PLASMA-CONCENTRATION, URINARY-EXCRETION AND RENAL CLEARANCE OF L-CARNITINE DURING PREGNANCY - A REVERSIBLE SECONDARY L-CARNITINE DEFICIENCY

Plasma concentration, urinary excretion and renal clearance of free, t otal and esterified L-carnitine were monitored monthly in 14 women dur ing the last 6 months of pregnancy and 1 month after delivery. Plasma concentration and renal clearance measured 1 month after delivery over lapped with normal values for females of comparable age, and were cons idered the reference values for further comparisons. Plasma concentrat ion of free, total and esterified L-carnitine decreased during pregnan cy, reaching values as low as half of those measured 1 month after del ivery, whereas urinary excretion and renal clearance, mainly of L-carn itine esters, increased, with renal clearance reaching apeak at the 16 th week of pregnancy. Pregnancy thus leads to a reversible secondary d eficiency of L-carnitine. The involvement of L-carnitine in the excret ion of an excess of acyl-S-coenzyme A groups to prevent a possible sys temic acidosis, as well as hormonal changes and a reduction of L-carni tine biosynthesis, could play a significant role in the variations in L-carnitine metabolism encountered in pregnancy. As physiological comp onents of L-carnitine are excreted via a saturable tubular reabsorptio n, their threshold seems to follow plasma concentration, even when the y decrease markedly, as in pregnancy.