Probucol preserves endothelial function by reduction of the endogenous nitric oxide synthase inhibitor level

Abstract

1. Oxide low-density lipoprotein (ox-LDL) is believed to play an important role in early events of atherogenesis, and asymmetric dimethylarginine (ADMA) is associated with the development of endothelial dysfunction. The present study examined the effect of a single injection of native low-density lipoprotein (LDL) on endothelium function and the serum level of ADMA and the effect of probucol on endothelium function and ADMA level in rats. 2. Endothelial injury was induced by intravenous injection of LDL at the dose of 2, 4, or 6 mg kg(-1) for 24, 48, or 72 h, and vasodilator responses to acetylcholine in the aortic rings and serum levels of ADMA, nitrite/nitrate (NO) and malondialdehyde (MDA) were determined. 3. Pretreatment with LDL markedly reduced endothelium-dependent relaxation in a concentration-dependent manner. Inhibition of vasodilator responses to acetylcholine by LDL was abolished in the presence of L-arginine (3 x 10(-4) M). Serum levels of ADMA and MDA were significantly elevated in the rats pretreated with LDL, while serum level of nitrite/nitrate was markedly decreased. 4. Pretreatment with probucol significantly improved endothelium-dependent relaxation, decreased concentrations of ADMA and MDA and increased nitrite/nitrate level in the rats treated with LDL. A similar effect was seen in the rats pretreated with an antioxidant vitamin E. 5. These results suggest that a single injection of native LDL causes endothelial dysfunction by elevation of ADMA levels and that the protective effect of probucol on endothelial cells is related to reduction of ADMA concentration.

Figure 1

The dose-effect curve (A) and the time-effect curve (B) of vasodilator responses to acetylcholine in the isolated rat thoracic aorta in the rats pretreated with native LDL. Native LDL was given intravenously. The aorta rings were precontracted by phenylephrine (10⁻⁶ M). Values are means±s.e.mean, n=6∼8. **P<0.01 compared with control.

Figure 2

Effect of probucol, vitamin E or L-arginine on endothelium-dependent relaxation to acetylcholine. Probucol and vitamin E were given orally (A). Rings was exposed to L-arginine (B). The rats were treated with LDL at the dose of 4 mg kg⁻¹ for 48 h. Values are means±s.e.mean, n=6∼8. *P<0.05, **P<0.01 compared with LDL.

Figure 3

Effect of LDL on serum levels of ADMA. The dose-effect (A) and the time-effect (B) relationship of LDL. Native LDL was given intravenously. Values are means±s.e.mean, n=6∼8. **P<0.01 compared with control.

Figure 4

Effect of probucol or vitamin E on serum levels of ADMA. Probucol and vitamin E were given orally. The rats were treated with LDL at the dose of 4 mg kg⁻¹ for 48 h. Values are means±s.e.mean, n=6∼8. ⁺⁺P<0.01 compared with control, **P<0.01 compared with LDL.

Figure 5

Effect of LDL on serum levels of NO. The dose-effect (A) and the time-effect (B) relationship of LDL. Native LDL was given intravenously. Values are means±s.e.mean, n=6∼8. **P<0.01 compared with control.

Figure 6

Effect of probucol or vitamin E on serum levels of NO. Probucol and vitamin E were given orally. The rats were treated with LDL at the dose of 4 mg kg⁻¹ for 48 h. Values are means±s.e.mean, n=6∼8. ⁺⁺P<0.01 compared with control, **P<0.01 compared with LDL.

Figure 7

Effect of LDL on serum concentrations of MDA. The dose-effect (A) and the time-effect (B) relationship of LDL. Native LDL was given intravenously. Values are means±s.e.mean, n=6∼8. *P<0.05, **P<0.01 compared with control.

Figure 8

Effect of probucol or vitamin E on serum levels of MDA. Probucol and vitamin E were given orally. The rats were treated with LDL at the dose of 4 mg kg⁻¹ for 48 h. Values are means±s.e.mean, n=6∼8. ⁺P<0.05 compared with control, *P<0.05, **P<0.01 compared with LDL.