In view of the important role played by the
cholinergic system in the neural regulation of
growth hormone (GH) secretion, the ability of
pirenzepine, a selective antagonist of
muscarinic cholinergic receptors, to blunt the GH response to GH-releasing
hormone (GHRH) was studied in adolescent females with
anorexia nervosa in the acute (AN-AP) five AN-AP patients, administration of
GHRH 1-40 (1 microgram/kg IV) evoked a significantly higher GH response than in controls at established intervals, whereas in eight AN-RP and seven AED patients it was higher than in controls at only one (150-min) and two (150-min, 180-min) time intervals, respectively. In the AN-AP patients, pretreatment with
pirenzepine (0.6 mg/kg IV) only partially blocked the GH response to GHRH, whereas in the same AN-AP patients tested during recovery, and in AN-RP and AED patients, the
drug completely suppressed the GH response to GHRH, as it did in controls. In view of
pirenzepine's mechanism of action, these findings are best explained by the existence in the hypothalamus of AN-AP patients of a
cholinergic hypertone and/or a diminished somatostatinergic function. Evaluation of the clinical and hormonal characteristics of the
anorectic patients studied would indicate that factors other than
undernutrition and its
biological consequences, which subside in the recovery stage of the disease and are not present in AED patients, contribute to the anomalous GH response pattern of AN-AP patients.