Formation of n.m.r.-invisible ADP during renal ischaemia in rats

Measurement of the adenine nucleotide and inorganic phosphate content of normoxic and ischaemic kidney in vivo has been made, comparing enzymic assay (after freeze-clamping and acid extraction) with quantification by 31P-n.m.r. Both methods give similar results for ATP, and n.m.r. quantification of Pi gives a value 25-50% of that obtained by enzymic assay. ADP, which is largely invisible to n.m.r. in the normoxic kidney, remains invisible during ischaemia despite a 2-3 fold rise in enzymically assayed ADP. N.m.r. and enzymic assay of the acid extracts give similar values for all metabolites measured. The question of ADP binding in the kidney is discussed, as are the implications for the metabolic regulation of ADP-dependent reactions.