Glycogenesis in the cultured fetal and adult rat hepatocyte is differently regulated by medium glucose.

Abstract

We examined the glycogenic response to glucose in cultured fetal and adult rat hepatocytes. After a 48-h culture in Dulbecco's modified Eagle's medium, 1 mM glucose, insulin, and cortisol, cells were cultured for 4 h in serum-free medium containing glucose (1-30 mM) and U-14C-glucose. Incorporation of 14C-glucose into glycogen was greater in fetal hepatocytes compared with adult hepatocytes at all glucose concentrations (p < 0.001). Net glycogenic rate in fetal cells was greatest between 1 and 8.3 mM (7.7- +/- 1.1-fold increase) compared with a 3.8- +/- 0.6-fold increase in adult cells. In contrast, there was a 19.4- +/- 2.7-fold increase in glycogen accumulated between 8.3 and 30 mM glucose in the adult and a 1.6 +/- 0.1-fold increase in the fetus. Total glycogen synthetase activity was higher in fetal than adult hepatocytes (p < 0.001), but the active a form was similar in fetal and adult hepatocytes. Glycogen synthase a/+b was stimulated at 8.3 mM or greater glucose in fetal hepatocytes, and 5.7 mM or greater in adult hepatocytes (p < 0.05). Total phosphorylase did not change with medium glucose, but glycogen phosphorylase a/a4+b decreased in adult hepatocytes incubated in 5.7 mM glucose or greater (p < 0.05). Fetal phosphorylase a/a+b was increased at 8.3 mM or greater glucose (p < 0.05). In contrast, both adult and fetal phosphorylase were activated by glycogen. A glucose-induced increase in active phosphorylase may induce the decrease in net glycogenic rate at high glucose in fetal hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)