Key result
Treatment with olmesartan restored insulin signaling and prevented microvascular rarefaction in the skeletal muscle of spontaneously hypertensive rats, whereas enalapril was less effective.
Why the study?
Does renin-angiotensin system blockade with olmesartan or enalapril improve insulin signaling and prevent microvascular rarefaction in spontaneously hypertensive rats?
Does renin-angiotensin system blockade with olmesartan or enalapril improve insulin signaling and prevent microvascular rarefaction in spontaneously hypertensive rats?
In a rat model of genetic hypertension, ARB therapy with olmesartan was superior to ACE inhibition with enalapril in restoring skeletal muscle insulin signaling, though both prevented microvascular rarefaction.
Answers are grounded in this paper and cite their sources.
Findings in hypertensive rats should not alter clinical RAS inhibitor selection; leaves open whether olmesartan offers unique benefits on insulin signaling in humans.
OBJECTIVE: Spontaneously hypertensive rats are an example of an animal model of genetic hypertension with insulin resistance. The aim of this study was to investigate insulin signaling in the heart and in the skeletal muscle of spontaneously hypertensive rats, as well as to evaluate the effects of renin-angiotensin system blockade. DESIGN AND METHODS: We investigated eight untreated spontaneously hypertensive rats of 12 weeks of age and eight age-matched normotensive Wistar-Kyoto controls. In addition, eight spontaneously hypertensive rats were treated for 8 weeks with the angiotensin receptor blocker olmesartan, and eight spontaneously hypertensive rats with the angiotensin-converting enzyme inhibitor enalapril. The heart and a skeletal muscle (quadriceps femoris) were promptly dissected and frozen. Insulin signaling was evaluated by Western blot analysis of involved proteins; in addition, microvessel density was indirectly evaluated by immunohistochemistry. RESULTS: Blood pressure values were normalized by both olmesartan and enalapril. In the heart, no statistically significant difference in the expression of proteins involved in insulin signaling was observed between untreated spontaneously hypertensive rats and Wistar-Kyoto controls. On the contrary, in the skeletal muscle of untreated spontaneously hypertensive rats, we noted a significant reduction of insulin receptors, of insulin-receptor substrate-1, and of phosphorylated-mammalian target of rapamycin. The treatment with olmesartan normalized insulin signaling, including expression of glucose transporter-4, whereas the treatment with enalapril was ineffective for the insulin receptor and less effective than olmesartan on the insulin-receptor substrate-1, phosphorylated-mammalian target of rapamycin and glucose transporter-4. There was a significant reduction in microvessel density in the skeletal muscle of spontaneously hypertensive rats compared with Wistar-Kyoto controls, and this was completely prevented by both olmesartan and enalapril. CONCLUSION: These results suggest that changes in insulin signaling occur in the skeletal muscle but not in the heart of untreated spontaneously hypertensive rats. In the skeletal muscle, insulin signaling was restored by olmesartan, whereas enalapril was less effective. Effective antihypertensive treatment with olmesartan or enalapril was associated with prevention of microvascular rarefaction.
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Rizzoni et al. (2008) studied Genetic hypertension with insulin resistance (animal model) (n=32). Olmesartan or enalapril vs. Untreated spontaneously hypertensive rats and Wistar-Kyoto controls was evaluated on Insulin signaling (protein expression) and microvessel density in heart and skeletal muscle. Treatment with olmesartan restored insulin signaling and prevented microvascular rarefaction in the skeletal muscle of spontaneously hypertensive rats, whereas enalapril was less effective.
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