Animal Reproduction Science 84 (2004) 337–348 Effect of plane of nutrition on endometrial sex steroid receptor expression in ewes C. Sosa a,∗ , J.M. Lozano b , C. Viñoles c , S. Acuña a , J.A. Abecia d , F. Forcada d , M. Forsberg e , A. Meikle a a Biochemistry, Department of Cellular and Molecular Biology, Faculty of Veterinary Medicine, University of Uruguay, Lasplaces 1550, Montevideo 11600, Uruguay b Veterinary Preclinical Studies, University of Glasgow Veterinary School, Glasgow, UK c School of Agriculture “Emilia Vigil de Olmos”, UTU, Lavalleja, Uruguay d Animal Production and Food Science, Faculty of Veterinary Medicine, Zaragoza, Spain e Clinical Chemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden Received 1 July 2003; received in revised form 27 October 2003; accepted 1 December 2003 Abstract The effect of plane of nutrition on progesterone receptor (PR) and estrogen receptor  (ER) expression in ovine endometrium was investigated. Rasa Aragonesa ewes (n = 26) were fed diets to provide either 1.5 (Group C) or 0.5 (Group L) times the daily maintenance requirement and were slaughtered at Days 5 or 10 of the estrous cycle (Day 0 = estrus). PR and ER immunoreactivity were analyzed in eight endometrial cell compartments, defined by cell type and location. Group L had less PR immunostaining on Day 5 (P< 0.05), which is consistent with lesser endometrial content of progesterone found in such animals. Most cell types of Group C had down regulation of PR at Day 10, but in Group L, this pattern was observed only in three cell compartments. The lesser PR contents found at Day 5 in Group L ewes may explain the lack of inhibition of PR. No effect of treatment or day of the estrous cycle was observed in ER. Results indicate that endometrial PR is affected in a cell type, in specific manner, by plane of nutrition. © 2004 Elsevier B.V. All rights reserved. Keywords: Estrogen; Progesterone; Receptors; Nutrition; Sheep 1. Introduction The establishment of pregnancy depends on the signal system between the embryo and the uterine environment. The alteration of this system results in failure of implantation, ∗ Corresponding author. Tel.: +598-2-6221195; fax: +598-2-6280130. E-mail address: cecis@adinet.com.uy (C. Sosa). 0378-4320/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2003.12.011