Abstract
We have investigated the role of ATP-sensitive potassium (K(ATP)) channels in an experimental model of a delayed phase of vascular hyporeactivity induced by lipopolysaccharide (LPS) in rats. After 24 h, from LPS treatment, in anaesthetized rats the bolus injection of phenylephrine (PE) produced an increase in mean arterial pressure (MAP) significantly (P<0.05) reduced in LPS-treated rats compared to the vehicle-treated rats. This reduction was prevented by pre-treatment of rats with glibenclamide (GLB), a selective inhibitor of K(ATP) channels. GLB administration did not affect the MAP in vehicle-treated rats but produced an increase of MAP in rats treated with LPS. Cromakalim (CRK), a selective K(ATP) channel opener, produced a reduction of MAP that was significantly (P<0.05) higher in LPS- than in vehicle-treated rats. In contrast, the hypotension induced by glyceryl trinitrate (GTN) in LPS-treated rats was not distinguishable from that produced in vehicle-treated rats. Experiments in vitro were conducted on aorta rings collected from rats treated with vehicle or LPS 24 h before sacrifice. The concentration-dependent curve to PE was statistically (P<0.005) reduced in aorta rings collected from LPS- compared to vehicle-treated rats. This difference was totally abolished by tetraethylammonium (TEA), a non-selective inhibitor of K+ channels. CRK produced a relaxation of PE precontracted aorta rings higher in rings from LPS- than in vehicle-treated rats. GLB inhibited CRK-induced relaxation in both tissues, abolishing the observed differences. In conclusion, our results indicate an involvement of K(ATP) channels to the hyporesponsiveness of vascular tissue after 24 h from a single injection of LPS in rats. We can presume an increase in the activity of K(ATP) channels on vascular smooth muscle cells but we cannot exclude an increase of K(ATP) channel number probably due to the gene expression activation.