Vasoactive intestinal peptide stimulates glycolysis in pituitary tumours; 1H-NMR detection of lactate in vivo.

1H- and 31P-NMR spectroscopy has been applied to rats carrying implanted tumours in vivo, and used to observe simultaneous changes in intracellular pH (pHi) and lactate concentration during the stimulatory action of vasoactive intestinal polypeptide (VIP). A maximal decrease in pHi to a mean of 0.29 units below basal values was recorded. At the same time, 11 min after VIP, a maximal increase in tumour lactate was found, with a mean value of 150% of the basal concentration. The magnitude of these changes was compatible with in vitro measurements of basal lactate concentration and buffering capacity made on the same tumour line. It is concluded that VIP stimulates glycolysis by the tumour cells, resulting in an accumulation of lactate and a consequent fall in pHi.