The effects of delta1-tetrahydrocannabinol on mammary gland growth, enzyme activity and plasma prolactin levels in the mouse.

DELTA1-tetrahydrocannabinol (delta1-THC), a highly lipid soluble and active principle of cannabis, was injected each day (25 mg/kg) s.c. in mice from the estimated 13th day of pregnancy. Delta1-THC-treated mice showed no increase in the wet weight or DNA content of their mammary glands during the period of investigation from before parturition until the 12th day post-partum. A marked increase in mammary-gland lipoprotein lipase activity w,s found in control mice at parturition and this was suppressed by delta1-THC. Prolactin rose to a peak level in plasma earlier in lactation in the control mice than in the delta1-THC-treated mice. This delayed rise in plasma prolactin due to delta1-THC may account for the depression of mammary gland growth and development by the drug and for the delay in the appearance of high activities of lipoprotein lipase until later in lactation.