Acute decreases in serum prolactin concentrations caused by delta 9-tetrahydrocannabinol in nonhuman primates

The acute effects of single injections of delta 9-tetrahydrocannabinol (THC) on serum prolactin (PRL) concentrations were studied in oophorectomized female and intact adult male rhesus monkeys. Some animals were challenged with thyrotropin-releasing hormone (TRH) to determine whether THC influences pituitary responsiveness to releasing hormone. THC markedly suppresses serum PRL concentrations in animals of both sexes. TRH injections resulted in normal PRL release when administered simultaneously with or 30 minutes after THC administration. These results suggest that the serum prolactin-lowering effect of THC occurs principally at a suprapituitary level.