Expression and localization of cannabinoid receptors in human immature oocytes and unfertilized metaphase-II oocytes

Endocannabinoid anandamide and cannabinoid receptors have been described in some organs of the female reproductive system, but little is known about the expression of these receptors in human oocytes. The aim of the study was to describe the expression of cannabinoid receptors in human oocytes and to investigate their differential distribution at various stages of meiotic resumption in human oocytes. A total of 750 human oocytes from 214 patients were analysed by Western blot, immunocytochemistry and PCR. For this study, oocytes that were not suitable for intracytoplasmic sperm injection (ICSI) (germinal-vesicle and metaphase- I stages), as well as metaphase-II oocytes that had not developed into an embryo after ICSI were used. Western blot analysis revealed the presence of CB1 and CB2 receptor proteins in human oocytes. CB1 and CB2 receptor immunostaining patterns changed during the various stages of meiotic resumption. Localization of CB1 receptor was peripheral at germinal-vesicle stage, homogeneous over the entire oocyte at metaphase I and peripheral at mature metaphase II. CB2 receptor localization was peripheral at germinal-vesicle and metaphase-I stages but homogeneous over the entire cell at metaphase II. This finding suggests a possible role for endocannabinoids, acting via receptors, in the maturation of female gametes and fertilization. (C) 2011, Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.