Effects of progesterone and norethisterone on cephalexin uptake in the human intestinal cell line Caco-2.

Little is known about the regulatory effects of steroid hormones on the intestinal H(+)/oligopeptide transporter PEPT1. In the present study, we investigated the effects of progesterone and its related compounds on the uptake of cephalexin, a typical PEPT1 substrate, using the human intestinal cell line Caco-2. Caco-2 cell monolayers were cultured on plastic cell culture plates coated with rat tail collagen type I. The determination of cephalexin uptake was performed with HPLC. To investigate the effect of progesterone treatment on cephalexin uptake, the monolayers were incubated with cephalexin after progesterone treatment. Progesterone decreased cephalexin uptake in a concentration-dependent manner, and the IC(50) value was calculated to be 2.3 microM. A significant decrease in cephalexin uptake was observed after progesterone treatment for 12 h, and the decrease was maximal when the monolayers were treated for 24-72 h. Cephalexin uptake was significantly inhibited by treatments with 17alpha-hydroxyprogesterone, norethisterone, and chlormadinone. By contrast, treatment with dehydroepiandrosterone, pregnenolone, estradiol, testosterone, hydrocortisone, and dexamethasone did not affect cephalexin uptake. The effects of progesterone and norethisterone treatment on the kinetic parameters of cephalexin uptake were investigated. The saturable component of cephalexin uptake was markedly inhibited by progesterone and norethisterone treatments. The J(max) of cephalexin uptake with progesterone and norethisterone treatments was significantly decreased compared with the control, whereas K(m) and K(d) values were not affected. Therefore the quantitative decrease in PEPT1 density is considered to be one cause of the decrease in cephalexin uptake with progesterone and norethisterone treatments.