PGF2α Administration Research Articles

Estrous behavior and the estrus-to-ovulation interval in nelore cattle ( [formula omitted] with natural estrus or estrus induced with prostaglandin F2α or norgestomet and estradiol valerate

Estrous behavior and the estrus-to-ovulation interval are essential for estimating the best time to artificially inseminate cattle. Because these parameters are not well characterized in the Nelore breed ( Bos indicus ), the main purpose of the this study was to determine the estrus-to-ovulation interval in Nelore heifers and cows with natural estrus or with estrus induced by treatments with PGF2α or norgestomet and estradiol valerate (NEV). The cows and heifers were observed continuously (24 h a day) to determine the onset of estrus and to study estrous behavior in the cows. Ten hours after the start of estrus the ovaries were scanned every 2 h by ultrasonography to monitor the dominant follicle until ovulation. Blood samples were collected periodically to determine progesterone levels by RIA. Administration of PGF2α (2 injections, 11 days apart) did not induce estrus in most Nelore females in spite of the presence of functional CL, indicated by progesterone concentrations above 6.0 ng/ml in 25 of 28 animals. Treatment with NEV induced high sexual receptivity in cows ( 10 11 ), but only 66% ovulated. Cows with natural or induced estrus exhibited behavioral estrus of 10.9 ± 1.4 h, and ovulation occurred 26.6 ± 0.44 h (n=26) after the onset of estrus. In most of the cows (53.8%) estrus began at night (between 1801 and 600 h), and 34.6% it started and finished during the night. It is concluded that in Nelore females ovulation occurs approximately 26 h after the onset of estrus. Additionally, estrous behavior is shorter than in European breeds, and there is a high incidence of estrus at night, which makes it difficult to detect and, consequently, impairs Al in Nelore cattle. The observation that a high percentage of Nelore females with an active CL did not respond to usual dosages of PGF2α warrants further investigation.

Messenger ribonucleic acid encoding monocyte chemoattractant protein-1 is expressed by the ovine corpus luteum in response to prostaglandin F2alpha.

To investigate expression of monocyte chemoattractant protein-1 (MCP-1) in the ovine corpus luteum, a partial cDNA was produced by reverse transcription-polymerase chain reaction. This cDNA was 89% identical to that reported for bovine MCP-1 mRNA. In experiment 1, steady-state concentrations of mRNA encoding MCP-1 were measured in pools of luteal tissue collected on Days 3, 6, 9, 12, and 15 of the estrous cycle (estrus = O; n = 4/day). There were no differences in mRNA concentrations for MCP-1 among any of the days studied (p = 0.43). In experiment 2, midluteal-phase corpora lutea were collected from ewes at 0 (untreated), 2, 4, 8, and 16 h after administration of a luteolytic dose of prostaglandin F2alpha (PGF2alpha; n = 4/time point). Concentrations of MCP-1 mRNA were undetectable in untreated controls, were detectable at 2 h post-treatment, had increased 4 and 8 h after administration of PGF2alpha when compared to those at 2 h (p < 0.05), and were decreased 16 h after administration of PGF2alpha when compared to those at 4 h (p < 0.05). In situ hybridization for MCP-1 mRNA combined with immunocytochemical labeling of tissue inhibitor of metalloproteinase-1 (TIMP-1) in large luteal cells was used to determine whether the steroidogenic cells that have PGF2alpha receptors express MCP-1 mRNA in response to PGF2alpha. Messenger RNA encoding MCP-1 and TIMP-1 were not colocalized, indicating that MCP-1 was not expressed by large steroidogenic luteal cells during luteolysis.

Hormonal regulation of monocyte chemoattractant protein-1 messenger ribonucleic acid expression in corpora lutea.

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that attracts monocytes and macrophages. It is known that macrophages accumulate in the corpus luteum (CL) during luteal regression in many species. In this study, we investigated the regulation of MCP-1 mRNA in ovine and bovine CL during prostaglandin (PG) F2alpha-induced luteolysis, after LH treatment, or after pharmacologic activation of the protein kinase (PK) A or PKC intracellular effector systems. In experiment 1, ewes on day 11 or 12 of the estrous cycle were infused with saline or PGF2alpha. PGF2alpha increased MCP-1 mRNA at 1 and 4 h after treatment. MCP-1 mRNA returned to basal level at 12 h and increased again at 24 h post treatment. In experiment 2, ewes received saline, PGF2alpha, phorbol 12-myristate 13-acetate (PMA), luteinizing hormone (LH), or forskolin infusion and CL were collected at 0 (untreated), 4, 12, or 24 h after infusion. Similar to experiment 1, PGF2alpha induced MCP-1 mRNA at 4 and 24 h post treatment. PMA increased mRNA for MCP-1 at 4, 12, and 24 h. Treatment with LH or forskolin transiently decreased MCP-1 mRNA expression. In experiment 3, cows were treated with a luteolytic dose (25 mg) of PGF2alpha on day 4 or day 11 of estrous cycle and expression of MCP-1 mRNA was quantified. Steady-state concentrations of mRNA for MCP-1 were induced by PGF2alpha treatment only in mid-cycle CL but not in early CL. In summary, administration of PGF2alpha or activation of PKC induced MCP-1 mRNA expression. Expression of MCP-1 may be important for stimulating immune processes during luteal regression.

Hormonal Regulation of Monocyte Chemoattractant Protein-1 Messenger Ribonucleic Acid Expression in Corpora Lutea

Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that attracts monocytes and macrophages. It is known that macrophages accumulate in the corpus luteum (CL) during luteal regression in many species. In this study, we investigated the regulation of MCP-1 mRNA in ovine and bovine CL during prostaglandin (PG) F2α-induced luteolysis, after LH treatment, or after pharmacologic activation of the protein kinase (PK) A or PKC intracellular effector systems. In experiment 1, ewes on day 11 or 12 of the estrous cycle were infused with saline or PGF2α. PGF2α increased MCP-1 mRNA at 1 and 4 h after treatment. MCP-1 mRNA returned to basal level at 12 h and increased again at 24 h post treatment. In experiment 2, ewes received saline, PGF2α, phorbol 12-myristate 13-acetate (PMA), luteinizing hormone (LH), or forskolin infusion and CL were collected at 0 (untreated), 4, 12, or 24 h after infusion. Similar to experiment 1, PGF2α induced MCP-1 mRNA at 4 and 24 h post treatment. PMA increased mRNA for MCP-1 at 4, 12, and 24 h. Treatment with LH or forskolin transiently decreased MCP-1 mRNA expression. In experiment 3, cows were treated with a luteolytic dose (25 mg) of PGF2α on day 4 or day 11 of estrous cycle and expression of MCP-1 mRNA was quantified. Steady-state concentrations of mRNA for MCP-1 were induced by PGF2α treatment only in mid-cycle CL but not in early CL. In summary, administration of PGF2α or activation of PKC induced MCP-1 mRNA expression. Expression of MCP-1 may be important for stimulating immune processes during luteal regression.

GnRH improves the recovery rate and the in vitro developmental competence of oocytes obtained by transvaginal follicular aspiration from superstimulated heifers

In this study we assessed the effect of GnRH on the recovery rate, meiotic synchronization and in vitro developmental competence of oocytes recovered close to the expected time of ovulation. Twenty-three heifers were superstimulated with FSH, and luteolysis was induced by PGF 2α injection 48 h after the start of treatment Twelve heifers received 200 μg GnRH at 34 h after PGF 2α treatment, Blood samples were collected between 35 to 47 h after PGF 2α administration to determine the time of the LH surge. Transvaginal follicular aspiration was performed at 60 h after PGF 2α, and the recovered oocytes were fertilized or fixed either immediately or after 24 h of maturation in vitro. GnRH-treated heifers showed an LH surge within 3 h after treatment, while only 4 of the 10 heifers in the control group exhibited an LH surge by 47 h after treatment with PGF 2α. The average number of large follicles (> 10 mm) was 21.3 ± 2.3 and 19.3 ± 2.4 for GnRH-treated and control heifers, respectively. The oocyte recovery rate was 87.7 and 63.1% (P < 0.05), respectively, and most of the cumulus-oocyte-complexes (COC) recovered from the 2 groups had an expanded cumulus (80.4 and 80.5%, respectively). Oocytes with an expanded cumulus from the GnRH group had completed meiotic maturation at higher rate than the controls (97 vs 20%;P < 0.05). In vitro development to the blastocyst stage of cumulus-expanded oocytes fertilized immediately after recovery was higher in GnRH-treated than in control heifers (60.3 vs 40.0%; P < 0.05). No difference was observed when oocytes with compact or expanded cumulus were matured in vitro for 24 h before fertilization. These results indicate that GnRH injections improve the oocyte recovery rate and that oocytes have a higher development competence than those obtained from non-GnRH-treated animals. We propose that this higher in vitro developmental competence may result from a more synchronous or further advanced meiotic maturation. However, due to the small number of oocytes in our study, we must emphasize that our findings on meiotic resumption are of preliminary nature.

Effect of the isoprostanes, 8-iso prostaglandin E 2 and 8-iso prostaglandin F 2α on the rabbit lung in vivo

8-Iso-prostaglandin (PG)E 2 and 8-iso-PGF 2α are members of the isoprostane class of prostanoids which are formed by free radical mediated oxidation of arachidonic acid. Both E 2- and F 2-isoprostanes are potent vasoconstrictors and are believed to act through the prostanoid TP-receptors or a closely related receptor. In lightly anaesthetised, spontaneously breathing rabbits, aerosolised administration of histamine ( (1.25–40 mg ml −1, n = 8) caused a modest dose-dependent increase in total lung resistance (R L) and a concomitant fall in dynamic lung compliance (C L dyn). Aerosolised methacholine (0.625 – 20 mg ml −1, n = 6) caused considerable bronchoconstriction, with a dose-dependent increase in R L, and a corresponding fall in C L dyn. In contrast, intratracheal administration of either 8-iso PGE 2 or 8-iso-PGF 2α (1ng ml −1, − 100μg ml −1, n = 8) had no significant effect on lung function. The TP-receptor agonist, U-46619, was similarly inactive in this model when given by aerosol. Intravenous administration of histamine or 8-iso PGF 2α, had no significant effect on the lung indices, R L and C L dyn, or on the pulmonary and systemic vasculature (n = 4 per drug group). 8-Iso PGE 2 caused a concentration-dependent decrease in the right ventricular systolic pressure from 3 nmol kg −1 to 100 nmol kg −1 (n = 4, p < 0.05), but showed no other activity. In contrast, U-46619 given intravenously caused an increase in transpulmonary pressure (n = 4, p < 0.05), but had no effect on airflow. At higher doses, it did cause a significant drop in both systemic and right ventricular systolic pressures (n = 4, p < 0.05), which were probably due to an interaction with platelets. The isoprostanes had no effect on the rabbit airway up to a concentration of 3μM. In contrast, 3μM U-46619 caused a modest contraction of tracheal smooth muscle, whilst 3μM methacholine was at least five-fold more potent in contracting the same tissues. We conclude that the aerosolised isoprostanes are not broncho-constriciting agents in the rabbit in vivo.

Prostaglandin F2α reduces steroidogenic acute regulatory (StAR) protein messenger ribonucleic acid expression in the rat ovary

Steroid biosynthesis begins with the enzymatic conversion of cholesterol to pregnenolone. This reaction is catalyzed by the cytochrome P450 side-chain cleavage enzyme (P450scc), which is located on the matrix side of the inner mitochondrial membrane. Although the rate-limiting enzymatic step in steroidogenesis is the conversion of cholesterol to pregnenolone by the side-chain cleavage enzyme, the true rate-limiting step in this process is the delivery of cholesterol to the inner mitochondrial membrane. Steroidogenic acute regulatory (StAR) protein is thought to mediate the rapid increase in steroid hormone biosynthesis in response to tropic hormones by facilitating cholesterol transport to the inner mitochondrial membrane. Cholesterol transport across the inner mitochondrial membrane has also been implicated as the target for prostaglandin F2α's (PGF2α) antisteroidogenic activity. Since cholesterol delivery to the P450scc is a rapidly regulated step in steroidogenesis, StAR mRNA levels were examined after the administration of a luteolytic injection of PGF2α. The results of this investigation revealed that both major StAR RNA transcripts were decreased in the ovary, 10 d after ovulation, following PGF2α administration. Serum progesterone levels were decreased following PGF2α administration in parallel with the decreased expression of StAR. Following PGF2α treatment, ovarian StAR transcripts at 3.4 and 1.6 kb were reduced 4-fold (p<0.01) and 2.5-fold (p<0.025), respectively, after 4 h. Ovarian P450scc mRNA levels were also reduced (70%) 4 h after PGF2α injection. Time course experiments following PGF2α administration showed a significant decrease in StAR expression as early as 30 min (p<0.02) following injection. In contrast to StAR's expression after PGF2α administration, StAR mRNA levels were elevated in response to human chorionic gonadotropin (hCG) 3 h postinjection. Administration of PGF2α followed by hCG injection effectively blocked induction of StAR expression. StAR mRNA levels were reduced 1.5-fold relative to control animals and 3.5-fold relative to the hCG-treated animals (p<0.05). The levels of serum progesterone paralleled the change in ovarian StAR mRNA in all experiments. This study provides the first evidence that StAR mRNA expression is mediated by prostaglandins in the rat ovary further supporting its important role in the regulation of steroid hormone biosynthesis.

Effects of prostaglandin F 2α, cloprostenol and fenprostalene on uterine clearance of radiocolloid in the mare

Uterine clearance of radiocolloid was measured by scintigraphy in 5 reproductively normal mares and in 4 mares exhibiting a delay in uterine clearance (DUC) after administration of PGF 2α, cloprostenol or fenprostalene. Scintigraphy studies were performed on the second or third day of estrus during 3 consecutive estrous cycles. Drugs, PGF 2α (5 mg IM), cloprostenol (CLO; 2mg IM) or fenprostalene (FEN; 250 μg subcutaneously) were given in random order, with only 1 drug given each estrus. Treatment response curves were generated, and the effect of each drug on uterine clearance of radiocolloid was compared to the clearance of radiocolloid when no drug was given and between treatments. In reproductively normal mares, CLO and PGF caused a rapid clearance of radiocolloid within 60 min (P < 0.01), with <25% of the initial dose of radiocolloid (% IDR) remaining by 120 min. Mean percentage of IDR at 120 min when no drug was given was 39% ± 4. Response of reproductively normal mares to FEN varied, with 3 mares clearing > 85% and 2 mares clearing <35%. In mares exhibiting DUC, all 3 drugs (CLO, PGF and FEN) caused rapid clearance of radiocolloid from the uterus by 60 min (P < 0.0001). Mares cleared significantly more colloid after treatment with CLO at 60 and 120 min than after PGF (P < 0.001). In conclusion, CLO appears to be the best drug of the 3 tested for stimulating clearance of intrauterine fluid since variation in response was observed following treatment with PGF and FEN.

Testosterone secretion during early pregnancy in mares

We have characterized the testosterone secretion pattern during the first 80 d of pregnancy in mares and determined the sources that contribute to circulating testosterone levels during this period. Ten untreated, pregnant mares (Group 1), 10 altrenogest-treated, pregnant mares (Group 2), and 10 altrenogest-treated, pregnant mares in which the CL was eliminated by administration of PGF-2α on Day 16 (Group 3) were used in this study. Complete luteolysis occurred following PGF-2α administration in all mares in Group 3. Six of the 10 mares in Group 3 did not have an active CL until after Day 60 of pregnancy (Group 3a) and were included in the analysis. The remaining four mares developed a new CL on Days 32, 40, 43 and 49 of pregnancy and were excluded from analysis. Mares without a functional CL (Group 3a) had significantly lower testosterone concentrations than mares with a functional CL (Groups 1 and 2), during the period before equine chorionic gonadotropin (eCG) secretion. At the onset of eCG secretion, testosterone concentrations increased rapidly but the rate of increase decreased with time in mares with a functional CL (Groups 1 and 2). In mares without a functional CL (Group 3a), testosterone concentrations did not increase at the onset of eCG secretion but increased at a gradually increasing rate after Day 50. The lower testosterone concentration in mares without a functional CL before eCG secretion suggests that the CL contributes significantly to the circulating testosterone concentration during the period before eCG secretion. The close time relationship between the onset of eCG secretion and the increase in testosterone secretion in mares with a functional CL and the lack of a testosterone increase in pregnant mares without a functional CL suggest that the increase in testosterone secretion after Day 35 of pregnancy is the result of eCG-stimulated, luteal testosterone synthesis.

Comparison of mRNA levels for the PGF2α receptor (FP) during luteolysis and early pregnancy in the ovine corpus luteum

Prostaglandin F(2α) (PGF(2α)) is the physiological signal that triggers luteolysis in the non-pregnant ewe. This is associated with a decline in circulating levels of progesterone, beginning around day 14 of a 16-17 day estrous cycle. Recently, the receptor for PGF(2α) (FP) was cloned from an ovine day 10 large luteal cell cDNA library. The purpose of this study was to measure relative abundance of FP mRNA as it may change with luteolysis during the luteal phase. Corpora lutea (CL) were collected from ewes on day 10, 12, 14 or 16 (n≥4/day; day 0=synchronized estrus); 12 h after PGE(2α)-treatment on day 10, 12 or 14 (n≥3/day) of the estrous cycle; or on day 16 of pregnancy (n=6). Pregnancy was confirmed by visualization of the conceptus. Blood samples were collected 12 h prior to and at the time of tissue collection to determine levels of progesterone. Serum concentrations of progesterone declined with the onset of luteolysis in control animals (day 14, day 16;P<0.05) as well as 12 h following PGF(2α)-treatment (day 10, day 12;P<0.05). Genomic DNA from these tissues was prepared and visualized by agarose gel electrophoresis. Internucleosomal fragmentation (indicative of apoptosis) was seen in CL from animals in which luteolysis had been initiated (all PGE(2α)-treated and day 16 control ewes), but not in ewes with functional CL. Total RNA isolated from each CL was separated through a denaturing 1% agarose gel, transferred to nylon membranes and hybridized to a radioactive ovine FP cDNA probe. Hybridization to a radiolabeled 18S ribosomal cRNA probe was used to confirm equal loading of RNA in each lane. By northern analysis, a major transcript was seen at ∼6.1 kb. A relatively high level of FP mRNA was measured in CL collected from control non-pregnant ewes during the mid luteal phase (day 10, 2.73±0.17; day 12, 2.47±0.91; FP/18S ratio), but varied among animals (3.09±1.59) on day 14. Administration of PGF(2α) resulted in the lowest amounts of FP mRNA on days 10, 12, and 14 (P<0.05). Amounts of FP mRNA were higher (P<0.05) on day 16 of pregnancy as compared to day 10 (by 1.9-fold) or to day 16 (by 5.9-fold) of the estrous cycle. From these observations we conclude that PGF(2α) or some event associated with luteolysis appears to down regulate amounts of the FP mRNA. Furthermore, pregnancy, and/or the antiluteolytic signals associated with maternal recognition of pregnancy may prevent the decline in the amount of FP mRNA.

Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate, 48-hour calf removal and PGF 2α

One hundred and sixty-five suckled postpartum beef cows were utilized to evaluate the effectiveness of 2 estrus synchronization systems for the initiation and synchronization of estrus. The treatment groups consisted of 1) melengestrol acetate (MGA)-PGF 2α (cows were given 0.5 mg MGA/head/day for 14 d with 25 mg PGF 2α injected 17 d after the last day of MGA administration); 2) MGA-48-h calf removal (CR)-PGF 2α (cows were given 0.5 mg MGA/head/day for 14 d with 48-h calf removal starting on the second day after completion of the MGA regimen plus 25 mg PGF 2α administered 17 d after the last day of MGA); and 3) unsynchronized controls. Cows were assigned to treatments by the numbers of days post partum, body condition, age, and breed of sire. The cows were observed for estrus at 12-h intervals for 5 d after PGF 2α administration and were artificially inseminated 12 to 18 h after the observed estrus. Both the MGA-PGF 2α and MGA-CR-PGF 2α treatments (64.8 and 61.8%) had greater (P < 0.05) 5-d estrus rates than the control treatments (34.5%). The synchronized pregnancy rate was greater (P < 0.05) for the MGA-CR-PGF 2α than the control treatment.(52.7 vs 30.9%, respectively). The MGA-CR-PGF 2α cows had a higher 25-d pregnancy rate than either the MGA-PGF 2α (P < 0.05) or control cows (P < 0.08). Of the anestrous cows at the beginning of treatment, more MGA-CR-PGF 2α (P = 0.1) and MGA-PGF 2α cows were cyclic posttreatment than control cows (58.7 and 55.1 vs 44.7%, respectively), suggesting that treatment initiated estrous cycles in only a small number of the anestrous cows. Both MGA-PGF 2α and MGA-CR-PGF 2α treatments appear to be effective methods of synchronizing estrus in suckled postpartum beef cows. However, MGA-CR-PGF 2α was more effective in establishing pregnancy earlier in the breeding season than MGA-PGF 2α.

The effects of exogenous gonadotropins on oocyte and embryo quality in cattle

It is well documented and unfortunately accepted that approximately 15 to 20% of all donor cattle superstimulated with eCG or FSH yield no transferable embryos. In the present paper, some factors leading to reduced oocyte and embryo quality are discussed. We have focused firstly on certain endocrine and oocyte maturational features which take place during the period of luteal regression, i.e. the period from PGF2α administration until the preovulatory LH surge, and secondly, on the relationship between the superovulatory response and the embryo quality on Day 7. We conclude that: 1) treatment with eCG or FSH causes increased estradiol-17β plasma levels, suppressed episodic LH secretion, earlier occurrence of the LH surge and the nucleoli of oocytes from undergoing the normal vacuolization in a certain proportion of donor cattle, 2) although subtle and hardly measurable, these deviations have a profound effect on the subsequent embryonic developmental capacity, 3) the superovulatory response does not affect the subsequent viability of embryos transferred on Day 7 and 4) optimization of the donor's reproductive physiology is the only way to reduce the incidence of non-transferable embryos.

Ovarian synchronization following ultrasound-guided transvaginal follicle ablation in heifers

In Experiments 1 and 2, ultrasound-guided transvaginal follicle aspiration was used as a method of follicle ablation to induce and synchronize subsequent follicular wave emergence and enhance ovulation synchrony following PGF 2α administration. Heifers were at unknown stages of the estrous cycle at the start of both experiments in which all follicles ≥5 mm in diameter were ablated; luteolysis was induced 4 d later with cloprostenol (500 ug/dose, im). In Experiment 1, heifers were randomly assigned to either an ablation (n=17) or a procedural control (no follicle ablation, n=17) group. Ablation-induced wave emergence was indicated by a significant increase in the total number of follicles ≥5 mm within 2 d of ablation (mean, 1.5 d), which was preceded by a significant surge in circulating FSH. Although the mean (±SEM) interval from PGF 2α administration to ovulation did not differ between follicle-ablated heifers (5.1±0.5 d range, 3 to 9 d) and control heifers (5.1±1.0 d; range, 1 to 5 d), the variability of the interval was different (P<0.05). Inequality of variance between the 2 groups was attributed to a greater (P<0.08) degree of ovulation synchrony in the ablation group than in the control group; 13 16 (81%) versus 9 17 (53%), respectively, ovulated within 5 d of cloprostenol administration. Relative asynchrony of ovulations in control heifers was associated with the status of the follicular wave at the time of PGF 2α administration and, in part, to incomplete luteolysis following a single dose of PGF 2α. Experiment 2 was designed to examine the efficacy of 2 doses of cloprostenol 12 h apart (n=7) versus a single dose (n=8) to induce complete luteolysis subsequent to follicle ablation-induced wave emergence. Two doses of cloprostenol potentiated ovulation synchrony; more (P<0.05) 2-dose heifers ( 7 7 , 100%) than single-dose heifers ( 4 8 , 50%) ovulated within 5 d after PGF 2α administration. In summary, ultrasound-guided transvaginal follicle ablation, done at random during the estrous cycle, induced and synchronized subsequent follicular wave emergence, and resulted in a high degree of ovulation synchrony among heifers after PGF 2α induced luteolysis, especially when 2 doses of PGF 2α were administered 12 h apart.

Intramammary pressure and luteal oxytocin after PGF2 alpha administration in cycling and early pregnant ewes.

The aim of this work was to investigate whether luteal oxytocin released after non-luteolytic prostaglandin F2 alpha (PGF2 alpha) challenge could explain the intramammary pressure (IMP) rises previously described in pregnant ewes after the normal life span of a corpus luteum. Blood oxytocin levels and IMP after challenge were measured in cycling and pregnant lactating ewes until the response ceased (approximately 55 d post oestrus). Oxytocin release was not significantly different for cycling and pregnant ewes, and fell to its lowest levels on days 16-18 post oestrus in both groups, i.e. with or without luteolysis. However, although IMP response fell with luteolysis in cycling ewes, the response persisted until day 55 in pregnant ewes. This lack of correlation between oxytocin release and IMP response raised interesting questions including: is there an unknown oxytocic compound that can be released after PGF2 alpha stimulation of the corpora lutea?

Inhibitory effect of vapiprost on contractile responses of isolated dog renal arteries to thromboxane A 2 analogue, U46619

1. Cumulative administrations of U46619, a thromboxane A 2 analogue, and prostaglandin (PG) F 2α produced concentration-dependent contractions of isolated dog renal arterial preparations, which were significantly and concentration-dependently inhibited by vapiprost. 2. A bolus administration of U46619 or PGF 2α produced sustained contracture of these preparations, which was concentration-dependently relaxed by cumulative vapiprost. 3. Results indicate that vapiprost inhibits U46619- and PGF 2α-induced dog renal arterial contractions through antagonism for so-called TP receptors.

Use of Milk Progesterone and Prostaglandin F2α in a Scheduled Artificial Insemination Program

We tested the efficacy of monitoring progesterone in dairy cows using a commercially available milk progesterone test as a determinant for administration of PGF2α, to induce estrus in cows before first AI. Holstein cows milked twice daily were assigned randomly for AI at their first estrus after d 42 postpartum (control) or to receive PGF2α, after a milk progesterone test. Milk progesterone was assessed in samples from the Monday morning milking in both groups of cows, but only those in the treatment received PGF2α, when milk progesterone tested high. Blood was collected before injection of PGF2α, on Monday afternoon to verify retrospectively the accuracy of the milk progesterone test. Agreement of serum concentrations of progesterone was 87% for high milk progesterone tests and 63% for low tests. Use of milk progesterone plus PGF2α, reduced days to first AI, calving intervals, rate of reproductive culling, and cost per pregnancy and increased the proportion of cows inseminated within 21 d of the beginning of breeding. As a management tool in an AI program, PGF2α use is warranted and cost effective. However, the milk progesterone test is not justifiable unless the cost is significantly lower than the cost of a weekly injection of PGF2α.

Effect of mid-luteal phase progesterone levels on the first wave dominant follicle in cattle

A wave-like-pattern of follicular growth and regression during the luteal phase has been described in the bovine. The factors responsible for inducing the onset of regression of nonovulatory dominant follicles are unknown. The present study was designed to examine the effect of progesterone (P4) administration early in the estrous cycle on the first wave dominant follicle. Nine heifers were administered P4 on day 3 (200 mg), day 4 (100 mg) and day 5 (50 mg) of the estrous cycle (Day 0 = day of estrus) and seven heifers received vehicle to serve as controls. All heifers received a luteolytic dose of prostaglandin F2α (PGF2α) on day 7. Follicular dynamics were monitored by daily ultrasonography. All seven control heifers ovulated the first wave dominant follicle. In four P4 treated heifers, the first wave dominant follicle regressed prior to PGF2α administration and a dominant follicle from the second pool of follicles ovulated. The remaining five P4 treated heifers ovulated the first wave dominant follicle. However, in these heifers the growth of the first wave dominant follicle was slower (0.65 ± 0.13 mm day−1 between days 3 to 7 for treated vs 1.46 ± 0.23 mm day−1 for control; P &lt; 0.05) and estrus and ovulation were delayed compared to controls (3.8 ± 0.3 vs 2.4 ± 0.2 and 5.2 ± 0.4 vs 3.9 ± 0.2 days after PGF2α, respectively; P &lt; 0.05). The results indicate that P4 administered early in the estrous cycle to mimic the mid luteal phase levels alters follicular dynamics and is capable of inducing premature regression of the first wave dominant follicle. Key words: Progesterone, dominant follicle, cattle, atresia, ovulation

Effect of exogenous gonadotrophins on oestrus, the LH surge and the timing and rate of ovulation in red deer (Cervus elaphus)

Red deer hinds (n = 38) were treated in the breeding season with five different gonadotrophin regimens to investigate the temporal relationship between oestrus, ovulation and the LH surge. All hinds were treated with progesterone-impregnated controlled internal drug release (CIDR) devices to synchronize oestrus. The five treatments were as follows: treatment 1, controls; treatments 2, 3 and 4, 1200 iu pregnant mares' serum gonadotrophin (PMSG) was administered i.m. 72 h before CIDR device withdrawal (treatments 3 an 4 were also injected i.v. with 0.4 mg synthetic GnRH 12 or 18 h after CIDR device withdrawal, respectively); treatment 5, 200 iu PMSG was administered i.m. 72 h before CIDR device withdrawal and 0.5 iu FSH was administered in eight equal doses at intervals of 12 h starting from the time of PMSG injection. The hinds were run with crayon-harnessed stages to determine the time of oestrus onset. Blood samples were collected every 2 days for 26 days after CIDR device removal to determine concentrations of plasma progesterone and every 2 h for 72 h after CIDR device removal to determine plasma LH profiles. Laparoscopy for ovary examination was performed 6 or 12 h after oestrus onset and was repeated twice at intervals of 12 h. Final ovulation rate was determined on day 7 after CIDR device removal. All hinds received 500 micrograms cloprostenol i.m. on day 13. A total of 30 and 34 hinds exhibited oestrus and ovulation, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of exogenous prostaglandin‐F2α (PGF2α) on pregnancy status in white‐tailed deer

AbstractAs part of a study to develop contraceptive methods for white‐tailed deer (Odocoileus virginianus), it was necessary to terminate pregnancies in some does. The abortifacient chosen was PGF2α. At 76 days or less of gestation, PGF2α administration (10 mg i.m.) did not decrease mean serum progesterone (P) concentrations, and only one doe of 13 aborted. Re‐administration of PGF2α (15 mg i.m.) on approximately day 97 of gestation (21 days after the first injection) did not alter mean serum P concentrations 6 days postinjection, and only one doe of 11 aborted. A third injection of PGF2α (25 mg i.v.) on approximately day 113 of gestation (16 days after the second injection) tended to decrease mean P concentrations by 1.4 ng/ml 2 days following treatment, and no doe of 11 aborted. A fourth injection of PGF2α (50 mg i.m.) on approximately day 124 of gestation (11 days after the third injection) decreased mean P concentrations by 2.9 ng/ml 2 days following treatment (P &lt; 0.05), and two of 11 does aborted. Finally, a combination of 50 mg PGF2α and 15 mg betamethasone was administered i.m. to the remaining pregnant does on approximately day 140 of gestation (16 days after the fourth injection). Mean serum P concentrations decreased from 4.8 ± 0.4 ng/ml to 0.7 ± 0.2 ng/ml 3 days postinjection, a mean decrease of 4.1 ng/ml (P &lt; 0.05). This treatment induced abortion in five of seven does. These data suggest that PGF2α alone, at a dose that causes luteolysis and pregnancy termination in cows and goats, does not do so in pregnant white‐tailed deer. However, a combination of betamethasone and PGF2α may prove to be an effective lu‐teolytic agent or abortifacient for white‐tailed deer. © 1994 Wiley‐Liss, Inc.

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.