Catecholamines, which contribute to regulating ovarian development and function, are thought to derive almost exclusively from the extrinsic innervation of the ovary. Recent studies from our laboratory have, however, demonstrated that the primate ovary contains a network of neuron-like cells, some of which are immunoreactive for tyrosine hydroxylase (Dees et al., Endocrinology 136:5760, 1995), and express the TH gene (Mayerhofer et al., Soc. Neurosci. Abstr. 20:11, 1994). Thus, these cells may represent an intragonadal source of catecholamines, as they contain the rate limiting enzyme in catecholamine biosynthesis. To determine if the primate ovary also expresses the gene encoding the enzyme responsible for the synthesis of norepinephrine, we subjected samples of total ovarian RNA to reverse transcription-PCR, using oligodeoxynucleotides complementary to highly conserved sequences of the human and rat dopamine-beta-hydroxylase (DBH) genes. A cDNA encoding an mRNA species identical to adrenal DBH mRNA was obtained; an antisense RNA transcribed from this cDNA template was fully protected by ovarian RNA in a ribonuclease protection assay, indicating that the ovary indeed expresses the DBH gene. Surprisingly, in situ hybridization identified oocytes as a major site of DBH mRNA expression, a localization verified by RT-PCR cloning and sequencing of a DBH cDNA from cumulus-free oocytes. Immunohistochemical localization of DBH protein by conventional and confocal laser microscopy showed that oocyte DBH mRNA is translated into its protein product. Oocytes do not contain TH mRNA or protein, but were found to express a dopamine (DA) transporter gene similar to the one found in human brain (99% homology at the amino acid level). The biological relevance of this transporter system was suggested by the ability of isolated oocytes to metabolize DA into norepinephrine (NE), as determined by HPLC-electrochemical detection. Exposure of isolated follicles to DA resulted in accumulation of cAMP in the culture medium. This effect was prevented by either removing the oocytes or adding a -adrenoreceptor blocker to the incubates, suggesting that an oocyte-mediated conversion of DA into NE is required for DA to affect cAMP formation in somatic follicular cells. Thus, follicular development in the primate ovary may be affected by a novel cell-cell regulatory loop involving a) DA released by nerve terminals and TH-positive neuron-like cells, b) uptake of DA by oocytes via a specific DA transporter system, and c) conversion of DA to NE, which may then feed back on cumulus/granulosa cells to affect their function. Derangement of this regulatory system may contribute to the etiology of ovarian dysfunction of neurogenic origin.
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