Changes in the ratio of the amount of mRNA for procollagen α 1(I) chain to β actin. The ratio of mRNA for procollagen α 1(I) chain to β actin from mice treated with etretinate for 1 day decreased significantly compared to that from negative control mice, and the ratio from mice treated with etretinate for 14 days increased compared to that in control mice (*1, Student's t test, P < 0.05).