A neuropeptide in human semen: oxytocin

The neuropeptide oxytocin (OT) has been detected in testis and epididymis of several mammals. The peptide affects steroidogenesis and sperm transport in vivo. Effects of OT on sperm motility in vitro seems to be contradictory. As no data are available on the presence of OT in human semen and on the relationship of OT with sperm characteristics, we assessed OT level in semen samples in 3 groups of patients: (I) normozoospermic, (II) astheno-/oligo-/teratozoospermic, and (III) azoospermic subjects. Furthermore, we studied the relationship between the concentration of OT in semen and the sperm characteristics. OT was measured in seminal plasma by radioimmunoassay after extraction. OT semen levels did not differ in control patients (I: 1.72 +/- 0.78 pg/mL; n = 10), patients with poor semen quality (II: 1.66 +/- 0.91 pg/mL; n = 11), or in vasectomized patients (III: 1.28 +/- 0.65 pg/mL; n = 11). No statistically significant relationships between the OT levels and sperm characteristics (density: 0.0693; total sperm count: 0.0845; percentage of motility: 0.1341; morphology: 0.3478) have been found. The neurosecretory peptide oxytocin is present in human seminal plasma of normal as well as of vasectomized subjects. OT is not only derived from the testis; OT levels in poor semen samples are not different from controls. No relationship was found between OT seminal plasma levels and sperm characteristics.