Caudal vena cava progesterone and LH release patterns on Day 14 of gestation in primiparous sows L. L. Hoving A,C,* , S. M. Haen B,D,* , B. F. A. Laurenssen A , O. A. T. Peltoniemi B , B. Kemp A and N. M. Soede A A Adaptation Physiology Group, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands. B Department of Production Animal Medicine, Faculty of Veterinary Medicine, University of Helsinki, Paroninkuja 20, 04920 Saarentaus, Finland. C Present address: Cargill Premix and Nutrition, Veerlaan 17-23, 3072 AN Rotterdam, The Netherlands. D Corresponding author. Email: silke.haen@helsinki.fi Abstract. The aim of the present study was to explore the relationship between systemic and local progesterone secretion and LH pulsatility during implantation in the pig. Differences in progesterone concentrations measured locally in the caudal vena cava and systemically in the jugular vein were studied in eight primiparous sows on Day 14 of pregnancy. LH pulsatility was analysed for its effects on the local progesterone-releasing pattern. Mean (Æ s.d.) progesterone concentra- tions in the vena cava (65.5 Æ 19.8 ng mL À1 ) were approximately double basal concentrations (33.6 Æ 13.1 ng mL À1 ). Basal concentrations of progesterone and LH were calculated as the average of the lowest six values. Basal caudal vena cava and mean jugular (27.6 Æ 1.5 ng mL À1 ) progesterone concentrations did not differ significantly. Pre- and postprandial jugular progesterone concentrations were significantly different in the morning and afternoon (P ¼ 0.025 and 0.023). Mean LH ranged from 0.24 to 0.43 ng mL À1 and was approximately double as high as basal LH in individual sows. In 60.8% of cases, LH pulses were followed by a progesterone pulse within 1 h. In conclusion, the present study showed that corpus luteum function appears to respond to LH pulsatility on Day 14 of pregnancy. However, the response varies at the level of individual sows. In addition, systemic postprandial decreases in progesterone were confirmed on Day 14 of pregnancy. Additional keywords: corpus luteum, early pregnancy, progesterone metabolisation, second parity. Received 14 January 2015, accepted 5 August 2015, published online 9 October 2015 Introduction Synchronised development of the porcine embryo and uterus largely depends on progesterone (P4) and is considered essential for successful placental attachment (Geisert et al. 1982; Pope 1988), which starts around Day 13 of gestation. P4 production in pigs is independent of LH stimulation in the early days of pregnancy (Anderson et al. 1967; Peltoniemi et al. 1995). Between Day 12 and Day 29 of gestation, P4 production becomes dependent on LH stimulation. This was shown in studies in which the use of gonadotrophin-releasing hormone (GnRH) antagonists blocked LH secretion and induced abortion, or decreased systemic P4 concentrations (Peltoniemi et al. 1995; Tast et al. 2000). In addition, Parvizi et al. (1976) reported that, in miniature pigs during late gestation, P4 release in the vena cava partly follows pulsatile LH release with a 20–60 min delay. More recent results reported by Virolainen et al. (2005) indicate that this may also be true for gilts around Day 22 of gestation. In contrast, Bru ¨ssow et al. (2011) did not establish a relationship between LH release and P4 concentration in the caudal vena cava between Days 11 and 17 of gestation. Most studies to date have measured either systemic P4 concentrations or only vena cava P4 concentrations. Vena cava P4 concentrations are usually much higher than systemic concentrations because P4 is meta- bolised in the liver (Prime and Symonds 1993) and taken up by the uterus and embryos (Magness et al. 1986). In contrast with metabolised P4, vena cava P4 is secreted in a pulsatile manner (Virolainen et al. 2005). Measuring P4 concentrations in the jugular vein may give a better understanding of the feedback P4 exerts on LH secretion, whereas P4 measured in the caudal vena cava could provide a deeper insight into the response of corpora lutea (CL) to LH. The aim of the present study was to clarify the extent to which P4 * These authors contributed equally to this work. CSIRO PUBLISHING Reproduction, Fertility and Development, 2017, 29, 476–481 http://dx.doi.org/10.1071/RD15016 Journal compilation Ó CSIRO 2017 www.publish.csiro.au/journals/rfd