15-ketodihydro-PGF2 alpha, progesterone and cortisol profiles in heifers after induction of parturition by injection of dexamethasone
Königsson, K.; Kask, K.; Gustafsson, H.; Kindahl, H.; Parvizi, N.
Acta Veterinaria Scandinavica 42(1): 151-159
2001
ISSN/ISBN: 0044-605X PMID: 11455895 Document Number: 536503
In order to study rapid changes in 15-ketodihydro-PGF2 alpha , cortisol and progesterone in the period preceding parturition in cattle, pre-term parturition was induced in 4 late pregnant heifers. Parturitions were induced by 2 intramuscular injections of 20 mg dexamethasone with a 24 h interval. The first injection was made on days 254, 258, 264 and 265 in gestation, respectively. 24 h before the first injection an intravenous polyurethane cannula was inserted. Blood samples were collected at least every h until 12 h after parturition and during the second stage of labour at least 6 times/h. Plasma was analysed for 15-ketodihydro-PGF2 alpha and progesterone by radioimmunoassays, and for cortisol by an ELISA. The average time from injection to parturition was 7.7 (6.6-8.9) days (mean (range)). Two of the heifers had retained fetal membranes (RFM). At the start of the experiment the levels of PGF2 alpha metabolite were low (<300 pmol/L) and increased slowly to levels between 1000 and 2000 pmol/L at 1 day before parturition. During the last day, however, the levels increased rapidly and the highest levels (>10000 pmol/L) were reached at the time of delivery. No pulsatile release was seen. Immediately after fetal expulsion the PG-metabolite levels decreased rapidly in all animals. In the 2 animals with RFM, however, this decline ceased within a few h. The PG-metabolite levels in these animals then started to increase and reached levels as high as during parturition. Luteolysis occurred between 1.6 and 0.4 days before parturition in all animals. The cortisol profile showed a distinct peak at the time of parturition in the RFM heifers. This peak was absent in the non-RFM heifers. This study shows that the PGF2 alpha release at prepartal luteolysis and parturition is not pulsatile in cattle and that cortisol profiles in heifers with retained fetal membranes might differ from the profiles in non-RFM heifers at the time of parturition.