Resorption, Stoffwechsel und Transport von Östradiol-(17β) und Östradiol-(17β)-3-monosulfat im Dünndarm der Ratte

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Abstract
To determine the conditions under which phenolic steroids can be transported from the mucosal to the serosal side of the small intestine, estradiol-17[alpha] and estradiol-17[alpha]-3-monsulfate were incubated with sacs of everted small intestine of the rat. After incubation of estra-diol-17[alpha], the following metabolites were found: estradiol-17[beta] 3-monoglucuronide, estrone and estrone glucuronide; when estradiol-17[beta] 3-monosulfate was incubated, free estradiol-17[beta], estrone and their glucuronides were detected. Quantitative determinations of the steroids were carried out on the incubation media and on the tissue. Free estradiol-17[beta] was rapidly taken up by the mucosa and partly transferred to the serosal side: in contrast, estradiol-17[beta] 3-monosulfate was not absorbed by the tissue. Both estradiol-17[beta] and estrone were transferred from the mucosal to the serosal side predominantly as free steroids, and to a lesser extent as glucuronides. When incubations were carried out in the presence of 2, 4-dinitrophenol or under N, the uptake of estrogens by the tissue was inhibited. Concentration gradients between mucosal and serosal side were observed only for the glucuronides of estradiol-17[beta] and estrone, but not for the free estrogens and for estradiol-17[beta] 3-monsulfate. The experiments reported here demonstrate that in the small intestine of the rat, no active transport of free or sulfated estrogens occurs; however, the evidence available suggests that the estrogen glucuronides are actively transported.