Phenytoin and electric shock-induced apoptosis in rat peripheral blood lymphocytes

The apoptotic index (AI) of peripheral blood lymphocytes (PBL) and plasma corticosterone (CS) levels were determined in Wistar rats treated with phenytoin (PHT) at therapeutic and toxic doses (100 or 200 mg/kg/day, respectively, over a period of 7 days) and stressed by bifrontal electric shock (60 Hz/40 mA/0.2 seg). The values of CS and AI were found to be significantly higher in rats submitted to electric shock (ES) and in rats treated with therapeutic and toxic doses of PHT plus ES, than in rats treated only with PHT (P<0.001). The plasma concentrations of PHT were found to be significantly higher in rats treated with toxic doses than in those treated with therapeutic doses (P<0.001), while the control group (without treatment) and vehicle group (propilenglycol–ethanol–water, 40:10:50), showed low levels of CS, and less than 1% of AI. The DNA analysis by electrophoresis in agarose in all the groups was positive, displaying the ladder pattern characteristic of apoptotic process (200 bp), except in the control groups (no treatment and vehicle treated). Our results demonstrate that chronic stress, caused by ES, produces an elevation of CS. The values of apoptosis were correlated with the CS levels, suggesting that the apoptotic inductor process is a consequence of an increase in the concentration of corticosterone in plasma, in response to the hypothalamic–pituitary–adrenals (HPA) axis activation, while phenytoin at therapeutic doses is only a moderate apoptosis inductor.