DOMESTIC ANIMAL ENDOCRINOLOGY Vol 1(1) 55-66,1984 EFFECTS OF ESTRADIOL-17/3, PARA-CHLOROPHENYLALANINE AND QUIPAZINE ON TONIC AND LHRH-INDUCED SECRETION OF LUTEINIZING HORMONE IN OVARIECTOMIZED EWES 1 D R Deaved and R A Dalley 3 Dwlslon of Ammal and Veterinary Sciences, West V~rgm~a Unwers~ty, Morgan- town, WV 26506-6108 (Recewed September9, 1983) ABSTRACT Changes in metabolism of serotonin (5-HT) might medlate the reduced tonlc luteinizing hormone (LH) and increased pituitary responsiveness to luteinizing hormone releasing hormone (LHRH) caused by estradiol-17~ (estradiol). Two experiments were conducted to determlne effects of estra- diol, para-chlorophenylalanine (PCPA), an inhibitor of synthesis of 5-HT, and quipazine, an agonist of 5-HT, on tonlc and LHRH-induced secretion of LH zn ovarlectomlzed ewes durlng the summer. Tonic levels of LH were reduced, the interval from LHRH to peak of the induced surge was longer and the magnitude of release of LH was greater in ovariectomlzed ewes treated with estradiol than in con- trois. Neither PCPA nor quipazlne affected tonic secretlon of LH. In ovarlectomlzed ewes not receiving estradlol, PCPA and quipazine increased the magnltude of the LHRH- Induced release of LH. However, PCPA reduced pituitary sensitivity to LHRH when admlnistered concomitantly with estradlol; treatment with quipazlne attenuated thls effect of PCPA. The Interval to the peak of the induced surge of LH was not affected by PCPA or qulpazine in estradiol- treated or control ovariectomlzed ewes. Based on these results it appears that 5-HT mediates or is requzred for estradiol to increase pltultary responsiveness to LHRI~. 55 Copyrtght© 1984 by DOMENDO, Inc 0739-7240/84/$3 O0