C3435T polymorphism of the MDR1 gene is not associated with blood levels of hypothalamus-pituitary-adrenal axis hormones in healthy male subjects.

In vitro studies have shown that multidrug resistance protein 1 (MDR1) has an affinity for cortisol; however, in vivo association studies on the relationship between MDR1 gene polymorphisms and blood cortisol levels have produced inconsistent results. Therefore, we examined the effects of the C3435T polymorphism of the MDR1 gene on blood levels of hypothalamus-pituitary-adrenal (HPA) axis hormones such as cortisol and adrenocorticotropic hormone (ACTH) in healthy subjects. The subjects comprised 30 healthy Japanese males. Ten subjects were recruited for each of the C3435T MDR1 genotypes: C/C, C/T, and T/T. Blood samples were taken at 6:00 pm on two occasions with an interval of 2 weeks. Blood levels of cortisol and ACTH were determined by an electrochemiluminescence immunoassay. There were no significant differences in the blood levels of the HPA axis hormones among the MDR1 genotypes. The present study suggests that the C3435T MDR1 polymorphism does not affect blood levels of HPA axis hormones in healthy Japanese males.