Utilizing anesthetized male rats, we exposed the median eminence, pituitary stalk and anterior pituitary as well as adjacent diencephalic structures. This exposure enabled us to inject or infuse solutions containing dopamine, epinephrine or norepinephrine into the third ventricle, a stalk portal vessel, peduncular artery, or a tuberalis ramus of an infundibular artery. The rate of FSH release was evaluated by determining the concentration of FSH in plasma. Within 10 min after 1.25 ng dopamine hydrochloride was injected into the third ventricle, the level of FSH in plasma had increased 4-fold. The plasma FSH level had increased 5-fold at 20 min, 6-fold at 30 min and 10-fold at 60 and at 90 min. At 120 min, the plasma FSH level was lower than that seen at 60 and 90 min. A similar response pattern was observed following the administration of 2.5 jug dopamine. For quantities of dopamine greater than 2.5 ng, the resulting plasma FSH levels were inversely related to the dosage, e.g., 60 min after the injection of 1.25, 2.5, 5 and 100 ng dopamine hydrochloride, the mean plasma FSH concentrations were 4.5, 4.8, 1.7 and 0.42 μg/ml, respectively. A similar response pattern was observed at 10, 20, 30, 90 and 120 min. Injection of 2.5 and 5 ng epinephrine or norepinephrine bitartrate into the third ventricle did not affect FSH release although the injection of 100 fig did do so. When dopamine, epinephrine or norepinephrine was perfused into the anterior pituitary for 30 min via a microcannula inserted into a hypophysial portal vein, FSH release was not affected. Furthermore, when dopamine was infused into the stalk-median eminence complex via the peduncular artery or a tuberalis ramus of an infundibular artery, no effect on the plasma FSH concentration was observed. These findings indicate that neither dopamine, epinephrine nor norepinephrine affected FSH release by a direct action on the anterior pituitary but indirectly through the hypothalamic-hypophysial complex.
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