The effect of oxytocin treatment on the levels of prostaglandin F in the blood of heifers

Abstract

Six heifers with normal oestrous cycles were treated i.m. with 100 i.u. oxytocin on 3 consecutive days, commencing on Days 1-6 after oestrus, and the levels of prostaglandin (PG) F in posterior vena cava plasma were compared with pretreatment values. An increase of PGF in response to oxytocin was significantly influenced by day, with the greatest response occurring on Day 3 after oestrus. In an ovariectomized heifer the levels of PGF in posterior vena cava plasma increased 24 h after priming with oestradiol, but no further increase occurred after oxytocin injection. Peak levels of PGF were higher in the plasma of the posterior vena cava than in the jugular vein. Various storage conditions of the blood before centrifugation and freezing (--20 degrees C) produced significant differences in plasma levels of endogenous PGF, but storage experiments with added labelled PGF-2alpha indicated that the PG was stable in plasma and whole blood.

Secretion of Prostaglandins E₂ and F_2α by the Bovine Endometrium in Response to Oxytocin during the Estrous Cycle

“…The stimulatory effects of OT on PGF2α secretion by the bovine endometrium were observed at the late, regressed and early luteal stages in the present study. Our results confirm the previous reports that the maximal stimulatory effects of OT on PGF2α secretion were demonstrated at the late estrous cycle [4], and that a high responsiveness in the endometrium to OT was maintained until the next early estrous cycle [30,31]. On the other hand, although PGE2 secretion like PGF2α secretion was stimulated by OT at the early luteal stage, OT suppressed the PGE2 secretion at the regressed luteal stage.…”

Development of some male characteristics supported by oestrone but not dehydroepiandrosterone in the boar

“…Total unconjugated oestrogen was determined by radioimmunoassay as previously described by Newcomb, Booth & Rowson (1977), where the cross-reaction of oestrone with the antiserum was 55%. The radioimmunoassay for DHA and DHA sulphate was carried out using the antiserum described by Smith et al (1975).…”

Factors affecting embryo survival and strategies to reduce embryonic mortality in cattle

“…The pulsatile secretion of PGF 2α in cattle was previously proposed to be generated by a positive feedback loop between ovarian and/or hypophyseal oxytocin and endometrial PGF 2α (Armstrong and Hansel 1959;Newcomb et al 1977). However, recent data suggest that oxytocin may not be essential for the initiation of luteolysis in cattle, but may play a supportive and modulatory role for the amplitude of pulsatile secretion of PGF 2α after the initiation of luteolysis (Parkinson et al 1992;Kotwica et al 1997Kotwica et al , 1999.…”