The imidazoline I-1 receptor (I-1 R) agonists are widely used to lower blood pressure, but their effects on hyperlipidemia are still obscure. The present study is aimed to evaluate the possible mechanism(s) of I-1 R in the regulation of lipid homeostasis. Farnesoid X receptor (FXR) plays an important role in blood lipid homeostasis; however, the role of FXR in rilmenidine-induced blood lipid lowering action is still unknown. Thus, we administered rilmenidine, a selective agonist of I-1 R, into high fat diet-fed (HFD) mice showing hypertriglyceridemia and hypercholesterolemia. Rilmenidine significantly ameliorated hyperlipidemia in HFD mice after 7 days of administration. Pretreatment with efaroxan, at a dose sufficient to inhibit I-1 R activation, blocked the effects of rilmenidine. Also, in cultured HepG2 cells, rilmenidine dose-dependently induced the expression of farnesoid X receptor (FXR). The rilmenidine-induced FXR expression and FXR-related genes were blocked by efaroxan. However, rilmenidine treatment did not affect the expression of enzymes related to β-oxidation. In conclusion, activation of I-1 R may activate FXR to lower plasma lipids, suggesting I-1 R as a new target for the treatment of hyperlipidemia.
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