Adjuvant arthritis in rat during pregnancy and lactation.

We have studied, in the female rat, the influence of pregnancy, lactation and pseudo-pregnancy on adjuvant arthritis. Pregnancy has a suppressive effect on the arthritis all the more marked as arthritis onset occurs during the third part of pregnancy. Pseudo-pregnancy with or without decidualization of the uterus does not modify the arthritis course; thus the corpus luteum and the decidual tissue cannot account for the observed improvement. Lactation has a beneficial effect that lasts until weaning. Amount of estradiol which insured approximate serum level of pregnant rats improves the polyarthritis. In the same conditions, progesterone remains inactive. Suppression by estradiol is observed in ovariectomized and intact females. Thus, in the female rat, pregnancy, lactation and physiological doses of estradiol improve adjuvant arthritis.