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Length-tension relationships of small arteries, veins, and lymphatics from the rat mesenteric microcirculation

¹Department of Pathology and Laboratory Medicine, The University of Texas Medical School at Houston, and ²Department of Systems Biology and Translational Medicine, Cardiovascular Research Institute, Division of Lymphatic Biology, College of Medicine, Texas A&M Health Science Center, College Station, Texas; and ³Department of Medical Pharmacology and Physiology, University of Missouri School of Medicine, Columbia, Missouri

Submitted 19 September 2005 ; accepted in final form 8 December 2006

The passive and active length-tension relationships of isolated rat mesenteric lymphatics (150 µm ID), and adjacent small arteries (240 µm) and veins (275 µm) 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⁺ + 5 x 10^–5 M norepinephrine was used for arteries, and 145 mM K⁺ + 1 x 10^–6 M substance P was used for lymphatics and veins. In response, arteries exhibited monotonic force development to a plateau level, whereas lymphatics and veins showed biphasic force development, consisting of a transient force peak followed by partial relaxation to a plateau over 5 min. The passive and the active length-tension curves were similar in shape among 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 was approximately fivefold 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.

vascular mechanics; wall stress; strain; isometric; preload; contraction

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