Abstract
A series of experiments was conducted to assess the effects of prior dosing and/or multiple modest blood withdrawal on subsequent carbon tetrachloride (CCl4)-induced hepatotoxicity. Adult male Wistar rats were randomly assigned to the following treatments: oil-CCl4, oil-bleed-CCl4, CCl4-CCl4, and CCl4-bleed-CCl4, with bleed groups having 1 ml of blood removed at baseline (time 0), 24, 48, 72, and 120 h. At these times the levels of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were determined. The serum enzyme levels of the CCl4 (0.9 ml/kg, vol/vol in corn oil, per os) treated rats (treated at time 0) had returned to untreated levels prior to the administration of the second dose (120 h). Serum enzyme (AST/ALT) levels were measured again 24 and 48 h after the second CCl4 (0.9 ml/kg, 1:1 vol/vol in corn oil, per os) treatment. The results indicated that the prior dose of CCl4 (0.9 ml/kg, 1:1 vol/vol in corn oil, per os) enhanced the hepatotoxicity of a subsequent identical dose of CCl4 three- to six-fold when the two doses were separated by 2–14 days, although the prior dose was protective when administered 24 h before the second dose. Prior multiple blood drawing also enhanced the hepatotoxicity of a subsequent dose of CCl4 (0.9 ml/kg, 1:1 vol/vol in corn oil, per os) three-fold. The effect of blood drawing has been demonstrated to cross sex and strain when tested on male and female Sprague-Dawley and Wistar rats. The combination of the two procedures (with the two CCl4 doses separated by 5 days) enhanced the hepatotoxicity of a subsequent identical dose of CCl4 (0.9 ml/kg, 1:1 vol/vol in corn oil, per os) 10-fold. Subsequent sham bleed experiments indicated that the increase in serum enzyme levels previously associated with blood withdrawal is substantially associated with the handling (i.e. stress) involved in blood withdrawal rather than the removal of modest amounts of blood per se.