Treatment with prostaglandin F2alpha increases expression of prostaglandin synthase-2 in the rat corpus luteum

Recent studies indicate that the corpus luteum (CL) may be a source of prostaglandin F2alpha (PGF2alpha) for regression. We investigated expression of mRNA and protein for prostaglandin G/H synthase (PGHS) in the CL of immature superovulated rats following administration of PGF2alpha. We observed an increase in mRNA for PGHS-2, the induced isoform, at 1 h and protein at 8 and 24 h after treatment. One hour after PGF2alpha, there was also a progressive decrease in plasma progesterone concentration. There were no changes, however, in expression of PGHS-1, the constitutive isoform, over the 24 h sampling period. These results indicate that PGHS-2 increases following PGF2alpha treatment and that expression of this enzyme in the rat CL may contribute to the luteolytic mechanism.     

Trypanosome-induced increase in prostaglandin F(2alpha) and its relationship with corpus luteum function in the goat

Plasma progesterone and 13,14-dihydro-15-keto Prostaglandin F(2alpha) (PGFM) were measured in normal (uninfected) and Trypanosoma congolense -infected adult goats for a period of 121 d, from May to August, during the breeding season in Kenya. Chronic trypanosomiasis rapidly increased the baseline plasma PGFM levels and the occurrence of irregular PGFM peaks in several infected goats. Progesterone luteal levels declined rapidly from the second and subsequent cycles post patency. Estrous cycles also became irregular but predominately shorter (8 to 19 d) before cessation from the second to fourth cycle following infection. The PGFM levels were still high during the acyclic period in all goats when progesterone levels were very low (1.4 to 2.4 nmol/l). The reciprocal increase in peripheral PGFM and decline in progesterone in these goats would suggest, in part, a trypanosome-induced PGF(2alpha) mediated luteolysis, and the possible involvement of prostaglandins in trypanosome-induced infertility in female goats.     

Response of the 1-5 day-aged ovine corpus luteum to prostaglandin F2alpha

The hypothesis that, in the ewe, prostaglandin (PG) F2alpha administration on day 3 after ovulation is followed by luteolysis and ovulation was tested using 24 animals. The ewes were treated with a dose of a PGF2alpha analogue (delprostenate, 160 microg) on days 1 (n=8), 3 (n=8) or 5 (n=8) after ovulation, was established by transrectal ultrasonography. Daily scanning and blood sampling were performed to determine ovarian changes and progesterone serum concentrations by radioinmunoassay. The treatment induced a sharp decrease of progesterone concentrations followed by oestrus and ovulation in all ewes treated on days 3 and 5 and in one ewe treated on day 1 (8/8, 8/8, 1/8; P<0.05). Seven ewes treated on day 1 did not respond to PGF2alpha treatment and had an inter-ovulatory cycle of normal length (17.4 +/- 0.5 days). However, the profile of progesterone concentrations during the cycle of these ewes was delayed 1 day (P<0.05) compared with a control cycle. The overall interval between PGF2alpha and oestrus for the 17 responding ewes was 42.4 +/- 2.3 h. In 15 of these ewes the ovulatory follicle was originated from the first follicular wave and the ovulation occurred at 60.8 +/- 1.8 h after PGF2alpha treatment. The other two responding ewes ovulated an ovulatory follicle originated from the second follicular wave between 72 and 96 h after treatment. These results support the hypothesis and suggest that refractoriness to PGF2alpha of the recently formed corpus luteum (CL) may be restricted to the first 1-2 days post-ovulation.     

Synchronization of estrus in beef heifers with a norgestomet implant and prostaglandin F2alpha

In a 5-year study (1973-1977), 281 cycling beef heifers were treated with a 7-day norgestomet (SC21009) ear implant and an intramuscular injection of prostaglandin F(2alpha) (PGF(2alpha)) at the time of implant removal or 24 hr before implant removal. Percentages of heifers in estrus by 36, 48, 60, 72, and 120 hr after implant removal were 32.4, 52.7, 71.6, 80.1, and 93.2, respectively. Onset of estrus occurred an average of 49.8 +/- 4.7 hr after treatment. Percentages of heifers in estrus 36 hr after treatment were 5.7 and 51.7 for those with a corpus luteum and those without a corpus luteum (or determined regressing by palpation) at implant removal, respectively. When PGF(2alpha) was injected 24 hr before implant removal, 55% of the heifers were in estrus by 36 hr after implant removal compared to 30% when PGF(2alpha) was injected at the time of implant removal; however, by 60 hr after implant removal the difference was 76% vs. 71%. First-service conception rates for synchronized and nonsynchronized heifers were 62.2% and 59.6%, respectively. During 1976 and 1977 heifers were checked for estrus every 4 hr and inseminated 2, 6, 10, 14, 18, 22, 26, or 30 hr after first detected to be in standing estrus. Conception rate was not significantly affected by time of insemination but tended to be higher for heifers bred 26 and 30 hr after first being detected in standing estrus (78.9% and 70.0% vs. average 59.2%). Treatment with a 7-day norgestomet implant plus a single injection of PGF(2alpha) 24 hr before or at implant removal appears to be a practical technique for synchronizing estrus in cycling heifers without affecting conception.     

The effect of intra-uterine prostaglandin F-2alpha on corpus luteum function in the human.

Prostaglandin F-2alpha (PGF-2alpha) was administered via a Foley catheter over a 12 hour period to 8 healthy volunteers awaiting laparoscopic sterilisation. The amount of PGF-2alpha infused varied between 500 mu-g and 2000 mu-g every 2 hours for 6 doses. Plasma progestins and oestradiol 17beta, and urinary estrogens and pregnanediol were assayed throughout the study period. There was no evidence of luteolysis in any patient although vaginal bleeding of varying duration occurred in all women within 36 hours of administration of PGF-2alpha.     

Changes in corpus luteum content of prostaglandin F2 alpha and E in the adult pseudopregnant rat

Conflicting reports exist regarding the source of luteolytic PGF2 alpha in the rat ovary. To assess the quantities of different PGs, measurements of PGF2 alpha, PGE and PGB were performed by radioimmunoassay in the adult pseudopregnant rat ovary throughout the luteal lifespan. Ovaries of 84 rats were separated by dissection into two compartments, corpora lutea of pseudopregnancy and remainder of ovary. Tissue samples were homogenized and prostaglandins extracted and determined by radioimmunoassay. During the mid-luteal and late-luteal phases, levels of PGs were significantly higher in the corpora lutea of pseudopregnancy than in the remainder of ovary. An increase of PGF2 alpha-content in the corpus luteum was registered with peak-levels of 53.9 +/- 8.5 (mean +/- SEM, N = 18) ng/g tissue wet weight at day 13 of pseudopregnancy. PGE-levels reached peak-values at day 11 of pseudopregnancy (271.6 +/- 28.4 ng/g w w, mean +/- SEM, N = 12). PGB-levels were below detection limits in all compartments for all ages studied. The present study demonstrates increased availability of PGF2 alpha in the corpus luteum during the luteolytic period, and points toward either increased luteal synthesis or luteal binding of PGF2 alpha during the luteolytic period.     

Effect of prostaglandin synthesis inhibition on human corpus luteum function

The hypothesis that human luteolysis is mediated by prostaglandin F_2α was initially tested through placebo-controlled observations of the effect of a single dose of ibuprofen on progesterone and luteinizing hormone levels late in the luteal phase in normal human subjects. Falling levels of progesterone at rest, not significantly attenuated by ibuprofen, did not support, and falling progesterone/luteinizing hormone ratios at rest, significantly attenuated by ibuprofen, did support this hypothesis. The pulsatile nature of progesterone levels in the human was confirmed in this study.     

Effect of prostaglandin synthesis inhibition on human corpus luteum function

The hypothesis that human luteolysis is mediated by prostaglandin F2 alpha was initially tested through placebo-controlled observations of the effect of a single dose of ibuprofen on progesterone and luteinizing hormone levels late in the luteal phase in normal human subjects. Falling levels of progesterone at rest, not significantly attenuated by ibuprofen, did not support, and falling progesterone/luteinizing hormone ratios at rest, significantly attenuated by ibuprofen, did support this hypothesis. The pulsatile nature of progesterone levels in the human was confirmed in this study.     

Effect of pregnancy on oxytocin-induced release of prostaglandin F2 alpha in heifers

The effect of pregnancy on the release of prostaglandin F2 alpha (PGF2 alpha) in response to oxytocin (OT) has been examined. Fourteen cyclic heifers received one intravenous injection of 1 IU OT (n = 6) or 100 IU OT (n = 8) 17, 18, or 19 days (Day 17-19) after the onset of estrus (Day 0). Five of these animals also received 100 IU OT at Days 6 and 13 to determine the effect of OT at different times of the cycle. Frequent blood samples were taken for 60 min before and for 90 min after OT injection for the measurement of 15-keto-13,14-dihydro-PGF2 alpha (PGFM) by radioimmunoassay. The experiment was then repeated using the same animals at Day 17-19 of pregnancy (confirmed by the recovery of an embryo the day after OT injection). Following the injection of 1 IU OT, plasma PGFM reached its peak within 30 min with the increase significantly lower (P less than 0.05) in pregnant (1.13 +/- 0.10-fold) than in nonpregnant animals (2.07 +/- 0.27-fold). However, because only 3 of the 6 cyclic animals showed a response to 1 IU OT, the dose was increased to 100 IU in subsequent experiments. The animals that received 100 IU at Days 6 and 13 had no significant increase in PGFM concentrations (1.18 +/- 0.05-fold and 1.01 +/- 0.04-fold, respectively). At Day 17-19 the increase in plasma PGFM reached its peak 5-15 min after 100 IU OT and the increase was significantly greater in nonpregnant (3.23 +/- 0.17-fold) than in pregnant (1.21 +/- 0.02-fold; P = 0.003) heifers. Six of 11 animals injected at Day 17-19 of the cycle showed a decrease in progesterone (P4) the day after OT administration. These data show that the release of PGF2 alpha in response to OT is suppressed in pregnant animals in vivo, suggesting an antiluteolytic role for the embryo in luteostasis.     

Canine prostaglandin F2alpha receptor (FP) and prostaglandin F2alpha synthase (PGFS): molecular cloning and expression in the corpus luteum

In the dog luteolysis is not affected by hysterectomy. This observation led to the hypothesis that paracrine/autocrine rather than endocrine mechanisms of PGF2alpha are responsible for luteal regression in the dioestric bitch. The present experiments tested for the capacity of canine CL to produce and respond to PGF2alpha by qualitatively and quantitatively determining the expressions of PGFS, the enzyme converting PGH2 into PGF2alpha, and the PGF2alpha-receptor (FP) in CL of non-pregnant dogs during dioestrus. Canine PGFS and FP were isolated and cloned; both genes show a high homology (82-94%) when compared to those of other species. Relatively weak FP mRNA expression was detected on day 5 of dioestrus. It had increased by day 25 and remained constant thereafter. In situ hybridization (ISH) localized FP solely to the cytoplasm of the luteal cells, suggesting that these cells are the only luteal targets of PGF2alpha in this species. Only negative results were obtained for the expression of PGFS in canine CL by routine qualitative RT-PCR. When Real Time (TaqMan) PCR was applied, repetitively more negative than positive results were obtained at all timepoints. Any positive measurements observed at any point were neither repeatable nor related to the stage of dioestrus. This led us to conclude that expression of PGFS is either absent or present at very low level only. These data suggest that luteal regression in non-pregnant bitches is not modulated by PGF2alpha. However, the FP seems to be constitutionally expressed, explaining the receptivity of canine CL to exogenous PGF2alpha.     

Effect of dexcloprostenol on endogenous prostaglandin F2alpha release in dairy heifers

Cloprostenol was previously believed to be unable to release endogenous prostaglandin F2alpha (PGF2alpha) when administered during early bovine diestrus. A prostaglandin release is, however, seen in late diestrus. The aim of this study is to find out whether dexcloprostoenol (containing the only biologically active isomer, d-isomer, of cloprostenol) induces endogenous PGF2alpha release during early and late diestrus. Twelve heifers of the Finnish Ayrshire breed were allocated into two equal groups. Their estrous cycles were synchronized with dexcloprostenol. A further luteolysis was induced with 0.15 mg of dexcloprostenol either on Day 7 (group D7 or early diestrus) or on Day 14 (group D14 or late diestrus) after ovulation. Blood for progesterone and the PGF2alpha metabolite 15-ketodihydro-PGF2alpha determinations was collected immediately before dexcloprostenol treatment and thereafter every second hour for 48 h. Five of the six heifers in both groups showed significantly increased blood levels of 15-ketodihydro-PGF2alpha at some time during the 48-h experimental period. The intervals from treatment to the first significant increases of the PGF2alpha metabolite were 32.8+/-2.3 h (min. 30 h, max. 36 h) and 20.0+/-4.2 h (min. 14 h, max. 24 h) in groups D7 and D14, respectively (P < 0.01). We have concluded that dexcloprostenol induced endogenous PGF2alpha release in most cases, regardless the time of its administration (early or late diestrus). This release, however, differs from that observed during spontaneous luteolysis.     

Effect of stage of the estrous cycle on interval to estrus after PGF(2alpha) in beef cattle

Effect of stage of the estrous cycle at the time of prostaglandin F(2alpha) (PGF(2alpha)) injection on subsequent reproductive events in beef females was studied in four trials involving 194 animals. Cycling animals were given two injections of 25 mg PGF(2alpha) 11 days apart or, in some cases, the interval was altered to allow the second injection to fall on a specific day of the cycle. Day of estrous cycle at time of the second injection was determined by estrous detection. Interval from the second PGF(2alpha) injection to the onset of estrus (interval to estrus) was shorter (P<.01) in heifers than in cows. Both cows and heifers injected on days 5 to 9 (early cycle) had a shorter (P<.01) interval to estrus (estrus = day 0) than did those injected on days 10 to 15 (late cycle). Conception rate was lower (P<.05) for early-cycle heifers than for late-cycle heifers inseminated by appointment at 80 hours. There was no significant difference in conception rate of early-or late-cycle heifers or cows inseminated according to estrous detection or early- or late-cycle cows inseminated at 80 hours. Progesterone concentrations in blood samples collected in heifers at 4-hour intervals after the second PGF(2alpha) injection on either day 7 or day 14 declined linearly (P<.05) through 36 hours. Day of the estrous cycle at PGF(2alpha) injection had no effect on rate of progesterone decline, even though heifers injected on day 7 had a shorter (P<.05) interval to estrus. All animals whose cycle length was not affected by the second PGF(2alpha) injection were treated on days 5 through 8 of the cycle, indicating that PGF(2alpha) was less effective in regressing the corpus luteum between days 4 and 9 of the cycle than later in the cycle.     

Estrus synchronization systems involving prostaglandin F(2alpha) and progesterone pretreatment in beef heifers

Two trials were conducted to evaluate treatments combining progesterone pretreatment and prostaglandin F(2alpha) (PGF(2alpha)) on estrus response, pregnancy and calving rate in heifers. Treatments in Trial 1 were 1) control (T(1); n=59), 2) 25 mg PGF(2alpha) on Day 0 (T(2); n=58), 3) 150 mg progesterone (P(4), i.m.) in corn oil on Day -24 plus PGF(2alpha) (T(3); n=61), and 4) 150 mg P(4) on Day -5 plus PGF(2alpha) (T(4); n=59). Trial 2 had T(2) and T(4) only. Heifers were artificially inseminated 8 to 16 h after detection of estrus for 10 and 5 d in Trials 1 and 2, respectively. In Trial 1 more heifers in T(3) and T(4) showed estrus by 72 h compared to T(1) and T(2). In T(3), percentages were greater at 84 and 96 h than in T(1) and T(2). There were no differences between T(3) and T(4) or T(1) and T(2) over time. Cumulative distributions of responses showed that more heifers in T(3) and T(4) were in estrus by 84 h after PGF(2alpha) than after other treatments, while T(3) showed the greatest total number of heifers in estrus by 84 h; this difference persisted for 180 h. In Trial 2, percentages of heifers observed in estrus for T(1) and T(4) were not different. Average interval from PGF(2alpha) to estrus was shorter in Trial 1 for T(3) heifers compared to other treatments. No difference was observed in interval to estrus for T(2) and T(4) in Trial 2; this interval averaged 58 h. Artificial insemination pregnancy rates were not different among treatments in either trial and averaged 67.4%. In Trial 1, a greater proportion of heifers in T(2), T(3) and T(4) calved by 35 days into the calving season compared to T(1), but in Trial 2 calving rates for T(2) and T(4) were not different. Progesterone pretreatment combined with PGF(2alpha) appeared to enhance estrus synchronization without influencing either pregnancy or calving rates.