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(500) PROGESTERONE INCREASES DYNORPHIN CONCENTRATIONS IN CSF COLLECTED FROM THE THIRD VENTRICLE OF EWES. Goodman, Robert1, Adams, Van1, Valent, Miroslav1, Connors, John1, Hardy, Steve1, McManus, Christina1, Hileman, Stanley1, 1 Dept of Physiology & Pharmacology, West Virginia University, Morgantown, WV ABSTRACT- Recent evidence has led to the hypothesis that dynorphin-containing neurons mediate progesterone negative feedback in the ewe. Specifically: 1) an antagonist to the dynorphin (kappa) receptors increases LH secretion during the luteal phase, 2) dynorphin neurons synapse on GnRH perikarya, and 3) most dynorphin neurons in the arcuate nucleus contain progesterone receptors. If these neurons mediate progesterone negative feedback, then progesterone should increase dynorphin release. We tested this hypothesis by monitoring dynorphin concentrations in CSF collected from the third ventricle (IIIV) in three groups of ewes: ovary-intact luteal phase ewes (n=6), ovariectomized (OVX) ewes (n=5), and OVX ewes treated with progesterone (OVX+P, n=5). Ovarian cycles were synchronized using prostaglandin (PGF) and on day 0 (3 days post PGF injection), a 17 gauge stainless steel tube was stereotaxically inserted into the IIIV. Ewes in the two OVX groups were OVX at this time and those in the OVX+P group had two progesterone packets placed sc. Seven days later, CSF and blood samples were collected every 10 min for 5 hours. CSF was collected on ice at a rate of approximately 50 KEY WORDS: dynorphin, progesterone, luteinizing hormone, sheep |
l/min via PE tubing that extended 1-2 mm into the IIIV and was connected to a peristaltic pump. Dynorphin was measured in CSF using a commercial RIA kit (Peninsula Laboratories, Inc) and LH and progesterone monitored in peripheral plasma by RIA. The progesterone treatment increased circulating concentrations of this steroid from 0.23 ± 0.05 ng/ml to 2.2 ± 0.3 ng/ml, levels that were similar to those in ovary-intact ewes (1.8 ± 0.3 ng/ml) on the day of CSF collection. As expected, LH pulse frequency was higher in the OVX (4.2 ± 0.6 pulses/5 hrs) than in the OVX+P (1.6 ± 0.6 pulses/5 hrs) and luteal phase (1.2 ± 0.3 pulses/5 hrs) ewes. CSF dynorphin concentrations in OVX+P ewes (43.0 ± 4.8 pg/ml) were significantly (P<0.05 by ANOVA) higher than those in OVX (27 ± 8.5 pg/ml) ewes. However, dynorphin levels in ovary-intact ewes fell between these two groups (30.5 ± 2.5 pg/ml) and were not significantly different from either group. These results demonstrate that progesterone can increase dynorphin release, but suggest that other factors may influence this action in ovary-intact ewes. (USDA 00-35203-9159)