MECHANICAL ALTERATIONS IN SENSITIZED CANINE SAPHENOUS-VEIN

Because it is likely that antigen sensitization is not restricted to airway smooth muscle but probably involves all tissues in the animal, we decided to test the hypothesis that saphenous vein from pollen extract-sensitized dogs is sensitized and is, in addition, mechanically altered. To this end, we studied responses to specific antigen challenge and length-tension and force-velocity relationships in sensitized (SSV) and control saphenous veins (CSV). The antigen challenge revealed that the venous smooth muscle was strongly sensitized and developed a Schultz-Dale response, the two main mediators of which were histamine and norepinephrine. Length-tension relationship studies showed that whereas there is no difference in maximum isometric tension development between SSV and CSV [93.95 ± 7.34 and 87.86 ± 4.00 (SE) mN/mm2, respectively], SSV exhibited a significantly greater maximum isotonic shortening capacity of 0.613 ± 0.009 optimal length (l0) vs. 0.578 ± 0.012 l0 for CSV. Unloaded shortening velocity (V0), which reflects the cross-bridge cycling rate, was determined at different times after the onset of electrical stimulation. Maximum V0 was attained early (5 s) in the contraction; a 15% decline in V0 was observed at the plateau of the contraction (15 s). At 5 s, V0 of SSV (0.316 ± 0.019 l0/s) was significantly higher than that of CSV (0.269 ± 0.018 l0/s), although V0s were same at 15 (0.249 ± 0.021 l0/s for SSV and 0.237 ± 0.019 l0/s for CSV). The increase in shortening likely results from the increase in the early cross-bridge cycling rate because our studies show that the bulk of shortening occurs in the first 5 s. These findings indicate that the mechanical properties of SSV are altered compared with those of CSV. The results of our pharmacological studies also suggest that the hemodynamic response of the venous circulation to agonists could also be altered in the sensitized model.