Expression of c-fos and c-myc genes in uterus and nonreproductive organs during the implantation period in the rat.

The c-fos and c-myc mRNA levels were investigated in the uterus and nonreproductive organs of rats during the implantation period (from day 5 to 7 of pregnancy). They were determined by densitometric analysis of slot blots and the mean values (n = 4) at a defined age of pregnancy were compared with those observed in nonpregnant control rats (NP group). No significant variations of c-fos level were observed in the liver and brain of pregnant rats. In the uterus, the c-fos level decreased, reached a minimum on day 6 (4-fold decrease compared with the NP group), and then increased. The c-fos level significantly increased in the kidney (2- and 2.5-fold on days 6 and 7), and in the lung (2.5-fold on day 7). The c-myc level did not significantly vary in the uterus, liver, and lung. It significantly increased in the kidney (3-fold on day 7) and in the brain (4.1-, 3.8-, and 6-fold, on days 5, 6, and 7). The changes in c-fos and (or) c-myc gene expression in the uterus and nonreproductive organs could be due to sexual steroids and (or) systemic factors from uterine cells or blastocysts.