Nicotine Effects and Receptor Expression on Human Spermatozoa: Possible Neuroendocrine Mechanism.

The aim of this experimental study was to investigate the mechanism by whichnicotine (NIC) alters spermatozoa and to evaluate the expression of nicotinic receptors(nAChR) subunits in human spermatozoa. We analyzed 30 healthy normozoospermicmen. Spermatozoa were incubated with NIC 100 ng/ml and the nAChR antagonist,hexamethonium (HEX) (0, 100, 1,000, 10,000 ng/ml) for 3 and 24 h. The following spermparameters evaluated: (a) progressive motility; (b) mitochondrial membrane potential(MMP); (c) chromatin compactness; (d) externalization of phosphatidylserine (PS); (e) lateapoptosis; (f) viability; (g) DNA fragmentation; (h) degree of lipid peroxidation (LP) by flowcytometry; (i) nAChR subunits expression by quantitative Real Time PCR and (j) proteinexpression evaluation by Western blot analysis. HEX fully antagonized the effects of NICboth after 3 and 24 h of incubation with significant improvement (p < 0.05) of spermprogressive motility, MMP, abnormal chromatin compactness, PS externalization, lateapoptosis and DNA fragmentation, already at the concentration of HEX 100 ng/ml. Thedegree of LP increased after incubation with NIC in raw semen but this effect was fullyantagonized (p < 0.05) by HEX after 3 and 24 h of incubation. Finally, 8 nAChR subunitsmRNA (α1, α3, α4, α6, α7, β2, β4, and δ) were found expressed in all samples examined,but only α7 subunit is translated, making an homomer receptor, in non-smokers subjects.The effects of NIC on sperm function are mediated by interaction with a specific nicotinicreceptor. The presence of nAChR subunits suggests the presence of a neuroendocrinemechanism on human spermatozoa