BACKGROUND: The purpose of this work was to examine the in vitro effects of three neuropeptides--vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and substance P (SP)--on the release of ovarian progesterone (Po), acting directly on the ovary (O) or on the celiac ganglion (CG) of rats in diestrus 1 (D1) and 2 (D2), because in these two cycle stages neural effects have been observed on P release. MATERIAL/METHODS: Hemiovaries of rats in D1 and D2 were incubated with each neuropeptide alone and in combination with norepinephrine. Also, the CG-superior ovarian nerve (SON)-O system was incubated with the addition of each neuropeptide to the CG. RESULTS: In D1 ovaries, NPY, VIP or SP, both alone and with norepinephrine, generally decreased the release of Po. The effect of each neuropeptide was modified by norepinephrine. In D2, NPY, VIP or SP, both alone and with norepinephrine, increased Po release. The effect of NPY and SP was modified by norepinephrine. In the CG-SON-O system, in D1, the addition of NPY and VIP alone increased Po release, while SP decreased it. In D2, the three neuropeptides increased Po release. CONCLUSIONS: Of the studied situations, only the effects of NPY and VIP on the CG during D1 mirror the changes of progesterone in blood during the rat estrous cycle. These effects are in agreement with others obtained by intracerebroventricular injection of epinephrine, suggesting that these neuropeptides might be released on CG after this injection and produce increased progesterone in blood.

Keywords: Diestrus - drug effects, Ganglia, Sympathetic - drug effects, Ovary - innervation, Progesterone - analysis, Progesterone - biosynthesis, Substance P - pharmacology, Diestrus - drug effects, Ganglia, Sympathetic - drug effects, Neuropeptide Y - pharmacology, Neuropeptides - pharmacology, Ovary - metabolism, Progesterone - biosynthesis, Substance P - pharmacology, Vasoactive Intestinal Peptide - pharmacology