The effects of dopamine (10−5 M) on growth hormone and prolactin secretion and the fractional rate of 86Rb efflux were investigated using perifused bovine pituitary cells. Dopamine decreased the control efflux rate, prevented the rise caused by thyroliberin (10−7 M) in the presence of 3-isobutyl-l-methyl-xanthine (10−4 M) and greatly decreased the rise caused by acetylcholine (2.5 × 10−5 M). Under these conditions it inhibited the prolactin secretion but it had no effect on growth hormone secretion induced by either treatment. Dopamine receptors in lactotrophs are therefore coupled to secretion and potassium permeability, but if somatotrophs contain dopamine receptors they are coupled only to K+ efflux.
