Nitrate reductasing and immunoblotting test were used to investigate the modulation of protein kinase C (PKC) activity in cultured rat vascular smooth muscle cells (VSMCs) with high concentration of insulin (HI) and the effect of HI on lipopolysaccharides + gamma-interferon (LPS + gamma-IFN)-induced nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression with or without PKC inhibitor H7. The results were that membrane PKC activity preincubated with HI was significantly higher than that with the control group(P < 0.05), and NO production pretreated by HI was obviously lower than that of the control group(P < 0.01). PKC inhibitor H7 ameliorated the down-regulation of LPS + gamma-IFN induced NO production by high concentration of insulin. Immunoblotting test revealed a decrease induced by the high level insulin in the expression of iNOS in VSMCs. It is suggested that hyperinsulinism may activate PKC to partly inhibit the expression of iNOS and decrease NO production in VSMCs.