5-HT1-, but not 5-HT2-serotonergic, M1-, M2-muscarinic cholinergic or dopaminergic receptors mediate the ACTH/cortisol response to metoclopramide in man.

The possible mediation of dopaminergic, muscarinic cholinergic and/or serotonergic receptors in the response of ACTH/cortisol to metoclopramide (MCP) was evaluated in 27 normal men. All subjects were tested with MCP (10 mg in an intravenous bolus plus placebo or saline, NaCl 0.9%, control test). For the other tests (experimental tests), the men were divided into three groups of 9 subjects each. One group was tested with MCP in the presence of the dopaminergic agonist bromocriptine (5 mg p.o. 3 h before MCP), another group was tested with MCP plus the M1- and M2-muscarinic-cholinergic antagonist atropine (1.2 mg in an intravenous bolus, just before MCP) or the M1-muscarinic receptor blocker pirenzepine (40 mg in an intravenous bolus 10 min before MCP). The third group was tested with MCP after treatment with the selective 5-HT1-serotonergic receptor blocker metergoline (10 mg/day p.o. in 5 divided doses for 4 days before MCP) or the 5-HT2-serotonergic receptor antagonist ketanserin (10 mg as a slow 3-min intravenous injection, 5 min before MCP). ACTH and cortisol rose by 45 and 55%, respectively, in response to MCP. The basal levels of ACTH and cortisol were not modified by bromocriptine, atropine, pirenzepine, metergoline or ketanserin treatment. Both ACTH and cortisol responses to MCP did not change significantly after bromocriptine, atropine, pirenzepine or ketanserin administration, whereas they were completely abolished by pretreatment with metergoline. Additional experiments were performed in order to evaluate whether the effect of metergoline on the ACTH/cortisol response to MCP depends on the amount of the serotonergic antagonist (dose-response study).(ABSTRACT TRUNCATED AT 250 WORDS)