TRANSPORT OF DEHYDROEPIANDROSTERONE AND DEHYDROEPIANDROSTERONE-SULFATE INTO RAT HEPATOCYTES

The purpose of the present study was to characterize the transport of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHE AS) into hepatocytes at physiological and pharmacological concentratio ns. Hepatocytes were isolated from female Sprague-Dawley rats by colla genase perfusion. Uptake of [H-3]DHEA and [H-3]DHEAS at increasing con centrations (3.5 nM-100 mu M) was measured by the rapid filtration tec hnique at 30 s intervals up to 120 s. The uptake of DHEAS by hepatocyt es was saturable (K-m = 17.0 mu M; V-max = 3.7 nmol/min/mg cell protei n). In contrast, a specific saturable transport system for DHEA could not be detected in rat hepatocytes. It is suggested that DHEA enters t he cell by diffusion. The uptake of DHEAS could be inhibited by antimy cin A, carbonylcyanide-m-chlorophenylhydrazone, and dinitrophenol (inh ibitors of the mitochondrial respiratory chain), by dinitrofluorobenze ne and p-hydroxymercuribenzoate (NH2- and SH-blockers, respectively), and by monensin (Na+-specific ionophore). No inhibition was seen in th e presence of ouabain (inhibitor of Na+-K+-ATPase) and phalloidin (inh ibitor of cholate transport and actin-blocker). Interestingly, DHEAS u ptake was inhibited by bile acids (cholate, taurocholate and glycochol ate). Conversely, [H-3]cholate uptake was strongly inhibited by DHEAS, which indicates a competition for the same carrier. Replacement of so dium ion with choline markedly decreased uptake velocity at pharmacolo gical DHEAS concentrations. The results suggest that DHEAS uptake is a saturable, energy-dependent, carrier-mediated, partially Na+-dependen t process, and that DHEAS may be taken up via the multispecific bile a cid transport system.