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1 Pathology & Laboratory Medicine, University of Texas Medical School at Houston, Houston, Texas, United States
2 Systems Biology & Translational Medicine, Texas A&M University System Health Science Center, College Station, Texas, United States
3 Medical Pharmacology & Physiology, University of Missouri School of Medicine, Columbia, Missouri, United States
* To whom correspondence should be addressed. E-mail: davismj{at}health.missouri.edu.
The passive and active length-tension relationships of isolated rat mesenteric lymphatics (~150 µm, ID), and adjacent small arteries (~240 µm) and veins (~275 um) were compared under isometric conditions using a wire myograph. About 60% of the lymphatic vessels developed spontaneous contractions in physiological saline solution at nominal preload. To maximally activate smooth muscle, 145 mM K+ / 5x10-5 M norepinephrine was used for arteries, and 145 mM K+ / 1x10-6 M Substance P for lymphatics and veins. In response, arteries exhibited monotonic force development to a plateau level, while lymphatics and veins showed biphasic force development, consisting of a transient force peak followed by partial relaxation to a plateau over ~5 minutes. The passive and the active length-tension curves were similar in shape between all three vessels. However, the maximal active tension of arteries (3.4±0.42 mN/mm) was significantly greater than peak active tension (0.59±0.04 mN/mm) or plateau tension (0.20±0.04 mN/mm) in small veins and greater than peak active tension (0.34±0.02 mN/mm) or plateau tension (0.21±0.02 mN/mm) in lymphatics. Maximal active medial wall stress was similar between lymphatics and veins, but ~5-fold higher in small arteries. For lymphatics, the pressure calculated from the optimal preload was significantly higher than that found previously in isobaric studies of isolated lymphatics, suggesting the capacity to operate at higher than normal pressures for increased responsiveness. Our results represent the first mechanical comparisons of arterial, venous, and lymphatic vessels in the same vasculature.
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