SMOKE AND SPERM:PRESENCE OF A NICOTINE NEUROENDOCRINE MECHANISM

Introduction.Nicotine (NIC) alters sperm progressive motility (PM) and nonconventional parameters. We found that this in vitro effects are observed at concentrations similar to (100 ng/ml) or lower (1-10 ng/ml) than those found in the seminal plasma of smokers (70 ng/ml). However, it is not clear whether NIC acts through a receptor-mediated mechanism. In the CNS system, NIC stimulates a class of cholinergic receptors called nicotinic receptors, though at high concentrations, NIC blocks them (toxic effect). Aim. To evaluate whether the in vitro effects of NIC on sperm PM, nonconventionalparameters and lipid peroxidation (LP) were mediated by interaction with nicotinic receptors. Methods. The study was conducted on semen samples obtained from 30 healthy, normozoospermic nonsmoker men. Spermatozoa were incubated with hexamethonium (HEX) (100 ng/ml), a selective NIC receptor antagonist, and/or NIC (100 ng/ml) or vehicle (control) for 3 and 24 h. Afterincubation,sperm PM and nonconventional parameters [early apoptosis (EA), mitochondrial membrane potential (MMP), degree of chromatin compaction (CC), sperm DNA fragmentation (DNA-FRAG)]were evaluated by flowcytometry. LP was evaluated in in totocell aliquots and after sperm separation by swim-up, after exposure to NICand/or HEX or vehicle for 3 and 24 h. BODIPY (581/591) C11, which after incorporation into cell membranes, responds to radical oxygen species changing its emission spectrum from red to green, was used by flowcytometry. Results. HEX alone did not have any effect on all parameters evaluated, whereas it antagonized the suppressive effect of NIC on sperm PM (p<0.05 vs. NIC alone) both after 3 and 24 h of incubation. Similarly, incubation with HEX lowered the percentage of spermatozoa with EA signs, low MMP, abnormal CC and DNAFRAG, and increased the percentage of viable cells orthose with high MMP both after 3 and 24 h (p<0.05 vs. NIC alone). HEX fully antagonized the effects of NIC restoring all parameters evaluated at levels similar to those seen with vehicle. NIC increased LP in in toto samples after 3 and 24 h (p<0.05 vs. NIC alone), whereas no effect occurred in samples containing spermatozoaalone, suggesting that other cells in the ejaculate (leukocytes) play a relevant role even if at normal concentrations.Theselatter effects were also fully antagonized by HEX. Conclusion. These data showed that the deleterious in vitroeffects of NIC on the sperm parameters examined were mediated by interaction with its specific receptor. This suggests the presence of a NIC neuroendocrine mechanism on human spermatozoa.