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This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0638v1 86/5/1124    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Renquist, B. J. Articles by Calvert, C. C. PubMed PubMed Citation Articles by Renquist, B. J. Articles by Calvert, C. C.

Dietary restriction reduces the rate of estradiol clearance in sheep (Ovis aries)

Department of Animal Science, University of California, One Shields Avenue, Davis 95616

¹ Corresponding author: cccalvert{at}ucdavis.edu

Three experiments were designed to test the effect of dietary restriction on clearance of 17β-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 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 libitumfed 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 in maintenancefed 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 in fed wethers. This fasting-dependent increase in biliary E₂ may be reflective of the increased serum E₂ in fasted animals, because 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, enterohepatic recirculation, or both are involved in the decreased E₂ clearance during dietary restriction.

Key Words: clearance • enterohepatic recirculation • estradiol • restriction • sex hormone-binding globulin • sheep