Lactate metabolism in patients with cancer.

Abstract

Tracer studies of pyruvate and lactate recycling to glucose have been carried out in patients with metastatic carcinoma. The experimental approach of determining the time course radioactivity curve of blood glucose after single injections of pyruvate-3-14C and glucose-6-14C on separate days allowed definition of the transfer function of lactate and pyruvate to blood glucose. Nine such experiments were done in eight patients. In six of the eight subjects, an increased fraction of the pyruvate and lactate turnover was recycled to glucose (.24 to.54 as compared to an average of.17 in normal subjects). The two subjects with normal Cori cycle activity, though debilitated from the localization site of their metastatic tumors, did not have widespread rapidly growing neoplasms. The subjects with increased Cori cycle activity had a high total turnover of glucose, but normal or only slightly elevated new glucose production rates. Thus, we postulate abnormally high lactate production in these subjects, perhaps related to the metabolism of the cancer itself. One subject studied during the presence of lactic acidosis, and again later when the lactate level was less, showed about twice as much recycling after acidosis was alleviated, suggesting inhibition of hepatic glucose production from lactate during acidosis. It is suggested that the potential for lactic acidosis exists in patients with widespread progressive tumor growth.