Comparison of mechanical and chemical properties of extra- and intralobar canine pulmonary arteries.

Segments of pulmonary arteries from five extralobar and intralobar sites in the form of circumferential rings were used for the determination of active and passive mechanics, analysis of connective tissue, and determination of water and electrolyte content. Measurements of ring length and tension were made under conditions of active (145 mM K+) and passive (Ca2+ free and 2 mM EGTA) smooth muscle and were used to compute values of segment stress and strain. Passive stress-strain relations among the various sites studied were not significantly different. Collagen and total connective tissue content increased from the largest extralobar to the smallest intralobar sites studied. This suggests differences in the organization of the connective tissue proteins at the secondary and tertiary levels in the various sites studied. The maximum active stress (force/area) developed in response to high K+ was largest in the intralobar arteries and lower in the larger extralobar arteries. The K+ content of these arteries decreased significantly with distance from the heart. The extracellular water content decreased with distance from the heart, whereas total water content was unchanged. These results suggest that relative cell volume decreased with distance from the heart in pulmonary arteries. Thus differences in the relative cell content per se were not responsible for the differences in maximum active stress development among the various arteries.