Sialyltransferase activities in cultured rat hepatocytes.

Previous studies on the age and sex dependency of the ganglioside patterns in rat liver in vivo and the concomitant determination of the activities of some enzymes involved in these pathways revealed the prominent role of the sialylation of GM3 to GD3 in determining the flow to the mono (a)- and polysialo (b)-series, respectively. Here, the influence of hormones on the activities of GM3 and GD3 synthases in isolated hepatocytes was studied. The combination of several factors (insulin, glucagon, epidermal growth factor, glucocorticoids) was found to be necessary for maintaining in vivo activity levels of GD3- but not of GM3-synthase.