Effects of Tumor-Induced Hyperprolactinemia on LH Secretion following Stimulation of the Medial Preoptic Area, Pituitary Responsiveness and the Estrogen-Induced LH Surge

Abstract

In the present study we utilized the 7315a PRL- and ACTH-secreting tumor to induce a hyperprolactinemic (HP) state sufficient to profoundly suppress the postcastration LH rise in female rats. Tumor-induced prolactin levels which ranged 2,000-3,000 ng/ml substantially reduced the LH rise in both ovariectomized (OVX) and OVX + estradiol-17 beta (E2)-treated rats. Bilateral electrochemical stimulation (ECS, 100 microA DC for 60 s) of the ventral diagonal band of Broca-medial preoptic area (DBB-MPOA) resulted in comparable LH responses in control and HP rats in the presence of absence of estradiol. Transient decreases in PRL release occurred following ECS of the DBB-MPOA. Pituitary responsiveness was assessed with two LHRH challenges spaced 60 min apart at doses of 25 and 50 ng LHRH/100 g body weight. The mean maximal LH increments (delta LH) to some of these LHRH challenges were decreased in HP rats. Finally, the LH surge induced in the afternoon in OVX + E2-treated rats was diminished 71% by the presence of the PRL-secreting tumor.(ABSTRACT TRUNCATED AT 250 WORDS)