Endomorphin-1 causes synovial hypoaemia in rat knee joints via a capsaicin-sensitive neural pathway

• Published in: Neuroscience letters Vol. 344; no. 1; pp. 21 - 24
• Main Authors: Barin, A.K., McDougall, J.J.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 19.06.2003; Elsevier
• Subjects: Analgesics, Opioid - pharmacology; Animals; Arthritis; Biological and medical sciences; Blood flow; Capsaicin; Capsaicin - pharmacology; Dose-Response Relationship, Drug; Fundamental and applied biological sciences. Psychology; Inflammation; Knee joint; Knee Joint - blood supply; Knee Joint - drug effects; Laser-Doppler Flowmetry; Male; Molecular and cellular biology; Mu opioid receptor; Nerve Fibers, Unmyelinated - drug effects; Neural Pathways - physiology; Neurogenic inflammation; Neuropeptides; Oligopeptides - pharmacology; Opioids; Rats; Rats, Wistar; Synovial Fluid - drug effects; Vascular Resistance - drug effects; Vasoconstriction - drug effects; Knee joint; Capsaicin; Opioids; Neuropeptides; Arthritis; Mu opioid receptor; Neurogenic inflammation; Blood flow; Knee; Edema; Endomorphin 1; Rat; Rodentia; μ Opioid receptor; Joint; Vertebrata; Mammalia
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/S0304-3940(03)00405-1

In joints, synthetic μ-opioids reduce inflammatory changes such as protein extravasation and associated oedema formation. However, the effect of endogenous opioid peptides on other inflammatory processes such as altered tissue blood flow has not been investigated. The present study examined the peripheral effects of the endogenous μ-opioid ligand endomorphin-1 (EM-1) on rat knee joint blood flow using laser Doppler perfusion imaging. Topical application of EM-1 (10 −16–10 −9 mol) to exposed rat knee joints resulted in a dose-dependent increase in synovial vascular resistance with a maximum rise of 56% occurring with the 10 −9 mol dose. Destruction of unmyelinated articular afferents by capsaicin treatment completely abolished the hypoaemic effects of EM-1. These findings suggest that EM-1 acts peripherally in knee joints to decrease synovial blood flow, and this hypoaemic response is dependent on the presence of capsaicin-sensitive nerves.