Presence of immunoreactive β-endorphin and calcitonin in human seminal plasma, and their relation to sperm physiology

Opioid peptides and calcitonin are found in high concentrations in the male reproductive tract. To further elucidate their role in sperm physiology, we studied semen samples from 49 infertile men and 25 men with proven fertility. β-endorphin and calcitonin were measured in each sample by radioimmunoassay and then were correlated with seminal plasma testosterone (T) and dihydrotestosterone levels as well as sperm count, total motile sperm/milliliter, and percentage of penetrated hamster eggs. The levels of β-endorphin (308 ± 22 pg/ml) and calcitonin (331 ± 32 pg/ml) in seminal plasma were 10 and 20 times higher than levels found in venous plasma (32 ± 2 and 14.5 ± 1.2 pg/ml, respectively) (P < 0.001). There was no difference between the levels of β-endorphin and calcitonin in seminal plasma of fertile and infertile men. However, seminal plasma T was significantly higher in fertile than infertile men (19.4 ± 2 versus 11.5 ± 1 ng/dl; P < 0.05). No correlation could be demonstrated between either β-endorphin or calcitonin and any of the parameters studied. In conclusion, β-endorphin and calcitonin are produced locally in the male reproductive tract; however, their role in male reproduction remains to be elucidated.