Oral absorption of sodium pentobarbital and effects on gastrointestinal function

An anaesthetic dose (40 mg/kg) of sodium pentobarbital (SP) was administered intragastrically to adult, fasted male rats at total dosing volumes of 1, 2, or 3 ml. Area under the plasma concentration-time curve did not differ for the various dosing volumes. During the initial (rapid) phase of gastric emptying all solutions containing drug appeared to empty at a faster rate than distilled water (2 ml). However, solutions containing drug emptied much more slowly than water during the terminal (slow) phase of gastric emptying. Drug solutions moved along the small intestine at approximately the same rate as distilled water. SP significantly lowered rectal temperature and slowed the propagation velocity of the migrating myoelectric complex (MMC) recorded from four serosal electrodes chronically implanted along the proximal small intestine. In addition, the drug significantly decreased the rate of MMC recurrence, extended the duration of MMC phases, and decreased slow wave frequency at all sites monitored. The results suggest that: 1) the relative oral bioavailability of sodium pentobarbital is not influenced by dosing volume within the range tested, 2) the various dosing volumes of SP tested moved through the gastrointestinal tract at an equal rate, and 3) orally administered SP significantly decreases the propagation velocity and periodicity of the MMC in the small intestine.