Lactate Genesis by Rat Liver and Muscle during Development

Abstract

ABSTRACT. 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 a s a hepatic lactate source a t 3 d of age. Thereafter, the production of lactate from galactose decreased to reach control levels by 1 5 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 agedependent manner similar to the development pattern of lactate formation from galactose by liver. Because lactosederived 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. (Pediatr Res 30: 331-336, 1991) Abbreviations UDP, uridine diphosphate Lactate is the major fuel for brain cortex in rat pups during the first postpartum week (I). The utilization of lactate accounts for more than 70% of cerebral oxidative metabolism in the 6-dold, normally ventilated rat pup, followed by the consumption of 3-hydroxybutyrate and glucose in approximately equal amounts. The extensive reliance of the young cerebral cortex upon lactate as a fuel prompted this investigation to evaluate the lactagenic' potential of several common metabolites when supplied to liver or muscle during the postnatal period.Milk, the sole food source available to suckling pups, consists principally of casein, fats, and sugars. Although fats comprise 70-80% of the caloric content of milk, it is most probable that a sugar provides the carbon for lactate synthesis. Lactose, a disaccharride of glucose and galactose, is the principal milk sugar.Although glucose-derived muscle lactagenesis is known, there is n o information available concerning the relative output of lactate from skeletal muscle as a function of age during the suckling period. In investigations of galactose metabolism during development, the primary emphasis has been the genesis of glucose in fasted animals (2-4). Even though it has been known for many years that the i.v. administration of galactose to infants results in the physiologic elevat~on of blood lactate levels (5), no attempt has been made to delineate the mechanism of this phenomenon or explain i...

Daily variation in plasma electrolyte and acid–base status in fasted horses over a 25 h period of rest

“…Slocombe et al 5 Most lactate 2 circulating in the resting state is derived from glycolysis in erythrocytes, adipocytes and myocytes 15,16 . In turn, lactate 2 serves as a substrate for either gluconeogenesis and is oxidized (via decarboxylation to acetyl-CoA) or may enter a lipogenesis pathway 14 .…”