Characterization of uptake of steroid glucuronides into isolated male and female rat hepatocytes.

The uptake of estradiol-17 beta(beta-D-glucuronide) (E(2)17G), estriol-16 alpha(beta-D-glucuronide (E(3)16G), estradiol-17 beta-3-(beta-D-glucuronide) (E(2)3G) and taurocholate (TC) into hepatocytes isolated from male and female rats was examined and found to be linear for at least 75 sec and to exhibit Michaelis-Menten kinetics. The Vmax (nanomoles per minute per milligram of protein) for uptake in female rat hepatocytes ranged from 0.56 for TC to 2.32 for E(3)16G and from 0.89 for TC to 1.62 for E(2)17G in males. For TC, E(2)17G and E(2)3G, the Vmax for uptake was the same or higher in males, whereas for E(3)16G the Vmax was approximately 2-fold higher in females. The Km for TC was approximately equal in males and females, whereas for E(2)17G and E(3)16G, males exhibited a 3- to 9-fold lower Km. The rate of uptake of E(2)17G (100 microM) was decreased in the presence of carbonylcyanide-m-chlorophenylhydrazone (23%), 2,4-dinitrophenol (54%), potassium cyanide (38%), iodoacetic acid (46%) and rotenone (50%) and was reduced by 30 to 40% when sodium was replaced with lithium or choline or in the presence of ouabain. The rate of uptake of all the organic anions was reduced by 80 to 85% at 0-4 degrees C and the cell/medium concentration ratios at 75 sec (37 degrees C) exceeded 1. Thus, the steroid glucuronides are taken up by the hepatocyte by a saturable process; E(2)17G uptake was found to be partially dependent upon metabolic energy and an intact sodium gradient. Substrate-dependent differences in the rate of uptake between male and female rat hepatocytes were also seen.