Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A decline in progesterone and a rise in estrogen levels in the maternal and fetal plasmas occur prior to parturition. I examined the hypothesis that similar changes in the ovine intrauterine tissues are associated with labour. I also determined whether the intrauterine tissues could produce progesterone and estrogens and whether these activities change in association with labour.;Samples of maternal and fetal bloods, fetal fluids, myometrium, endometrium, chorion, amnion and allantois were obtained from pregnant sheep of different gestational ages and in labour occurring either at term or induced prematurely by administration of ACTH to the fetus. Steroids were measured using radioimmunoassay techniques. Subcellular and dispersed cell preparations were used to examine conversion of endogenous and exogenous substrates to progesterone and estrogens.;At term, labour was associated with a decline in the levels of progesterone in the maternal and fetal bloods, endometrium and myometrium and a rise in the levels of estrone and estradiol-17{dollar}\beta{dollar} in the myometrium. At ACTH-induced labour, only the rise in the levels of estrogens in the myometrium was reproduced. Concentrations of progesterone and estrogens in fetal fluids and fetal membranes were not affected by labour.;Subcellular preparations of chorion and, to a lesser extent amnion, converted {dollar}\sp3{lcub}\rm H{rcub}{dollar}-pregnenolone to {dollar}\sp3{lcub}\rm H{rcub}{dollar}-progesterone. At term this conversion in the chorion was quantitatively similar to that in the cotyledons and could be inhibited by several steroids including estrogens. Cells from all tissues converted {dollar}20\alpha{dollar}-dihydroprogesterone to progesterone but only the chorion and endometrium converted pregnenolone to progesterone. Cells from all tissues converted estrone sulphate to estrone and estradiol-17{dollar}\beta{dollar} but only the chorion converted androstenedione to estrone. {dollar}\sp3{lcub}\rm H{rcub}{dollar}-progesterone was converted to {dollar}\sp3{lcub}\rm H{rcub}{dollar}-20{dollar}\alpha{dollar}-dihydroprogesterone by all tissues and to {dollar}\sp3{lcub}\rm H{rcub}{dollar}-17{dollar}\alpha{dollar}-hydroxyprogesterone by chorion. These conversions did not change significantly with labour.;In conclusion (1) labour was associated with alterations in the levels of progesterone and estrogens in the myometrium and endometrium, but not in the fetal membranes; (2) the intrauterine tissues have the steroidogenic potential to alter the local steroid milieu but no change in this potential was identified at parturition, and (3) steroids may inhibit steroid metabolizing enzymes in the intrauterine tissues and alter steroid production.



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