Methylprednisolone and adrenergic mechanisms in vascular smooth muscle

The influence of methylprednisolone on noradrenaline-induced contractions and 3H-noradrenaline release was investigated in isolated preparations of rat aorta and portal vein. 20-200 micro M of methylprednisolone had a slight inhibitory effect on the contractions of the aorta but had no effect in the portal vein. The EC50-values noradrenaline were about 10-6 M in both vessels; methylprednisolone did not change it. The steroid changed neither spontaneous nor potassium (127 mM) induced release of 3H-noradrenaline. The potassium (127 mM) induced contracture in the portal vein had 2 phases; the second, at least partly, was produced by released intramural noradrenaline as it was depressed by reserpinization of the animal. Injection of methylprednisolone to the animal 2 h before sacrifice induced a better maintained second phase of the potassium contracture in the portal vein. Although this could mean the release of increased amounts of noradrenaline, other explanations are also possible.