We recently identified neuron-like cells as a novel source of catecholamines in the rhesus monkey ovary, and observed that these cells express the gene encoding tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis. Thus, neuron-like cells and the extrinsic innervation appear to be two sources of norepinephrine and dopamine (DA) in the ovary. Although high levels of DA have been found in follicular fluid of the primate ovary, the intraovarian functions of DA are not known. A direct action of DA on ovarian cells requires specific DA receptors. The present study is addressing this issue. Using reverse transcription-PCR amplification and specific oligonucleotide primers, we isolated a 275 bp cDNA that corresponded to the monkey DA1 receptor (D1-R) mRNA. Semiquantitative RT-PCR studies followed by Southern blotting showed that the D1-R mRNA levels were lower in prepubertal than in the adult ovaries. Immunohistochemistry with a D1-R antiserum revealed that D1-R immunoreactivity was predominantly present in cells of the corpus luteum (CL). RT-PCR experiments supported this finding by showing a greater abundance of D1-R mRNA in luteal cells than in freshly isolated GC from preovulatory follicles and in luteinizing GC (derived form monkeys undergoing IVF). D1-R mRNA levels were more abundant during the second half of the luteal phase. Incubation of either isolated midphase luteal cells, or luteinized, cultured GC, with DA in the absence or presence of hCG failed to consistently affect P release. Thus, activation of ovarian D1-R does not appear to be coupled to P secretion. Taken together, our results suggest the existence of a novel regulatory complex within the ovary involving DA and DA type 1 receptors, which are present primarily in the CL. The luteal functions affected by activation of these receptors remain to be identified.
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