The liver tissue was homogenized in 0.1 M Tris–HCl buffer, pH 7.4 and the super- natant was used for the assay of hexokinase (Brandstrup et al. 1957), glu- cose-6-phosphatase (Koide and Oda 1959), fructose-1,6-bisphosphatase (Gancedo and Gancedo 1971), lactate dehydrogenase (King 1959), glyco- gen synthase (Leloir and Goldenberg 1979) and glycogen phosphorylase (Cornblath et al. 1963). Another portion of wet liver was used for the esti- mation of glycogen content (Morales et al. 1973).