MODULATION OF LYMPHATIC SMOOTH-MUSCLE CONTRACTILE RESPONSES BY THE ENDOTHELIUM

The endothelium regulates smooth muscle tone in blood vessels through the release of endothelium-derived relaxing factor (EDRF). We hypothesized that the lymphatics possess endothelium-dependent relaxant properties analogous to those in blood vessels. Fresh porcine tracheobronchial lymphatic vessel rings were mounted in organ baths and connected to force-displacement transducers. Rings were submaximally precontracted with 10-5M histamine and exposed to cumulative addition of acetylcholine (ACH; 10-7 -3 × 10-4M) or bradykinin (BRD; 10-8-3 × 10-6M), both of which are known to promote release of EDRF. ACH caused concentration-dependent relaxation (maximum effect = -2.3 ± 2.6% of initial histamine-induced active tension), while a similar but less pronounced effect was seen with BRD (39.6 ± 5.4%). The relaxant effects of ACH and BRD were inhibited by collagenase pretreatment and mechanical endothelial denudation. The results confirm our hypothesis that lymphatic vessels possess endothelium-dependent relaxant properties and suggest that lymph vessels can regulate lymph flow through processes similar to those found in blood vessels. © 1992.