Effects of Estradiol-17β and Progesterone on Prostaglandins F in Sheep Uteri and Uterine Venous Plasma1

Effects of progesterone and oestradiol-17 on oxytocininduced release of prostaglandin F-2 in heifers

“…This suggests that in the cyclic animal the interactions between these hormones are more complex, the changes in oestradiol and progesterone that occur at the beginning of the cycle possibly affecting events later on. Differences between intact and ovariectomized sheep have also been reported; for example, oestradiol does not stimulate prostag¬ landin release in intact cyclic animals without progesterone priming of the uterus but some studies have shown that it is able to do so in ovariectomized (Ford et al, 1975) or anoestrous (Sharma & Fitzpatrick, 1974) (1984) have reported that the same dose of oestradiol, when given intravenously during the midluteal phase of the oestrous cycle, caused a rise in PGFM concentration that began at 3 h and reached a peak by 6 h before returning to basal levels by 9 h after oestradiol administration. The time course of the oestradiol stimulation differs from that reported for the sheep when an almost immediate increase in PGF-2a release was seen (Roberts et al, 1975) suggesting that oestradiol may be acting via different mechanisms in these species.…”

“…Many studies (Caldwell et al, 1972;Warren et al, 1973;Ford et al, 1975;Louis et al, 1977) have demonstrated that progesterone priming is necessary for PGF release by the uterus. However, progesterone alone does not seem to be responsible for provoking the surges of PGF-2a seen during luteolysis (Fairclough et al, 1983).…”

The secretion of prostaglandin F from the autotransplanted uterus of the ewe

“…Earlier reports have shown that ovariectomized ewes treated with progesterone and oestrogen had increased levels of PGF in jugular venous (Caldwell et al, 1972) or uterine venous blood (Ford et al, 1975;Harrison & Heap, 1975). The present results confirm and extend these findings.…”

Role of the uterus in oestradiol-induced luteal regression in the ewe

“…If the ewes are hysterectomized on Days 5 or 9 of the cycle, oestradiol administered between Days 9 and 13 does not cause regression of the CL, suggesting an involvement of the uterus in the effect of oestradiol on the CL (Stormshak et al, 1969;Bolt & Hawk, 1975). It has been proposed that the uterine luteolysin in the ewe is prostaglandin F-2\g=a\(McCracken et al, 1972), and oestradiol injection on Days 9 and 10 of the cycle results in an increased concentration of prostaglandin F-2\g=a\in uterine venous plasma 18 hr after the last injection (Ford et al, 1975 …”

“…It has been proposed that the uterine luteolysin in the ewe is prostaglandin F-2\g=a\(McCracken et al, 1972), and oestradiol injection on Days 9 and 10 of the cycle results in an increased concentration of prostaglandin F-2\g=a\in uterine venous plasma 18 hr after the last injection (Ford et al, 1975 The results of the present experiment indicate that the uterus needs to be present for more than 24 hr after injection of oestradiol for the hormone to bring about premature luteal regression during mid-cycle in the ewe. The CL failed to regress when the uterus was removed before (0 hr) or 24 hr after the initial oestradiol injection.…”