INTRAMAMMARY PRESSURE AND LUTEAL OXYTOCIN AFTER PGF2-ALPHA ADMINISTRATION IN CYCLING AND EARLY PREGNANT EWES

The aim of this work was to investigate whether luteal oxytocin releas ed after non-luteolytic prostaglandin F2 alpha (PGF2 alpha) challenge could explain the intramammary pressure (IMP) rises previously describ ed in pregnant ewes after the normal life span of a corpus luteum. Blo od oxytocin levels and IMP after challenge were measured in cycling an d pregnant lactating ewes until the response ceased (similar to 55 d p ost oestrus). Oxytocin release was not significantly different for cyc ling and pregnant ewes, and fell to its lowest levels on days 16-18 po st oestrus in both groups, i.e. with or without luteolysis. However, a lthough IMP response fell with luteolysis in cycling ewes, the respons e persisted until day 55 in pregnant ewes. This lack of correlation be tween oxytocin release and IMP response raised interesting questions i ncluding: is there an unknown oxytocic compound that can be released a fter PGF2 alpha stimulation of the corpora lutea ?