Effect of haloperidol and L-dopa on plasma prolactin in stalk-sectioned and intact monkeys.

To investigate further possible direct effects of dopamine agonists and antagonists upon the lactotropic cell in vivo, the PRL response to L-dopa and haloperidol was studied in stalk-sectioned monkeys. Six rhesus monkeys, four of which had undergone pituitary stalk-section, were tested twice over a 10-day period. In the stalk-sectioned monkeys baseline PRL levels were elevated as compared to those of controls. L-Dopa (20 mg), the precursor of DA, significantly (P < 0.01) depressed these elevated baseline PRL levels within 30 min; haloperidol (0.5 mg), a DA antagonist, injected after L-dopa, significantly (P < 0.01) elevated plasma PRL concentrations towards the original baseline within 45 min. In the second session, drugs were administered in reverse order: haloperidol did not increase further the elevated baseline PRL levels; L-dopa, this time injected after haloperidol, failed to decrease PRL concentrations significantly. These findings indicate a direct effect of haloperidol and DA upon the lactotropic...