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.
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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 the specialized organ of the reproductive tract, the epididymis. It is vital in transporting long-chain fatty acids into the mitochondria for oxidation and energy production. In addition, L-carnitine regulates the Acyl-coenzyme A / Coenzyme A ratio, stores energy in acetylcarnitine, and moderates the toxic effects of acyl groups by eliminating them as carnitine esters.
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 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 accumulates in the testicles. Carnitine plays an important role not only in initiating sperm motility but also in promoting their maturation and enhancing their ability to fertilize. It regulates Sertoli cell function, protects spermatozoa from oxidative damage, and reduces DNA fragmentation and sperm agglutination.