HETEROGENEITY OF TRACHEOBRONCHIAL LYMPHATIC SMOOTH-MUSCLE RESPONSES TO HISTAMINE AND 5-HYDROXYTRYPTAMINE

We assessed the responsiveness of tracheobronchial lymphatic smooth mu scle to mediators of inflammation to determine whether homogeneous res ponses to histamine and 5-hydroxytryptamine (5-HT) are demonstrated am ong species typically used in studies of lymph vessels. Fresh porcine and bovine tracheobronchial lymph vessels were suspended from force-di splacement transducers in baths containing oxygenated Krebs solution. Concentration-response curves were generated by cumulative addition of histamine (10(-7) to 10(-3)M) or 5-HT (10(-7) to 3x10(-4)M). Active t ension (AT) was expressed in milligrams and as a percentage of initial vessel ring response to 65mM KCl. Histamine elicited concentration-de pendent contraction, yielding maximum AT in porcine rings of 1116+/-12 7mg (n=39; 129.1+/-10.5% of KCl response) and in bovine rings of 733+/ -106mg (n=20; 65.8+/-12.9%; P=0.0005 for percent responses). PD2 value s (negative log(10) of the concentration at half-maximum effect) were 4.49+/-0.08 and 4.82+/-0.08; (P=0.0034). 5-HT elicited concentration-d ependent contraction, yielding maximum AT of 560+/-50mg in porcine rin gs (n=15; 97.2+/-9.7%) and 2892+/-454mg in bovine rings (n=27; 159.0+/ -29%; P<0.0001 for percent responses). PD2 values were 6.25+/-0.05 and 5.28+/-0.04 (P<0.0001). The data demonstrate a role for inflammatory mediators in the modulation of tracheobronchial lymphatic smooth muscl e tone that is species- and mediator-specific, and support the potenti al for paracrine regulation of tracheobronchial lymph flow.