Primary cultures of hepatocytes in serum and hormone-free medium: identification of conditions which stimulate an in vivo-like induction of G6PD.

Recent results from several laboratories suggest that complex interactions between hormones and dietary carbohydrate may be responsible for regulating the induction of several hepatic lipogenic enzymes. Elucidation of these interactions requires the ability to culture hepatocytes for several days in serum-free medium where the hormones or carbohydrate or both present is strictly controlled. The functional response of primary adult rat hepatocytes was examined in a medium without exposure to serum, hormones, or carbohydrates and on three substrata commonly used to culture cells in a defined medium. Hepatocytes cultured on a floating collagen gel in which is embedded a nylon mesh possess cell attachment and morphologic characteristics superior to either cells cultured on a collagen-coated or fibronectin(Fn)-coated substratum. Cells cultured on the gel-mesh system retain insulin responsivity, as measured by protein synthesis rates and glucose-6-phosphate dehydrogenase (G6PD) induction, for at least 6 d in culture. Under these conditions, insulin, dexamethasone, and fructose increase G6PD specific activity to levels comparable to that seen in an induced animal. Hepatocytes cultured on the gel-mesh system tolerate restricted medium conditions better than cells cultured on collagen or Fn-coated substratum, and remain viable for sufficient times to allow, for the first time, full expression and maximal induction (i.e. like in vivo) of G6PD in cultured cells. This system represents a satisfactory model for in vivo liver metabolism and a superior system for studying the effects of hormones and metabolites on G6PD levels, as well as other nutritional-hormonally regulated enzymes.