Prolonged Hyperprolactinemia Influencesβ-Endorphin and Met-Enkephalin in the Brain*

The effects of several hyperprolactinemic conditions on β-endorphin and met-enkephalin concentrations in pituitary and brain regions have been investigated in female rats. In Buffalo rats bearing a PRL- and ACTH-secreting tumor (7315a) for 5 weeks, a decrease (P < 0.01) in β-endorphin, but not met-enkephalin, concentrations was present in the hypothalamus, midbrain, hindbrain, and pituitary when compared to intact rats. In rats bearing the tumor for 3 weeks, a similar pattern was present, except for the midbrain in which no change was evident. In Wistar Furth rats bearing a PRL- and GHsecreting tumor (MtTWl5) for 8 weeks, a decrease (P < 0.01) in β-endorphin concentrations in the hypothalamus and midbrain was present. Met-enkephalin concentrations decreased (P < 0.02) in the hypothalamus, midbrain, and hindbrain. In rats bearing the tumor for 5 weeks, the decreases (P < 0.001) in β-endorphin concentrations were similar in magnitude. In rats bearing two pituitaries transplanted under the kidney capsule for 5 days, no change in β-endorphin or met-enkephalin concentrations was observed. When four pituitaries were transplanted and the experiments were conducted 4 weeks later, a decrease (P < 0.05) in β-endorphin concentrations was present in the hypothalamus and hindbrain. In lactating rats 8 days post parturn, a decrease (P < 0.01) in β-endorphin concentrations was present in the hypothalamus and midbrain. Met-enkephalin decreased (P < 0.01) in the hypothalamus, midbrain, and hindbrain. β-Endorphin concentrations were not changed in rats weaned 8 or 2 days after 6 days of lactation. A decrease (P < 0.05) in β-endorphin concentrations in the pituitary was present immediately after delivery, while no change was observed in the brain. (Endocrinology106: 1804, 1980)