Effect of cholinergic muscarinic receptor blockade on human growth hormone (GH)-releasing hormone-(1-44)-induced GH secretion in anorexia nervosa.

The presence of hypothalamic disturbances affecting GH secretion in anorexia nervosa has been suggested, although a normal GH response to GH-releasing hormone (GHRH) administration has been shown in these patients. The present study was performed to investigate the role of acetylcholine in regulating GH secretion by using pirenzepine, which selectively blocks muscarinic cholinergic receptors. Paired tests were performed in nine anorexia nervosa patients (age +/- SEM, 19.1 +/- 1.2 yr; percent ideal body weight, -32.7 +/- 2.2%) and in six normal controls (20.1 +/- 0.3 yr; -3.1 +/- 1.8%). GHRH-(1-44) (1 microgram/kg) was infused iv with and without pirenzepine pretreatment (0.6 mg/kg, iv). Basal levels of GH were not different in anorexia nervosa compared to normal controls, whereas, somatomedin-C levels were significantly lower in anorexia nervosa patients. However, after pirenzepine administration, the GHRH-stimulated GH responses were completely blocked in normal controls, but not in anorexia nervosa patients. These results suggested that altered muscarinic cholinergic mechanism are involved in the modulation of GH secretion in patients with anorexia nervosa.