Caudal vena cava progesterone and LH release patterns on Day 14 of gestation in primiparous sows

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 (± s.d.) progesterone concentrations in the vena cava (65.5 ± 19.8 ng mL–1) were approximately double basal concentrations (33.6 ± 13.1 ng mL–1). 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 ± 1.5 ng mL–1) progesterone concentrations did not differ significantly. Pre- and postprandial jugular progesterone concentrations were significantly different in the morning and afternoon (P = 0.025 and 0.023). Mean LH ranged from 0.24 to 0.43 ng mL–1 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.