The important role of renal gluconeogenesis in blood glucose homeostasis has been widely accepted. In order to clarify the details of this phenomenon, gluconeogenesis from various substrates in the kidney from starved and/or partially hepatectomized rats was studied using perfusion techniques.
Gluconeogenesis from oxaloacetate, 2-oxoglutarate, glutamate and glutamine was stimulated significantly by 24h fasting whereas, glucose production from pyruvate and lactate was not enhanced by fasting. With a combination of 24h fasting and partial hepatectomy, gluose production from the latter two substrates showed a tendency to increase. Glucose formation from fructose was stimulated significantly by 24h fasting, but there was no additive enhancement with combined partial hepatectomy.
These data suggest that, (1) the gluconeogenic process from fructose was stimulated by 24h fasting, but that partial hepatectomy combined with fasting was not effective, and that (2) the gluconeogenic process after oxaloacetate was enhanced by 24h fasting, while the process after pyruvate and lactate was stimulated by the addition of partal hepatectomy to fasting. In other words, phosphoenolpyruvate carboxykinase (PEPCK) in kidney was induced by 24h fasting or by partial hapatectomy, and pyruvate carboxylase was induced by the combination of 24h fasting and partial hepatectomy.
In fact, a significant increase in renal PEPCK activity after 24h fasting, and an additive effect of partial hepatectomy to enzyme activity, were demonstrated. The changes in the levels of corticosterone and glucagon in plasma did not correlate with the magnitude of gluconeogenesis or PEPCK activity. Metabolic acidosis was observed neither in fasting nor in partially hepatectomized rats.
The possible role of the reduction of plasma insulin levels and/or blood glucose as a trigger of the above-mentioned metabolic changes might be considered.