Opposite effect of diabetes mellitus induced by streptozotocin on oral and intravenous pharmacokinetics of verapamil in rats

The aim of this study was to report the effect of diabetes mellitus on the pharmacokinetics of verapamil in a route-dependent manner. Diabetes in rats was induced by streptozotocin. Plasma concentrations of verapamil and its metabolite, norverapamil, were measured after oral (10 mg/kg) or intravenous (1 mg/kg) administration. The concentrations of verapamil in portal plasma after oral administration were also determined. Norverapamil formation was used for assessing CYP3A activity in hepatic and intestinal microsomes of diabetic rats. The protein levels of CYP3A1 and CYP3A2 in liver and intestine were measured by Western blot. It was found that diabetes significantly increased the plasma concentration of verapamil and norverapamil after oral administration, which resulted in a 74% increase in the area under the concentration-time curve (AUC) of verapamil, but the ratio of AUC_{(norverapamil)}/AUC _(verapamil) was significantly decreased by 38%. In contrast, diabetes significantly decreased the AUC of verapamil by 22% after intravenous administration. Diabetes also resulted in increased AUC of verapamil in portal vein by 3.8-fold compared with that in control rats. The absolute bioavailability of verapamil was higher than that of control rats. An in vitro study showed that increased CYP3A activity in the hepatic microsome and decreased CYP3A activity in the intestinal microsome were accompanied by an increase and decrease in the protein expression of CYP3A1/2 in liver and intestine of diabetic rats, respectively. In conclusion, diabetes mellitus revealed a tissue-specific effect on CYP3A activity and expression (induced in liver and inhibited in intestine), resulting in opposite pharmacokinetic behaviors of verapamil after oral and intravenous administration to diabetic rats.