Seminal carnitine and acetylcarnitine content and carnitine acetyltransferase activity in young Maremmano stallions

Abstract

The reproductive characteristics and seminal carnitine and acetylcarnitine content as well as carnitine acetyltransferase activity of young Maremmano stallions ( n=25) are reported. The stallions were subjected to semen collection in November and January; in each trial two ejaculates were collected 1 h apart. The total motile morphologically normal spermatozoa (TMMNS) and the progressively motile spermatozoa at collection and during storage at +4°C were evaluated. Seminal l-carnitine (LC), acetylcarnitine (AC), pyruvate and lactate were measured using spectrophotometric methods, whereas carnitine acetyltransferase activity was measured by radioenzymatic methods. Since there were no major significant differences in seminal and biochemical characteristics between the November and January trials, data were also pooled for the first and second ejaculates. Significant differences ( P<0.001) were observed between the first and second ejaculates for sperm count (0.249±0.025 versus 0.133±0.014×10 9/ml), total number spermatozoa by ejaculate (12.81±1.23 versus 6.36±0.77×10 9), progressively motile spermatozoa (48.6±3.0 versus 52.6±3.0%) and TMMNS (3.35±0.50 versus 2.02±0.37×10 9). In the raw semen the LC and AC were significantly higher in the first ejaculate than in the second ( P<0.001), whereas, pyruvate and pyruvate/lactate ratio were higher in the second ejaculate ( P<0.05). Seminal plasma AC and LC concentrations resulted higher in the first ejaculate ( P<0.001). The pyruvate/lactate ratio was higher in the second ejaculate ( P<0.05). Both raw semen and seminal plasma LC and AC concentrations were positively correlated with spermatozoa concentration ( P<0.01); in raw semen AC was also correlated to TMMNS ( P<0.01). Lactate levels of raw semen was correlated to progressively motile spermatozoa after storage ( P<0.01). In the second ejaculate, significant correlations were also observed among AC/LC ratio in raw semen and progressively motile spermatozoa after 48 and 72 h of refrigeration. Furthermore, AC levels were correlated to lactate concentration. The positive correlation between LC, AC and spermatozoa concentration, and between AC and TMMNS indicated carnitine as potential semen quality marker. Moreover, the correlation between AC/LC ratio and progressive spermatozoa motility after refrigeration, suggests that carnitine may contribute towards improving the maintenance of spermatozoa viability during in vitro storage.