Temporal relationships between peripheral plasma concentrations of oxytocin, progesterone and 13, 14-dihydro-15-keto-prostaglandin F2α during the oestrous cycle and early pregnancy in the ewe

Peripheral plasma concentrations of oxytocin, 13,14-dihydro-15-keto-prostaglandin F_2α(PGFM), progesterone and LH were determined at 3 hourly intervals during the oesterous cycle (n = 3) and in early pregnancy (n = 4) in sheep. The progesterone and LH concentrations showed that the cycling ewes were samples during the periods of luteal regression (decreasing progesterone concentrations), the preovulatory gonadotrophin surge and the beginning of the next luteal phase (increasing progesterone concentrations). The pregnant ewes had basal LH concentrations and luteal phase concentrations of progesterone (>lng/ml afte day 5 following mating) throughout the whole of the sampling period. Oxytocin concentrations in the non-pregnant ewes decreased around the time of luteal regression to reach low concentrations (mean concentrations of approximately 18pg/ml) during the preovulatory period and then increased after the preovulatory surge. PGFM concentrations exhibited a pulsatile pattern with increasing concentrations as progesterone levels fell. In the pregnant ewes oxytocin concentrations gradually fell until approximately 16 days post-mating (approximately 7–8pg/ml). The magnitude of the pulses in PGFM concentrations were also lower than in the cycling ewes. These results demonstrate that the increased concentrations of PGFM which are found during the period of luteal regression are not caused by increased peripheral concentrations of oxytocin.     

Inhibition of uterine prostaglandin-F2α production by bovine conceptus secretory proteins

The effect of bovine conceptus secretory proteins (CSP) on uterine prostaglandin (PG)-F_2α production was evaluated in dairy cattle following injection of estradiol-17β. Intrauterine injections of dialyzed serum proteins (Control, n=5) or CSP (n=5) were administered from days 15 through 18 post-estrus. Following intrauterine treatments on day 18, all cows were injected with E₂ (3 mg) to stimulate uterine PGF_2α production. Plasma concentrations of progesterone (P₄) and 15-keto-13,14-dihydro-PGF_2α (PGFM) were determined by RIA. The PGFM responses following E₂ challenge were decreased (p<0.01) for cows receiving CSP versus serum proteins into the uterine lumen. Individual PGFM, P₄ and cycle length responses are discussed. Data suggest that proteins secreted by the bovine conceptus suppress uterine PGF_2α production during pregnancy recognition in the cow.     

Concentrations of circulating hormones normalized to pulses of a prostaglandin F2α metabolite during spontaneous luteolysis in mares

The temporal relationships between a pulse of 13,14-dihydro-15-keto-PGF_2α (PGFM) and the concentrations of circulating hormones during the luteolytic period were studied for 11 pulses in 11 mares (Equus caballus) using samples collected hourly. Mean PGFM pulses encompassed 4 h before to 4 h after the peak, and hormone data were normalized to the PGFM peak (Hour 0). Concentration of progesterone decreased (P < 0.05) between Hours –4 and –3 and continued to decrease linearly throughout the PGFM pulse. The concentrations of cortisol and prolactin increased (P < 0.004) during Hours –4 to 0 and decreased (P < 0.002) during Hours 0 to 4. Estradiol concentration increased (P < 0.02) during Hours –4 to 0 but did not change significantly after Hour 0. Concentrations of follicle-stimulating hormone and luteinizing hormone did not change significantly during the PGFM pulse, and the oxytocin results were equivocal. Percentage of corpus luteum area with color-Doppler signals of blood flow did not change significantly between Hours –4 and 0 and first began to decrease (P < 0.004) between Hours 0 and 2. Results demonstrated that concentrations of progesterone decreased linearly during a PGFM pulse, and cortisol, prolactin, and estradiol increased during the ascending portion of the pulse. The progesterone and gonadotropin results supported the hypothesis that the initial progesterone and gonadotropin increases that have been reported to occur in response to a single bolus luteolytic treatment with prostaglandin F_2α do not occur in response to the natural secretion of prostaglandin F_2α.     

Stimulation of pulses of 13,14-dihydro-15-keto-PGF2α (PGFM) with estradiol-17β and changes in circulating progesterone concentrations within a PGFM pulse in heifers

A single physiologic dose (0.1 mg) of estradiol-17β in sesame-oil vehicle or vehicle alone (n = 8) was given to heifers on day 14 after ovulation to study the effect on circulating 13-14-dihydro-15-keto-PGF2α (PGFM), PGFM pulses, and changes in progesterone concentrations within a PGFM pulse. Blood samples were collected hourly for 16 h after treatment. The estradiol group had a greater mean concentration of PGFM, greater number of heifers with PGFM pulses and number of pulses/heifer, and greater prominence of the PGFM pulses. Changes in progesterone concentrations were not detected during the 16 h sampling session in the vehicle group, indicating that the heifers were in preluteolysis. Progesterone decreased after 12 h in the estradiol group, indicating a luteolytic effect of the estradiol-induced PGF secretion as represented by PGFM concentrations. Intrapulse changes in progesterone were detected during a PGFM pulse in the estradiol group (P < 0.006), but not in the vehicle group. Progesterone increased (P < 0.01) between Hours −2 and −1 of an estradiol-induced PGFM pulse (Hour 0 = peak of pulse), decreased (P < 0.004) between Hours −1 and 0, and increased (P < 0.01) or rebounded between Hours 0 and 1. Results were compatible with previous reports of a role for estradiol in the induction of PGFM pulses in cattle and demonstrated intrapulse changes in progesterone concentrations during an induced PGFM pulse.     

Intrauterine infusion of ovine conceptus secretory proteins reduces prostaglandin F2α release without affecting endometrial oxytocin receptor concentrations

Chronically ovariectomized ewes were pretreated with progesterone and oestradiol to induce oestrus and randomly allocated into four treatment groups. Progesterone injections were given to Groups 1 and 2 on Days 1–12 and Groups 3 and 4 on Days 1–15. Ewes in Groups 2 and 4 were infused with conceptus secretory proteins (oCSP), via an intrauterine catheter, twice daily on Days 13–15. Ewes in Groups 1 and 3 were similarly infused, but with serum proteins (oSP). Endometrial oxytocin receptor (OTr) concentrations and oxytocin-induced 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM) release were measured on Day 16.Progesterone concentrations in ewes receiving 12 days of progesterone treatment declined after Day 12, reaching a nadir on Day 14. In contrast, plasma progesterone concentrations remained elevated until Day 16 in ewes receiving the extended progesterone treatment. On Day 16, endometrial OTr concentrations were significantly higher in ewes given 12 days of progesterone treatment than in ewes given 15 days of progesterone irrespective of the presence of oCSP or oSP. Treatment with oCSP significantly decreased oxytocin-induced PGFM release in ewes given 12 days of progesterone treatment compared with those ewes receiving oSP infusions. The extended 15 day progesterone treatment resulted in a further decrease in oxytocin-induced PGFM release in both oCSP and oSP infused ewes.These data indicate that, in steroid treated ovariectomized ewes, intrauterine infusion of oCSP will reduce oxytocin-induced PGFM response but not OTr concentrations. Progesterone appears to play a dominant role in the regulation of OTr as well as oxytocin-induced PGFM release.     

Intrapulse temporality between pulses of a metabolite of prostaglandin F2α and circulating concentrations of progesterone before, during, and after spontaneous luteolysis in heifers

Pulses of the prostaglandin F_2α (PGF) metabolite 13,14-dihydro-15-keto-PGF_2α (PGFM) and the intrapulse concentrations of progesterone were characterized hourly during the preluteolytic, luteolytic, and postluteolytic periods in seven heifers. The common hour of the end of preluteolysis and the beginning of luteolysis was based on a progressive progesterone decrease when assessed only at the peaks of successive oscillations. The end of the luteolytic period was defined as a decrease in progesterone to 1 ng/mL. Blood samples were taken hourly from 15 d after ovulation until luteal regression as determined by color-Doppler ultrasonography. Between Hours −2 and 2 (Hour 0 = PGFM peak) of the last PGFM pulse of the preluteolytic period, progesterone decreased between Hours −1 and 0, and then returned to the prepulse concentration. Concentration did not change significantly thereafter until a PGFM pulse early in the luteolytic period; progesterone decreased by Hour 0 and transiently rebounded after Hour 0, but not to the prepulse concentration. In the later portion of the luteolytic period, progesterone also decreased between Hours −1 and 0 but did not rebound. After the defined end of luteolysis, progesterone decreased slightly throughout a PGFM pulse. Results demonstrated for the first time that the patterns of progesterone concentrations within a PGFM pulse differ considerably among the preluteolytic, luteolytic, and postluteolytic periods.     

Temporal relationship between plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F and neurophysin I/II around luteolysis in sheep

Plasma concentrations of neurophysin I/II (N-I/II), 13,14-dihydro-15-keto-prostaglandin F (PGFM) and progesterone were measured by radioimmunoassay in plasma samples collected from four sheep at hourly intervals between 0700 and 1900 h from Days 12–17 of the estrous cycle. Plasma samples were also collected from a fifth sheep at 2-hourly intervals during Days 12–16 of the cycle. In all sheep, intermittent surges in the plasma concentrations of PGFM and N-I/II occurred during the period of luteal regression. On at least one occasion in each sheep a surge in the plasma concentration of N-I/II was observed coincident with a rise in PGFM concentrations. In general, the highest levels of N-I/II were observed early in luteolysis (Days 13–14 of the cycle) while the corresponding levels of PGFM in plasma were maximal around Day 15 when luteolysis was well advanced.It is suggested from this temporal data that oxytocin, which is considered to be released in association with N-I/II, may play an important role in ovine luteolysis by stimulating the secretion of prostaglandin F from the uterus during Days 13–15 of the estrous cycle.     

Levels of progesterone and changes in prostaglandin F(2alpha) release during luteolysis and early pregnancy in llamas and the effect of treatment with flunixin meglumine

The secretory patterns of progesterone in relation to concentrations of 15-ketodihydro-PGF(2alpha) (PGFM) during the period of luteolysis or of maternal recognition of pregnancy were determined in the blood of llamas mated either with an intact or a vasectomized male. The ability of flunixin meglumine (FM) to postpone luteolysis in non-pregnant llamas was investigated by injecting the drug intravenously every 6 h at a dose of 2.2 mg/kg from days 6 to 12 post-copulation into a group of non-pregnant llamas. A pulsatile pattern of prostaglandin release was recorded during luteolysis in non-pregnant llamas, giving further support to the hypothesis that PGF(2alpha) is the luteolytic agent in llamas. The mean number of peaks per animal rose from 0.3 on day 7 to 3.8 on day 10 and then declined to 1.1 on day 12 with corresponding mean peak amplitude changing from 465 to 1234 and 566 pmol l(-1), respectively. In pregnant llamas, prostaglandin pulsatile release also occurred. The mean number of peaks per animal rose from 0.4 on day 7 to 0.8 on day 10 and then declined to 0.2 on day 11 and 0.6 on day 12, with corresponding mean peak amplitude changing from 494 to 676, 388 and 547 pmol l(-1), respectively. The transient decrease and subsequent recovery in progesterone concentrations was observed to occur in connection with prostaglandin release during early pregnancy. Oestradiol-17beta plasma peak concentrations attained after luteolysis were significantly higher than those recorded in early pregnant animals (around 30 pmol l(-1) and ll pmol l(-1)). Concentrations of PGFM decreased rapidly after the first administration of FM and remained low throughout the first 2 days of treatment. Thereafter, pulsatile release of prostaglandins started, and luteolysis proceeded; but a delay of 1-1.5 days in the progesterone decline was observed. Thus, it might be suggested that a higher dose and/or a more intensive injection schedule is required in llamas than in other ruminants to prevent luteolysis.     

Effects of PGF2α and PGF2α, 1–15 lactone on the corpus luteum and on early pregnancy in the rhesus monkey

The effects of prostaglandin (PG)F_2α and PGF_2α, 1–15 lactone were compared in luteal phase, non-pregnant and in early pregnant rhesus monkeys. Animals treated with either PG after pretreatment with human chorionic gonadotropin (hCG) had peripheral plasma progesterone concentrations that were not statistically different from those in animals treated with hCG and vehicle. However, menstrual cycle lengths in monkeys treated with PGF_2α, 1–15 lactone were significantly (P <0.02) shorter than those in vehicle treated animals. In the absence of hCG pretreatment, plasma progesterone concentrations were significantly (P <0.008) lower by the second day after the initial treatment with either PGF_2α or PGF_2α, 1–15 lactone than in vehicle treated monkeys. Menstrual cycle lengths in monkeys treated with either PG were significantly (P <0.04) shorter than those in animals treated with vehicle. There were no changes in plasma progesterone concentrations in early pregnant monkeys treated with PGF_2α, and pregnancy was not interrupted. In contrast, plasma progesterone declined and pregnancy was terminated in 5 of 6 early pregnant monkeys treated with PGF_2α, 1–15 lactone. These data indicate that PGF_2α, 1–15 lactone decreases menstrual cycle lengths in non-pregnant rhesus monkeys. More importantly, PGF_2α, 1–15 lactone terminates early pregnancy in the monkey at a dose which is less than an ineffective dose of PGF_2α.     

Effect of estradiol-17β on peripheral plasma concentration of 15-keto,14-dihydro PGF2α and luteolysis in cyclic cattle

Friesian heifers (n = 10) were assigned randomly to receive an intravenous injection of estradiol-17^β (E₂; 3 mg) or saline: ethanol vehicle solution (6 ml; 1:1) on day 13 of the estrous cycle. Blood was collected collected from the jugular vein by venipuncture into heparinized vacutainer tubes at 30 minute intervals for 2 hours (h) preinjection, 10.5 h postinjection and then at 3 h intervals until estrus. Repeated hormone measurements of 15-keto-13,14-dihydro-PGF_2α (PGFM) and progesterone (P₄) were evaluated by split-plot analysis of variance. Mean concentration of PGFM for the 12.5 h acute sampling phase was 164.1 ± .14 pg/ml. A treatment by time interaction was detected (P < .01). After treatment with E₂, PGFM concentrations began to increase at approximately 3.5 h, reached a mean peak of 330.4 ± 44.5 pg/ml (n = 5) at 5.5 ± .3 h, and returned to basal concentration by 9.0 ± .6 h. Vehicle treatment did not alter concentrations of PGFM. Injections of E₂ on day 13 of the estrous cycle caused luteolysis (P₄ concentration < 1 ng/ml) to occur earlier following injection (96.9 ± 10.6 h < 153.6 ±17.7 h; P, 0.05) than did the vehicle control treatment. During the chronic sampling phase of 3 h intervals, 39 of 606 samples (6.4%) were classified as PGFM spikes (323.0 ± 50.0 pg/ml); 21 (53%) of the spikes occurred at a mean interval of 18.9 ± 3.86 h before the time of completed luteolysis. Exogenous E₂ induced an acute increase in PGFM that may be indicative of uterine PGF_2α production. Peaks of PGFM in plasma were temporally associated with luteolysis on a within cow basis.     

Plasma 13, 14-dihydro-15-keto-PGF2 (PGFM) in pregnant and nonpregnant heifers prior to and during surgery and following intrauterine injection of PGF2

On day 17 postestrus or postmating, heifers were given intrauterine injections of saline (2 pregnant, 2 non-pregnant) or 200 μg PGF₂α (7 pregnant, 6 nonpregnant) through cannulae installed surgically into the uterine horn ipsilateral to the corpus luteum bearing ovary. Jugular blood samples were collected prior to the laparotomy at which the cannulae were installed during surgery, and for 90 min following the intrauterine injection. Plasma was assayed for progesterone and 13,14-dihyro-15-keto-PGF₂α )PGFM). Laparotomies were reopened to confirm proper cannula placement and to determine if blastocysts were present in mated heifers. Concentrations of PGFM were higher in pregnant compared to nonpregnant heifers during the presurgery (68 26 24 26 pg/ml; P < 0.25) and surgery (186 47 65 17 pg/ml; P < .05) periods. Pregnancy status did not alter the mean concentrations of PGFM (pregnant, 554 70 pg/ml; nonpregnant, 422 81 pg/ml) or the half-life of its decline in concentration (18 min) following intrauterine injection of PGF₂α. Pregnancy at 17 days in cattle does not appear to influence PGF₂α transport from the uterine lumen or its metabolism in the uterus or elsewhere in response to an acute intrauterine injection.     

Effect of oxytocin on plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha during the oestrous cycle and early pregnancy in the goat.

The effect of subcutaneous oxytocin on plasma concentrations of 13,14-dihydro-15-keto-prostaglandin (PG) F2 alpha (PGFM) was examined in the goat at various periods during the oestrous cycle and early pregnancy. 100 i.u. oxytocin was administered daily for 4 day, the dose being divided and given at 0900 and 2100 h; PGFM concentrations were assessed after the first treatment of each day. On days 3-6 (oestrus, day 0) PGFM concentrations increased significantly (P less than 0.001) within 15 minutes and both non-pregnant and mated goats exhibited oestrus behaviour by day 7. Significant (P less than 0.01) increases in PGFM were also produced on days 7-10, in both non-pregnant and pregnant goats, but the responses diminished from day 7 to day 10; only one goat (non-pregnant) came into oestrus. There was a marked difference in response between groups, however, during days 12-15. In non-pregnant goats significant (P less than 0.05) increases in PGFM were detected on days 13-15, but in pregnant animals oxytocin was without effect. Similarly, oxytocin did not increase PGFM concentrations on days 17-20 of pregnancy. However, uterine responsiveness reappeared in pregnant goats with significant (P less than 0.01) increases in PGFM on days 24 and 25.     

Peripartal changes in plasma progesterone and 15-keto-13,14-dihydro-prostaglandin F2α concentrations in Holstein cows with or without retained foetal membranes

Peripheral blood plasma concentrations of progesterone and the main metabolite of prostaglandin F_2α, (15-keto-13,14-dihydro-PGF_2α) PGFM, were determined in 10 Holstein cows with retained foetal membranes (RFM) and 12 Holstein cows without RFM (NRFM) during the peripartal period. The rate of uterine involution in the postpartum cows was monitored.There was no difference in the rate of uterine involution between cows with or without RFM. Cyclical ovarian activity was resumed within a month after parturition in both group. Increases in the mean peripheral plasma PGFM concentrations were evident in the RFM cows 6 days before parturition, compared to 48 h before parturition in the NRFM cows. A gradual decline in PGFM to prepartum concentrations occurred in both groups by Day 12 after parturition, although in the RFM cows, PGFM concentrations remained high until the placenta was shed.In both groups, the mean peripheral plasma concentrations of progesterone showed a marked decline beginning 48 h before partusition. The mean plasma progesterone concentrations were less than 1 ng/ml during the immediate postpartum period.     

Uterine prostaglandin and blood flow responses to estradiol-17β in cyclic cattle

Normal cyclic dairy cattle (n=7) underwent a midventral laparotomy on day 17 of the estrous cycle and were fitted, ipsilateral to the CL, with: an electromagnetic flow transducer around the uterine artery (UA; n=5); catheters within the ovarian vein (OV; n=7) via a uterine branch of the ovarian vein, uterine branch of the ovarian artery (UBOA; n=5) and facial artery (FA; n=7). On day 18, blood samples were collected at 30 min intervals for 1 h prior to injection of estradiol-17β (E₂; 3 mg) and 12 h post-E₂. Uterine blood flow (UBF) was monitored continuously and plasma samples analyzed for PGF_2α and PGFM. Exact locations of catheters in reproductive tracts were verified post-slaughter. Data were analyzed by method of least squares analysis of variance. Uterine blood flow (ml/min) increased above pre-E₂ flow rates within 30 min post-E₂ injection, peaked between 2.5 to 3.5 h and declined between 4 to 8.5 h. A small secondary rise in UBF occurred between 9 and 12 h. Regression analysis for concentrations (pg/ml) of PGF_2α and PGFM in the OV (i.e., [OV]-[FA]) demonstrate a similar response as PGFM concentration in the FA in that all increased at approximately 3 h, peaked between 5 and 7 h and returned to near baseline levels by 9 to 10 h post-E₂. Facial artery PGFM concentrations were positively correlated with uterine production of PGF_2α (r=.66) and PGFM (r=.30), whereas FA PGF_2α concentrations were not. In three of five cows, a difference in PGF_2α was detected between UBOA and FA (UBOA > FA); supportive of a local countercurrent exchange between the uterine venous drainage and the ovarian artery.     

Effect of progesterone administration on the release of uterine prostaglandin F2α and ovarian oxytocin in the goat

The effects of intramuscular progesterone administration (20 mg·day⁻¹) on plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM-pulmonary metabolite of prostaglandin F_2α) and oxytocin were examined in seventeen goats after either bilateral ovariectomy, hysterectomy or during days 12–16 of the estrous cycle. Daily mean values of PGFM in animals treated with progesterone after ovariectomy were significantly greater (P<0.001) than in their corresponding controls on the last two treatment days (10 and 11); concentrations of oxytocin, however, remained at or near the limits of assay sensitivity. In hysterectomized goats PGFM concentrations remained extremely low and oxytocin release appeared steady rather than pulsatile. In the intact animals, undergoing luteolysis, daily mean concentrations of both PGFM and oxytocin were significantly greater (P<0.01) in progesterone-treated goats than in their oil-treated controls; furthermore, in the progesterone-treated goats, increases in PGFM concentrations, observed after the peaks of progesterone, were either coincident with or prior to pulses of oxytocin. These results demonstrate that uterine PGF_2α stimulates the pulsatile release of oxytocin from the ovary during luteolysis in the goat.     

Effects of prostaglandins, dibutyryl camp, LHRH, estrogens, progesterone, and potassium on output of prostaglandin F2α, 13, 14-dihydro-15-keto-prostaglandin F2α, HCG, estradiol, and progesterone by placental minces

In order to compare the endocrine response of placental minces to luteinizing hormone releasing hormone (LHRH) and dibutyryl cAMP (dbcAMP) and to screen for effects of potential stimulatory and inhibitory substances, the simultaneous outputs of PGF_2α, 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM), progesterone, 17β-estradiol, and hCG were evaluated during a 4 hour incubation in 5 placentas. The output of hCG was highest for 12-week placentas, intermediate for a 16 week placenta, and lowest for term placentas. The output of 17β-estradiol by 12 and 16 week placentas in the presence of 30 μM dehydroepiandrosterone sulfate (DHEAS) was greater than that by term placentas. Progesterone output was apparently independent of gestational age although some variation between 12-week placentas was demonstrated. Output of PGF_2α was lower in 12 and 16-week placentas than in term placentas and that of PGFM was lower in 12-week placentas than in term placentas. LHRH (100 nM) produced stimulation of PGF_2α output (P<.005) and a trend toward inhibition of progesterone output (which failed to achieve statistical significance) but no stimulation of hCG under these conditions. Stimulation of the outputs of hCG (P<.005) and PGF_2α (P<.001) and inhibition of that of progesterone (P<.005) was produced by 20 mM dbcAMP. DHEAS inhibited output of progesterone (P<.01) and PGF_2α (P<.01). There were no effects of potassium, estrogens, progesterone, or prostaglandins on output of any measured substance.     

Luteolysis in the rhesus monkey: Ovarian venous estrogen, progesterone, and prostaglandin F2α-metabolite

The role of prostaglandin F₂α (PGF₂α) in luteolysis in the non-human primate is poorly understood. We have recently reported that chronic PGF₂α infusion to the corpus luteum via Alzet pump, induced premature, functional luteolysis in the rhesus monkey. In the present study we sought to determine the ovarian events leading to spontaneous luteolysis in the monkey. Rhesus monkeys underwent laparotomy during the early luteal (4–5 days after the preovulatory estradiol surge, PES), mid-luteal (7–9 days PES), and late luteal (10–14 days PES) phases or at the first day of menses (M). Concentrations of progesterone, estradiol, estrone, and 13, 14-dihydro-15-keto-PGF₂α (PGFM) were measured in the ovarian venous effluents ipsilateral and contralateral to the ovary bearing the corpus luteum. Steroid levels in the ovarian vein on the corpus luteum side were significantly higher than the non-corpus luteum side throughout the cycle. PGFM levels were similar on both sides until the late luteal phase, when the effluent of the ovary bearing the corpus luteum contained significantly more PGFM (206±3) vs. 123±9 pg/ml, mean±sem); this disparity increased further at the time of menses (241±38 vs. 111±22 pg/ml). These data are the first to show an asymmetric secretion of PGFM in the ovarian venous effluent in the primate and suggest that PGF₂α of ovarian and possibly of corpus luteum origin may be directly involved in luteal demise.     

Role of progesterone in regulating uteroovarian venous concentrations of PGF2 α and PGE2 during the estrous cycle and early pregnancy in ewes

The role of progesterone in regulation of uteroovarian venous concentrations of prostaglandins F₂ α (PGF₂α) and E₂ (PGE₂) during days 13 to 16 of the ovine estrous cycle or early pregancy was examined. At estrus, ewes were either mated to a fertile ram or unmated. On day 12 postesturus, ewes were laparotomized and a catheter was inserted into a uteroovarian vein. Six mated and 7 unmated ewes received no further treatment. Fifteen mated and 13 unmated ewes were ovariectomized on day 12 and of these, 7 mated and 5 unmated ewes were given 10 mg progesteron sc and an intravaginal pessary containing 30 mg of progesterone. Uteroovarian venous samples were collected every 15 min for 3 h on days 13 to 16 postestrus. Mating resulted in higher mean daily concentrations of PGE₂ in the uterovarian vein than in unmated ewes. Ovariectomy prevented the rise in PGE₂ with day in mated ewes but had no effect in unmated ewes. Progesterone treatment restored PGE₂ in ovariectomized, mated ewes with intact embros. Mating had no effect on mean daily concentrations of PGF₂α or the patterns of the natural logarithm (ln) of the invariance of PGF₂α. Ovariectomy resulted in higher mean concentrations and ln invariances of PGF₂α on day 13 and lower mean concentrations and ln invariances of PGF₂α on days 15 and 16. Replacement with progesterone prevented these changes in patters of mean concentrations and ln variances of PGF₂α following ovariectomy. It is concluded that progesterone regulates the release of PGF₂α from the uterus, maintaining high concentrations while also preventing the occurrence of the final peaks of PGF₂α which are seen with falling concentrations of progesterone. This occurs in both pregnant and non-pregnant ewes. Progesterone is also needed to maintain increasing concentrations of PGE₂ in mated ewes.     

Effect of partial fetectomy on plasma 13,14-dihydro-15-keto-prostaglandin F2α in late pregnancy of sows

The aim of this study was to ascertain if partial fetectomy in late pregnancy affected prostaglandin F_2α levels, thereby influencing the time of delivery of the remaining fetuses in the sow. Sham fetectomy or surgical removal of one, two, three or four fetal piglets was performed on each of ten sows during the last 3 weeks of pregnancy. Removal of no fetuses (two sows) and in one sow a single fetus was followed by a continuation of pregnancy to the expected time of parturition. Plasma values for oestrone, progesterone and 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM) were similar to those reported previously for normal sows. Removal of one (two sows), two (two sows), three (two sows) or four (one sow) fetuses was followed by premature parturition, within 42–144 h of surgery. Labour lasted 24 to 30 h. Almost immediately after fetectomy, PGFM levels in plasma increased and were accompanied by a decline in progesterone concentrations. High PGFM values (13–60 ng/ml) were present at parturition. Oestrone concentrations were variable or rose slightly at this time. The results suggest that all fetuses in a litter must be present to maintain pregnancy to term. Pregnancy may depend upon fetal suppression of prostaglandin F_2α production and release until the appropriate time for parturition.     

Interrelationships between progesterone, 13,14-dihydro-15-keto PGF-2 alpha (PGFM) and LH in cyclic and early pregnant cows

Plasma progesterone and LH secretion patterns were examined in 18 mature dairy cows during the oestrous cycle and after insemination. Blood samples were collected every 15 min for 8 h per day on Days 3, 5, 6, 7, 8, 9, 10, 12, 14, 16, 17, 18, 19, 20 and 21 of the oestrous cycle, then, in the same cows, at the same times during early pregnancy. PGF-2 alpha secretion rates (as determined by plasma PGFM concentrations) were also monitored on Days 14, 16 and the day of, or equivalent to, luteal regression. Mean daily plasma progesterone concentrations were similar until Day 16 in cyclic and pregnant cows, after which values in non-pregnant animals declined. Regression analysis indicated that progesterone concentrations were best described by a quadratic expression with fitted maximum values on Day 13 in non-pregnant animals but values increased linearly over the whole period to Day 21 in pregnant cows. The frequency, amplitude and area under the curve of LH episodes showed no significant differences between cyclic and pregnant animals. In pregnant cows, the amplitude and area under the curve of progesterone episodes increased linearly between Days 8 and 21, although no such increase occurred in cyclic cows. Low-level PGFM episodes were present in cyclic and pregnant cows on Days 14 and 16 after oestrus, and high amplitude episodes occurred in non-pregnant cows during luteal regression. Pregnant cows showed a significant depression of the amplitude, but not the frequency of episodes at the expected time of luteal regression. These results confirm that the corpus luteum of pregnancy secretes an increasing amount of progesterone per se and per unit of LH until at least Day 21 after mating. They further suggest that the corpus luteum of the cyclic cow may experience small episodes of PGF-2 alpha and be subjected to initial degenerative changes by Day 14 after oestrus, some time before the onset of definitive luteolysis.