upregulation and an impairment of somatostatinergic function are operative in the regulation of GH secretion in dementia. An underlying hyperactivity of the hypothalamic-pituitary-adrenal axis impairs the responses of ACTH and cortisol to CRH in this disorder.