Differential time course of liver and kidney glucose-6 phosphatase activity during fasting in rats

We have studied the time course of hepatic and renal microsomal glucose-6 phosphatase (Glc-6Pase) during long-term fasting in the rat. Liver microsomal Glc-6Pase increases up to 48 hr and significantly decreases after 48 hr of fasting. The following activities were determined at 0, 24, 48, 72 and 96 hr: 0.31 ± 0.02; 0.50 ± 0.02; 0.54 ± 0.03; 0.44 ± 0.03; 0.44 ± 0.01 μmol min⁻¹ mg protein⁻¹, respectively (all values are means ± SEM, n = 6). Concomitantly, kidney microsomal Glc-6Pase progressively increases throughout the fast (V_m = 0.21 ± 0.01; 0.26 ± 0.004; 0.30 ± 0.01; 0.37 ± 0.02; 0.40 ± 0.01 μmolmin⁻¹ mg protein⁻¹, from 0 to 96 hr, respectively). These data suggest that the differential expression of Glc-6Pase activity in the liver and the kidney during long-term fasting could have an important role in the shift from a principally hepatic gluconeogenesis to a hepatic and renal gluconeogenesis.