Leu-enkephalin provokes naloxone-insensitive pulmonary vasoconstriction

Area of Science:

• Pharmacology
• Physiology

Background:

• Leu-enkephalin is an endogenous opioid peptide.
• Its effects on the pulmonary circulation are not fully understood.

Purpose of the Study:

• To investigate the mechanism of leu-enkephalin-induced pulmonary vasoconstriction in isolated perfused rat lungs.
• To determine if opiate, histamine, or serotonin receptors mediate these effects.

Main Methods:

• Isolated perfused rat lung model.
• Administration of leu-enkephalin to assess pulmonary arterial pressure.
• Use of receptor antagonists (naloxone, naltrexone, pyrilamine, methysergide) and agonists (morphine).

Main Results:

• Leu-enkephalin caused a dose-dependent increase in pulmonary arterial pressure.
• Naloxone, naltrexone, pyrilamine, and methysergide did not attenuate these pressor responses.
• Morphine did not mimic the pressor effects of leu-enkephalin.

Conclusions:

• The pulmonary vasoconstrictor effects of leu-enkephalin in isolated perfused rat lungs are not mediated by conventional opiate, histamine, or serotonin receptors.
• Leu-enkephalin may exert direct vasoconstrictor effects on the pulmonary circulation independent of these known receptor systems.