Mechanics of canine iliac artery smooth muscle in vitro

Transmural pressure and external diameter were continuously recorded from intact segments of canine iliac artery and used to determine wall responses to maximal smooth muscle (SM) activation by norepinephrine (NE). Three different approaches were used:a) step inflations from low pressure following NE, B) slow, continuous inflation from low pressure following NE, and c) direct isometric and isobaric responses to NE. Passive pressure-diameter data were determined. The results show that active wall stress and diameter responses to NE determined using direct isometric and isobaric responses and from slow inflation responses (less than 1 mmHg/s) were not significantly different. Pressure-diameter and stress-strain curves determined using continuous (0.2 mmHg/s) and step pressure inflations after NE were not signficantly different. Pressure-diameter curves obtained at different inflation rates were not those expected from a simple viscoelastic material. The results suggest that slow inflation of iliac arteries with activated SM is a reasonable method for assessing contractile properties of SM. Furthermore, they also suggest that activation of iliac artery SM at high contractile element length (L greater than Lo) does not produce attenuated constriction responses.