Metabolites of PGF2α in Blood Plasma and Urine as Parameters of PGF2α Release in Cattle

The metabolism of PGF2α in cattle results initially in the formation of 15-keto-13,14-dihydro-PGF2α (15-ketodihydro-PGF2α) and later the 11-ketotetranor PGF metabolites. Both types of metabolites appear in the peripheral circulation and finally the 11-ketotetranor PGF metabolites are found in large quantities in the urine in a species-related pattern. Several approaches can be made to the quantitative analysis of PGF2α release during reproductive studies. First, assay of the 15-ketodihydro-PGF2α metabolite in the peripheral circulation; second, analysis of the longer-lived 11-ketotetranor PGF metabolites in the peripheral circulation; and finally analysis of the latter metabolites in the urine. The antibodies used in radioimmunoassays of both types of metabolites of PGF2α were found to be specific and the results agree well with those obtained earlier by mass spectrometric analysis. The assay of 11-ketotetranor PGF metabolites was used to study the excretion of urinary metabolites in the cow after i.v. infusion of PGF2α and also during the normal estrous cycle and early pregnancy. These studies suggest that 11-ketotetranor PGF metabolites in cow urine serve as a good parameter of PGF2α release, especially for long–term studies, but when a precise pattern of PGF2α release is required, measurement of 15-ketodihydro-PGF2α levels in frequently collected plasma samples is preferable.     

Role of PGF2α in luteolysis based on inhibition of PGF2α synthesis in the mare

The effects of inhibition of PGF2α synthesis on luteolysis in mares and on the incidence of prolonged luteal activity were studied in controls and in a group treated with flunixin meglumine (FM), a PGF2α inhibitor (n = 6/group). The FM was given every 8 hours (1.0 mg/kg) on each of Days 14.0 to 16.7. Concentration (pg/mL) of PGF2α metabolite averaged over 8 hours of hourly blood sampling at the beginning of each day, was lower in the FM group than in the controls on Day 14 after ovulation (6.7 ± 1.3 vs. 13.8 ± 2.9, P < 0.05), Day 15 (15.0 ± 3.9 vs. 35.2 ± 10.4, P < 0.10), and Day 16 (21.9 ± 5.7 vs. 54.7 ± 11.4, P < 0.03). Concentration (ng/mL) of progesterone (P4) was greater in the FM group than in the controls on Day 14 (10.1 ± 0.9 vs. 7.7 ± 0.9, P < 0.08), Day 15 (9.2 ± 1.0 vs. 4.3 ± 1.0, P < 0.008), and Day 16 (5.6 ± 1.6 vs. 1.2 ± 0.4, P < 0.02). The interval from ovulation to the beginning of a decrease in P4 and to the end of luteolysis (P4 < 1 ng/mL) was each delayed (P < 0.03) by ∼1 day in the FM group. Intervals involving the luteal phase were long (statistical outliers, P < 0.05) in two mares in the FM group, indicating prolonged luteal activity. Results supported the hypotheses that (1) inhibition of PGF2α synthesis interferes with luteolysis in mares and (2) inhibition of PGF2α at the expected time of luteolysis may lead to prolonged luteal activity.     

Direct effect of PGF2α pulses on PRL pulses, based on inhibition of PRL or PGF2α secretion in heifers

The relationships between PRL and PGF_2α and their effect on luteolysis were studied. Heifers were treated with a dopamine-receptor agonist (bromocriptine; Bc) and a Cox-1 and -2 inhibitor (flunixin meglumine [FM]) to inhibit PRL and PGF_2α, respectively. The Bc was given (Hour 0) when ongoing luteolysis was indicated by a 12.5% reduction in CL area (cm²) from the area on Day 14 postovulation, and FM was given at Hours 0, 4, and 8. Blood samples were collected every 8-h beginning on Day 14 until Hour 48 and hourly for Hours 0 to 12. Three groups of heifers in ongoing luteolysis were used: control (n = 7), Bc (n = 7), and FM (n = 4). Treatment with Bc decreased (P < 0.003) the PRL concentrations averaged over Hours 1 to 12. During the greatest decrease in PRL (Hours 2-6), LH concentrations were increased. Progesterone concentrations averaged over hours were greater (P < 0.05) in the Bc group than in the controls. In the FM group, no PGFM pulses were detected, and PRL concentrations were reduced. Concentrations of PGFM were not reduced in the Bc group, despite the reduction in PRL. Results supported the hypothesis that a decrease (12.5%) in CL area (cm²) is more efficient in targeting ongoing luteolysis (63%) than using any day from Days 14 to ≥19 (efficiency/day, 10-24%). The hypothesis that PRL has a role in luteolysis was supported but was confounded by the known positive effect of LH on progesterone. The hypothesis was supported that the synchrony of PGFM and PRL pulses represents a positive effect of PGF_2α on PRL, rather than an effect of PRL on PGF_2α.     

Effects of estriol on PGF2α output by cultures of human endometrium and endometrial cells

We have shown that the rate of release of PGF_2α by monolayer cultures of epithelial cells from proliferative endometrium is markedly elevated by addition of estradiol to the medium. In cultures maintained in HAM F-10 medium containing charcoal stripped calf serum, estradiol (10⁻⁸M) increased the levels of PGF_2α several fold during the second and third days in culture. Similar responses were obtained with estradiol at 10⁻¹⁰M concentration.When this system was used to compare the effects of estradiol and estriol at equal concentrations (10⁻⁸M), similar elevation (10–16-fold) of PGF_2α levels were noted during 3 consecutive days in culture. When cultures of epithelial cells derived from secretory endometrium were used for these tests, estriol was as effective as than estradiol in elevating PGF_2α levels in the medium.When the effects of estradiol and estriol were compared using fragments of secretory endometrium in organ culture, the increases in PGF_2α levels noted in the medium were about equal (2- to 10-fold) for the two estrogens at the same concentration (10⁻⁹−10⁻⁸M).Exposure of the tissue to either estradiol or estriol for only 1 h resulted in increases in PGF_2α output for the following 3 days.These results clearly show that estriol is as effective as estradiol in stimulating PGF_2α output by human endometrial tissue.     

Abortion after PGF2α in heifers with multiple pregnancies following superovulation with FSH and PGF2α

Multiple ovulations were induced with follicle stimulating hormone and estrus was synchronized with prostaglandin F_2α (PGF_2α) in 23 Holstein heifers. In 19 heifers which responded to the treatments, an average of 1.8 corpora lutea were formed after the induced estrus and 6 of 19 heifers conceived (total of ten fetuses at 39 days gestation) to artificial insemination at 60 and 84 hr after the PGF_2α injection. Injection of 33 mg PGF_2α Tham salt into the six pregnant heifers on day 40 of gestation caused abortion between 54 and 66 hr after treatment in all heifers.     

Fixed-time deep uterine insemination in PGF2α-synchronized goats

The aim of this investigation was to optimize fixed-time insemination in goats by clustering ovulations in prostaglandin F_2α-synchronized goats either with gonadotropin releasing hormone (GnRH) or human chorionic gonadotropin (hCG). The underlying intention was to reduce the incidence of short cycles by providing a more sustained stimulation of the corpus luteum by substituting the commonly used GnRH with longer-acting hCG. It was conjectured that this might render the corpus luteum less prone to premature regression. Sixty pluriparous does were administered 5 mg of the prostaglandin F_2α preparation dinoprost (Dinolytic; Pharmacia and Upjohn, Erlangen, Germany) during the luteal phase of the estrous cycle. Twenty of these does were administered 0.004 mg of the GnRH analog buserelin (Receptal; Intervet, Unterschleissheim, Germany) 48 hours later; another 20 does received 500 IU hCG (Chorulon; Intervet, Unterschleissheim, Germany) instead. Sixteen hours later the does were inseminated with frozen-thawed semen. The remaining 20 does served as controls and were inseminated 16-18 h after the onset of detected estrus. All 60 treated goats displayed estrous symptoms, the time of onset being similar for all groups (42.6, 37.6, and 40.5 hours after treatment for GnRH-treated, hCG-treated, and control does, respectively). The duration of estrus in the GnRH-treated group was 10 h less than in the other groups (45.1 vs. 56.4 and 54.4 h, P < 0.05). The number of ovulations (assessed by ultrasound monitoring) did not differ among groups (2.4, 2.1, and 2.5, P > 0.05). Monitoring of serum progesterone revealed that the incidence of corpus luteum insufficiency was significantly higher in GnRH- and hCG-treated does than in the control group (40% and 35% vs. 5%, P < 0.05). The pregnancy rate was 50% in the GnRH and 35% in the hCG group as compared with 60% in the controls. Corresponding kidding rates were 40%, 35%, and 60% (P > 0.05). When disregarding does with corpus luteum insufficiency, pregnancy rates would have been 83%, 54%, and 63%, and kidding rates 67%, 54%, and 63%, respectively. The average number of kids born was 1.88, 1.71, and 1.83, respectively (P > 0.05). It may be concluded that fixed time insemination of cycling does treated with prostaglandin F_2α during the luteal phase, followed by ovulation induction with GnRH or hCG, would be an effective management tool if it were possible to control the high incidence of corpus luteum insufficiency. The attempt to achieve this by substituting GnRH with hCG, was not met with success. Until a solution for the problem has been found, it is advisable to inseminate prostaglandin-synchronized does 16-18 hours after the onset of detected estrus.     

Fixed-time deep uterine insemination in PGF2α-synchronized goats

The aim of this investigation was to optimize fixed-time insemination in goats by clustering ovulations in prostaglandin F_2α-synchronized goats either with gonadotropin releasing hormone (GnRH) or human chorionic gonadotropin (hCG). The underlying intention was to reduce the incidence of short cycles by providing a more sustained stimulation of the corpus luteum by substituting the commonly used GnRH with longer-acting hCG. It was conjectured that this might render the corpus luteum less prone to premature regression. Sixty pluriparous does were administered 5 mg of the prostaglandin F_2α preparation dinoprost (Dinolytic; Pharmacia and Upjohn, Erlangen, Germany) during the luteal phase of the estrous cycle. Twenty of these does were administered 0.004 mg of the GnRH analog buserelin (Receptal; Intervet, Unterschleissheim, Germany) 48 hours later; another 20 does received 500 IU hCG (Chorulon; Intervet, Unterschleissheim, Germany) instead. Sixteen hours later the does were inseminated with frozen-thawed semen. The remaining 20 does served as controls and were inseminated 16–18 h after the onset of detected estrus. All 60 treated goats displayed estrous symptoms, the time of onset being similar for all groups (42.6, 37.6, and 40.5 hours after treatment for GnRH-treated, hCG-treated, and control does, respectively). The duration of estrus in the GnRH-treated group was 10 h less than in the other groups (45.1 vs. 56.4 and 54.4 h, P < 0.05). The number of ovulations (assessed by ultrasound monitoring) did not differ among groups (2.4, 2.1, and 2.5, P > 0.05). Monitoring of serum progesterone revealed that the incidence of corpus luteum insufficiency was significantly higher in GnRH- and hCG-treated does than in the control group (40% and 35% vs. 5%, P < 0.05). The pregnancy rate was 50% in the GnRH and 35% in the hCG group as compared with 60% in the controls. Corresponding kidding rates were 40%, 35%, and 60% (P > 0.05). When disregarding does with corpus luteum insufficiency, pregnancy rates would have been 83%, 54%, and 63%, and kidding rates 67%, 54%, and 63%, respectively. The average number of kids born was 1.88, 1.71, and 1.83, respectively (P > 0.05). It may be concluded that fixed time insemination of cycling does treated with prostaglandin F_2α during the luteal phase, followed by ovulation induction with GnRH or hCG, would be an effective management tool if it were possible to control the high incidence of corpus luteum insufficiency. The attempt to achieve this by substituting GnRH with hCG, was not met with success. Until a solution for the problem has been found, it is advisable to inseminate prostaglandin-synchronized does 16–18 hours after the onset of detected estrus.     

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.     

Concentrations of circulating hormones during the interval between pulses of a PGF2α metabolite in mares and heifers

The temporal relationship of several hormones to a metabolite of prostaglandin F2α (PGFM) was studied in mares and heifers from the beginning of the first PGFM pulse during luteolysis to the end of the second pulse. Mares (n=7) were selected with a 9-h interval between the peaks of the two pulses. In mares, estradiol-17β (estradiol) increased (P<0.05) within each PGFM pulse and plateaued for a mean of 6h between the pulses, resulting in a stepwise estradiol increase. Progesterone decreased linearly (P<0.0001) throughout the intra-pulse and inter-pulse intervals of PGFM. In heifers (n=6), inter-pulse intervals were variable, and therefore Hours 1-4 of the first pulse (Hour 0=PGFM peak) and Hours -4 to -1 of the second pulse were used to represent the mean 8-h interval between peaks of the two pulses. Estradiol increased (P<0.05) during the ascending portion of each PGFM pulse and then decreased (P<0.05) beginning at Hour -1 of the first PGFM pulse and Hour 0 of the second pulse. The 1-h delay during the second pulse was accompanied by an apparent increase in PRL. A transient decrease in estradiol occurred in individuals between PGFM pulses at a mean of 5h after the first PGFM peak, concomitant with a transient LH increase (P<0.05). Results indicated that estradiol plateaued in mares and fluctuated in heifers during the interval between PGFM pulses. Heifers also showed temporal relationships between estradiol and LH and apparently between estradiol and PRL.     

Determination of 15-keto-13,14-dihydro-metabolites of PGE2 and PGF2α in plasma using high performance liquid chromatography and gas chromatography-mass spectrometry

A method is described for the measurement of 15-keto-13,14-dihydrometabolites of PGE₂ and PGF_2α in peripheral human plasma. This involves purification by high performance liquid chromatography followed by determination of levels by combined gas chromatography-mass spectrometry using tetradeuterated analogs of the metabolites as internal standards. The levels of these metabolites in plasma are considered to be a more reasonable index of the entry of PGE₂ and PGF_2α into peripheral blood than are the levels of the corresponding primary prostaglandins. The endogenous levels of 15-keto-13,14-dihydro-PGE₂ and 15-keto-13,14-dihydro-PGF_2α found in peripheral plasma are 33 ± 10 pg/ml (SD; n=6) and 40 ± 16 pg/ml (SD; n=6), respectively.     

Opposite effects of methanandamide on lipopolysaccharide-induced prostaglandin E2 and F2α synthesis in uterine explants from pregnant mice

Prostaglandins (PG) are effective abortifacients and are important mediators of lipopolisaccharide (LPS)-induced embryonic resorption (ER). Besides, anandamide (AEA) has been described as one of the major endocannabinoids present in the uterus suggesting that it might play a role in reproduction. It has been reported that high levels of AEA are associated with pregnancy failure and that LPS increases AEA production. Also, it has been observed that AEA modulates PG production in different tissues. In this sense, we studied whether LPS-induced PG production is modulated by AEA and we also assessed the effect of this endocannabinoid on PG metabolism in an in vitro model. Uterine explants from BALB/c implantation sites were cultured in the presence of LPS plus cannabinoid receptor (CB) specific antagonists and PG production was assessed. Then, we studied the effect of exogenous AEA on different steps of PG metabolic pathway. We showed that AEA is involved in LPS-induced PG biosynthesis. Also, we observed that AEA exerts opposite effects on PGE(2) and PGF(2α) biosynthesis, by inhibiting PGE(2) production and increasing PGF(2α) levels. We suggest that AEA could be involved in the mechanisms implicated in LPS-induced ER. A better understanding of how AEA could be affecting ER could help developing specific interventions to prevent this pathology.     

Ovarian and PGF2α responses to stimulation of endogenous PRL pulses during the estrous cycle in mares

The effects of a PRL-stimulating substance (sulpiride) on PRL and PGF2α secretion and on luteal and ovarian follicular dynamics were studied during the estrous cycle in mares. A control group (n = 9) and a sulpiride group (Sp; n = 10) were used. Sulpiride (25 mg) was given every 8 h from Day 13 postovulation to the next ovulation. Repeated sulpiride treatment did not appear to maintain PRL concentrations at 12-h intervals beyond Day 14. Therefore, the hypothesis that a long-term increase in PRL altered luteal and follicular end points was not testable. Hourly samples were collected from the hour of a treatment (Hour 0) to Hour 8 on Day 14. Concentrations of PRL increased to maximum at Hour 4 in the Sp group. The PRL pulses were more prominent (P < 0.008) in the sulpiride group (peak, 19.4 ± 1.9 ng/mL; mean ± SEM) than in the controls (11.5 ± 1.8 ng/mL). Concentrations of a metabolite of PGF2α (PGFM), number, and characteristics of PGFM pulses, and concentrations of progesterone during Hours 0 to 8 were not affected by the increased PRL. A novel observation was that the peak of a PRL pulse occurred at the same hour or 1 h later than the peak of a PGFM pulse in 8 of 8 PGFM pulses in the controls and in 6 of 10 pulses in the Sp group (P < 0.04), indicating that sulpiride interfered with the synchrony between PGFM and PRL pulses. The hypothesis that sulpiride treatment during the equine estrous cycle increases concentrations of PRL and the prominence of PRL pulses was supported.     

Effect of early postpartum PGF2α treatment on reproductive performance in dairy cows with calving and puerperal traits

The objective of this study was to evaluate the effects of early postpartum PGF two alpha treatment on reproductive performance in dairy cows with calving and puerperal traits. A total of 363 Holstein cows (128 primiparous and 235 multiparous) were selected based on the presence of at least one of calving and puerperal traits (dystocia, retained placenta, twin, abortion, and postpartum uterine infections) and were assigned to two groups (treatment and control) irrespective of presence or absence of luteal tissue. Cows in the treatment group were treated twice with 25 mg dinoprost 8 h apart on day 20 postpartum, and for the control group saline placebo was administered. As it was speculated that the timing of a second dose would mimic the release of endogenous PGF2α from the uterus, our hypothesis was that two doses of PGF2α 8 h apart may increase the duration of elevated plasma prostaglandin F2α metabolite concentration in these cows. Recorded reproductive variables included days to first estrus, days to first AI, first service conception rate, pregnancy by 150 days in milk, service per conception, open days, and the percentage of repeat breeder animals. The data were analyzed using SPSS (Version 15) (IBM North America, New York, NY, USA) and Minitab (Version 14) (Minitab, State College, PA, USA). Although early postpartum PGF2α treatment had no effect on days to first estrus (36.7 days vs. 34.9 days, P = 0.056) and days to first AI (70.5 days vs. 72.2 days, P = 0.537), it increased first service conception rate (47.1% vs. 27.6%, P < 0.001); and this was more remarkable in primiparous cows (64.7% vs. 25%, P < 0.001). PGF2α treatment reduced the mean service per conception (1.92 vs. 2.72, P < 0.001) and the mean open days (112 days vs. 144 days, P < 0.001), and increased pregnancy by 150 days in milk (DIM) (80% vs. 66%, P = 0.004). The prevalence of repeat breeder syndrome in cows with calving and puerperal traits was reduced by PGF2α treatment (10% vs. 29.8%, P < 0.001). In conclusion, treatment of cows with calving and puerperal traits twice with a luteolytic dose of PGF2α 8 h apart on Day 20 postpartum improved reproductive performance and reduced the prevalence of repeat breeder syndrome.     

Utero-ovarian venous concentrations of prostaglandin E2 (PGE2 and prostaglandin F2α (PGF2α) following PGE2 intrauterine infusions

The uterine horns and utero-ovarian veins of nine crossbred mature gilts were bilaterally cannulated on day 9 of the estrous cycle (day 0 - first day of estrus). Each uterine horn in treated gilts (N=5) was infused with 150 μg PGE₂ in 3 ml of saline at 0900 h on day 12, 15 and 18 of the estrous cycle. Control gilts (N=4) received 3 ml saline intrauterine infusions on the corresponding day. Blood samples were collected from the utero-ovarian veins 15 min before each infusion and for the following 6 h with 15, 30 and 60 min intervals through the first, second and third two-hour periods, respectively. Venous concentrations of PGE₂ and PGF_2α were determined by radioimmunoassay procedures. Infusion of PGE₂ resulted in an immediate elevation in PGE₂ concentration in utero-ovarian venous drainage. Coincident elevations of PGF_2α utero-ovarian venous concentrations were observed after PGE₂ infusion. Plasma PGF_2α concentrations in the utero-ovarian veins were elevated (P<.01) in PGE₂ treated gilts for one hour post-treatment. The duration of PGE₂ and PGE₂α elevations as well as the peak values were influenced by day of the cycle.     

Methyl ethers of prostaglandins F2α and I2

Regiospecific monomethyl prostaglandin F₂α ethers (at 0–9, 0–11, and 0–15) have been prepared by total synthesis. The 9,15-bis-ether was also prepared. The 11- and 15-monoethers have been converted to the corresponding prostacyclins. Nuclear Magnetic Resonance (NMR) spectral comparisons indicate conformational changes associated with ether formation; nonetheless, the PGF₂α monoethers all retain significant biological activity: 3–420% of natural PGF₂α. The 9- and 15-methyl ethers show increased selectivity for luteolytic activity as measured in the hamster antifertility (HAF) assay. In contrast the prostacyclin ethers are essentially devoid of agonist activity on both the platelet and vasculature. Prostacyclin diastereomers [5a] also lack activity and it appears that any modification at or of the C-11 or C-15 functions reduces receptor binding by at least a factor of 100.     

Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy

The objectives were (1) to determine the effects of gonadorelin hydrochloride (GnRH) injection at controlled internal drug release (CIDR) insertion on Day 0 and the number of PGF2α doses at CIDR removal on Day 5 in a 5-day CO-Synch + CIDR program on pregnancy rate (PR) to artificial insemination (AI) in heifers; (2) to examine how the effect of systemic concentration of progesterone and size of follicles influenced treatment outcome. Angus cross beef heifers (n = 1018) at eight locations and Holstein dairy heifers (n = 1137) at 15 locations were included in this study. On Day 0, heifers were body condition scored (BCS), and received a CIDR. Within farms, heifers were randomly divided into two groups: at the time of CIDR insertion, the GnRH group received 100 μg of GnRH and No-GnRH group received none. On Day 5, all heifers received 25 mg of PGF2α at the time of CIDR insert removal. The GnRH and No-GnRH groups were further divided into 1PGF and 2PGF groups. The heifers in 2PGF group received a second dose of PGF2α 6 hours after the administration of the first dose. Beef heifers underwent AI at 56 hours and dairy heifers at 72 hours after CIDR removal and received 100 μg of GnRH at the time of AI. Pregnancy was determined approximately at 35 and/or 70 days after AI. Controlling for herd effect (P < 0.06), the treatments had significant effect on AI pregnancy in beef heifers (P = 0.03). The AI-PRs were 50.3%, 50.2%, 59.7%, and 58.3% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PRs were ranged from 50% to 62.4% between herds. Controlling for herd effects (P < 0.01) and for BCS (P < 0.05), the AI pregnancy was not different among the treatment groups in dairy heifers (P > 0.05). The AI-PRs were 51.2%, 51.9%, 53.9%, and 54.5% for No-GnRH + PGF + GnRH, No-GnRH + 2PGF + GnRH, GnRH + PGF + GnRH, and GnRH + 2PGF + GnRH groups, respectively. The AI-PR varied among locations from 48.3% to 75.0%. The AI-PR was 43.5%, 50.4%, and 64.2% for 2.5 or less, 2.75 to 3.5, and greater than 3.5 BCS categories. Numerically higher AI-PRs were observed in beef and dairy heifers that exhibited high progesterone concentrations at the time of CIDR insertion (>1 ng/mL, with a CL). In addition, numerically higher AI-PRs were also observed in heifers receiving CIDR + GnRH with both high and low progesterone concentration (<1 ng/mL) initially compared with heifers receiving a CIDR only with low progesterone. In dairy heifers, there were no differences in the pregnancy loss between 35 and 70 days post-AI among the treatment groups (P > 0.1). In conclusion, GnRH administration at the time of CIDR insertion is advantageous in beef heifers, but not in dairy heifers, to improve AI-PR in the 5-day CIDR + CO-Synch protocol. In addition, in this study, both dairy heifers that received either one or two PGF2α doses at CIDR removal resulted in similar AI-PR in this study regardless of whether they received GnRH at CIDR insertion.     

The use of PGF2α as ovulatory stimulus for timed artificial insemination in cattle

The objective of this study was to evaluate the effect of a PGF2α-analogue (PGF) on ovulation and pregnancy rates after timed artificial insemination (TAI) in cattle. In experiment 1, crossbred dual-purpose heifers, in a crossover design (3 × 3), were given an intravaginal progesterone-releasing insert (controlled internal drug release [CIDR]) plus 1 mg estradiol benzoate (EB) intramuscularly (im) and 250 μg of a PGF-analogue im on Day 0. The CIDR inserts were removed 5 days after follicular wave emergence, and the heifers were randomly divided into three treatment groups to receive the following treatments: (1) 1 mg of EB im (EB group, n = 13); (2) 500 μg of PGF im (PG group, n = 13); or (3) saline (control group, n = 13), 24 hours after CIDR removal. Ovulation occurred earlier in EB (69.81 ± 3.23 hours) and PG groups (73.09 ± 3.23 hours) compared with control (83.07 ± 4.6 hours; P = 0.01) after CIDR removal. In experiment 2, pubertal beef heifers (n = 444), 12 to 14 months of age were used. On Day 0, the heifers were given a CIDR insert plus 2 mg EB im. On Day 9, the CIDR was removed and the heifers were given 500 μg of PGF im. Heifers were randomly assigned into one of three treatment groups: (1) 1 mg of EB (EB group; n = 145); (2) 500 μg of PGF (PG group; n = 149), both 24 hours after CIDR removal; or (3) 600 μg of estradiol cypionate (ECP group; n = 150) at CIDR removal. Timed artificial insemination occurred 48 hours after CIDR removal in the ECP group and 54 hours in the PG and EB groups. The percentage of heifers ovulating was higher in the PG group compared with the other groups (P = 0.08). However, the pregnancy rates did not differ among groups (47.6%, 45%, and 46.6%, for EB, PG, and ECP, respectively; P = 0.9). In experiment 3, 224 lactating beef cows, 40 to 50 days postpartum with 2.5 to 3.5 of body condition score were treated similarly as described in experiment 2, except for the ECP group, which was excluded. The treatments were as follows: 1 mg EB (EB group; n = 117) or 500 μg PGF (PG group; n = 107), 24 hours after CIDR removal. The calves were temporarily separated from their dams from Days 9 to 11. No difference was detected on the pregnancy rate between the EB and PG groups (58.1% vs. 47.6%, respectively; P = 0.11). Taken together, the combined results suggested that PGF2α could be successfully used to induce and synchronize ovulation in cattle undergoing TAI, with similar pregnancy rates when compared with other ovulatory stimuli (ECP and EB).     

Comparative study of the biosynthesis of PGE2, PGF2α and TXA2 by different organs of genetically hypertensive (SHR) and obese-hypertensive (SHR-fa/fa) rats

As an experimental model, we used 6-week-old genetically obese-hypertensive rats (SHR-fe/fa) which were obtained by transferring the fatty/fa gene of hyperlipaemic obese rats into the genome of the SHR strain: the SHR-fa/fa were bigger and more hypertensive than their SHR littermates. Studying the capacitity of the hearts, kidneys, spleens, brains and lungs to synthesize PGE2, PGF2α and TXA2, enabled us to show that

• •- the hearts and lungs of SHR-fa/fa synthesized more PG than those of SHR
• •- DHR-fa/fs brains generated less icosanoids than those of SHR
• •- the amounts of PGE2 and TXA2 produced by the kidneys are similar in SHR and in SHR-fa/fa.

From the experimental data we can infer that the introduction of the fatty/fa gene into the genome of SHR does not significantly alter the capacity of the kidneys to synthesize icosanoids; the more severe hypertension in the SHR-fa/fa would result from an increase in TXA2 biosynthesis by cardiac tissue which, at the same time, synthesized more PGE2, which could be a means of defence against hypertension. Moreover this genetical manipulation inhibited the icosanoid-synthesizing capacity of the brain which thus attenuated the central nervous system activity of the animals.