Studies on the effects of L-thyroxine, L-carnitine and an L-thyroxine-L-carnitine combination on dipalmitoyl phosphatidylcholine content and on phosphatidylcholine species composition in fetal rat lungs.

The aim of the present study was to examine the effects of maternal carnitine treatment combined with thyroxine, a hormone influencing both lung maturation and carnitine metabolism. Administration of a carnitine-thyroxine combination to pregnant rats resulted in a significant increase of DPPC content in fetal rat lungs to 8.8 +/- 1.8 mg/g dry weight (mean +/- SD), compared with the control group, the carnitine-treated group, and the thyroxine-treated group [5.4 +/- 1.8 (p less than 0.01), 5.6 +/- 1.5 (p less than 0.01), and 6.6 +/- 1.0 mg/g dry weight, respectively]. The portion of DPPC in the PC species increased significantly from 20.9 +/- 2.1% in the control group and to 27.2 +/- 3.5% (p less than 0.01) in the carnitine-thyroxine combination group. A significant (p less than 0.01) diminution of the palmitoyl-palmitoleyl PC (16:0/16:1-PC) portion in the PC species was found. Maternal carnitine administration resulted in an elevation of the carnitine levels in the fetal lungs to approximately twice those of the controls (p less than 0.01). The combined administration of carnitine and thyroxine resulted in no increase in the total carnitine content but in a significant (p less than 0.01) increase of the short chain acylcarnitine content. The present results demonstrate that carnitine potentiates the effects of thyroxine on DPPC content and support the concept of an interrelationship between carnitine and thyroxine metabolism.