Effect of Oestrus Synchronization with PGF2a/eCG/hCG on Luteal P4 Synthesis in Early Pregnant Gilts M Szymanska, E Morawska-Pucinska, K Krawczynski, J Kiewisz*, AJ Ziecik and A Blitek Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Olsztyn, Poland Contents Administration of hormones to synchronize oestrus is a useful tool in animal breeding. However, exogenous ovarian stimu- lation may be detrimental to reproductive function. This study was aimed to examine whether an oestrus synchronization with PGF2a/eCG/hCG could affect luteal P4 synthesis in early pregnant gilts. Corpora lutea (CLs) were collected on days 9, 12 and 16 of pregnancy from gilts with natural (n = 16) and synchronized (n = 18) oestrus and analysed for (i) the expre- ssion of steroidogenic acute regulatory protein (StAR), cyto- chrome P450 family 11 subfamily A polypeptide (CYP11A1), and 3b-hydroxysteroid dehydrogenase (3bHSD); (ii) the con- centration of P4 in the luteal tissue and blood; and (iii) the expression of luteinizing hormone receptors (LHR) and oestrogen receptors (ERa and ERb). Additionally, the effect of LH on P4 secretion from CL slices collected from synchronized and naturally ovulated animals has been studied in vitro. PGF 2a /eCG/hCG administration increased mRNA expression of StAR, CYP11A1, 3bHSD, and LHR on day 9 and CYP11A1 and LHR on day 12 of pregnancy compared with the control group (p < 0.05). CYP11A1, 3bHSD, LHR, ERa and ERb proteins were not affected by synchronization; only StAR protein increased in hormonally treated animals (p = 0.017). The concentration of P4 in luteal tissue was greater on day 9 (p < 0.01), but lower on day 16 (p < 0.05) in gilts with hormonally induced oestrus compared with control animals. Blood serum levels of P4 were lower in synchronized than control gilts (p < 0.001). Synchronization did not affect LH-stimulated P4 secretion from luteal slices; however, greater basal concentration of P4 in incubation medium was detected for CLs collected from synchronized than control gilts (p < 0.05). In conclusion, synchronization of oestrus with PGF2a/eCG/hCG protocol in gilts did not impair the expres- sion of luteal P4 synthesis system, although decreased P4 concentration in the blood. Introduction Oestrus synchronization is a useful tool in animal breeding often applied to arrange the time of insemina- tion, control the farrowing rate, reduce problems with poor oestrus detection and to perform an efficient replacement of sows following weaning. Moreover, superovulation and synchronization protocols are used to obtain animals as embryo donors or recipients in the application of in vitro fertilization, transgenesis, nuclear transfer and other reproductive biotechniques. Methods of oestrus synchronization vary, but all are based either on controlling events leading to follicular maturation and ovulation or altering luteal lifespan (Estill 1999). The treatment protocol based on a combination of equine chorionic gonadotropin (eCG) and human cho- rionic gonadotropin (hCG) is typically used to induce puberty in commercial gilts (Estill 1999; Degenstein et al. 2008). Effective methods developed for oestrus induction in cyclic swine include prolonged administra- tion of progestogens, injections of estradiol benzoate or applications of prostaglandin (PG) F2a followed by gonadotropin treatment (Estill 1999). However, exoge- nous ovarian stimulation can be detrimental to repro- ductive function. Particularly, gilts treated with eCG/ hCG had decreased pregnancy rates (Webel and Day 1982). Moreover, morphological and biochemical devel- opment of follicles differs in pigs with natural and gonadotropin-stimulated ovulation (Wiesak et al. 1990), which may result in disturbance of oocyte maturation and increased embryonic mortality. It has been reported that hormonally treated gilts had greater number of degenerated embryos (Ziecik et al. 2005). Progesterone (P4) produced by the corpus luteum (CL) is the hormone of pregnancy in mammals that plays a pivotal role in the establishment and mainte- nance of pregnancy (Spencer et al. 2004). Sustained P4 action on the uterus is essential for the attainment of endometrial receptivity for implantation in ruminants and pigs (Spencer et al. 2004; Bazer et al. 2010; Ziecik et al. 2011). P4 regulates the expression of several genes important for embryo–maternal interactions (for review see Spencer et al. 2004; Ziecik et al. 2011). Pharmaco- logical manipulations to synchronize oestrus in domestic animals may cause decreased level of P4 in blood serum, which results from impaired luteal P4 metabolic path- way (Kineman et al. 1987a) and reduced sensitivity to gonadotropic stimulation (Kineman et al. 1987b; Skarzynski et al. 2009). Low concentrations of circulat- ing P4 altered the expression of endometrial genes that potentially contribute to histotroph composition and conceptus elongation in cattle (Forde et al. 2011, 2012). In the pig, lower serum concentrations of P4 were detected in pregnant gilts after induction of puberty with eCG/hCG. It was accompanied by decreased endometrial expression of homeobox A10, leukaemia inhibitory factor and transforming growth factor b1 genes (Blitek et al. 2010a). Moreover, administration of gonadotropins to induce oestrus affected the expression of prostaglandin synthesis enzymes in the endometrium and PG concentrations in the endometrium and blood serum (Blitek et al. 2010b). These changes may be attributed to impaired endometrial development caused by insufficient P4 synthesis and/or release. Although oestrus synchronization with PGF2a/eCG/ hCG was demonstrated as an effective method to obtain pronuclear stage embryos (Sommer et al. 2007), our previous study revealed decreased concentrations of P4 in the blood serum of gilts synchronized with this method (Kiewisz et al. 2011). Therefore, this study was conducted to examine the effect of oestrus synchronization with © 2014 Blackwell Verlag GmbH Reprod Dom Anim 49, 1034–1042 (2014); doi: 10.1111/rda.12433 ISSN 0936–6768