Pregnancy reduces the responsiveness of the pituitary–adrenal axis to dexamethasone

This study aimed to examine the influence of pregnancy on responsiveness of the pituitary–adrenal (PA) axis to dexamethasone (Dx) in rats. Dams and virgins were injected with Dx in three consecutive daily doses of 1.0, 0.5, 0.5 mg/kg/bw, starting from day 16 of pregnancy, and sacrificed 24 and 72 h after termination of treatment. Immunocytochemical, morphometrical and biochemical methods were used to assess pituitary and adrenal function. Three-way ANOVA revealed Dx inhibition of the PA axis in virgin and pregnant females after 24 and 72 h. Pregnant females demonstrated a significantly lower (p < 0.05) degree of suppression regarding ACTH volume density and blood concentrations and the volume and number of the zona fasciculata and zona reticularis cells, comparing with virgin females 72 h following Dx administration, accompanied by total recovery of the zona glomerulosa. In contrast to virgin females, the corticosterone levels on day 21 of gestation reached control levels. Between days 19 and 21 of pregnancy, a significant increase in estrogen levels and the fall of progesterone influence, at least partially, the presented differences. It can be concluded that the PA axis response to the inhibitory influence of Dx is less pronounced in gravid females during late pregnancy than in virgin rats.