LACK OF INVOLVEMENT OF THE CHOLINERGIC MECHANISM IN VASOACTIVE INTESTINAL PEPTIDE AND PEPTIDE-HISTIDINE METHIONINE-INDUCED GROWTH-HORMONE (GH) RESPONSES IN ACROMEGALY - COMPARISON WITH THE GH-RESPONSES TO THYROTROPIN-RELEASING-HORMONE AND GH-RELEASING HORMONE

We examined whether the cholinergic mechanism is involved in the parad oxical GH responses to vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) in acromegaly. 28 patients with active acr omegaly underwent i.v. bolus injections of thyrotropin-releasing hormo ne (TRH, 500 mu g), GH-releasing hormone (GHRH, 100 mu g), VIP (100 l. (g), and PHM (100 mu g) with or without a prior atropine treatment (1 mg, i.m., 30 min before). Blood samples were collected before and at i ntervals up to 120 min after the injection, and plasma GH levels were measured. In response to TRH, GHRH, VIP and PHM, 23 (82%), 24 (86%), 1 3 (46%) and 7 (25%) patients, respectively, responded with a significa nt GH increase (> 50% and 6 mu g/l above the basal level). The effect of atropine pretreatment was examined in only these responders to the respective peptides. When the GH responses were estimated by the area under the response curve, the atropine pretreatment was able to signif icantly suppress the GH response to GHRH, but not to TRH, VIP, or PHM. Although the lack of cholinergic involvement in the TRH-induced GH re lease in acromegaly is confirmatory to previous reports, the same resu lts with the VIP- and PHM-induced GH release are novel. The present st udy may suggest that in acromegaly the physiological GH response is me diated by the cholinergic mechanism, but the paradoxical ones are not.