Abstract
Endogenous opioid peptides are substances involved in cell communication. They are present in various organs and tissues of the male and female reproductive tract, suggesting that they may regulate some of the processes involved in reproductive function. In fact, the opioid system that operates as a multi-messenger system can participate in the regulation of reproductive physiology at multiple levels, for example, at the levels of the central nervous system, at the testes level and at sperm level. A better understanding of the implication of the opioid system in reproductive processes may contribute to clarifying the etiology of many cases of infertility and the effect of opiate abuse on fertility. Indeed, a novel biochemical tool for the diagnosis and treatment of male infertility could be based upon components of the opioid system. The presence of the opioid system in sperm cells also represents a novel opportunity for reproductive management, for either enhancing the probability of fertilization or reducing it through the development of novel targeted contraceptives.
Highlights
The opioid system is a biological communication system for which activity is mediated by the so-called endogenous opioid peptides (EOPs)
These peptides are synthesized from the processing of their precursors, which are encoded by three different genes: pro-enkephalin (PENK), pro-opiomelanocortin (POMC) and pro-dynorphin (PDYN) [1]
Met- and leuenkephalin are considered to be endogenous ligands for delta-opioid receptor (DOR), since they have higher affinity for DOR. They are capable of binding with lower affinity to the muopioid receptor (MOR). β-Endorphins bind to DOR and MOR with similar affinity, whereas dynorphins preferentially bind to kappaopioid receptor (KOR) [10]
Summary
The opioid system is a biological communication system for which activity is mediated by the so-called endogenous opioid peptides (EOPs). These peptides are synthesized from the processing of their precursors, which are encoded by three different genes: pro-enkephalin (PENK), pro-opiomelanocortin (POMC) and pro-dynorphin (PDYN) [1]. EOPs exhibit different affinities for these opioid receptors. Met- and leuenkephalin are considered to be endogenous ligands for DOR, since they have higher affinity for DOR. They are capable of binding with lower affinity to the MOR. Evidence of the widespread presence of opioid peptides and receptors in different organs and tissues of the male reproductive system indicates that EOPs likely
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