Scientists from the University of Buffalo have smoked out what may cause some cases of infertility: marijuana. Today at the annual meeting of the American Society for Cell Biology, Herbert Schuel and his colleagues describe a cellular signaling system that responds to THC--the active substance in marijuana--and that may regulate sperm functions necessary for normal egg fertilization. The signaling system may be activated by anandamide, a cannabinoid-like molecule which this study shows for the first time is found in human seminal plasma, mid-cycle oviductal fluid and follicular fluid.

"These findings suggest that defects in the cannabinoid receptor-signaling system could account for certain types of infertility," Schuel says. "A better understanding of these mechanisms might lead to the development of novel drugs useful in reproductive medicine. For heavy marijuana users, the study results raise the possibility they are jeopardizing fertility by overloading this system."

To be sure, the process by which sperm prepare to fertilize an egg in the female reproductive tract is still mysterious. They must first become "capacitated" before they can begin swimming vigorously towards an egg and secrete the enzymes necessary to penetrate the egg's protective coat, a process called the acrosome reaction. But Schuel's work shows that both AM-356--a synthetic version of natural anandamide--and THC affect this sequence of events in three distinct ways: first, although low amounts of AM-356 stimulate sperm to swim more vigorously, too much of it has the exact opposite effect. Both AM-356 and TCH inhibit structural changes over the acrosome. And AM-356 significantly impairs sperm from binding to an egg's protective coat.

"The increased load of cannabinoids in people who abuse marijuana could flood natural endocannabinoid-signal systems in reproductive organs and adversely impact fertility," Schuel adds. "This possibility may explain observations made over the past 30 to 40 years that marijuana smoke drastically reduces sperm production in males."