Expression of Messenger Ribonucleic Acid Species Encoding Steroidogenic Enzymes in Human Follicles and Corpora Lutea throughout the Menstrual Cycle*

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Abstract
The levels of expression of mRNA species encoding cholesterol side-chain cleavage cytochrome P-450 (450scc), 17.alpha.-hydroxylase cytochrome P450 (P45017.alpha.), aromatase cytochrome P-450 (P-450AROM), and 3.beta.-hydroxysteroid dehydrogenase (3.beta.HSD) were examined in human follicles and corpora lutea (CL) throughout the menstrual cycle. Tissues were obtained from women undergoing hysterectomy and oophorectomy. The largest follicle or the CL was dissected from the ovary depending on whether the surgery was performed in the follicular or luteal phase. The day of the cycle was determined by onset of last menstrual period and was confirmed by endometrial histology. Total RNA was examined by Northern blot analysis, using as probes specific 32P-labeled cDNA inserts encoding each human enzyme. Early follicles demonstrated detectable mRNA for both P450scc and P450P45017.alpha., but not for P450AROM or 3.beta.HSD. P450AROM was detectable late in the follicular phase and appeared markedly induce din the CL. 3.BETA.HSD was detected only in the CL. Levels of P45017.alpha. mRNA remained relatively unchanged throughout the cycle, whereas P450scc mRNA levels were greatly increased in the CL. The presence of P45017.alpha. mRNA in the human CL is of interest, since it is absent from the bovine CL, and this is consistent with the ability of the human, but not the bovine, CL to synthesize 17.alpha.-hydroxyprogesterone and estrogens. The fact that P450AROM expression is highest in CL is surprising, since plasma estrogen levels are highest during the late follicular phase of the cycle, and may suggest that CL estrogen biosynthesis is limited by 17.alpha.-hydroxylase or 17,20-lyase activities.

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