An automated method to control preload by compensation for stress relaxation in spontaneously contracting, isometric rat mesenteric lymphatics.
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OBJECTIVE: Our objective was to devise a system to automatically correct for stress relaxation of isometric rat mesenteric lymphatics (90-120 microm, ID). Stress relaxation is a particular problem in isometric studies of highly distensible vessels and is evident as a time-dependent, secondary decline in force after an abrupt length increase. Because the phasic contraction pattern of lymphatics is exquisitely sensitive to changes in preload, stress relaxation makes stable contraction patterns difficult to achieve and analyze. METHODS: A DMT wire myograph was modified to accommodate an Inchworm piezo stack in series with a standard micrometer drive to permit automated control of vessel caliber/force. The force output of the myograph was digitized and computer algorithms were devised to servo control force by changing vessel diameter. RESULTS: The system was tested on passive lymphatics, passive small veins, and lymphatics exhibiting spontaneous force transients. The software was designed to temporarily disable servo control during a spontaneous force transient. For both active and passive lymphatics, stable preloads were very well maintained, indicating that the system was adequately compensating for stress relaxation. CONCLUSIONS: The method works well with isometric rat mesenteric lymphatics without disturbing spontaneous activity. It should be applicable to arterial, venous, and lymphatic vessels (80-500 microm in diameter) isolated from other tissues and species.
