Naloxone-induced enhancement of carbon dioxide stimulated respiration |
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Authors: | G E Isom R M Elshowihy |
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Institution: | 1. Department of Pharmacology and Toxicology School of Pharmacy and Pharmacal Sciences Purdue University West Lafayette, IN 47907, USA;2. Department of Anesthesiology New Jersey College of Medicine and Dentistry Newark, NJ 07101, USA |
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Abstract: | In unanesthetized rats, naloxone (5 mg/kg, s.c.) produced an increase in both respiratory frequency and tidal volume as compared to saline administered animals. Maximal respiratory stimulation was observed within 5 minutes after naloxone injection and duration of the response was greater than 30 minutes. Exposure to different atmospheres of carbon dioxide potentiated the increase in ventilation in a step-wise manner as the carbon dioxide concentration was increased. Pretreatment with low doses of morphine sulfate (2 mg/kg daily for 2 days) or naloxone HCl (5 mg/kg daily for 5 days) enhanced respiratory stimulation induced by naloxone. It was concluded that naloxone increases the sensitivity of central ventilatory response to carbon dioxide as a result of displacement of endogenous endorphins from central opioid receptors. |
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