EXPRESSION AND LOCALIZATION OF INDUCIBLE AND ENDOTHELIAL NITRIC-OXIDESYNTHASE IN THE RAT OVARY - EFFECTS OF GONADOTROPIN STIMULATION IN-VIVO

Nitric oxide is reportedly involved in the regulation of several ovari an processes, yet the isoforms of nitric oxide synthase (NOS) expresse d in the ovary are unknown. Our purpose was to identify and localize N OS isoenzymes in the rat ovary and to examine if mRNA expression of NO S isoenzymes change after gonadotropin stimulation, Using reverse tran scriptase-PCR, we demonstrated that inducible (iNOS) and endothelial ( eNOS), but not neuronal, NOS mRNAs are expressed in the ovary, In a go nadotropin-stimulated rat model, unstimulated ovaries had the highest levels of iNOS mRNA as quantified by ribonuclease protection assay, Af ter gonadotropin injection, iNOS mRNA declined to undetectable levels in ovaries containing ovulatory follicles before increasing slightly i n ovaries containing coporalutea. In situ hybridization studies locali zed iNOS to granulosa cells of secondary follicles and small antral fo llicles, Western blots of unstimulated ovaries demonstrated INOS prote in, In contrast to iNOS, eNOS mRNA levels, determined by quantitative PCR, increased after gonadotropin stimulation and peaked in ovaries co ntaining ovulatory follicles before declining in the luteal phase. eNO S protein was localized to blood vessels in the ovary by immunohistoch emistry, We conclude that two isoforms of NOS are expressed in the ova ry and the mRNA levels for these isozymes are differentially regulated .