Mechanistic insights into opioid-induced pulmonary edema: receptor specificity and sodium transport

Opioids such as morphine and fentanyl are widely used for pain management and in cardiovascular conditions; however, their misuse has become a significant public health concern. Non-cardiogenic pulmonary edema is a hallmark of opioid intoxication, often associated with impaired alveolar fluid clearance (AFC), a sodium transport-driven process that removes excess fluid from the alveoli.

This study aimed to elucidate the potential mechanisms of morphine-induced pulmonary edema by investigating the effects of μ-, δ-, and κ-opioid receptor (MOR, DOR, and KOR) modulation on AFC in rat lungs and determining whether receptor-specific blockade alters sodium transport across the alveolar epithelium.

Adult male Wistar rats were anesthetized, and a 5% BSA solution was instilled intratracheally to quantify alveolar fluid clearance (AFC) using bronchoalveolar lavage (BAL). A dose-response analysis (0.1-10 µM morphine) identified 10 µM as the concentration that significantly impaired AFC. Immunohistochemistry was performed to identify MOR, DOR, and KOR localization in lung tissue. To assess receptor-specific involvement, rats received intratracheal co-administration of morphine with selective antagonists (10 µM)-β-Funaltrexamine (μ), Naltrindole (δ), or Nor-binaltorphimine (κ)-and/or the ENaC inhibitor amiloride (1 mM).

All receptor subtypes were expressed in type II alveolar cells and macrophages. Morphine (10 µM) reduced AFC significantly. DOR antagonism produced the most marked impairment, whereas μ- and κ-blockade caused ENaC-dependent reductions comparable to amiloride.

Opioid-induced AFC impairment involves receptor-specific alterations in alveolar fluid regulation, with the DOR playing a dominant inhibitory role, suggesting its involvement in the development of pulmonary edema.