CHARACTERIZATION OF CONTRACTILE PROPERTIES OF PORCINE MESENTERIC AND TRACHEOBRONCIDAL LYMPHATIC SMOOTH MUSCLE

Abstract

We performed morphometric and lengthtensionanalyses comparing mesenteric andtracheobronchial lymph vessel segments todetermine the potential of the latter tissue toregulate pulmonary and mediastinal lymphflow via alterations in smooth muscle tone.Fresh porcine lymph vessel rings were preparedfor 1) in vitro assessment oflength-tensionrelationships and 2) histologic preparation andmeasurement ofsmooth muscle cross-sectionalarea (SMA). Mesenteric and tracheobronchialoptimal vessel ring lengths were 3.1±0.2 and3.5±0.2 mm, and maximum active tensionswere 1518±25 and 1703±162 mg. Smoothmuscle formed indistinct layers in each tissue,and only 30% of the smooth muscle wasoriented circumferentially. Stress generated bythe circular smooth muscle was similar to thatgenerated by other types of vascular smoothmuscle. 1n 75% of mesenteric vessel ringsspontaneous contractions were observed thathad a mean contraction frequency of1. 7±0.2min-1 and a mean contraction amplitude of349±35 mg, while only 40% of tracheobronchialvessels exhibited spontaneouscontractions (p<O.OOl) that had a meanfrequency ofO.6±0.2 min-1 (p=0.0021) and amean contraction amplitude of 118±10mg(p<O.OOOl). We conclude that tracheobronchiallymphatic vascular smooth muscle is capable ofdeveloping stress similar to that generated bymesenteric lymph vessels, and thatspontaneous rhythmic contractile activity isqualitatively and quantitatively different intracheobronchial than in mesenteric porcinelymph vessels. The data suggest that tracheobronchiallymph vessels are capable ofregulating pulmonary and mediastinal lymphflow through intrinsic mechanisms. Suchregulation may occur by alterations in vascularresistance rather than via spontaneouspumping activity.