EFFECT OF PHENYLEPHRINE ON THE COMPARTMENTATION OF INORGANIC-PHOSPHATE IN PERFUSED-RAT-LIVER DURING GLUCONEOGENESIS AND UREA SYNTHESIS - A P-31-NMR-SPECTROSCOPIC STUDY

The transport of P-i between the cytosol and the mitochondria was investigated in perfused rat liver stimulated with phenylephrine and metabolic precursors of glucose and urea: pyruvate, lactate, NH4+ and ornithine. The relative concentrations of phosphorus metabolites in the liver were measured by P-31-n.m.r. spectroscopy. When added simultaneously, phenylephrine and the precursors induced a decrease in the P-i level which in 4-5 min reached a new steady state at 73 % of the control level. After 5 min or more of stimulation the ATP level had also decreased. When the stimulation ended, P-i and ATP returned to their initial levels within 15 min. In mitochondria isolated after 5 min of stimulation, P-i was increased more than 2-fold as compared with control mitochondria and, in addition, an accumulation of P-i from the perfusion buffer into the liver was observed. Phenylephrine by itself did not cause any significant changes in the ATP or P-i levels, whereas the glucose and urea precursors in the absence of phenylephrine induced a 9% decrease in P-i, while ATP remained constant. The, P-i content of mitochondria isolated under these conditions was not significantly increased as compared with control mitochondria. These results showed that P-i accumulated into the mitochondria by a mechanism possibly involving exchange for malate, and that a major part of the intramitochondrial P-i was invisible by n.m.r.