Use of loperamide as a phenotypic probe of mdr1a status in CF-1 mice.
OBJECTIVE
A subpopulation of the CF-1 mouse strain (approximately 25%) lacks P-gp expression, and consequently, increased brain penetration of many substrates is observed in these animals. Mice lacking the mdr1a gene represent an important research tool to study the potential effects of P-gp on CNS substrate disposition.


METHODS
Adult CF-1 mice were used in all experiments. Loperamide-induced antinociception was determined by the hotplate latency test at 0.25, 2, and 4 h post-dose. At the conclusion of the pharmacodynamic experiment(s), trunk blood and brain tissue were collected and analyzed by high-performance liquid chromatography-mass spectrometry (LC-MS/MS). Mice were also genotyped for their mdrla status via RT-PCR.


RESULTS
All mice with three consecutive effects of maximum hotplate latency (60 s) showed considerable opioid-like behavior in addition to antinociception. Mice without three consecutive effects of maximum hotplate latency (< or = 30 s) showed no opioid-like behavior. The loperamide brain-to-serum ratio in mice identified as P-gp-deficient was 65-fold higher compared to the P-gp-competent animals (10.1 +/- 1.0 vs. 0.155 +/- 0.018). All animals identified as phenotypically P-gp-competent based on the hotplate assay evidenced the mdrla(+/+) genotype.


CONCLUSIONS
This assay appears to offer a rapid and unambiguous measure via a relatively non-invasive, simple technique to identify P-gp status in the CF-1 subpopulation of mice.
Kalvass
J Cory
JC
Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Graff
Candace L
CL
Pollack
Gary M
GM
D018435:ATP Binding Cassette Transporter, Subfamily B / Q000235:genetics*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000502:physiology; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001812:Blood-Brain Barrier / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D005838:Genotype; D008139:Loperamide / Q000097:blood; D051379:Mice; D018345:Mice, Knockout; D010641:Phenotype; D011930:Reaction Time / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D008139:Loperamide; C095122:multidrug resistance protein 3