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EXPRESSION OF ANDROGEN RECEPTORS IN THE RAT CORPORA LUTEA OF PREGNANCY.
Calvo, Virginia1, Goyeneche, Alicia1,2, Telleria, Carlos1,2,3, 1 2 3
ABSTRACT- Aromatizable androgens, such as testosterone and androstenedione, have extensively been shown to stimulate luteal steroidogenesis indirectly by their transformation into estrogens. An explanation for this is provided by the presence of both alpha and beta nuclear estrogen receptors in the rat corpus luteum. There is also evidence that 5 alpha-dihydrotestosterone, a non-aromatizable androgen, is able to stimulate luteal progesterone production; however, no studies have proven the existence of androgen receptors (AR), which would thereby account for the direct luteal effects of androgen. The purpose of the present investigation was to study this expression of AR in the rat corpora lutea (CL) during pregnancy. CL were obtained from rats on different days of pregnancy and total RNA was extracted and subjected to semiquantitative RT-PCR using specific AR primers. L19 mRNA was co-amplified and used as an internal control. Prostate and epidydimus were used as positive controls. RT-PCR products were run on 1.8 % agarose gels, stained with ethidium bromide and the bands were subjected to densitometry. The results showed that the rat CL express the classical AR receptor mRNA throughout pregnancy at levels found in positive control tissues. However, receptor expression decreased significantly at the end of pregnancy but rose again on the day of parturition. To determine whether the AR mRNA is translated in rat CL, total protein from CL obtained on different days of pregnancy were separated by 8% SDS-PAGE, electrotransferred to nitrocellulose, subjected to immunoblot using a specific AR antibody (N-20), and developed by ECL. The luteal AR protein, detected at approx. 120 KDa, was abundantly expressed throughout pregnancy, although at lesser amounts than in epidydimus or prostate. In summary, the results of this investigation have established the expression of AR mRNA and protein in the rat CL during pregnancy. This is the first report that demonstrates the presence of AR in the rat CL indicating that androgens not only regulate luteal function through estrogen-mediated effects, but also could act through classical genomic AR. Supported by Grants from the Ministry of Health, Antorchas Foundation, National Agency for Research, and University of Cuyo, Argentina (CMT), and by NIH Grant FIRCA 1R03 TW01049-02 (GG,CMT).
KEY WORDS: androgen receptor, corpus luteum, rat, pregnancy