Effect of anterior pituitary perfusion and intraventricular injection of catecholamines on prolactin release

In rats, the median eminence, pituitary stalk and anterior pituitary were exposed parapharyngeally and catecholamines were injected into the third ventricle or infused into a stalk portal vessel, peduncular artery, or a tuberalis ramus of an infundibular artery. Ten min after 1.25 μg dopamine hydrochloride was injected into the third ventricle, the plasma prolactin concentration was 70% of the preinjection value; 47% at 20 min; 42% at 30 min; 57% at 60 min; 69% at 90 min; and 93% at 120 min. Similar responses occurred following the administration of 2.5 μg dopamine. Quantities of dopamine greater than 2.5 jug caused less inhibition of release, however. Intraventricular injection of 2.5 or 5 μg of epinephrine or norepinephrine bitartrate did not affect prolactin release although 100 μg did. Dopamine, epinephrine, or norepinephrine, perfused into the anterior pituitary for 30 min via a hypophysial portal vein, had no effect on prolactin release. Dopamine, infused into the stalk-median eminence complex via the peduncular artery or a tuberalis ramus of an infundibular artery, had no effect on plasma prolactin levels. These findings indicate that neither dopamine, epinephrine, nor norepinephrine affected prolactin release by a direct action on the anterior pituitary but indirectly through the hypothalamic-hypophysial complex.