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We and others previously have shown that when ewes are undernourished (LOW intake) or overnourished (HIGH intake) during pregnancy, they exhibit a 15-40% reduction in placental weight and blood flow, leading to reduced lamb birthweight compared with moderately-fed (MOD intake) ewes. Further, nutrient intake during pregnancy also affects maternal circulating estrogen concentrations, which are either similar or elevated in LOW and are reduced in HIGH compared with MOD intake ewes. We hypothesized that maternal dietary intake level would affect the ability of the placental to synthesize estrogen. We also wanted to examine whether placental tissue type or stage of gestation affects placental estrogen synthesis. We therefore examined the effects of: (1) maternal dietary intake level, (2) placental tissue type (i.e., whole placentome [PLAC], maternal caruncle [CAR], or fetal cotyledon [COT]), and (3) stage of gestation on placental activity of the 3 key enzymes in the pathway from progestins to estrogens; namely, 3B-hydroxysteroid dehydrogenase (3BHSD), 17A-hydroxylase (P450C17), and aromatase using microsomal preparations, radioactive substrates (H3-DHEA, 14C-P4, and H3-androstenedione for 3BHSD, P450C17, and aromatase, respectively), and thin-layer chromatography, with methods similar to those we have previously described. All enzyme activities are reported as pmol of product per mg of microsomal protein per min. In experiment 1, samples of PLAC, CAR, and COT were obtained from MOD intake ewes (n=4) on day 135 of gestation. Based on the results of exp. 1, for experiment 2 only samples of COT were obtained from LOW (n=7), MOD (n=6), and HIGH intake ewes (n=7) at term (approx. day 145-150). In exp. 1, at day 135 of gestation, activity of 3BHSD and aromatase were less (P<0.01) for CAR than COT or PLAC, which were similar (52 and 0.45 vs. 592 and 4.7 or 541 and 4.4, respectively; overall SEM 81 and 0.7 for 3BHSD and aromatase); activity of P450C17, in contrast, was undetectable. For exp. 2, at day 131 (approx. 15-20 days prepartum) maternal systemic estrogen concentrations (pg/ml) were similar for LOW and MOD and reduced (P<0.05) in HIGH ewes (30.9 and 29.6 vs. 12.1; overall SEM 3.2). In exp. 2, at term, placental and total COT weights were similar among LOW, MOD, and HIGH ewes. However, activity of 3BHSD and aromatase in COT at term were less (P<0.05) for MOD compared with LOW or HIGH ewes (238 and 0.2 vs. 686 and 2.5 or 366 and 1.6, respectively; overall SEM 86 and 0.7 for 3BHSD and aromatase). Similarly, P450C17 activity was less (P<0.05) for MOD compared with LOW or HIGH ewes (5.4 vs. 14.9 or 13.3; overall SEM 3.1). Thus, activity of placental steroidogenic enzymes at term was affected by maternal intake, with 3BHSD, P450C17, and aromatase being less in moderately fed compared with undernourished or overnourished ewes. In addition, fetal COT seems to be the major sight of estrogen synthesis in the sheep placenta. Lastly, the most dramatic gestational change was for P450C17, which was undetectable at day 135 but elevated dramatically at term. Supported by USDA-NRI grants Grant No. 2003-35206-13621 and 2005-35206-15281 and by NIH grant HD045784.

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Copyright 2010 by The Society for the Study of Reproduction.
Issue Section:
8/2/2010
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