Release of spasmogens from rat isolated lungs by tryptamines

Area of Science:

• Pharmacology
• Physiology

Background:

• Pulmonary circulation plays a key role in drug metabolism and mediator release.
• Tryptamines, including serotonin (5-HT), are endogenous compounds with diverse physiological effects.

Purpose of the Study:

• To investigate the effects of tryptamine and 5-HT on isolated rat lungs.
• To characterize the nature of released spasmogenic and PGE-like activities.
• To compare the receptors involved in mediator release with known tryptamine receptors.

Main Methods:

• Infusion of tryptamine and 5-HT into isolated rat lungs.
• Extraction and characterization of released substances (SRS-T and PGE-like activity).
• Pharmacological evaluation using agonists and antagonists (methysergide, BC 105, BW 501c67, morphine).
• Comparison with tryptamine receptor activity on rat stomach strip and pulmonary artery.

Main Results:

• Tryptamine and 5-HT released a novel SRS-T, not extractable by organic solvents.
• A dose-dependent PGE-like activity was observed, with a threshold effect.
• The release of PGE-like activity was inhibited by methysergide, BC 105, and BW 501c67, but not morphine.
• Receptors mediating release differed from myotropic receptors, showing closest similarity to rat stomach strip receptors.

Conclusions:

• Pulmonary infusion of tryptamines induces the release of a unique SRS-T and PGE-like activity.
• The release mechanism involves specific receptors distinct from smooth muscle receptors.
• Antagonist specificity suggests these release receptors are most closely related to those found in the rat stomach strip.