Oxytocin receptors in the primate ovary: molecular identity and link to apoptosis in human granulosa cells.

BACKGROUND Oxytocin (OT) is produced by granulosa cells (GCs) of pre-ovulatory ovarian follicles and the corpus luteum (CL) in some mammalian species. Actions of OT in the ovary have been linked to luteinization, steroidogenesis and luteolysis. Human IVF-derived (h)GCs possess a functional OT receptor (OTR), linked to elevation of intracellular Ca(2+), but molecular identity of the receptor for OT in human granulosa cells (hGCs) and down-stream consequences are not known. METHODS AND RESULTS RT-PCR, sequencing and immunocytochemistry identified the genuine OTR in hGCs. OT (10 nM-10 microM) induced elevations of intracellular Ca(2+) levels (Fluo-4 measurements), which were blocked by tocinoic acid (TA; 50 microM, a selective OTR-antagonist). Down-stream effects of OTR-activation include a concentration dependent decrease in cell viability/metabolism, manifested by reduced ATP-levels, increased caspase3/7-activity (P < 0.05) and electron microscopical signs of cellular regression. TA blocked all of these changes. Immunoreactive OTR was found in the CL and GCs of large and, surprisingly, also small pre-antral follicles of the human ovary. Immunoreactive OTR in the rhesus monkey ovary was detected in primordial and growing primary follicles in the infantile ovary and in follicles at all stages of development in the adult ovary, as well as the CL: these results were corroborated by RT-PCR analysis of GCs excised by laser capture microdissection. CONCLUSIONS Our study identifies genuine OTRs in human and rhesus monkey GCs. Activation by high levels of OT leads to cellular regression in hGCs. As GCs of small follicles also express OTRs, OT may have as yet unknown functions in follicular development.