EVIDENCE THAT NEUROPEPTIDE-Y SECRETION IN THE MEDIAN-EMINENCE INCREASES PRIOR TO THE LUTEINIZING-HORMONE SURGE IN OVARIECTOMIZED STEROID-PRIMED RATS - ESTIMATION BY PUSH-PULL PERFUSION

Utilizing the push-pull perfusion technique, we examined the secretory profiles of neuropeptide Y (NPY) and luteinizing hormone (LH)-releasing hormone (LHRH) in the median eminence (ME) of ovariectomized adult rats which were primed with estrogen and progesterone to provoke LH and prolactin (PRL) surges. The ME was perfused with artificial cerebrospinal fluid between 13.00 and 18.00 h, and perfusates and blood samples were collected every 20 min. NPY and LHRH in the ME started to significantly increase 40 min earlier than the initial significant rise in the plasma LH, and the highest ME levels of the neuropeptides clearly preceded the occurrence of the LH surge. Regarding the PRL surge, however, such temporal relationship was not apparent. These in vivo data appear to support the putative facilitatory role of NPY in the generation of the steroid-induced LH surge. This is the first study to characterize the temporal profile of in vivo release of NPY in rat ME in terms of its relationship to LH and PRL surges.