Influence of mercury of the anesthetic response to and distribution of thiopental in rats.

Pretreatment with HgCl2 (2 mg/kg sc) 24 h before administration of thiopental (35 mg/kg ip) significantly potentiated the duration of thiopental sleeping time in adult male rats but did not influence the onset time for anesthesia. The plasma concentration of free thiopental was significantly higher in the Hg-treated animals 15 and 45 min after thiopental injection (i.e., during the period of thiopental anesthesia), with a concomitant increase of the free thiopental concentration in the brain at 15 min. However, total and free brain thiopental concentrations in Hg-treated rats at the time of awakening were not different from those in saline-treated animals. Urinary thiopental remained unchanged from 0 to 2 h, but was increased in the treated urine from 0 to 27 h. In vitro studies showed a strong inhibition of thiopental binding in 24-h Hg-treated plasma. The results suggest that the prolongation of thiopental anesthesia induced by Hg pretreatment is probably related to changes in the disposition of thiopental in the plasma and brain rather than to an alteration in the sensitivity of the central nervous system.