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Expression and Localization of -, -, and µ-Opioid Receptors in Human Spermatozoa and Implications for Sperm Motility

Department of Physiology (E.A., L.C., J.G., N.S., J.I.), Faculty of Medicine and Dentistry, University of the Basque Country, Leioa, 48940 Bizkaia, Spain; Department of Nursing II (A.V.). School of Nursing, University of the Basque Country, Donostia, 20014 Gipuzkoa, Spain; Department of Biochemistry and Molecular Biology I (A.C.), School of Biology, Complutense University, Madrid, 28040 Spain; and Laboratory of Seminology and Clinical Embryology (C.O.), Euskalduna Clinic, Bilbao, 48080 Bizkaia, Spain

Address all correspondence and requests for reprints to: Ekaitz Agirregoitia, Department of Physiology, Faculty of Medicine and Dentistry, University of the Basque Country, PO Box 699, Bilbao, 48080 Bizkaia, Spain. E-mail: e.agirregoitia{at}ehu.es.

Context: Endogenous opioid peptides signal through -, -, and µ-opioid receptors. Some of these peptides such as endorphins and enkephalins are present in the male reproductive tract, but the presence of the corresponding receptors in human sperm cells has not yet been reported.

Objective: Our objective was to study the expression and localization of -, -, and µ-opioid receptors on human spermatozoa and the implication in sperm motility.

Methods: The expression of receptors was studied by RT-PCR, Western blot, and immunofluorescence techniques. We evaluated the effects of activation of each opioid receptor by specific agonist and antagonist.

Results: Human spermatozoa express -, -, and µ-opioid receptors. These receptors were located in different parts of the head, in the middle region, and in the tail of the sperm. Progressive motility of spermatozoa, an important parameter to evaluate male fertility, was found to be significantly reduced after incubation with the µ-receptor agonist morphine, whereas this effect was antagonized in the presence of the corresponding antagonist naloxone. The -receptor antagonist naltrindole significantly reduced progressive motility immediately after its addition. However, the -receptor agonist DPDPE had no significant effect. Finally, neither the -receptor agonist U50488 nor its antagonist nor-binaltorphimine significantly affected the progressive motility of human spermatozoa.

Conclusion: We report for first time the presence of functional -, -, and µ-opioid receptors in human sperm membranes. These findings are indicative of a role for the opioid system in the regulation of sperm physiology.

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