Growth hormone secretion in Alzheimer's disease: studies with growth hormone-releasing hormone alone and combined with pyridostigmine or arginine.

There is evidence that GH secretion is reduced in normal elderly subjects as well as in patients with Alzheimer's disease (AD). To clarify the mechanisms underlying this GH hyposecretory state in 14 elderly subjects (age 65-75 years) and 15 AD patients (age 61-78 years), we studied the effects of both pyridostigmine (PD, 120 mg orally), a cholinesterase inhibitor, and arginine (ARG, 0.5 g/kg i.v.), two substances likely acting via inhibition of hypothalamic somatostatin, on GH response to GHRH (1 microgram/kg i.v.). The GH response to PD alone was also studied. Twenty-two young healthy volunteers were studied as control group. Basal GH levels were similar in young, elderly and AD subjects (0.7 +/- 0.2, 0.8 +/- 0.2 and 0.9 +/- 0.2 microgram/l). IGF-I levels were lower (p < 0.005) in elderly (73.9 +/- 8.2 microgram/l) and in AD subjects (108.0 +/- 5.9 micrograms/l) than in young subjects (288.7 +/- 22.1 micrograms/l); however, they were higher (p < 0.01) in AD patients than in the elderly subjects. The PD-induced GH release did not significantly differ in young, elderly and AD subjects while the GH responses to GHRH in the elderly (AUC: 297.9 +/- 49.2 micrograms/l) and in AD subjects (437.6 +/- 93.5 micrograms/l/h) were lower (p < 0.01) than in young subjects (658.6 +/- 100.1 micrograms/l/h). PD potentiated the GH response to GHRH both in elderly and in AD subjects (901.7 +/- 222.4 and 1,070.3 +/- 207.2 micrograms/l/h, p < 0.005) but these responses were lower (p < 0.0001) than those recorded in young subjects (2,041.1 +/- 245.6 micrograms/l/h).(ABSTRACT TRUNCATED AT 250 WORDS)