Supporting tissue tension and microvascular reactions

Abstract

The effects of stretch of supporting tissue on resting vessel lumen size and of its response to standard amounts of norepinephrine were examined in striated (cremaster) muscle of the rat. Controlled amounts of stretch were imposed upon cremaster muscle using a microtensor device. The amount of stretch was determined by attaching the tissue via thin (10-0) nylon thread to the actuating pin of a calibrated (0–1000 mg) strain-gauge transducer. In rats lightly anesthetized with pentobarbital sodium (25 mg/kg), after control measurement of vessel lumen and its response to topical norepinephrine, the tissue tension was increased at 8-min intervals, and the measurement repeated at every newly achieved tissue tension. In 6 out of 10 arterioles in 10 rats, lumen expanded (av. 25%) with increasing tissue tension. The vessel response to norepinephrine increased in three of the expanded vessels, decreased in two, and remained unchanged in one. Two of the vessels showed no change in lumen but decrease in sensitivity, and two showed decrease in lumen size and increase in sensitivity to the drug stimuli. The results indicate that only overt stretch of supporting tissue >150 mg, will affect microvessel size and reactivity.