J. Anim Sci., doi: 10.2527/jas.2007-0638
©Copyright, 2008, The American Society of Animal Science
Dietary restriction reduces the rate of estradiol clearance in sheep (Ovis Aries)
B. J. Renquist 1,
T. E. Adams 1,
B. M. Adams 1,
C. C. Calvert 1*
1 Department of Animal Science, University of California, One Shields Avenue, Davis, CA 95616
* To whom correspondence should be addressed. E-mail: cccalvert{at}ucdavis.edu.
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Abstract |
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Three experiments were designed to test the effect of dietary restriction on clearance of 17
-estradiol (E2) in sheep. A preliminary experiment examined the effect of a 4-d fast on the rate of E2 clearance in wethers. The second experiment tested the hypothesis that either long-term restriction (7 wk) or a 5 d fast would increase steroid binding capacity of serum by increasing the concentration of sex hormone binding globulin (SHBG) in the blood of ovariectomized (ovx) ewes. In Exp. 3, we hypothesized that nutrition-dependent regulation of E2 clearance by the liver would result in divergence in biliary extraction of E2 in fed and fasted wethers receiving comparable levels of exogenous E2. A marked difference in E2 clearance between fed and fasted wethers was noted in the preliminary study. Relative to ad libitum fed wethers, a 4-d fast decreased E2 clearance by 52%. Serum concentrations of SHBG were increased in long-term energy restricted and fasted ewes, relative to the concentration noted in maintenance fed ewes (P = 0.015). Furthermore, a 5-d fast nearly doubled serum steroid binding capacity in wethers. The E2 concentration in bile was 2 times greater in fasted than fed wethers. This fasting-dependent increase in biliary E2 may be reflective of the increased serum E2 in fasted animals, since each 1 pg/mL increase in serum E2 increased bile E2 by 0.86 ± 0.12 pg/mL independent of nutrition (P = 0.002). Our results demonstrate that the rate of clearance of E2 is decreased during nutritional restriction. Additionally, these data indicate that altered SHBG expression and/or enterohepatic recirculation are involved in the decreased E2 clearance during dietary restriction.
Key Words:
clearance, enterohepatic recirculation, estradiol, restriction, sex hormone binding globulin, sheep
