Inhibitory effects of atropine on growth hormone release in normal subjects and acromegaly

Growth hormone (GH) secretion is mediated by hypothalamic factors, mainly growth hormone releasing factor (GRF) and somatostatin (SS). The hypothalamic hormones, under direct neurotransmitter control, stimulate GH secretion through different central mechanisms. Atropine, an anticholinergic agent, can cross the blood-brain barrier and inhibit GH secretion stimulated by exercise and sleep in normal persons. In order to study the inhibiting effect of atropine on GH release and whether glucose can be replaced by atropine, normal persons and acromegaly patients were observed during exercise, after atropine, and 100 g glucose loading. The results confirmed that GH secretion increases after exercise and that this GH elevation can be inhibited by atropine in normal subjects. But in acromegaly patients high basal GH levels can not be inhibited by 100 g glucose loading or 0.6 mg atropine during the active phase of the disease. Blood sugar levels remained unchanged during the atropine test. It is suggested that the atropine test can be used as a GH inhibitory test in acromegaly patients with overt diabetes.