Metabolism of the renal medulla

Slices of the inner medulla of kidneys removed from hydropenic dogs were incubated with glucose and succinate under aerobic and anaerobic conditions. When theoretical maximum ATP generation was calculated from oxygen uptake and lactate production, the calculated energy production from oxidative degradation of glucose was twice that from glycolysis. Hypertonic solutions of NaCl and urea, in concentrations comparable to those present in vivo, depressed both lactate production from glucose and oxygen uptake in succinate to the same extent. Studies of CO2 generation by medullary slices from labeled glucose in 100% O2 showed a C1/C6 ratio of 3.7, compared to 1.7 for cortex. It is suggested that oxidative metabolism may play a critical role in the renal medulla of intact animals in providing energy for active transport of sodium and thereby facilitating the process by which urine is concentrated.