Effect of preload on rat aortic smooth muscle sensitivity to vasoactive agents

Concentration-response curves to potassium chloride, phenylephrine, serotonin and calcium chloride were obtained from rat aortic strips subjected to preloads of 0.75, 1.5 or 3.0 g. The sensitivity of the aortic smooth muscle to potassium chloride, phenylephrine and serotonin increased with increasing preload; whereas the calcium chloride concentration-response curves of K+-depolarized strips were unaffected by preload. These results demonstrate that the sensitivity of rat aortic smooth muscle to many vasoactive agents is a function of preload and also indicate that an alteration in the influx of external Ca2+ is not sufficient to explain the effect of preload on sensitivity.