In vivo modulation of the splenocyte yield and composition by female sex steroid hormones

The study was designed to shed more light on the controversial role of the two main ovarian steroid hormones (i.e. estradiol and progesterone) in shap ing the size and phenotypic characteristics of the splenic lymphocyte pool. For this purpose ovariectomized adult rats (OVX) were treated for 14 subse quent days with either estradiol or progesterone (to attain physiological c oncentrations of the hormones). Afterwards, the splenocyte yield, and overa ll number of splenocytes bearing TCR alpha beta receptor, CD4 and CD8 corec eptor were evaluated. Fourteen-day-long ovarian hormone deprivation produce d an increase in the splenic weight and splenocyte yield ton the account of a rise in the number of TCR alpha beta (-) cells), although the number of TCR alpha beta (+) cells was reduced as a result of a decrease in the size of the CD4(+) cell subpopulation. Replacement of either estradiol or proges terone prevented the increase hn splenic weight and reduced the splenocyte yield to values significantly lower than that in sham-OVX rats. Both the tr eatments completely abolished the effect of ovariectomy on the size of TCR alpha beta (-) cell population, but had differential effects on that of TCR alpha beta (+) cell population: estradiol did not affect its size, while p rogesterone caused a reduction on the account of a decrease in the numbers of both CD4+ and CD8(+) cells. The results suggest that: a) estradiol and p rogesterone have similar effects on the size of the splenic B cell populati on and that replacement of either estradiol or progesterone can prevent the effects of ovariectomy on the size of this population and b) estradiol doe s not affect while progesterone reduces the size of splenic T cell populati on. Thus, replacement of none of them is able to compensate the removal of gonads.