Ghrelin prevents levodopa-induced inhibition of gastric emptying and increases circulating levodopa in fasted rats

Authors

  • L. Wang,

    1. Department of Medicine, CURE/Digestive Diseases Center and Center for Neurobiology of Stress, Digestive Diseases Division, University of California at Los Angeles, and Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, USA
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  • N. P. Murphy,

    1. Department of Psychology, Brain Research Institute, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, USA
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  • A. Stengel,

    1. Department of Medicine, CURE/Digestive Diseases Center and Center for Neurobiology of Stress, Digestive Diseases Division, University of California at Los Angeles, and Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, USA
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  • M. Goebel-Stengel,

    1. Department of Medicine, CURE/Digestive Diseases Center and Center for Neurobiology of Stress, Digestive Diseases Division, University of California at Los Angeles, and Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, USA
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  • D. H. St Pierre,

    1. University of Montréal, Montréal, Québec, Canada
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  • N. T. Maidment,

    1. Department of Psychology, Brain Research Institute, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, USA
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  • Y. Taché

    1. Department of Medicine, CURE/Digestive Diseases Center and Center for Neurobiology of Stress, Digestive Diseases Division, University of California at Los Angeles, and Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA, USA
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Address for Correspondence
Lixin Wang, MD, PhD, Bldg. 115, Rm. 117B, 11301 Wilshire Blvd, Los Angeles, CA 90073, USA. Tel: +310 478 3711 ex 41831; fax: +310 268 4963;
e-mail: lixinw@ucla.edu

Abstract

Background  Levodopa (l-dopa) is the most commonly used treatment for alleviating symptoms of Parkinson’s disease. However, l-dopa delays gastric emptying, which dampens its absorption. We investigated whether ghrelin prevents l-dopa action on gastric emptying and enhances circulating l-dopa in rats.

Methods  Gastric emptying of non-nutrient methylcellulose/phenol red viscous solution was determined in fasted rats treated with orogastric or intraperitoneal (i.p.) l-dopa, or intravenous (i.v.) ghrelin 10 min before orogastric l-dopa. Plasma l-dopa and dopamine levels were determined by high pressure liquid chromatography. Plasma acyl ghrelin levels were assessed by radioimmunoassay. Fos expression in the brain was immunostained after i.v. ghrelin (30 μg kg−1) 10 min before i.p. l-dopa.

Key Results  Levodopa (5 and 15 mg kg−1) decreased significantly gastric emptying by 32% and 62%, respectively, when administered orally, and by 91% and 83% when injected i.p. Ghrelin (30 or 100 μg kg−1, i.v.) completely prevented l-dopa’s (15 mg kg−1, orogastrically) inhibitory action on gastric emptying and enhanced plasma l-dopa and dopamine levels compared with vehicle 15 min after orogastric l-dopa. Levodopa (5 mg kg−1) did not modify plasma acyl ghrelin levels at 30 min, 1, and 2 h after i.v. injection. Levodopa (15 mg kg−1, i.p.) induced Fos in brain autonomic centers, which was not modified by i.v. ghrelin.

Conclusions & Inferences  Ghrelin counteracts l-dopa-induced delayed gastric emptying but not Fos induction in the brain and enhances circulating l-dopa levels. Potential therapeutic benefits of ghrelin agonists in Parkinson’s disease patients treated with l-dopa remain to be investigated.

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