Dopamine receptors regulate Met-enkephalin content in pituitary.

Met-enkephalin-like immunoreactive material (ME-LI) in the neurointermediate lobe of rat pituitary was dramatically altered by the long-term administration of drugs altering dopamine receptor activity. Treatment with the dopamine receptor antagonist haloperidol resulted in significant increases of ME-LI and treatment with the dopamine receptor agonist bromocriptine resulted in significant decreases of ME-LI in the neurointermediate pituitary. The treatments had considerably less effect on ME-LI in the anterior lobe of the pituitary. These results suggest that dopamine receptor activation or inhibition influences the content of ME-LI in the rat pituitary gland.