Specific adaptations of estrogen receptor alpha and beta transcripts in liver and heart after endurance training in rats.

Estrogens exert their biological roles mainly through estrogen receptors (ER) that function as ligand-activated transcription factors. ER content in a cell is regulated by many factors and is decisive for estrogen action. The purpose of the present study was to investigate the influence of an 8-wk endurance training program on ER expression in the liver, right atrium (RA), and left ventricle (LV) of intact and ovariectomized (Ovx) rats. We measured ERalpha and ERbeta mRNA content by reverse transcription-polymerase chain reaction (RT-PCR). We found an important increase in ERalpha mRNA levels in the liver (300%; P < 0.01) and in ERbeta mRNA levels in the RA (200%; P < 0.05), and a marked decrease in ERalpha (80%; P < 0.01) and ERbeta (40%; P < 0.05) transcripts content in the LV of intact rats after endurance training. On the other hand, ERalpha mRNA levels were depressed by 50% (P < 0.01) in the liver, and increased by 60% (P < 0.01) in LV of Ovx rats after exercise training. These results first indicate that endurance training is associated with modifications of ER transcripts levels in the liver, LV, and RA of female rats. More specifically, these effects are tissue and isoform-specific and the direction of the response (increase or decrease) is different in intact and Ovx rats. It is suggested that some of the adaptations to endurance training in liver and heart may be mediated by an ER-dependent mechanism.