The most recent study is reported in the October issue of the journal Biology of Reproduction, published by the Society for the Study for Reproduction.
Chemicals in marijuana called cannabinoids interfere with pregnancy and often end it before the embryo has implanted in the uterus, according to the studies by S.K. Dey, PhD, professor of physiology at KU Medical Center.
Research from Dey's laboratory shows that signals from cannabinoids are readily received by two-day-old mouse embryos. The researchers also have found that the uterus naturally produces a cannabinoid-like compound.
In humans, an aberrant presence of the cannabinoids -- either from marijuana smoking or from the uterus -- or an abnormality of the receptors in the embryo could contribute to the large percentage of all human pregnancies that are lost at an early stage, said Dey.
Dey's research has shown that mouse embryos have a high concentration of cannabinoid receptors, and thus would be expected to be highly sensitive to cannabinoids. The receptors found in the embryos are the same as those found in the brains of adults. In the brain, the cannabinoid called THC (delta-9-tetrahydrocannabinol) prompts the "high" associated with marijuana smoking.
The recently reported study shows that activation of the embryonic cannabinoid receptors brings development to an abrupt -- and abnormal -- halt. Development ceased at or before the eight-cell stage (approximately three days of age). When the cannabinoid action was interfered with by adding a compound that blocked the brain-type cannabinoid receptors, the embryos developed normally. This indicates that the embryos contain the same receptors that are responsible for the psychoactive effects in the brain.
Marijuana use is not the only way that cannabinoid receptors in the embryo can be activated. Dey and his collaborators found that a naturally occurring cannabinoid-like compound, called anandamide, is produced by the uterus. It, too, can interfere with the developing embryo.
Dey said that the presence of anandamide in the uterus indicated that it probably had a role in fertility and normal pregnancy. Further research will be necessary to understand its importance.
The findings are reported in an article titled "Activation of brain-type cannabinoid receptors interferes with preimplantation mouse embryo development" by Zeng-Ming Yang, Ph.D., former postdoctoral student, B.C. Paria, Ph.D., research assistant professor of physiology, and Dey. The study was funded by the National Institute on Drug Abuse and the National Institute of Child Health and Human Development.
For copies of the article, contact Judith Jansen, managing editor, Society for the Study of Reproduction, 1526 Jefferson St., Madison, WI, 53711-2106 [telephone (608) 256-2777; fax (608) 256-4610].