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 inve stigated in perfused rat liver stimulated with phenylephrine and metab olic precursors of glucose and urea: pyruvate, lactate, NH4+ and ornit hine. The relative concentrations of phosphorus metabolites in the liv er were measured by P-31-n.m.r. spectroscopy. When added simultaneousl y, phenylephrine and the precursors induced a decrease in the P-i leve l which in 4-5 min reached a new steady state at 73 % of the control l evel. After 5 min or more of stimulation the ATP level had also decrea sed. When the stimulation ended, P-i and ATP returned to their initial levels within 15 min. In mitochondria isolated after 5 min of stimula tion, P-i was increased more than 2-fold as compared with control mito chondria and, in addition, an accumulation of P-i from the perfusion b uffer into the liver was observed. Phenylephrine by itself did not cau se any significant changes in the ATP or P-i levels, whereas the gluco se and urea precursors in the absence of phenylephrine induced a 9% de crease in P-i, while ATP remained constant. The, P-i content of mitoch ondria 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 ex change for malate, and that a major part of the intramitochondrial P-i was invisible by n.m.r.