Hormonal Regulation of Immunoglobulins: Influence of Estradiol on Immunoglobulins A and G in the Rat Uterus*

Abstract

Uterine secretions from rats at various stages of the estrous cycle, after ovariectomy or hypophysectomy and after steroid administration to ovariectomized animals, were examined to assess the influence of hormone [estradiol [E2], progesterone, testosterone, estriol and cortisol] on the presence of immunoglobulins A and G (IgA and IgG). Both Ig increased at the proestrus stage of the estrous cycle. At estrus, IgG dropped to low levels while IgA remained partially elevated. At diestrus, Ig levels are similar to those measured after ovariectomy. Changes in Ig levels during the estrous cycle are probably due to estradiol, since of those hormones studied, only E2 increased uterine IgA and IgG in ovariectomized or hypophysectomized rats. In addition to being specific for E2, the uterine Ig response was dependent upon the length of time and the E2 dose administered. Short term E2 administration (2-3 days) resulted in marked elevations in IgA and IgG, whereas long term exposure (6-14 days) failed to maintain the initial increase. IgA to IgG ratios were measured in uterine secretions and serum samples from rats at various stages of the estrous cycle and after E2 administration to ovariectomized rats. In all cases examined, ratios of IgA to IgG were higher in uterine secretions than in serum. The presence of IgA and IgG in the uterus apparently cannot be accounted for solely by serum leakage; E2 plays an important role in regulating uterine IgA and IgG. The increase in the Ig levels that occur spontaneously during the estrous cycle is probably due to the action of E2 in the uterus.