P-glycoprotein has negligible effects on estradiol and testosterone in mice

P-glycoprotein (P-gp) is an important factor at the blood-brain barrier preventing passage of a wide variety of substances into the brain. Several studies have provided evidence that some drugs and certain steroid hormones are substrates or inhibitors of P-gp. However, the situation is unclear with regard to gonadal steroids, which have considerable central nervous effects. In vitro, experiments on the relationship between estradiol and P-gp are equivocal. We used abcb1ab knock-out mice and wild-type mice to determine the uptake of [3H]-17-beta-estradiol and [3H]-testosterone into the cerebrum and other organs after subcutaneous administration. The organ/plasma quotients showed no significant group effects. We concluded that P-gp does not influence the penetration of testosterone and estradiol to a biologically significant extent.