INFLUENCE OF DIABETES ON NOREPINEPHRINE-INDUCED INOSITOL 1,4,5-TRISPHOSPHATE LEVELS IN RAT AORTA

The effects of norepinephrine on total tissue levels of inositol 1,4,5-trisphosphate were measured by protein binding assay in aortas from rats with chronic streptozotocin-induced diabetes and from age-matched control rats. In both control and diabetic aortas, norepinephrine induced a rapid, transient and concentration-dependent elevation of inositol 1,4,5-trisphosphate content during contraction. Maximum production of inositol 1,4,5-trisphosphate in response to norepinephrine was greater in diabetic than in control aortas. However, the sensitivities of control and diabetic aortas to norepinephrine for inositol 1,4,5-trisphosphate production were not significantly different. Enhanced norepinephrine-induced production of inositol 1,4,5-trisphosphate in diabetic aortas may contribute to the increased maximum contractile responsiveness of these arteries to the agonist. However, since enhanced contractile responses of diabetic aortas to norepinephrine were also detected at times when inositol 1,4,5-trisphosphate levels were not significantly increased, other factors also appear to be involved in mediating enhanced contractions of diabetic arteries to norepinephrine.