Effects of Chronic LHRH Treatment on Brain LHRH Content, Pituitary and Plasma LH and Ovarian Follicular Activity in the Anestrous Ewe

Nine mature, anestrous ewes were used in the experiment. Osmotic minipumps (AIza Corp.) containing 1.7 mg synthetic LURU in 170 pl saline were implanted s.c. into 4 sheep. Each ewe received 4 minipumps, implanted 1 week apart. This treatment resulted in a relatively uniform level (54 ± 2 pg/mI, X ± SEM) of LHRH-like immunoreactivity in plasma during the 4 week period. After 4 weeks, the sheep were killed and the stalk-median eminence (SME), hypothalamus proper (HP), preoptic-suprachiasmatic area (P0-SC), a sample of cerebral cortex (C) and the pineal gland (PG) were removed from the brain, homogenized in acidified ethanol and assayed for LI-IRH. Chronic exposure to LHRU was without effect on the contents of LHRH in the SME, HP or P0-SC, which were 50 ± 5, 5.1 ± 0.6 and 4.8 ± 0.8 ng, respectively. LHRU was not detected in C. LHRH treatment did increase the content of LHRH in the PG (treated = 125 ± 24 pg, control = 80 ± 12 pg, P 2mm in diameter (P<0.01). The initial response of LU to the sustained administration of LHRU appears to be sufficient to induce ovulation and subsequent luteal function. The long term response, however, is not adequate to maintain ovarian follicular development.