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Absence of metabolism of morphine during accumulation by isolated perfused rabbit lung
Abstract:
Pulmonary accumulation and metabolism of morphine was studied in an isolated perfused lung system. No metabolism of morphine or N-demethylation of ethylmorphine was found. Accumulation from the recirculating perfusate was nonsaturable over a concentration range of 3-400 microM morphine. Inhibition of sodium transport or sodium depletion decreased morphine accumulation. The results are most consistent with passive diffusion of morphine down an electrochemical gradient and subsequent nonspecific binding to tissue anions. Normal movement of sodium and potassium is required to maintain this gradient.
Insights
Morphine does not metabolize in the lungs. Its accumulation is driven by passive diffusion and requires normal sodium and potassium transport to maintain the electrochemical gradient.
Area of Science:
- Pharmacology
- Pulmonary Physiology
- Drug Metabolism
Background:
- Understanding drug behavior in the lungs is crucial for effective pulmonary drug delivery and toxicity assessment.
- Morphine is a widely used analgesic, but its pulmonary pharmacokinetics require further elucidation.
Purpose of the Study:
- To investigate the pulmonary accumulation and metabolism of morphine using an isolated perfused lung model.
- To determine the mechanisms underlying morphine's disposition within the lung tissue.
Main Methods:
- Utilized an isolated perfused lung system to study morphine.
- Assessed morphine metabolism and N-demethylation of ethylmorphine.
- Investigated the effect of sodium transport inhibition and depletion on morphine accumulation.
- Examined morphine accumulation across a range of concentrations (3-400 microM).
Main Results:
- No evidence of morphine metabolism or ethylmorphine N-demethylation was observed in the perfused lung.
- Morphine accumulation was nonsaturable within the tested concentration range.
- Inhibition or depletion of sodium transport significantly reduced morphine accumulation.
- Results suggest passive diffusion down an electrochemical gradient, coupled with tissue anion binding.
Conclusions:
- The isolated perfused lung does not metabolize morphine.
- Morphine lung accumulation is primarily mediated by passive diffusion, dependent on the sodium-potassium electrochemical gradient.
- Maintaining normal ion transport is essential for morphine's pulmonary disposition.