Methylprednisolone-induced vasodilatation in the isolated hind limb of dogs before and after adrenoceptor blockade.

The vasodilatory effect of the synthetic glucocorticoid methylprednisolone was studied in the vascular bed of the isolated hind limb of the dog. The isolated hind limb was perfused with the animal's blood by means of a roller pump at a flow to maintain a constant control pressure. The effects on hind limb pressure of alpha- and beta-agonists, sodium nitroprusside, and methylprednisolone sodium succinate were observed in unblocked (Group I) as well as in alpha- and beta-adrenoceptor blocked (Group II) animals. The agonists epinephrine (2 micrograms) and isoproterenol (0.5 micrograms) caused significant increases (+45%) and decreases (-43%) in hind limb pressure, respectively, and both sodium nitroprusside (100-200 micrograms) and methylprednisolone (500 mg) caused significant decreases in hind limb pressure of unblocked animals. In animals with adrenoceptors blocked by phenoxybenzamine and propranolol (Group II) the agonists produced no significant effects, but the methylprednisolone and sodium nitroprusside caused significant decreases in pressure, 45% and 28%, respectively. Following vasodilatation by methylprednisolone, sodium nitroprusside caused a slight, but not significant decrease in hind limb pressure. These data show that methylprednisolone will produce significant vasodilatation even in the presence of alpha- and beta-adrenoceptor blockade, indicating that adrenoceptors alone cannot account for the vasodilatory actions of the steroid in the isolated hind limb.