PT - JOURNAL ARTICLE AU - Cuiping Chen AU - Gary M. Pollack TI - Altered Disposition and Antinociception of [<span class="sc">d</span>-Penicillamine<sup>2,5</sup>] Enkephalin in<em>mdr1a</em>-Gene-Deficient Mice DP - 1998 Nov 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 545--552 VI - 287 IP - 2 4099 - http://jpet.aspetjournals.org/content/287/2/545.short 4100 - http://jpet.aspetjournals.org/content/287/2/545.full SO - J Pharmacol Exp Ther1998 Nov 01; 287 AB - This study was undertaken to test the hypothesis that P-glycoprotein (P-gp) modulates opioid peptide pharmacodynamics. [d-Penicillamine2,5]enkephalin (DPDPE) (10 mg/kg i.v.) was administered to mdr1a(−/−) and wild-type mice to assess systemic disposition and antinociception. A subsequent dose-response experiment examined the impact of P-gp on DPDPE antinociception. In addition, the time course of antinociception was determined after a 0.9-mg/kg [mdr1a(−/−) mice] or 24-mg/kg (FVB mice) i.v. dose. Data were fit with a series of pharmacokinetic-pharmacodynamic models to compare the disposition and action of DPDPE in the two mouse strains. A 10-mg/kg dose produced &gt;80% maximum possible response at all time points inmdr1a(−/−) mice; peak antinociception was &lt;20% maximum possible response in FVB mice. DPDPE systemic disposition did not differ between the two mouse strains. Although brain tissue concentrations were 2- to 4-fold higher in mdr1a(−/−)compared to FVB mice, the dose required to elicit comparable antinociception was nearly 30-fold lower in mdr1a(−/−)mice; brain tissue EC50 differed by an order of magnitude in the two mouse strains. Pharmacokinetic-pharmacodynamic modeling indicated that the difference in antinociception betweenmdr1a(−/−) and FVB mice was a function of DPDPE distribution within brain, as well as between blood and brain, and not due to differences in intrinsic response. The results of this study suggest that DPDPE is a substrate of P-gp, and that P-gp is responsible, in part, for the low penetration of DPDPE into brain. The substantial difference in brain tissue EC50 in the absence vs. presence of P-gp suggests that P-gp modulates DPDPE-associated antinociception at sites other than the blood-brain interface. The American Society for Pharmacology and Experimental Therapeutics