Sulphate
ions have been known for some years to enhance the activity of
hepatic glycogen phosphorylase b in vitro. Here we report that
intravenous injections of 4.92 mmol of Na2SO4/kg body wt. to rats induced marked hepatic glycogenolysis in vivo, accompanied by
polyuria,
glycosuria and a mild hyperglycaemia. These effects were observed both in normal (Wistar) rats and in gsd/gsd rats that lacked hepatic
phosphorylase kinase. In both rat strains the activity of
glycogen phosphorylase in
liver extracts was enhanced by pretreatment of the animals with Na2SO4, but in
phosphorylase kinase-deficient livers the enhancement was solely in
phosphorylase b activity, whereas both the a and b forms of the
enzyme were activated in normal livers. Hepatic glycogenolysis was also induced by perfusing rat livers, both normal and gsd/gsd, with 25 mM-Na2SO4. Under these conditions both the rat strains showed only enhanced activities of
glycogen phosphorylase b. This suggested that the increased activity of
phosphorylase a in the extracts of normal livers after Na2SO4 administration in vivo was due to a hormonally mediated conversion of the b form into the a form. The activation of
glycogen phosphorylase b was stable to dilution and appeared to be due to a long-lasting structural change in the
enzyme or very tight binding of an activator.