Comparison between the effects of intraperitoneal injection of LDL and intravenous injection of LDL on arterial endothelial cells apoptosis.

To observe the effect of oxidized low density lipoprotein (OxLDL) on arterial endothelial cells apoptosis in vivo, we established a model in which Sprague-Dawley rats were given intraperitoneal and intravenous injection of unmodified LDL (8 mg/kg every day) via the tail vein. Seven days after the injection, the aortic endothelial cells specimens were prepared by an en face preparation of rat aorta. The apoptotic cells were identified and counted by in situ nick and labelling (TUNEL) method and light microscopy. The numbers of the apoptotic cells were 12.52 +/- 4.71/field in the intraperitoneal injection control group, 11.41 +/- 2.94/field in the intravenous injection control group, 22.98 +/- 8.01/field in the intraperitoneal injection LDL group and 103.8 +/- 11.5/field in the intravenous injection LDL group, respectively. The difference was significant between injection LDL group and control (P < 0.01), and the difference was also significant between two LDL injection groups (P < 0.01). These findings suggest that injection of LDL can induce apoptosis in arterial endothelial cells and the effect is especially significant with intravenous injection LDL. After injection, oxidative modification of LDL may occur in local arteries and causes injury to the endothelial cells.