Delta-9-tetrahydrocannabinol inhibition of suckling-induced prolactin release in the lactating rat

To study effects of delta-9-tetrahydrocannabinol (THC) on the regulation of prolactin (PRL) release, a chronic cannula was placed in the right atrium of postpartum lactating rats. Two or more days later their pups were removed for 6--8 hours. A blood sample was drawn from the mother just prior to reintroducing the pups, for determination of basal levels of plasma PRL. A second sample was drawn following 30 min of continuous suckling. THC (1.25 or 4.0 mg/Kg) or vehicle was then injected intravenously and blood samples obtained 30, 60, 120 min later. Relative to vehicle-injected controls, both doses of THC significantly reduced plasma PRL levels and disrupted all components of maternal behavior. These findings indicate that THC inhibits suckling-induced PRL release in the postpartum rat.