Effect of short‐term exercise on gluconeogenesis by rat kidney cortex

Abstract

The effect of physical training on renal gluconeogenesis has been described by Krebs et al. [ 11, who showed enhanced rates of gluconeogenesis from lactate, pyruvate and fumarate. We have found an increase in the activity of phosphoenolpyruvate carboxykinase (PEPCK) in rat kidney after 2 hr of swimming [2] which is probably related to the accompanying metabolic acidosis. The latter is known to accelerate renal gluconeogenesis by increasing PEPCK activity [3-71. In this paper, we report the effect of short-term exercise on gluconeogenesis from several substrates in slices from rat kidney cortex. To evaluate further the role of acidosis in exercise-induced renal gluconeogenesis, kidney slices from animals given bicarbonate were also studied. ExperimentalFemale Wistar rats weighing 150-200 g were used. The animals were forced to swim in a water bath (22") for 2 hr. In some experiments acidosis was prevented by tubefeeding the rats with 10 ml of a 200 mM NaHC03 solution prior to the exercise, the control animals being fed 10 ml of a 200 mM NaCl solution.The rats were'sacrificed by cervical dislocation. The measurement of gluconeogenesis was carried out according to Krebs [8], by incubating washed cortex slices in a saline medium to which substrates had been added in a 10 mM concentration, at 40" for 1 hr, with 0, t CO2 (95:5) as the gas phase. Tissue North-Holland Publishing Company -Amsterdam(3-10 mg dry wt) was suspended in 4 ml of the medium and shaken in 25 ml conical flasks. After incubation, the slices were removed and weighed after drying at 110". Glucose was determined by the glucase-oxidase method [8,9].The PEPCK activity was assayed spectrophotometrically in the direction of oxalacetate synthesis as previously described [ 21. Results and discussionThe results given in the table show that the production of glucose was significantly greater with slices from exercised animals when L-lactate, pyruvate, L glutamine and L-glutamate were used as gluconeogenie substrates than with slices from control animals. When dihydroxyacetone and fructose were used, the increases of glucose production were lower.These findings indicate that, as expected, glucose production is considerably enhanced only from substrates that enter the gluconeogenic pathway before the step catalysed by PEPCK. They are in agreement with the results obtained by Goodman et al. [lo], who demonstrated an acceleration of gluconeogenesis from glutamine, glutamate, a-ketoglutarate and oxalacetate but not from fructose or glycerol in kidney slices from rats made acidotic by ammoniun chloride administration.The similarity between the metabolic behaviour of rat kidney cortex in experimental metabolic acidosis and after muscular exercise is evident as far as gluconeogenesis is concerned. It suggests that the stimulatory effect of exercise on renal PEPCK activity and gluconeogenesis is produced by the increase in lactic acid production leading to metabolic acidasis. 25

Stimulation of rat renal phosphoenolpyruvate carboxykinase activity after an intravenous lactic acid load

“…Although the acidosis produced by this system is not as pronounced as that found after swimming (where blood lactate reaches 10 mM in 15 min [S]) the magnitude of renal PEPCK activity and gluconeogenic capacity increases was similar to that found after 2 h swimming [6,7]. These findings suggest that kidney cortex PEPCK is very sensitive to acidosis.…”

Metabolic control of hepatic gluconeogenesis during exercise

“…9-fold. Several investigators have also demonstrated that exercise increases gluconeogenesis in rat kidney-cortex slices incubated in vitro (Krebs & Yoshida, 1963;Sanchez-Medina et al, 1972).…”