Possible Role of N-Methyl-D-Aspartate Glutamate Receptors in The Induction of Acrosome Reaction in Human Sperm.

Abstract

Objective: Acrosome reaction is a receptor and Ca²⁺-dependent process. N-Methyl-D- aspartate (NMDA) glutamate receptors are expressed in the human sperm and are involved in the Ca²⁺ influx. Therefore, the present study aimed to investigate whether these receptors could be concerned with the induction of acrosome reaction in the human sperm.

Materials and methods: In this experimental study, human spermatozoa were divided into five groups: i. Spermatozoa at 0 hour, ii. Control group, iii. Spermatozoa treated with NMDA glutamate receptor agonist (L-glutamate), iv. Spermatozoa treated with NMDA glutamate receptor antagonist and agonist (MK-801 and L-glutamate respectively), and v. Spermatozoa treated with non-NMDA glutamate receptor agonist (Kainic acid). Spermatozoa from groups of 2 to 5 were incubated in a Co₂ incubator for 60 minutes. To study the acrosome reaction in the different groups' the sperm samples were stained with Pisum sativum. In addition, cytosolic Ca²⁺ levels were assessed in the experimental groups. One-way ANOVA followed by Tukey's test was used to determine the statistical significance of the data. A P<0.05 was considered significant.

Results: In the present study, applying L-glutamate significantly (P<0.001) induced an acrosome reaction compared to the control group. In the MK-801+ L-glutamate group, MK-801 could significantly (P=0.010) inhibit the induction of acrosome reaction compared to the L-glutamate group. The application of kainic acid did not affect the induction of acrosome reaction compared to the control group. In the L-glutamate group, cytosolic Ca²⁺ levels were significantly (P=0.044) increased when compared with the control group. The application of MK-801+ L-glutamate could significantly (P=0.047) reverse the effect of L-glutamate on cytosolic Ca²⁺ levels compared to the L-glutamate group.

Conclusion: The results of the present study showed that NMDA glutamate receptors play an essential role not only in the increase of cytosolic Ca²⁺ levels but also in the induction of the acrosome reaction in human sperm.