EFFECTS OF EXOGENOUS PROGESTERONE AND OESTRADIOL ON PROSTAGLANDIN F AND 13,14-Dihydro-15-Oxo PROSTAGLANDIN F2α CONCENTRATIONS IN UTERI AND PLASMA OF OVARIECTOMIZED EWES

Abstract

The control of prostaglandin (PG) production by steroid hormones has been investigated in non-pregnant bilaterally ovariectomized sheep, prepared with indwelling utero-ovarian venous catheters and treated with physiological amounts of oestradiol and progesterone. Oestradiol treatment alone (2 \ m=x\ 15 \g=m\g/day for 9 days) had no effect on the prostaglandin F (PGF) concentration in uterine caruncles or intercaruncular tissue, on the release of PGF or of 13,14-dihydro-15-oxo PGF (PGFM) from these tissues during incubation in vitro, or on the concentrations of PGF in the utero-ovarian vein or PGFM in the jugular vein. However, oestradiol did accumulate in the uterine tissues. Progesterone treatment alone (2 \ m=x\10 mg/day for 9 days) provoked a significant increase in the concentration of PGF in the caruncles, a significant increase in the release of PGF from the caruncles during incubation with arachidonic acid and increased mean concentrations of PGFM in the jugular vein. When oestradiol was superimposed on a progesterone-primed system, there was a further marked increase in the PGF content of the caruncles, release of PGF into the utero-ovarian vein, and increased concentrations of PGFM in the jugular vein. The caruncles always contained more PGF than the intercaruncular area, and released more PGF and PGFM during incubation in vitro. In the progesterone+oestradiol group, there was good correlation between the PGF concentrations in simultaneous samples from the right and left utero-ovarian veins, and for all groups there was a high correlation between utero-ovarian PGF and peripheral PGFM concentrations. The caruncular epithelium of the progesterone-treated animals contained more lipid droplets than those of the other groups.These data are consistent with a requirement for progesterone in activating 'prostaglandin synthetase' activity, and promoting PGF production, largely from the caruncles. After progesterone priming, the synthesis of PGF by the caruncles and PG release into the vascular system was increased further by oestradiol treatment, whereas oestradiol alone was without effect.

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

“…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).…”

“…Bartol et al (1981) showed that oestradiol administered in the mid-luteal phase of the cow stimulated uterine synthesis and/or release of PGF into the uterine flushings and increased the peripheral plasma concentration of 13,14-dihydro-15-keto-PGF-2a (PGFM). The luteolytic effect of oestradiol in the ewe is augmented by prior administration of progesterone (Caldwell et al, 1972;Warren et al, 1973;Louis et al, 1977 5,15,30,45 and 60 min after each injection. Three blood samples were also taken at 15-min intervals during the 3rd and 4th hour after the first oxytocin injection.…”

Prostaglandin Mediates Premature Delivery in Pregnant Sheep Induced by Estradiol at 121 Days of Gestational Age

“…Estrogen can produce a clear shedding of the endometrium in the nonpregnant uterus only after progesterone priming (29,30). Estradiol administered to ovariectomized sheep after a period of progesterone treatment caused a much larger increase in uterine PGF2␣ output than occurred in the absence of progesterone priming (30).…”

Demonstration that progesterone 'blocks' uterine activity in the ewe in vivo by a direct action on the myometrium

“…The fact that the response is blocked argues for a direct action of progesterone on the myometrium, although this might not be so if transfer of PGs from the lumen to the myometrium was impaired by progesterone. This possibility would seem remote because synthesis of PGs by the endometrium is enhanced by progesterone (Louis, Parry, Robinson, Thorburn & Challis, 1977) and Harrison, Heap & Poyser (1976) have shown that both uterine fluid and uterine vein blood contain substantial amounts of PGs (i.e. synthesis and re¬ lease are unimpaired) in ewes with high plasma progesterone levels.…”