Interference of heparin in plasma levocarnitine determination with radioenzyme assay.

This paper describes the interference of heparin (CAS 9005-49-6) in whole plasma used for free and total levocarnitine (L-carnitine, CAS 541-15-1) analysis. Alkaline hydrolysis required for total L-carnitine measurement does not overcome the problem. The same interference is also present in long-chain acyl-L-carnitine assay, because heparin precipitates together with proteins and long-chain esters of L-carnitine in the acid insoluble fraction of perchloric acid treated plasma sample.

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, total and esterified L-carnitine were monitored monthly in 14 women during the last 6 months of pregnancy and 1 month after delivery. Plasma concentration and renal clearance measured 1 month after delivery overlapped with normal values for females of comparable age, and were considered the reference values for further comparisons. Plasma concentration of free, total and esterified L-carnitine decreased during pregnancy, reaching values as low as half of those measured 1 month after delivery, whereas urinary excretion and renal clearance, mainly of L-carnitine esters, increased, with renal clearance reaching a peak at the 16th week of pregnancy.

Protein binding of L-carnitine family components.

L-carnitine and its short-, medium- and long-chain acyl esters constitute the L-carnitine family. These compounds in the body are equilibrated according to a homeostatic equilibrium preserved and, when impaired, restored by a dynamic inter-exchange between L-carnitine and its esters, catalysed by carnitine acyl transferases, and a tubular reabsorption process with differentiated thresholds for each component. The interaction of these compounds with albumin and plasma proteins of rats, dogs and humans was carefully investigated by means of ultrafiltration and gel filtration techniques.