These experiments were conducted to determine 1,2-diacylglycerol (DAG) in the thoracic aorta obtained from streptozocin-induced diabetic rats because 1,2-DAG is assumed to be a second messenger associated with phosphoinositide metabolism. After preincubation for a 25-min stabilization, 1,2-DAG content in isolated thoracic aortas 4 and 8 wk after streptozocin injection was significantly decreased by 42 and 31%, respectively, compared with age-matched control rats on 10-min norepinephrine stimulation (10−5 M). However, 4 wk of daily insulin injection after 4 wk of untreated diabetes significantly shifted 1,2-DAG toward normal levels. Analysis of its fatty acid composition showed a significant difference between control and diabetic rat aortas at both 4 and 8 wk. In particular, the percentage of arachidonate, a precursor of eicosanoids, decreased. Such alteration in the fatty acid profile in diabetic rat aortas was inhibited by insulin treatment. 1,2-DAG content in the 8-wk diabetic group was also significantly decreased by 33% compared with control in the absence of norepinephrine, whereas 1,2-DAG content was lower than in the presence of norepinephrine in both the control and diabetic groups. Cholesterol, triglyceride, and phosphatidylcholine content in diabetic rat aortas was lower than control. Lower levels of 1,2-DAG in the thoracic aorta from diabetic rats were observed in the presence and absence of norepinephrine, suggesting that a defect in 1,2-DAG production may be associated with abnormalities of vascular smooth muscle responsiveness by agonists, as described previously.

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