The Effect of Anesthesia and Surgery on Cyp3a Activity in Rats

Abstract

ABSTRACT:The purpose of this investigation was to examine the effects of surgery and anesthesia on in vivo CYP3A activity and portal venous blood flow. Midazolam, a CYP3A probe for both rats and humans, was administered orally (2.7 mg), intravenously (0.57 mg), or via the portal vein (0.57 mg) to rats 4 h after anesthesia with ketamine/ xylazine and surgery for placement of indwelling vascular and duodenal catheters´and 3 days after surgery (chronic). The systemic clearance of midazolam was 51 ؎ 4 ml/min/kg in the chronic animals, and this was significantly decreased (29 ؎ 1 ml/min/kg, P ‫؍‬ 0.024) in acute rats studied 4 to 6 h after anesthesia and surgery. The hepatic availability (F H ), directly determined from the aortic and hepatic venous concentration gradient, was significantly higher in the acute animals (0.57 ؎ 0.05) compared with the chronic animals (0.33 ؎ 0.07, P ‫؍‬ 0.001). Hepatic availability was determined using a classical approach in which F H was calculated from the area under the plasma concentration versus time curve ratio after portal venous or intravenous administration. F H was higher in the acute rats (0.48) compared with the chronic animals (0.27 ؎ 0.03). Portal venous blood flow was significantly lower in the acute animals (5.0 ؎ 0.4 ml/min/100 g body weight) compared with the chronic animals (9.1 ؎ 0.9 ml/min/100 g body weight, P ‫؍‬ 0.015). The effect of surgery and anesthesia was confirmed using the indicator dye dilution method after infusion of [ 14 C]polyethylene glycol 4000 into the superior mesenteric artery. Our data suggest that anesthesia and surgery decreases both hepatic CYP3A activity and hepatic blood flow in rats. Studies performed in rats within 3 days of surgery and anesthesia are conducted under nonphysiologic conditions and therefore provide inaccurate assessment of drug disposition, in particular, clearance and bioavailability.During drug development, in vivo drug absorption and hepatic first-pass metabolism studies commonly are performed in rats, dogs, and primates after surgical manipulation to implant vascular and gastrointestinal catheters. The absorption and bioavailability of orally administered drugs is dependent on intestinal and liver function, including metabolism. The ability to quantify the extent and variability of first-pass metabolism and the inhibition of metabolism in vivo are important for the development of oral dosage forms. To separately determine the effects of the liver on hepatic first-pass metabolism from the contribution by the gut, the area under the plasma concentration versus time curve (AUC) following drug administration via the portal vein is compared with the AUC obtained after oral and intravenous drug administration. These experiments are typically conducted using rodents and are often conducted shortly after the animal has regained its righting reflex. Consciousness and mobility, not gastrointestinal or liver function, are therefore frequently used as parameters of surgical recovery. Although studies have clearly demonstrated tha...

Hydroxyitraconazole, Formed During Intestinal First-Pass Metabolism of Itraconazole, Controls the Time Course of Hepatic CYP3A Inhibition and the Bioavailability of Itraconazole in Rats

“…Experiments were performed at least 5 to 7 days after surgery and anesthesia, which permitted full return to preoperative physiological baseline. This chronically catheterized rat model, in which multiple vascular catheters can be simultaneously sampled under nonstressed, physiological conditions, has been previously described (Uhing and Kimura, 1995a,b) and validated (Beno et al, 2001;Uhing et al, 2004).…”

“…14 C]-PEG in our 5-catheter rat model (Uhing et al, 2004), we assumed that portal venous blood flow (Q PV ) and hepatic artery flow (Q HA ) account for 75 and 25%, respectively, of total hepatic blood flow (Q H ). The rate of ITZ leaving the liver (Rate OUT ) can be represented by…”

“…1), we administered ITZ intraduodenally and obtained blood samples simultaneously from aorta, portal vein, and hepatic vein. In particular, this recently validated model (Beno et al, 2001;Uhing et al, 2004) obviated the need to administer ITZ by both the intravenous and duodenal route. The measurement of the real-time changes in the absorption rate of ITZ and in hepatic availability, F H , of ITZ and OH-ITZ permitted us to assess the separate roles of the liver and intestine in the disposition of ITZ in rats.…”

“…1), we administered ITZ intraduodenally and obtained blood samples simultaneously from aorta, portal vein, and hepatic vein. In particular, this recently validated model (Beno et al, 2001;Uhing et al, 2004) obviated the need to administer ITZ by both the intravenous and …”

“…However, the contribution of the intestinal epithelia to the overall "first-pass effect" of drugs is difficult to quantify because the small intestine and liver are connected in series. Correct assessment of the separate roles of hepatic and intestinal drug metabolizing capacity in determining drug bioavailability and the extent of first-pass metabolism led us to develop (Uhing and Kimura, 1995a,b;Beno et al, 2001) and validate (Esguerra et al, 2000;Shaw et al, 2002;Uhing et al, 2004) a 5-catheter rat model for pharmacokinetic and drug-drug interaction studies in rats. Drug disposition studies can be conducted in awake, free-moving animals that have fully recovered from surgery and anesthesia and have regained their preoperative weight.…”