Expression of ERalpha and ERbeta mRNA in the two populations of CL found in the post-partum ovaries. Old indicates CL from previous pregnancy. New indicates newly formed CL after post-partum ovulation. Total RNA was isolated from old or new CL on day 4 post-partum, and from CL obtained from animals on day 15 of pregnancy, and was analyzed by RT-PCR. In panel (A) a representative gel is shown. Results were quantified by densitometry and corrected using L19. Normalized mRNA levels are graphically represented in panel (B) as the mean ± SEM (n = 3).