Anaerobic Metabolism

Muscle Glycolysis and Lactate Production

Lactate Dehydrogenase (LDH)

When oxygen is scarce, pyruvate generated in glycolysis cannot be processed via oxidative phosphorylation. Instead, lactate dehydrogenase (LDH) facilitates the reduction of pyruvate to lactate, oxidizing NADH to NAD+.

This step also ensures that the NAD+ pool is replenished to continue glycolysis.

Lactate transport

Lactate moves out of muscle cells via monocarboxylate transporters (MCTs), and enters the bloodstream, often binding to albumin for transportation. In the bloodstream, lactate is largely directed toward the liver, though it can also go to other tissues capable of lactate uptake.

Liver Gluconeogenesis

Lactate to Pyruvate

Once in the hepatocytes of the liver, lactate is converted back into pyruvate through the reverse action of LDH. This reaction also recovers NADH. The pyruvate will then be converted to glucose via gluconeogenesis and will be released back into the blood.

Lactic acid serves as an intermediary between glycolysis in the muscle cells and gluconeogenesis in the liver. It ensures that the products of muscle metabolism are not wasted but are recycled back into glucose, thus maintaining blood glucose levels.

Alanine Cycle

The Alanine Cycle is a parallel pathway. The Alanine Cycle involves the transamination of pyruvate to alanine, which is then transported to the liver to be converted back into pyruvate and subsequently into glucose.