Interaction of levodopa and metoclopramide on gastric emptying

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Abstract
Dopamine is postulated as an inhibitory neurotransmitter in the alimentary tract. The effect of L-dopa [LD] on the rate of gastric emptying [GE] in man and the interaction of LD and metoclopramide [MC] (a putative dopamine antagonist) on GE were investigated. On separate days, 7 normal male subjects received oral LD, 1000 mg, and placebo in a randomized double-blind fashion 20 min before taking a mixed solid-liquid test meal labeled with 99mTc-diethylenetriamine pentaacetic acid. GE was measured over 90 min by a .gamma. camera technique. At 90 min, the mean percent isotope remaining in the stomach after placebo, 54.7 .+-. 5.0%, was less than after LD, 85.1 .+-. 4.9% (P < 0.01). Four of these normal subjects were studied further, and received LD, 1000 mg, and MC, 10 mg, by i.m. injection, 20 min before the same labeled test meal. In these 4 subjects, at 90 min, mean percent isotope remaining in the stomach after the combination of LD and MC, 48.5 .+-. 2.2%, was less than after LD alone, 83.3 .+-. 7.0% (P < 0.05), and in the same range as mean percent after placebo, 47.3 .+-. 3.6%. Apparently, LD inhibited GE of isotope in a mixed solid-liquid meal in normal subjects and MC antagonized this effect returning GE to normal. Dopaminergic receptors may have an inhibitory effect on GE of the human stomach.