Intramammary pressure and luteal oxytocin after PGF2α administration in cycling and early pregnant ewes

Abstract

SummaryThe aim of this work was to investigate whether luteal oxytocin released after non-luteolytic prostaglandin F2α (PGF2α) challenge could explain the intramammary pressure (IMP) rises previously described in pregnant ewes after the normal life span of a corpus luteum. Blood oxytocin levels and IMP after challenge were measured in cycling and pregnant lactating ewes until the response ceased (˜ 55 d post oestrus). Oxytocin release was not significantly different for cycling and pregnant ewes, and fell to its lowest levels on days 16–18 post oestrus in both groups, i.e. with or without luteolysis. However, although IMP response fell with luteolysis in cycling ewes, the response persisted until day 55 in pregnant ewes. This lack of correlation between oxytocin release and IMP response raised interesting questions including: is there an unknown oxytocic compound that can be released after PGF2α stimulation of the corpora lutea?