Erythropoietin (EPO)-induced hypertension in the patients on maintenance hemodialysis is a matter of paticular interest in clinical nephrology. Although various possibility is indicated on the mechanism of the EPO-induced hypertension, we have examined it with special reference to nitric oxide (NO) metabolism in cultured rat vascular smooth muscle cells (VSMC). We already demonstrated that EPO inhibited interleukin -1β induced iNOS mRNA and protein expression and NO production in VSMC.Recent studies have shown that several cytokines could induce apoptosis to VSMC via the induction of NO.In addition, EPO induces cytosolic free calcium ([Ca^<2+>]i) mobilization and also modulates the sensitivity of the cardiovascular system to vasoconsrictive substances such as angiotensin II (AgII), norepinephrine (NE) or endothelin (ET). Therefore, in the present project, we explored whether EPO has a modulatory effect of apoptosis on IL-1β or NO donor sodium nitroprusside (SNP) induced apoptosis in VSMC.

高血圧や糖尿病薬

Furthermore, we explored the mechanism of EPO induced [Ca^<2+>]i mobilization and its role in the activation of MAP kinase and DNA synthesis and explored the effect of EPO on the responsiveness of AgII, NE or ET induced [Ca^<2+>]i mobilization in VSMC.

Our present study demonstrated that rHuEPO inhibited IL-1β or SNP induced VSMC apoptosis. The TK dependent pathway, particularly the PI 3-kinase dependent pathway seems to be critical to the countervailing effect of rHuEPO on IL- 1β and SNP induced VSMC apoptosis.

Concerning the effects of EPO on [Ca^<2+>]i, (1) EPO increases [Ca^<2+>]i by both Ca^<2+> influx and Ca^<2+> release from intracellular stores. Tyrosine phosphorylation is critical in the regulation of [Ca^<2+>]i, but PKC activation is important only in the regulation of Ca^<2+> influx. Dihydoropyridine sensitive L-type Ca^<2+> channel seems to be involved in EPO induced Ca^<2+> influx. In addition, increase of [Ca^<2+>]i by EPO stimulates MAP kinase activation and DNA synthesis in VSMC.Furthermore, EPO has synergistic effects on AgII, NE or ET induced [Ca^<2+>]i mobilization, particularly on intracellular Ca^<2+> release, in VSMC.This may be one of the potential mechanisms that contribute to hypertension associated with EPO therapy. However, further investigations were needed to clarify the effect of lower concentaration of EPO on the dynamics of [Ca^<2+>]i.

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