Cannabinoid Receptors in Sperm

Abstract

Mammalian and invertebrate sperm contain receptors for a wide variety of neurotransmitters that regulate sperm functions required for fertilization such as motility and the initiation of the acrosome reaction. The acrosome reaction is a ligand-stimulated secretory event in sperm that enables the sperm to penetrate the egg’s investments and to fuse with the egg’s plasma membrane. Previous studies in our laboratory using [3H]CP-55,940 showed that sea urchin sperm contain cannabinoid receptors that are remarkably similar to cannabinoid receptors found in mammalian brain and peripheral organs. Cannabinoid agonists and anandamide (an endogenous ligand for cannabinoid receptors in mammalian tissues) inhibit fertilization in sea urchins by blocking the acrosome reaction. These findings, taken together with other studies showing that the gene for the human brain cannabinoid receptor also is expressed in the human testis and that anandamide is synthesized in the female reproductive tract in mammals, suggested to us that human sperm may contain cannabinoid receptors. We have obtained preliminary evidence that [3H]CP-55,940 binds to putative cannabinoid receptors in live human sperm in a saturable manner, and that cannabinoid ligands affect in vitro capacitation of human sperm. These findings show that functional cannabinoid receptors are present in sperm, suggest that sperm cannabinoid receptors and their endogenous ligands may regulate normal sperm functions required for fertilization within the female reproductive tract in humans, and also imply that smoking marijuana may affect these processes in vivo.KeywordsZona PellucidaHuman SpermAcrosome ReactionFemale Reproductive TractNormal Sperm FunctionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.