Endothelial-dependent vasodilation is associated with increases in the phosphorylation of a small heat shock protein (HSP20)

Purpose: Increases in the phosphorylation of a small heat shock protein (HS P20) are associated with cyclic nucleotide-dependent vasorelaxation. The ef fect-of pressure and now on vessel diameter was studied. We hypothesized th at physiologic conditions that induce vasorelaxation would lead to increase s in HSP20 phosphorylation. Methods: Flow-dependent changes in vessel diameter, at different intralumin al pressures, were measured with a laser optical micrometer in intact bovin e carotid arteries. Experiments were performed in the presence and absence of norepinephrine (10(-5) moI/L). Increases in the phosphorylation of HSP20 were determined with isoelectric focusing immunoblots. Results: The increase in vessel diameter was most significant at low intral uminal pressures (20 mm Hg), high flow rates (200 mL/min), and in the prese nce of the vasoconstrictor norepinephrine (10(-5) mol/L). The addition of m ethylene blue (a guanylate cyclase inhibitor) completely inhibited now-indu ced vasodilation. Under conditions in which maximal flow induced vasodilati on occurred, there were significant-increases in the phosphorylation of HSP 20. Conclusion: Flow-dependent vasodilation in isolated perfused segments of bo vine carotid arteries was maximal when the intraluminal pressures were low and when the vessels were precontracted with norepinephrine. Flow-dependent vasodilation was inhibited by methylene blue and was associated with incre ases in the phosphorylation of HSP20, suggesting, that the vasodilation was mediated by endothelial production of nitric oxide.