Prostaglandins play an important role in diurnal changes of tuberoinfundibular dopaminergic neuronal activity and prolactin secretion in ovariectomized, estrogen-treated rats

Abstract Intracerebroventricular injection of prostaglandins (PGs) has long been shown to stimulate the secretion of prolactin (PRL). The action of specific PG and the underlying mechanism, however, remain inconclusive. In this study, we evaluated the involvement of PGs in the diurnal changes of the tuberoinfundibular dopaminergic (TIDA) neurons and PRL secretion in ovariectomized (OVX) rats treated with estrogen (E 2 ). Prior treatment of indomethacin (50 mg/kg, subcutaneous) for 24 h significantly prevented the afternoon decrease of TIDA neuronal activity and blocked the PRL surge. Intracerebroventricular injection of PGE 1 (5 μg/3 μl/rat) at 1000 h significantly lowered the activity of TIDA neurons, while similar treatment of PGE 2 was without effect. In OVX + E 2 rats pretreated with indomethacin, PGE 1 given at 15, but not 30 or 180 min before decapitation at 1500 h significantly reversed the effects of indomethacin on TIDA neuronal activity, while the blocked PRL surge was not reversed. The PGs also exhibited a stimulatory effect on nigrostriatal dopamine (DA) neurons with PGE 2 being the most effective agent. These results indicate that endogenous PGs play a significant role in the control of central DA neurons, especially the diurnal changes of TIDA neuronal activity and PRL secretion in OVX + E 2 rats.