Neuroendocrine responses to intravenous infusion of arecoline in patients with Alzheimer's disease

Abstract

We have reported that arecoline, a muscarinic receptor agonist replicably enhanced verbal memory in five of nine subjects with Alzheimer's disease (AD). To investigate the mechanism of cognitive improvement, circulating hormone measurements were made during high-dose acute and low-dose chronic intravenous (i.v.) arecoline administration to AD patients. Acute hormone responses were measured during, and for 6 h after, infusion of arecoline 5 mg i.v. over 30 min. Chronic responses were measured in cognitive responders during continuous i.v. infusion of arecoline escalating over 2 weeks (0.5-40 mg/day) and then during a 1 week infusion of the dose optimizing cognition (4-16 mg/day). Acute arecoline administered to 14 subjects produced unpleasant side-effects (e.g. nausea, vomiting), mean adrenocorticotrophic hormone (p = .0006), cortisol (p = .0001) and beta-endorphin (p = .0001) levels were elevated. During chronic arecoline treatment, no side-effects occurred and plasma cortisol, adrenocorticotrophic hormone and beta-endorphin levels were unchanged in nine subjects overall and in five cognitive responders. Thus, high-dose arecoline activates the hypothalamic-pituitary-adrenal (HPA) axis and may increase other anterior pituitary hormone levels, likely representing a 'stress response', but cognition-enhancing, low doses of arecoline do not produce a glucocorticoid response. Hence, arecoline-induced memory improvement is not due to the induction of 'stress' nor to the elevation of peripheral corticosteroid levels.