Effect of simulated weightlessness on phase II drug metabolism in the rat.
BACKGROUND
Exposure to weightlessness is known to alter physiological processes in humans and animals. As a result of these changes, hepatic drug metabolism may be altered as well. Indeed, short term simulated weightlessness in the rat has been shown to increase oxidative metabolism.


OBJECTIVE
Simulated weightlessness will increase Phase II drug metabolism in the rat during short-term tail suspension.


METHODS
The tail-suspended rat model was used to simulate weightlessness. Rats were subjected to 1, 3, 7, or 10 d of tail-suspension in order to mimic the effect of exposure to a microgravity environment. One additional rat group was not suspended and served as a control. On the final day of the study, rats we administered a single intravenous bolus dose of acetaminophen 25 mg x kg(-1) through an implanted jugular catheter and serial blood samples were taken for 90 min. Serum acetaminophen concentrations were measured by high-performance liquid chromatography. Pharmacokinetic parameters were determined by using standard model independent methods.


RESULTS
The results show that simulated weightlessness in the rat has no effect on Phase II drug metabolism, using acetaminophen as a marker compound.


CONCLUSIONS
These data support the hypothesis that simulated weightlessness in the rat modulates oxidative metabolism, but not drug conjugation to glucuronide or sulfate metabolites. These data offer insight into the physiological changes and variability seen in hepatic metabolic profiles in humans and animals following actual spaceflight.
Brunner
L J
LJ
Pharmaceutics Division, College of Pharmacy, The University of Texas at Austin, USA. ljb@mail.utexas.edu
Bai
S
S
Abdus-Salaam
H
H
D000082:Acetaminophen / Q000097:blood* / Q000493:pharmacokinetics*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004734:Energy Metabolism; D008297:Male; D023421:Models, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D018474:Weightlessness Simulation
D000082:Acetaminophen