Leptin exists in tubuli seminiferi and in seminal plasma.

Leptin is a 167-amino acid protein that stimulates gonadotrophin-releasing hormone secretion and exerts indirect effects on the gonads via neuropeptide Y, NPY. Recent research has suggested that leptin may also have an effect on testosterone secretion. To investigate the role of leptin in reproduction, leptin in testicular tissue and seminal plasma was examined in relation to leptin in serum, semen sample qualities and vasectomy. Seminal plasma and serum of 64 infertility patients, and 15 individuals after vasectomy, were assayed for leptin using a competitive 'in house' radioimmunoassay. The concentration of leptin in seminal plasma was significantly lower in the 'normal' semen sample group than in the 'pathological' group (Mean +/- SEM; 1.45 +/- 0.18 vs. 3.19 +/- 0.57 ng ml-1; P < 0.05), and showed a significantly negative correlation with percentage of motile spermatozoa (r = -0.46; P = 0.0005) and with the velocity straight line, VSL, (r = -0.30; P = 0.029). In contrast, leptin concentration in serum did not show any relationship with the spermiogram parameters. In testicular tissue, leptin was preferentially found within the tubuli seminiferi using anti-leptin polyclonal antibody, Ob A-20 Sc 842. The amount of leptin per ejaculate did not significantly change after vasectomy, and was not correlated to fructose, zinc or neutral alpha glucosidase in seminal plasma (P > 0.05). These results suggest that the amount of leptin in the genital tract, including the tubuli seminiferi, may influence the mechanisms involved in the motility development of spermatozoa.