The influence of partial hepatectomy on the pharmacokinetics of preoperatively injected 4'-epidoxorubicin in rats

Influence of partial hepatectomy in rats on the activity of hepatic microsomal enzymatic systems

The influence of partial hepatectomy on the activity of the hepatic microsomal enzymatic systems was determined in rats. Cytochrome P-450, cytochrome b5, four mixed functional oxidase (MFO) activities (microsomal aniline hydroxylase, p-nitroanisole O-demethylase, aminopyrine N-demethylase and NADPH cytochrome c reductase) and glutathione levels were measured in unhepatectomized rats (control group) and in hepatectomized rats 12 h, 24 h, 3 days and 6 days after 70% hepatectomy. Following surgery the remaining lobes of the liver grow rapidly in order to restore the original liver mass. Partial hepatectomy significantly reduces cytochrome P-450 and b5 content in the remaining liver as well as the four MFO activities studied. But when the enzymatic systems are expressed as nmoles/mg microsomal protein, only cytochrome P-450 shows statistical differences. The hepatic biotransformation capacity of drugs and xenobiotics decreases during the regeneration period due to the reduction of hepatic mass rather than because of a reduction of their metabolic capacity. Glutathione levels are increased after partial hepatectomy but increased glutathione-dependent protector mechanisms are not expected.

Influence of partial hepatectomy on theophylline pharmacokinetics in rats

The influence of partial hepatectomy on the pharmacokinetics of theophylline was determined in rats. The pharmacokinetics of intravenous theophylline was studied in unhepatectomized rats (control group: CG) and in hepatectomized rats (HG) 12 h after 70% hepatectomy. Liver function was monitored in both groups by measurements of total and direct bilirubin, transaminases GOT and GPT, and plasma protein. Seventy per cent hepatectomy caused significant liver dysfunction: transaminase levels (GOT and GPT) increased by 118 and 683%, respectively, and the total and direct bilirubin levels increased by 28.6 and 9.1%, respectively. At the same time, plasma concentrations of theophylline decreased significantly and half-life increased from 4.16 +/- 0.57 h (CG) to 7.08 +/- 0.69 h (HG), as did the distribution volumes values of central (Vc) and peripheral (Vp) compartments (Vc: CG, 0.18 +/- 0.03 L; HG, 0.24 +/- 0.03 L) (Vp: CG, 0.08 +/- 0.05 L; HG, 0.13 +/- 0.05 L). The percentage of theophylline binding to plasma proteins decreased from 44.3% in CG to 33.8% in HG. The theophylline intrinsic clearance (CLint) dropped from 1.35 +/- 0.43 mL/min (CG) to 0.93 +/- 0.10 mL/min (HG)1, which can be attributed to a significant fall in the quantity of hepatic microsomal enzymes. These modifications on the pharmacokinetics of drugs with low hepatic extraction coefficients, such as theophylline, should be considered when dosage regimens during the posthepatectomy hepatic regeneration period are planned.