PGF2α Metabolite Research Articles

Effect of food deprivation during early pregnancy on endocrine changes in primiparous sows

Abstract The effect of food deprivation during early pregnancy on maternal plasma endocrine levels and on embryonic survival was studied in primiparous sows. Twelve cross-bred (Swedish Yorkshire × Swedish Landrace) primiparous sows at the same stage of pregnancy were used. Six sows were fasted on Days 10 and 11 of pregnancy, with free access to water. The other six sows were fed as usual and used as controls. Blood samples were collected from Days 7 to 14 of pregnancy for cortisol, corticosteroid-binding globulin (CBG), progesterone (P4), oestradiol-17β (E2), oestrone sulphate and prostaglandin F2α metabolite (PG-metabolite) analysis. The sows were slaughtered on Day 17 of pregnancy and embryos recovered. Cortisol concentrations rose (P

Effect of oral administration of flunixin meglumine on the inflammatory response to endotoxin in heifers

Abstract Objective To compare the effect of oral and IV administrations of flunixin meglumine on the endotoxin-induced inflammatory response in heifers. Design The study was conducted in 2 experimental sets in which heifers were exposed to low IV doses of Escherichia coli endotoxin. Within each set, heifers were allocated to 3 treatment groups; pretreatment with flunixin meglumine orally and IV prior to endotoxin administration, or endotoxin administration only. The dose of flunixin used was the recommended therapeutic dose in cattle. Animals 11 clinically normal heifers weighing from 400 to 640 kg. Procedure A permanent cannula was inserted into the jugular vein on the day prior to the experiment. Blood samples were collected regularly during the experiment and analyzed for the content of prostaglandin F2α metabolite, Cortisol, blood mononuclear cells, and polymorphonuclear neutrophilic leukocytes and rectal temperature was measured. Results Endotoxin administration caused clinical signs and hematologic changes characteristic of endotoxemia in cattle. Flunixin administered orally prior to experimentally induced endotoxemia exerted an effect equal to that after its IV administration. Significant increases in rectal temperature and prostaglandin F2α metabolite concentrations after administration of endotoxin were abrogated when the heifers were pretreated with flunixin, irrespective of route of administration. Cortisol concentrations were lower after pretreatment with flunixin. However, flunixin did not prevent the decrease in blood mononuclear cells and polymorphonuclear neutrophilic leukocytes seen after endotoxin administration. Conclusion Owing to no major difference in the inflammatory response between oral and IV flunixin dosing, flunixin granules may be an alternative to parenteral use in bovine practice.

Influence of low plasma progesterone concentrations on the release of prostaglandin F 2α during luteolysis and oestrus in heifers

A study was conducted to determine the effect of suprabasal plasma concentrations of progesterone on the release of prostaglandin F 2α (PGF 2α) at luteolysis and oestrus. Heifers received silicone implants containing 2.5 ( n = 4), 5 ( n = 4), 6 ( n = 3), 7.5 ( n = 3), 10 ( n = 4), or 15 ( n = 3) g of progesterone, or an empty implant (controls, n = 4) between Days 8 and 25 post ovulation. Blood was collected frequently between Days 14 and 28 and assayed for progesterone and 15-ketodihydroprostaglandin F 2α. Basal progesterone concentrations in control heifers did not differ from those in heifers with 2.5- or 5-g implants and remained around 0.4−0.5 nmol l −1 until ovulation in all three groups. In the heifers treated with 6–15 g of progesterone, basal concentrations were maintained at higher ( P < 0.05) levels compared with those in the controls, ranging from 0.8 to 1.6 nmol 1 −1. The effect of these elevated progesterone levels was to delay ovulation by prolonging the growth of the ovulatory follicle, which continued growing until the implant was removed. In all experimental groups, the first significant increase of the PGF 2α metabolite occurred between Days 15.3 and 16.3 ( P > 0.05) and was associated with the onset of a decrease in progesterone concentrations, which had reached levels below 3 nmol 1 −1 by Days 17.4−19.1. PGF 2α metabolite peaks associated with luteolysis were frequent until Day 20. In the period from Day 20 until implant removal, sporadic peaks were observed, ranging in number from 1.0 ± 1.2 (mean ± SEM) in the control group to 3.0 ± 1.4 peaks in the heifers treated with 7.5 g of progesterone ( P > 0.05). The number of PGF 2α metabolite peaks during that period was higher ( P < 0.05) in heifers treated with 10 and 15 g than in controls. A positive correlation was found between the basal concentration of progesterone and the number of PGF 2α peaks after luteolysis ( r = 0.54; P < 0.01). Plasma progesterone concentrations above approximately 1.4 nmol l −1 were able to maintain the release of PGF 2α until the progesterone implants were removed and plasma levels decreased to basal values. These heifers had a preovulatory PGF 2α release pattern resembling that found in repeat breeder heifers.

Endocrine Changes after Mating in Pregnant and Non-Pregnant Llamas and Alpacas

Plasma concentrations of oestradiol-17 beta, progesterone, 15-keto-dihydro-PGF2 alpha and luteinizing hormone (LH) were monitored in llamas and alpacas after mating with an intact male. Concentrations of LH and PGF2 alpha metabolite were high immediately after copulation. Ovulation occurred in 92% of the animals. The first significant increases in progesterone were recorded on day 4 after mating. In non-pregnant animals the lifespan of the corpus luteum was estimated to be 8-9 days. Luteolysis occurred in association with the release of PGF2 alpha. In pregnant animals, a transient decrease in progesterone concentrations was observed between days 8 and 18 in both species. No significant changes in PGF2 alpha secretion were registered during this period. Oestradiol-17 beta concentrations were high on the day of mating, declined to low values on day 4, and started to increase again on day 8. Peak values after luteolysis in non-pregnant animals were significantly higher than those registered in pregnant ones. Furthermore, concentrations of oestradiol-17 beta were elevated for a longer period in non-pregnant than in pregnant animals. The results suggest that progesterone from the corpus luteum exerts a negative influence on follicular activity in pregnant animals by reducing oestradiol-17 beta secretion.

Hematological and Blood Biochemical Effects of Fasting and Subsequent Oral Administration of Endotoxin in Prepubertal Gilts

The main objective of the present study was to investigate the effects of short-term fasting in gilts on endocrinological and blood biochemical parameters and, further, the effects of subsequent oral endotoxin (ET) administration. Group 1 was fasted for 30 h and then received feed with ET added. Group 2 was fasted for 30 h but received standard feed at refeeding. In group 3, gilts were fed every 6 h for 30 h. The major effects of fasting were: gradually increased concentration of plasma prostaglandin F2α metabolite, serum total bilirubin, serum free fatty acids, and decreased serum glucose. The values were normalized within 1–4 h of refeeding. Twelve hours after refeeding, the ET-refed gilts showed higher levels of serum total bile acids and polymorphonuclear leukocytes than those in group 2. It is possible that the observed changes during fasting reflect either an increased intestinal uptake of naturally present endotoxin or a reduced endotoxin detoxifying capacity of the liver. The increased bile acid concentration and polymorphonuclear leukocyte count following refeeding with ET-feed may indicate that orally administered ET is to some extent absorbed from the gut.

Identification of functional high and low affinity states of the prostaglandin F2 alpha receptor in the ovine corpus luteumin vivo and their role in hormone pulsatility

Equivocal evidence has accumulated for the presence of high and low affinity receptors for PGF(2α) in the corpus luteum based on binding affinities of(3)H-PGF(2α) to cell membranes or separated whole cells. Some studies report only high affinity sites, while others report the occurrence of both high and low affinity sites. We have previously demonstrated, using subluteolytic levels of PGF(2α), the existence of functional high affinity luteal PGF(2α) receptors which show desensitization and recovery after 6 to 9 h. The present study, using direct intra-arterial infusions of PGF(2α) into the autotransplanted ovary in conscious sheep, was designed to probe for the existence of functional high and low affinity states of the PGF(2α) receptor in the corpus luteumin vivo. Subluteolytic and luteolytic concentrations of PGF(2α) (100 pg/min and 2500 pg/min, respectively) were infused sequentially, each for 2 h, into the ovary during the luteal phase (n=7 sheep). The same low and high concentrations of the inactive metabolite of PGF(2α) (PGFM) were given over the same time periods as negative controls (n=4 sheep). During the 2 h intra-arterial infusion of 100 pg/min of PGF(2α) the secretion rate of oxytocin increased (P<0.01) while the secretion rate of progesterone was unaffected. In contrast, during the 2 h intra-arterial infusion of 2500 pg/min of PGF(2α), secretion rate of oxytocin increased (P<0.01) and secretion rate of progesterone now began to decline (P<0.05). During the 2 h infusions of identical concent-rations of PGFM, the secretion rate of oxytocin and progesterone remained unchanged. These results indicate the existence of functional high and low affinity states of the PGF(2α) receptor within the ovine corpus luteumin vivo.

Effects of Calf Removal at Parturition on Postpartum Ovarian Activity in Zebu (Bos indicus) Cows in the Humid Tropics

To assess endocrine and morphological responses of ovaries to total weaning at parturition, 6 Zebu (Bos indicus) cows 5 years or older were investigated. Following parturition, blood samples were collected daily during the first month and twice weekly thereafter until day 60 to determine concentrations of progesterone (P4) and prostaglandin F2 alpha metabolite. It took between 25 to 32 days to complete uterine involution. The prostaglandin metabolite remained elevated for a mean period of 14.2 days (range, 4-21) postpartum. Five of the animals resumed cyclicity with a short estrous cycle starting between days 7 to 34 and lasting between 7 and 14 days. No estrous behavior was recorded prior to the short estrous cycles, but subsequent normal-length estrous cycles were all preceded by signs of estrus. In the 1 animal that resumed cyclicity with an estrous cycle of normal length on day 37 (length 20 days), the cycle was preceded by estrous behavior. Progesterone concentrations reached a mean maximum of 4.8 nmol liter-1 during the short estrous cycles, and prostaglandin metabolite concentrations peaked while P4 concentrations were decreasing. P4 concentrations reached a mean maximum of 12.2 nmol liter-1 during the estrous cycles of normal length. The interval from parturition to the first estrous cycle of normal length varied between 16 and 48 days, and the length of the cycle was 18 to 22 days. Starting 2 days postpartum, ovaries from 5 of the cows were scanned by ultrasonography every second day until day 30 postpartum. Medium-sized follicles were detected between days 4 to 7 postpartum in 4 of the scanned cows that later had short estrous cycles. The time between parturition and the appearance of the first dominant follicle was 7.6 days (range 6-10 days). The interval between parturition and the appearance of the first ovulatory-sized follicle was 10.2 days (range 8-13 days). In 3 of the scanned cows this ovulatory-sized follicle ovulated. We conclude that cyclic ovarian activity in Zebu cows can start early in the postpartum period in the absence of offspring, and that short luteal phases, not preceded by estrous behavior, may play an important role in establishing normal postpartum ovarian activity.

Prostaglandin F2α Metabolite Levels Following an Embryo Transfer Procedure in the Mare

Hormonal, chemical, and mechanical stimuli can activate the arachidonic acid cascade and result in formation of prostaglandins and related substances. These compounds can have a profound role in the initiation of the inflammatory process (Higgins & Lees 1984). Prostaglandin (PG) F2α is the key hormone in reproductive physiology with well-known effects on reproductive performance e.g. luteolysis and abortion. An activation of the arachidonic acid cascade, caused by mechanical manipulation during an embryo transfer procedure, might be one explanation for early embryonic loss.

Effect of mimicking prepartum concentration of estradiol-17β on the inflammatory response to endotoxin in gilts

Summary The effect of mimicking prepartum concentration of estradiol-17β on the inflammatory response to endotoxin in gilts was studied. The study was performed in a split-litter design and comprised 5 pairs of littermates. A catheter was inserted into the jugular vein 2 days prior to the start of the study. In each pair, 1 littermate was treated im with 2.5 mg of estradiol-17β/75 kg of body weight, and the other littermate was given peanut oil im as a control. The day after treatment, all gilts were challenge-exposed with a Salmonella typhimurium-derived endotoxin (1 µg/kg, iv) and the inflammatory response to challenge exposure was monitored. There was no effect of estradiol treatment on the transient clinical signs of endotoxemia or on the increase in rectal temperature. The increase in blood concentrations of prostaglandin F2α metabolite and cortisol after endotoxin challenge exposure was not affected by estradiol. Decrease in number of circulating blood mononuclear cells and polymorphonuclear leukocytes was not changed by estradiol treatment. Taken together, mimicking prepartum concentration of estradiol did not affect either the magnitude or the kinetics of the inflammatory response to endotoxin in gilts. Relevance of these findings to development of endotoxinmediated diseases, such as the postpartum agalactia syndrome, needs further study.

Effects of onapristone on uterine prostaglandin production and plasma progesterone concentrations in guinea-pigs during early and mid-pregnancy.

Onapristone (a progesterone receptor antagonist) administered to guinea-pigs on days 11-14 of pregnancy had no effect on uterine PGF2 alpha output and endometrial PGF2 alpha synthesizing capacity when measured on day 15. Peripheral plasma progesterone concentrations were still high on day 15, although the weight of the conceptuses was decreased by 50%. These findings indicate that the lack of increase in PGF2 alpha production by the uterus during early pregnancy is not due to an inhibitory action of progesterone on uterine PGF2 alpha synthesis and release. The output of PGF2 alpha from the guinea-pig uterus remained low during early pregnancy, showing that the uterus is not the source of increased PGF2 alpha secretion, as indicated previously by an increase in PGF2 alpha metabolite concentrations in the urine, after day 24 of pregnancy. Of the conceptual tissues examined, the fetal placenta had the highest PGF2 alpha synthesizing capacity, and it increased 2.3-fold between days 29 and 36 of pregnancy. The fetal placenta may therefore be the source of increased PGF2 alpha production during pregnancy. Onapristone administered to guinea-pigs on days 27 and 28 or on days 34 and 35 of pregnancy resulted in the guinea-pigs being in the early, middle or late stages of abortion when examined on days 29 or 36, respectively. Increased PG production, particularly of PGF2 alpha, by the uterus occurred in those guinea-pigs that were in the middle or late stages of abortion; uterine PG production in guinea-pigs that were in the early stages of abortion remained low.(ABSTRACT TRUNCATED AT 250 WORDS)

Bovine Acute Mastitis: Effects of Intravenous Sodium Salicylate on Endotoxin-Induced Intramammary Inflammation

Effects of the nonsteroidal anti-inflammatory agent sodium salicylate on endotoxin-induced mastitis were evaluated in lactating cows. Escherichia coli endotoxin was administered to a mammary quarter 1h after initiation of a 12-h i.v. infusion of sodium salicylate. Milk SCC, BSA concentrations in milk, mammary inflammation, rectal temperature, appetite, milk production, and plasma and lymph PGF2α, were monitored. Gross mammary inflammation was not reduced by salicylate infusion, nor did sodium salicylate prevent increased milk SCC or BSA concentrations in milk, although treatment tended to decrease the magnitude of these responses. Sodium salicylate decreased subcutaneous abdominal vein PGF2α, metabolite, and PGF2α, metabolite tended to be reduced in lymph during the acute phase of inflammation. The increased rectal temperature after endotoxin infusion was reduced in cows treated with sodium salicylate. Appetite was reduced after endotoxin infusion in untreated cows and those treated with sodium salicylate. Milk production declined after endotoxin challenge in all cows. Although sodium salicylate did not substantially reduce mammary inflammation, it had an antipyretic effect and reduced PGF2α metabolite in mammary blood.

A Study on the Effects of Inhibition of Prostaglandin Biosynthesis with Flunixin Meglumine and Later Administration of Prostaglandin F2α on the Intraluminal Pressure Variations in the Isthmus of the Oviduct in Unrestrained Gilts

Three gilts were each equipped with 2 ultra-miniature pressure sensors, placed at 2 different points along the same isthmus of the oviduct. Following base recordings of isthmic intraluminal pressure, the gilts were treated with 2.2 mg flunixin meglumine (FM) per kg body weight. After FM treatment, the peripheral plasma levels of 15-ketodihydro-PGF2α, the major metabolite of prostaglandin F2α (PGF2α), decreased within 30 min. The frequency of the phasic pressure fluctuations in the isthmus of the oviduct decreased after FM treatment. Exogenous administration of PGF2α increased the peripheral plasma levels of 15-keto- dihydro-PGF2α. When administered at a dose of 0.1 mg, PGF2α produced an increase in the frequency of the phasic pressure fluctuations in the oviductal isthmus. When the PGF2α dose was increased to 0.5 mg, a marked increase in the base and total pressures was seen in addition to the increase in the frequency of the phasic pressure fluctuations.

Effects of lumbar epidural analgesia on prostaglandin F 2α release and oxytocin secretion during labor

The concentrations of plasma oxytocin and prostaglandin F 2α metabolite (PGFM) were measured in 10 parturients with and 10 without lumbar epidural analgesia. A blood sample was taken immediately before analgesia and another 60 min later. The control patients were matched for the stage of cervical dilatation at the time of the first blood sample; the second was drawn 60 min later. Plasma PGFM decreased significantly after lumbar epidural anesthesia and increased in controls resulting in a highly significant difference between the groups (P < 0.005). Plasma oxytocin concentrations levels also changed in opposite directions in the two groups but the difference did not reach statistical significance (P < 0.1). Uterine activity increased in the controls and decreased in the analgesia group resulting in a significant difference between the groups (P < 0.05). All subjects delivered vaginally. The total duration of labor was longer in the analgesia group (7.8 ± 1.0 h vs. 4.7 ± 0.6 h; P < 0.05) as was the duration after analgesia (5.1 ± 0.9 h vs. 2.5 ± 0.8 h; P < 0.05), whereas the duration of the second stage was not significantly different. We conclude that lumbar epidural anesthesia results in suppression of PGF 2α release which may be the cause of the diminished uterine activity and the prolonged duration of the first stage of labor.

Effect of intrauterine bacterial infusions and subsequent endometritis on prostaglandin F2 alpha metabolite concentrations in postpartum beef cows.

Multiparous Angus and crossbred Angus cows were used to determine the effect of induced endometritis on plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) and progesterone (P4) and on duration of the estrous cycle of treatment. Beginning on the day of calving (d 0), blood samples were collected on alternate days. On three consecutive days, ranging from d 8 to 14 of the first postpartum estrous cycle, uterine horns were inoculated transcervically with either 3 x 10(9) colony forming units (cfu) of Actinomyces pyogenes and 1.5 x 10(9) cfu of beta-hemolytic Escherichia coli (treated; n = 9) in sterile PBS or with sterile PBS alone (control; n = 9). Samples of uterine fluid were collected by transcervical aspiration twice weekly from just before the start of each series of inoculations until the end of the experiment. Endometrial biopsies were collected transcervically between d 4 to 6 and 11 to 13 after inoculation. Based on clinical observations and results of bacterial cultures, all treated cows developed acute uterine infections. Controls did not develop uterine infections. Endometrial biopsies indicated that there were no significant diffuse or focal cellular reactions in response to the infection. The interestrous interval was greater (P less than .0003) for treated (27.7 +/- 1.0 d) than for control (20.6 +/- 1.0 d) cows, but P4 concentrations were similar between the two groups. Mean PGFM concentration and PGFM profiles were similar (P greater than .10) between treated and control cows before bacterial infusions. Bacterial infusions increased mean PGFM concentration (P less than .0001) and changed the shape of the PGFM profile (P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of progesterone treatment on the oxytocin-induced prostaglandin F2 alpha response and the levels of endometrial oxytocin receptors in ovariectomized ewes.

The oxytocin-induced uterine prostaglandin (PG) F2 alpha response and the levels of endometrial oxytocin receptors were measured in ovariectomized ewes after they had been given steroid pretreatment (SP) with progesterone and estrogen to induce estrus (day of expected estrus = Day 0) and had subsequently been treated with progesterone over Days 1-12 and/or PGF2 alpha over Days 10-12 postestrus. The uterine PGF2 alpha response was measured after an i.v. injection of 10 IU oxytocin on Days 13 and 14, using the PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), as an indicator for PGF2 alpha release. The levels of oxytocin receptors in the endometrium were measured on Day 14. During the treatment with progesterone, the peripheral progesterone concentrations were elevated and remained above 1.8 ng/ml until the morning of Day 14. The PGFM responses to oxytocin in untreated controls and SP controls were low on both Days 13 and 14 whereas the levels of endometrial oxytocin receptors in the same ewes were high. Treatment with progesterone either alone or in combination with PGF2 alpha significantly (p less than 0.04) increased the PGFM response on Day 14 and reduced the levels of endometrial oxytocin receptors; treatment with PGF2 alpha alone had no effect. It is concluded that progesterone promotes the PGFM response to oxytocin while simultaneously suppressing the levels of endometrial oxytocin receptors. PGF2 alpha treatment had no effect on either the uterine secretory response to oxytocin or the levels of oxytocin receptors in the endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovine conceptus secretory proteins and bovine recombinant interferon alpha (1)-1 decrease endometrial oxytocin receptor concentrations in cyclic and progesterone-treated ovariectomized ewes.

A series of experiements was performed to determine whether proteins produced by the sheep conceptus (oCSP) during the time of maternal recognition of pregnancy or bovine recombinant interferon alpha 1-1 (brIFN) decrease oxytocin receptor concentrations in the endometrium of cyclic or ovariectomized progesterone-treated ewes. In experiment 1, cyclic ewes received intrauterine infusions of serum proteins (oSP), oCSP or brIFN on days 12, 13 and 14 of the oestrous cycle. Ewes then received an oxytocin challenge (1 microgram in 0.9% NaCl), and blood samples were taken just before and every 10 min for 1 h after the challenge; these were measured for 13,14-dihydro-15-ketoprostaglandin F 2 alpha (PGFM), the stable metabolite of prostaglandin F 2 alpha. Endometrial oxytocin receptor concentrations were then measured. The oCSP and brIFN treatments suppressed both endometrial oxytocin receptor concentrations and oxytocin-induced increases in PGFM concentrations. In experiment 2, ewes were ovariectomized and then pretreated with a fluorogestone acetate-releasing intravaginal device for 10 days followed by oestradiol (25 micrograms i.m. twice daily for 2 days). Ewes were then treated with progesterone (10 mg i.m. twice daily for 12 days). Ewes received intrauterine infusions of oSP, oCSP and brIFN on days 10, 11 and 12 of progesterone treatment. On the day after the last progesterone treatment, ewes were challenged with oxytocin and blood samples collected to measure PGFM. Endometrial oxytocin receptors were also measured. Treatment with oCSP, but not brIFN, suppressed endometrial concentrations of oxytocin receptor, and neither oCSP nor brIFN altered oxytocin-induced increases in PGFM concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of constant infusion of oxytocin on luteal lifespan and oxytocin-induced release of prostaglandin F 2α in heifers

Two experiments were conducted to determine whether constant infusion of oxytocin would prolong the luteal phase and inhibit uterine prostaglandin F 2α (PGF 2α) secretion in heifers. In Experiment 1, twelve heifers, treated with saline (SAL) or oxytocin (OXY) via jugular cannulae infusions (INF) or osmotic minipumps (OMP), were allotted at estrus into four treatment groups (n = 3). Treatments were: SAL-INF, SAL-OMP, OXY-INF and OXY-OMP. Physiological saline or oxytocin was given from Days 10 to 23 (Day 0 = estrus) of the estrous cycle. Method of treatment (jugular cannula infusion or osmotic minipump) had no effect (P > 0.05) on estrous cycle length or pattern of secretion of progesterone; therefore, data were pooled. Estrous cycle lengths were extended (P < 0.01) for heifers which received oxytocin (25.3 ± 0.4 d) compared to saline (20.5 ± 0.4 d). Luteolysis did not occur in oxytocin-treated heifers until after treatment ceased. Experiment 2 was designed and conducted identically to Experiment 1 with the addition of a “challenge” injection of oxytocin (100 IU oxytocin, i.v.) given on Day 16 of the estrous cycle. Treatment of heifers with oxytocin extended (P < 0.05) estrous cycle length by an average of 3 d compared to heifers treated with saline. The “challenge” injection induced (P < 0.05) secretion of PGF 2α (as measured by the stable PGF 2α metabolite, 15-keto-13,14-dihydro-PGF 2α) in saline-treated but not oxytocin-treated heifers. In both Experiment 1 and 2, serum concentrations of FSH were elevated (P < 0.05) in oxytocin-treated heifers. No increase was observed for LH or prolactin. The rise in estradiol-17β at luteolysis was not affected (P > 0.10) by treatment. In summary, constant infusion of oxytocin extended luteal lifespan, prolonged secretion of progesterone, and inhibited oxytocin-induced secretion of PGF 2α. Constant infusion of oxytocin did not affect serum concentrations of estradiol-17β, LH or prolactin; however, serum concentrations of FSH were elevated during the oxytocin treatment period.

Plasma Levels of Prostaglandin F2α Metabolite and Progesterone in Repeat Breeder Heifers

A detailed clinical-endocrine investigation was performed in 6 repeat breeder heifers (RBH) with the aim being to ascertain whether endocrine asynchronism exists at luteal regression and during early pregnancy. The heifers were first studied during an open cycle and then after insemination when 3 heifers became pregnant. Circulating plasma levels of PGF2 alpha metabolite were measured every 2nd h, while progesterone (P4) levels were measured every 6th h. The oestrous period and intervals between the onset of oestrus and ovulation were relatively longer, compared with what is normally seen in heifers. Plasma levels of P4 at the onset of oestrus were higher than normal, but it was concluded that the plasma levels of PGF2 alpha metabolite and P4 in RBH at luteal regression and early pregnancy were normal.

First Postpartum Luteal Function in Dairy Cows After Ovulation Induced by Progestogen and Gonadotropin-Releasing Hormone

The objective was to determine the effects of progestogen treatment on the lifespan of the first corpus luteum induced by GnRH in periparturient-milked cows. Dairy cows (n = 55) were assigned randomly following normal parturitions to receive either a progestogen implant (6mg of norgestomet) or a blank implant (control) for 6 d beginning 2 to 5 d after calving. Fifty micrograms of GnRH were administered i.m. 72h after implant removal to induce ovulation. Concentrations of LH and FSH in serum from 24 to 30h and from 66 to 72h after implant removal were similar among treatments. The magnitude of LH released after GnRH injection was higher in progestogen-treated cows (7.6±.9ng/ml) than in controls (5.3±.9ng/ml). Concentrations of estradiol in serum from the beginning of the implant period until 3 d after GnRH injection were higher in cows receiving progestogen (9.1±1.7 pg/ml) than in controls (5.6±1.7 pg/ml). The proportion of cows that responded to GnRH (elevated concentration of progesterone in serum greater than .5ng/ml within 3 to 5 d after injection) tended to be higher in cows receiving progestogen (24 of 28) than in control cows (19 of 27). By definition, interval to first ovulation after GnRH injection was shorter in cows responding to GnRH (3.8±.5 d) than in those failing to respond (20.2±.9 d). Fewer cows had short (3 to 10 d) luteal phases when treated with progestogen implants (3 of 22) when compared with those controls (7 of 19). Concentrations of 13,14-dihydro-15-keto-prostaglandin F2α in serum were lower in progestogen-treated cows than in controls for 12 d after GnRH injection. We conclude that progestogen treatment had a priming effect on hypothalamic-pituitary function resulting in increased LH release after GnRH injection. These progestogen-mediated changes in LH secretion followed increased secretion of estradiol by preovulatory follicles and resulted in decreased concentrations of prostaglandin F2α metabolite in periparturient milked cows that was associated with prolonged postovulatory luteal function.

Effect of seminal oestrogens of the boar on prostaglandin F 2α release from the uterus of the sow

Boar semen is rich in oestrogens which lead to an increase of the myometrial contraction frequency in the sow at day 0 (onset of standing heat). To clarify whether this effect is mediated by an endometrial release of prostaglandin F 2α (PGF 2α) two experiments were carried out. 1. (1) Transcervical intrauterine infusion of 10 μg oestradiol in 100 ml saline led to an increase of PGF 2α in utero-ovarian vein plasma of three chronically cannulated sows within 2 min. Elevated concentrations were measured for 40 min. The maximum at 6 min was 4-fold compared to the period before infusion. Oestrone-sulphate (10 μg in 100 ml saline) led to a minor rise (2.5-fold) for only 10 min, saline alone had no effect. 2. (2) Measurements of the PGF 2α metabolite (PGFM) in peripheral plasma of other sows were carried out for a systematic evaluation. No apparent change was found over a 6-h period in sows which were not infused (controls, n = 7). Both infusion of saline (100 ml, n = 7) and saline with oestrone (10 μg, n = 6) 1 h after the onset of sampling led to only a slight increase during the first hour after treatment (saline 0.79 vs. 1.17 ng/ml, P ≤ 0.01; oestrone 0.78 vs. 0.99 ng/ml, P ≤ 0.01) due to mechanical stimulation. Oestrone-sulphate (10 μg, n = 6) increased the concentrations 2-fold (0.92 vs. 2.2 ng/ml, P ≤ 0.01). The increase was paralleled by a peripheral increase in oestrone-sulphate concentrations. Both the infusion of oestradiol (10 μg, n = 5) and mating ( n = 6) led to a pronounced peripheral rise of PGFM which was up to 3.5-fold ( P ≤ 0.001) after oestradiol and up to 2.5-fold ( P ≤ 0.001) after mating when compared to the control period. Both patterns of increased PGFM concentrations were reflected by a similar course of oestradiol concentrations in peripheral plasma. Mating led to a biphasic release of PGFM (2.7 ng/ml at 10 min, 2.6 ng/ml at 80 min) and also a biphasic pattern of peripheral oestradiol was measured. This biphasic course is explained by an immediate effect of seminal plasma oestrogens and a later effect of oestrogens which are bound to the sperm surface. It is concluded that oestrogens lead to a release of PGF 2α from the endometrium. This release explains an increase of the contraction frequency reported earlier.