Central effect of prostaglandin e₁ (pge₁ on prolactin release

PGE₁ or PGE₂ injected iv at different doses (5, 20 or 50 μg/100 g body wt) in ovariectomized rats failed to modify plasma prolactin levels 20, 60 or 90 min after injection. The diluent (95% ethanol) was also ineffective. Third ventricular injection of PGE₁ (5 μg in 5 μl 95% ethanol: 0.02% Na₂CO₃, 1:9) in ovariectomized rats induced a marked increase in plasma prolactin levels 15 min later. Levels then declined but were still elevated at 30 min. At 60 min they were not different from the initial values. PGE₂, PGF_lα or PGF_2α at the same dose failed to modify plasma prolactin at any time interval studied. The diluent also did not alter plasma prolactin. Intraventricular injection of different doses of PGE₁ (0.5, 1.0, 2.5 or 5.0 μg in 5 μl) induced a dose-related increase of plasma prolactin 15 min after the injection. In ovariectomized, estrogen-treated rats (estradiol benzoate, Eb, 10 μg, SC, 48 hr before), PGE₁ increased plasma prolactin 15 min later, in spite of the elevated initial plasma prolactin levels induced by the estrogen treatment. PGE₂, PGF_lα) PGF_2α or the diluent were again ineffective. Intrapituitary injection of PGE₁ (2.5 μg in 2.5 μl into each lobe) in ovariectomized rats slightly increased plasma prolactin levels at 15 min (p < 0.05). Similar injections of PGE₂ did not alter plasma prolactin at any time interval studied. Intrapituitary injections of PGE₁ or PGE₂ in ovariectomized estrogen-treated rats at the same dose used before failed to increase plasma prolactin. These results indicate that PGE₁ can stimulate prolactin release by acting on the central nervous system and that this effect is not inhibited by estrogen treatment. PGE₂, PGF_1α and PGF_2α appear to be ineffective. Under certain conditions, PGE₁ may also stimulate prolactin release by acting on the adenohypophysis, but this effect was inhibited by estrogen pretreatment.