[Animal experiment and clinical studies of the significance of carnitine for energy metabolism in pregnant patients and the fetus during the pre- and perinatal period].
Carnitine was discovered at the beginning of this century, but was nearly forgotten until its importance in fatty acid metabolism was established 50 years later. In the past years, several other functions of carnitine in cellular metabolism have been described. The lung contains more than 40 different cell types, most of them involved in lipid metabolism. Pulmonary surfactant, a complex of 90% lipids and 10% lung specific apoproteins, is synthesized and secreated from type II cells. Surfactant is present as a monolayer at the air-liquid interface in the alveoli and decreases surface tension. Dipalmitoyl phosphatidylcholine (DPPC) is functionally and quantitatively the most important constituent of the surfactant complex. A deficiency in fetal lung surfactant is the primary cause of the respiratory distress syndrome (RDS), the most severe complication of preterm infants. Glucocorticoids are frequently used to accelerate fetal pulmonary maturation. However, a considerable number of infants fail to respond to this therapy. Maternal administration of L-carnitine significantly increased the DPPC content of fetal rat lungs. The effect of maternal treatment with a carnitine-betamethasone combination was synergistic, especially with lower betamethasone doses. Consequently the minimal dose of betamethasone which affects the DPPC content and accelerate the morphological maturation of the fetal lung was determined. This minimal dose in combination with L-carnitine increased the DPPC content on day 19 of gestation to levels found on the 20th gestational day which allows the survival of most of the preterm rats (term 22 days). Results of clinical trials show that antenatal treatment with a low dose betamethasone-L-carnitine combination has a clear advantage over standard betamethasone therapy. A multicenter study is in progress. Plasma carnitine levels at delivery are decreased to about half of the concentrations seen in non-pregnant women. Similar low levels are found only in patients with carnitine deficiency. Already in the 12th week of gestation the mean whole blood and plasma carnitine levels were found to be significantly lower than those of controls. The reason for increased excretion of acylcarnitines during pregnancy is not known, but could be a detoxifying function similar to that found in patients with inborn errors of fatty acid metabolism and organic acidurias. Carnitine substitution (1 g daily) from the 20th gestational week up to parturition resulted in an increase of free carnitine levels in maternal plasma. A dosage of 0.5 g/day was without effect. Prolonged substitution in pregnant women, especially in risk pregnancies may be preferable to high doses of carnitine administered shortly before imminent premature delivery.