Molecular adaptations to the diving habit: on the possible role of glycerol in the ischemic seal kidney

Abstract

1. 1. Isolated perfused kidneys of the spotted seal ( Phoca vitulina richardsi) are able to withstand long periods of ischemia and resultant anoxia. In this state the major source of energy of the kidney cortex appears to be glycogen, wich is converted stoichiometrically to lactate. 2. 2. After about 45 min of ischemia glycogen stores in kidney cortex are effectively depleted: yet lactate concentrations continue to rise, albeit at a lower rate. 3. 3. On the basis of an observed rapid increase in concentrations of the free fatty acids in the tissue, the source of this additional lactate is glycerol from triglycerides within the tissue. 4. 4. When seal kidney, which is ischemic during the dive, is compared to seal heart, which is perfused during the dive, the activities of the enzymes glycerokinase, α-glycerophosphate dehydrogenase and triosephosphate isomerase are substantially higher in seal kidney cortex than in seal heart, or kidney of the domestic dog. 5. 5. This suggests the existence of a short metabolic sequence that can augment the finite stores of carbohydrate in this usually active tissue during a long and arduous dive. 6. 6. This sequence does not become active until glycogen stores are virtually depleted and the kidney cortex cell's energy charge is much reduced (from 0.84 to 0.71). 7. 7. These results suggest the existence of a late metabolic “reserve” for an ischemic tissue of the diver during a particularly strenuous or long dive.