Lactate genesis by rat liver and muscle during development

Lactate has been shown to be an important fuel for brain metabolism during early postnatal development (1). In an attempt to identify the source(s) of lactate in the postnatal rat, we have studied the in vitro catabolism of glucose, galactose, fructose, alanine, glycerol, and octanoate in liver and muscle minces prepared from suckling rat pups. Whereas galactose, fructose, and octanoate were found to be lactagenic (lactate generating) in liver, glucose was the sole lactate precursor in muscle. Galactose was most effective as a hepatic lactate source at 3 d of age. Thereafter, the production of lactate from galactose decreased to reach control levels by 15 d of age. In contrast, fructose or octanoate were lactagenic throughout development. Lactate formation from galactose was completely halted by iodoacetate, inhibited by high galactose concentrations, and suppressed by fasting. The absence of oxygen increased lactate production from either fructose or octanoate, but it did not affect lactagenesis from galactose. Muscle minces produced lactate from glucose in an age-dependent manner similar to the development pattern of lactate formation from galactose by liver. Because lactose-derived galactose is readily available during suckling, it is suggested that galactose-based hepatic lactagenesis serves a unique role in maintaining the supply of lactate during early postnatal development. This hepatic capability may augment glucose-based muscle lactate synthesis at a time when lactate is a major brain fuel.