Influence of mating and intra-uterine oestradiol infusion on peripheral oxytocin concentrations in the sow

Oxytocin concentrations were measured radioimmunologically in sows on the day of standing oestrus over a 6-h period (controls, n = 6) or 1 h before and 5 h after mating (n = 5) or transcervical infusion of either 100 ml saline (0.9% (w/v) NaCl, n = 7) or saline plus 10 μg oestradiol (simulation of seminal oestrogens, n = 5). In the controls, oxytocin was low, at around 1.0 pmol/l, throughout the investigation period. Similarly, saline infusion did not lead to a noticeable change in oxytocin concentrations in six out of seven sows. In one sow, however, infusion led to a maximum of 86 pmol/l at 1 min after infusion. Oestradiol led to no immediate increase in oxytocin concentrations. Later in the post-treatment period (2-5 h) they were only slightly increased (1 pmol/l vs 3 pmol/l). All mated sows reacted with a rapid and clear increase in oxytocin. Maximal concentrations (42.0 ± 5.1 pmol/l; mean ± S.E.M.) appeared 2 min after the onset of ejaculation. Clearly increased concentrations were found for 40 min. It was concluded that mating specifically leads to a rise in oxytocin, probably due to both mechanical and pheromonal stimuli provided by the boar.