The measurement of Carnitine in semen is used in the investigation of male infertility, especially in the investigation of patients with azoospermia and normal testosterone levels.
L-Carnitine is a biologically active amino acid. About 75% of the body's L-carnitine stores come from the diet and only 25% are synthesized de novo from lysine and methionine.
L-Carnitine is concentrated in high-energy tissues such as skeletal and heart muscles and in the specialized organ of the reproductive tract, the epididymis. Carnitine plays an important role in the transport of long-chain fatty acids into the mitochondria for oxidation and energy production. In addition, regulation of the Acyl-coenzyme A / Coenzyme A ratio, energy storage in the form of acetylcarnitine, and moderation of the toxic effects of acyl groups by their elimination as carnitine esters are the basic functions of L-carnitine.
Spermatozoa accumulate carnitine derived from the epididymis, a process that is closely related to the ability for fertilization. In the epididymis, free L-Carnitine is taken from the blood plasma and transferred to the epididymal fluid. Carnitine then diffuses passively into the spermatozoa, where both free and acetylated L-Carnitine accumulate. The onset of sperm motility occurs in parallel with an increase in the concentration of free L-Carnitine in the epididymal lumen.
Despite the blood-testis barrier, new studies show that carnitine also accumulates in the testicles. Carnitine plays an important role not only in initiating sperm motility, but also promotes their maturation and enhances their ability to fertilize, regulates Sertoli cell function and protects spermatozoa from oxidative damage, reduces DNA fragmentation and sperm agglutination.