Serum Carnitine Concentrations Research Articles

Effect of Carnitine on Liver Fat and Nitrogen Balance in Intravenously Fed Growing Rats

Carnitine is an essential metabolite whose function is to transport activated long-chain fatty acids across the mitochondrial membrane. It is consumed in the diet and is synthesized from lysine and methionine to meet body needs. Hepatic fat deposition has been reported in experimental animals and patients receiving total parenteral nutrition (TPN) fluids devoid of preformed carnitine. In the present experiment, nitrogen balance, hepatic fat deposition and serum and tissue carnitine were determined in rats receiving a hypercaloric TPN regimen containing 0, 10, 50, and 100 mg dl-carnitine per 100 g body weight for 14 days. Rats fed a stock diet served as controls. Increased nitrogen balance was observed in TPN rats receiving the highest dose of carnitine supplementation. Hepatic fat deposition induced by the hypercaloric infusion was ameliorated but not eliminated by infusing carnitine. Serum, liver and skeletal muscle carnitine concentrations were maintained, whereas that of heart decreased in TPN rats without carnitine supplementation. Between 90 and 100% of the administered l-carnitine was excreted. It is suggested that the observed effects of carnitine on nitrogen balance and hepatic fat deposition are due to as yet undefined pharmacological properties. The significant decrease of carnitine in cardiac muscle resulting from TPN in a patient population already stressed and traumatized and the metabolic and physiological effects of this decrease deserve further exploration.total parenteral nutrition carnitine fatty infiltration nitrogen balance

843 HIGHER SERUM CARNITINE LEVELS AND KETOGENESIS IN BREAST FED AS COMPARED TO FORMULA FED INFANTS

The normal newborn infant undergoes a marked metabolic transition in the first days of life. A major feature of this postnatal metabolic adaptation is development of the capacity to utilize fatty acids and ketone bodies as energy substrates. Because of the essential role of carnitine in fatty acid oxidation and ketogenesis, we have investigated relationships between serum carnitine concentrations and serum levels of ketone bodies in breast fed as compared to formula fed newborns. The mean carnitine concentrations in cord blood of normal fullterm newborns was 34 nmoles/ml. At 42 hours of age, breast fed newborns demonstrated higher carnitine levels (56 nmoles/ml) as compared with canitine levels of formula fed infants (32 nmoles/ml). Correspondingly, by 42 hours of age, serum ketone body concentrations (β-hydroxybutyrate plus aceto-acetate) were higher in breast fed (5.9 nmoles/ml) as compared with formula fed infants (3.0 nmoles/ml). The mean glucose concentrations in both groups of infants showed no significant differences. Carnitine concentrations of isolated samples of human breast milk ranged between 50-100 nmoles/ml and were similar to that of formula (40-80 nmoles/ml) suggesting that the carnitine in breast milk may be better absorbed than carnitine in commercial formulas. The data further suggests a relationship between serum carnitine concentration and ketogenesis in newborn infants.

Urinary excretion of carnitine and serum concentrations of carnitine and lipids in patients with hypofunctional endocrine diseases: Involvement of adrenocorticoid and thyroid hormones in ACTH-induced augmentation of carnitine and lipids metabolism

The promoting effect of ACTH on carnitine and lipid metabolism was studied in patients with various endocrine hypofunctions. The results were compared with those of normal subjects. In adrenocortical insufficiency, hypothyroidism and hypopituitarism urinary excretion of carnitine was significantly lower than in normal subjects. On intramuscular injection of synthetic β 1–24 ACTH-Z urinary excretion of carnitine in normal subjects increased sixfold on the day of the injection and returned to the pretreatment level on the third day. Serum concentrations of carnitine and FFA increased in parallel with carnitine excretion, while serum triglyceride was lowered in response to ACTH administration. These responses were totally lacking or substantially suppressed in patients with the above endocrine insufficiencies. In hypothyroid and hypopituitary patients substitution therapy restored the responses to ACTH in the same fashion as those in normal subjects. These findings suggest that the promoting effect of ACTH on carnitine and lipid metabolism requires the presence of intact adrenocortical and thyroid functions.

Urinary excretion of carnitine in patients with hyperthyroidism and hypothyroidism: Augmentation by thyroid hormone

Urinary excretion of carnitine and serum concentrations of carnitine, triglyceride, and free fatty acids were measured in 54 hyperthyroid and 13 hypothyroid patients, and the results were compared with those of normal subjects. In hyperthyroid patients urinary excretion of carnitine was highly increased above that of the control subjects. On adequate treatment with antithyroid drug, carnitine excretion was reduced to the normal range, and serum lipids changed in parallel. In contrast, carnitine excretion was markedly reduced in hypothyroid patients. After substitution therapy with thyroid hormones the excretion increased in these patients. This change was associated with a marked reduction of serum triglyceride. There was an inverse correlation between urinary excretion of carnitine and serum triglyceride concentration. Carnitine excretion was significantly correlated with serum thyroxine concentration in hyper- and hypothyroid patients. The results suggest that thyroid hormones play an important role in carnitine metabolism, which in turn influences serum triglyceride metabolism.

Increased serum carnitine concentration in renal insufficiency.

We measured serum carnitine in groups of patients with various diseases. The concentration was frequently above normal in patients with renal insufficiency. The clinical significance of such an increase in renal insufficiency may be analogous to that of increases in urea nitrogen, creatinine, or uric acid in the serum.