| The transfer of free and conjugated estrogens across guinea pig fetal membranes was studied in view of the fluctuating estrogen conjugating and deconjugating activities reported in these tissues. Amnion and chorion laeve were obtained from three different stages of gestation: mid (45 days) and late gestation, before (late;Early amnion exhibited barrier function, only transferring the free steroids: estrone (E1), 17-beta-estradiol (E2) and pregnenolone (Preg). Neither the conjugated steroids. estrone-sulfate (E1S), estrone-glucuronide (E1G) and pregnenolone-sulfate (PregS), nor inorganic sulfate was recovered within or below the tissue after 90 min of incubation. This behaviour was consistent with the evidence for tight junctions obtained using the confocal laser scanning microscope (CLSM). In contrast, late;Early chorion laeve was capable of transferring both free and conjugated steroids, as well as sulfate, despite identification of tight junctions on CLSM XZ scans. Double-label experiments with (3H/14C) E1G and (3H/35S) E1S indicated that transfer occurred in the absence of deconjugation, in a nonsaturable and energy-independent manner. The similarity in rate and concentration dependency of transfer across 45 day chorion and late;Near term, chorion laeve was characterized as a viable tissue, containing regions with tight junctions but overall a permeable epithelium. While both free and conjugated steroids were transferred across late;This work indicated that although conjugation and deconjugation may modulate the location and activity of estrogen, this is a function separate from the transfer of conjugate between fetal and maternal compartments. |
