Luteolytic Dose Of Prostaglandin F2α Research Articles

Clinical prospects proposing an increase in the luteolytic dose of prostaglandin F2α in dairy cattle.

Over the past few decades, the luteolytic dose of prostaglandin F2α (PGF2α) and its analogs, used to synchronize estrus for fixed-time insemination in dairy cattle, have remained unchanged. Given the beneficial effects of PGF2α on a young corpus luteum and on multiple ovulations in a fixed-time insemination protocol, and its therapeutic abortive effects on multiple ovulations in pregnant cows, we propose the use of a double PGF2α dose or two PGF2α treatments 24 hours apart. Ultrasonography procedures serve to identify luteal structures and may therefore help to determine the best PGF2α dose to improve the fertility of high-producing dairy cows.

12 Ovulation Timing Following an Aromatase Inhibitor-Based Synchronization Protocol in Beef Heifers and Cows

The study was conducted to determine the effects of parity/lactation and the timing of gonadotropin-releasing hormone (GnRH) treatment on the efficacy of a non-steroidal aromatase inhibitor-based synchronization protocol in cattle. Results from previous studies confirmed drug-release from a new letrozole-impregnated intravaginal silicone device, which was used in the present study. Hereford-cross cows with suckling calves (41 to 65 days postpartum; n = 30) and sexually mature heifers (n = 30), at random stages of the oestrous cycle, were given a letrozole intravaginal device for 4 days followed by a luteolytic dose of prostaglandin F2α (PGF2α). Following PGF2α treatment, animals were assigned randomly to 3 groups and given GnRH (100 μg of gonadorelin) intramuscularly at 48 or 60 h, or no GnRH (n = 10 cows and 10 heifers per group). Ovaries were examined by transrectal ultrasonography every 8 h starting at the time of PGF2α treatment to record follicle diameter and ovulation. After ovulation, ultrasonography was done every 24 h until Day 10 (Day 0 = ovulation) to assess the corpus luteum (CL) diameter profile. The timing of ovulation, diameter of the preovulatory follicle, synchrony of ovulation, and Day-7 CL diameter were compared using two-way ANOVA, and CL diameter profiles were compared by two-way ANOVA for repeated measures. There was no treatment × parity/lactation status interaction for any endpoint. The ovulation rate within 96 h of PGF2α treatment was not different between heifers and cows (24/30 v. 27/30; P = 0.14) or treatment group (18/20, 18/20, and 15/20 in the 48 h, 60 h, and no GnRH groups, respectively; P = 0.18). The interval from PGF2α treatment to ovulation was not influenced by parity/lactation (83.1 ± 2.4 h) but was shortest in the GnRH 48 h group (mean ± SEM; 74.2 ± 2.7 h, 85.6 ± 4.8 and 89.2 ± 4.1, respectively; P < 0.05). Similarly, the variation in the interval to ovulation (mean ± s.e.M of residuals) was not influenced by parity/lactation (16.0 ± 2.0 h), but was lower in the GnRH groups than the no-GnRH group (P < 0.01), and tended to be lower (P = 0.1) in the GnRH 48-h v. 60-h group (10.0 ± 2.8, 14.2 ± 3.5, and 24.1 ± 3.1 h, respectively). The maximum diameter of the ovulatory follicle was larger for cows than heifers (17.0 ± 0.4 v. 15.1 ± 0.5; P < 0.01), and was smaller in the GnRH groups than the no-GnRH group (15.3 ± 0.3, 15.4 ± 0.7 and 17.3 ± 0.5 mm, respectively; P < 0.01). The diameter of the CL on Day 7 was larger for cows than heifers (22.3 ± 0.8 v. 20.2 ± 0.6 mm; P < 0.05) and was influenced by treatment (21.9 ± 0.5, 19.5 ± 0.7, 22.3 ± 1.1 mm, respectively; P = 0.05). A tendency for a treatment effect on CL diameter profile (P = 0.1) was attributed to a smaller profile in the GnRH 60-h group. In conclusion, GnRH treatment 48 h after PGF2α treatment increased synchrony of ovulation without adverse effects on ovulating follicle diameter or resulting CL growth, and may be incorporated into a novel steroid-free oestrous synchronization protocol for use in beef heifers and lactating cows. Research was supported by the Alberta Livestock and Meat Agency and Vencofarma, Brazil.

Histological analysis of arteriovenous anastomosis-like vessels established in the corpus luteum of cows during luteolysis.

BackgroundThe mechanisms regulating the function and regression of the corpus luteum (CL) have not yet been elucidated in detail. The regressed CL of cows was previously reported to be filled with unusual vessels like arteriovenous anastomosis (AVA); however how these vessels are being established during luteolysis remains unknown.MethodsThe bovine CL at different luteal stages and regressing bovine CL induced by prostaglandin F2α (PGF) were histologically analyzed using light and electron microscopic levels. The changes in mRNA expression of genes encoding α-smooth muscle actin (SMA; Acta2) and transforming growth factor β1 (Tgfb1) in luteal tissues were analyzed by quantitative RT-PCR.ResultsAVA-like vessels appeared in the regressed CL with a diameter less than 1.5 cm in which no functional luteal cells and macrophages were observed. Epithelioid cells in the AVA-like vessel wall were immunoreactive for SMA, and the lumen of the vessels were narrow. Immunoreaction for SMA was found in the tunica media of typical arteries and arterioles, and pericytes around capillary vessel. Cells with elongated cytoplasmic processes ―resident fibroblasts expressing vimentin― distributed in the CL parenchyma without any association with blood vessels are also immunoreactive for SMA, and accumulated around arteries and arterioles during the late-luteal stage. In the regressed CL, walls of arteries and arterioles consisted of more than two layers of epithelioid cells positive for both SMA and desmin, suggesting that they are myofibroblasts transformed from fibroblasts. The percentage of the area positive for SMA and the mRNA expression of Acta2 were significantly increased in the regressed CL; however, they did not alter when a luteolytic dose of PGF was injected in vivo and collected within 24 h after the injection. On the other hand, Tgfb1, a known regulator for myofibroblast transformation, was significantly increased in PGF-induced regressing CL as well as in the CL during the late-luteal stage.ConclusionsSMA-positive myofibroblasts accumulates around the arteries and arterioles to form AVA-like vessels during luteolysis in cows. PGF indirectly regulates myofibroblast transformation through enhancing the expression of TGFβ1. These peculiar AVA-like vessels may be involved in the regulation of blood flow in the bovine CL during luteolysis.

Maintenance of Pregnancy in Beef Cattle after a Luteolytic Dose of ProstaglandinF2α

Abstract The increased use of assisted reproductive technologies (ARTs), increase the risks of erroneous prostaglandin F2α (PGF2α) administration. The objective of this study was to determine if

Role of the cell cycle in regression of the corpus luteum

The corpus luteum contains differentiated steroidogenic cells that have exited the cell cycle of proliferation. In some tissues, deletion of quiescent, differentiated cells by apoptosis in response to injury or pathology is preceded by reentry into the cell cycle. We tested whether luteal cells reenter the cell cycle during the physiological process of luteolysis. Ovaries were obtained after injection of cows with a luteolytic dose of prostaglandin F(2)(α) (PGF). In luteal sections, cells co-staining for markers of cell proliferation (MKI67) and apoptosis (cPARP1) increased 24 h after PGF, indicating that cells that reenter the cell cycle undergo apoptosis. The percent of steroidogenic cells (CYP11A1-positive) co-staining for MKI67 increased after PGF, while co-staining of non-steroidogenic cells did not change. Dispersed luteal cells were stained with Nile Red to distinguish lipid-rich steroidogenic cells from nonsteroidogenic cells and co-stained for DNA. Flow cytometry showed that the percent of steroidogenic cells progressing through the cell cycle and undergoing apoptosis increased after PGF. Culturing luteal cells induced reentry of steroidogenic cells into the cell cycle, providing a model to test the influence of the cell cycle on susceptibility to apoptosis. Blocking cells early in the cell cycle using inhibitors reduced cell death in response to treatment with the apoptosis-inducing protein, Fas ligand (FASL). Progesterone treatment reduced progression through the cell cycle and decreased FASL-induced apoptosis. In summary, steroidogenic cells reenter the cell cycle upon induction of luteal regression. While quiescent cells are resistant to apoptosis, entry into the cell cycle promotes susceptibility to apoptosis.

Fertility in dairy cows following presynchronization and administering twice the luteolytic dose of prostaglandin F2α as one or two injections in the 5-day timed artificial insemination protocol

The objectives were to evaluate pregnancy per AI (P/AI) of dairy cows subjected to the 5-day timed AI protocol under various synchronization and luteolytic treatments. Cows were either presynchronized or received supplemental progesterone during the synchronization protocol, and received a double luteolytic dose of PGF2α, either as one or two injections. In Experiment 1, dairy cows (n = 737; Holstein = 250, Jersey = 80, and crossbred = 407) in two seasonal grazing dairy farms were randomly assigned to one of four treatments in a 2 × 2 factorial arrangement. The day of AI was considered study Day 0. Half of the cows were presynchronized (G6G: PGF2α on Day −16 and GnRH on Day −14) and received the 5-day timed AI protocol using 1 mg of cloprostenol, either as a single injection (G6G-S: GnRH on Day −8, PGF2α on Day −3, and GnRH + AI on Day 0) or divided into two injections of 0.5 mg each (G6G-T: GnRH on Day −8, PGF2α on Day −3 and −2, and GnRH + AI on Day 0). The remaining cows were not presynchronized and received a controlled internal drug-release (CIDR) insert containing progesterone from GnRH to the first PGF2α injection of the 5-day timed AI protocol, and 1 mg of cloprostenol either as a single injection on Day -3 (CIDR-S) or divided into two injections of 0.5 mg each on Days -3 and -2 (CIDR-T). Ovaries were examined by ultrasonography on Days −8 and −3 and plasma progesterone concentrations were determined on Days −3 and 0. In Experiment 2, 655 high-producing Holstein cows had their estrous cycle presynchronized with PGF2α at 46 ± 3 and 60 ± 3 days postpartum and were randomly assigned to receive 50 mg of dinoprost during the 5-day timed AI protocol, either as a single injection or divided into two injections of 25 mg each. Pregnancies per AI were determined on Days 35 and 64 after AI in both experiments. In Experiment 1, presynchronization with G6G increased the proportion of cows with a CL on Day −8 (80.6 vs. 58.8%), ovulation to the first GnRH of the protocol (64.2 vs. 50.2%), and the presence (95.6 vs. 88.4%) and number (1.79 vs. 1.30) of CL at PGF2α compared with CIDR cows. Luteolysis was greater for two injections compared to a single PGF2α injection (two PGF2α = 95.9 vs. single PGF2α = 72.2%), especially in presynchronized cows (G6G-T = 96.2 vs. G6G-S = 61.7%). For cows not presynchronized, two PGF2α injections had no effect on P/AI (CIDR-S = 30.2 vs. CIDR-T = 34.3%), whereas for presynchronized cows, it improved P/AI (G6G-S = 28.7 vs. G6G-T = 45.4%). In Experiment 2, the two-PGF2α injection increased P/AI on Days 35 (two PGF2α = 44.5 vs. single PGF2α = 36.4%) and 64 (two PGF2α = 40.3% vs. single PGF2α = 32.6%) after AI. Presynchronization and dividing the dose of PGF2α (either cloprostenol or dinoprost) into two injections increased P/AI in lactating dairy cows subjected to the 5-day timed AI protocol.

Effect of the ovulatory follicle diameter and progesterone concentration on the pregnancy rate of fixed-time inseminated lactating beef cows

The objective of this study was to evaluate the influence of the ovulatory follicle diameter on the reproductive performance of lactating beef cows subjected to low progesterone fixed-time artificial insemination (FTAI) protocols. Ninety-three lactating beef cows (60-80 days postpartum) at random stages of estrous cycle were given a luteolytic dose of prostaglandin F2α (500 μg cloprostenol; PGF) twice, 11 d apart. Ten days after the second PGF treatment, cows were given 1.5 mg of estradiol benzoate im and a progesterone-releasing intravaginal device (Cue-Mate) with a single pod containing 0.78 g progesterone (Day 0). Cows received another luteolytic dose of PGF on Day 0. On Day 8, the Cue-Mate was removed. Fifty-four to 56 hours later, cows received 12.5 mg of porcine LH (pLH) i.m. and were concurrently artificially inseminated. Ultrasound examinations of the ovaries were performed on Days 10 and 17 to evaluate the diameter of ovulatory follicle and corpus luteum, respectively. Cows which presented ovulatory follicle > 19 mm resulted in larger corpus luteum than cows that had ovulatory follicle <15 mm in diameter. However, cows with ovulatory follicle between 13-15 mm had higher pregnancy rate than other categories of ovulatory follicle. Although larger ovulatory follicles result in larger corpus luteum and consequently higher progesterone production, the optimal size of ovulatory follicles (13-15 mm) may result in positive benefits on pregnancy rate for cows subjected to FTAI with low progesterone concentration protocols.

Rapid induction of interleukin 8 (IL8) expression during prostaglandin F2alpha induced regression of the corpus luteum: role in neutrophil degranulation and chemotaxis

The corpus luteum (CL) is essential for the maintenance of early pregnancy. Prostaglandin F2α (PGF) is a luteolytic factor in many species and has been implicated in luteal regression in women. Recent studies suggest that cytokines may mediate the luteolytic action of PGF. Our objective was to identify cytokines induced by PGF in vivo and to determine their effect on specific luteal cell types in vitro. In vivo and in vitro approaches were used to determine the cytokines produced by the CL. Purified luteal cell types (steroidogenic, endothelial and fibroblast cells) and peripheral blood cells were used to identify which cells respond to cytokines. The study was approved by animal and human studies committees. Midcycle (day 10) cows (n = 15) were injected with saline or a luteolytic dose of PGF. Ovaries were removed after 0.5-4 hr and CL processed for protein or flash frozen for mRNA isolation. Gene expression was analyzed using Affymetrix Bovine Microarrays and validation performed by real-time RT-PCR. Steroidogenic cells, endothelial cells and fibroblasts were prepared for analysis of signaling molecules by western blot and progesterone by RIA. Neutrophils from peripheral blood were analyzed for activation. IL8, CXCL2, CCL2, CCL8 were significantly increased within 60 min of PGF treatment. Ten-fold increases in IL8 were apparent with 60 min and 35 fold increases were observed after 4 hr of treatment. Results confirmed previous findings that PGF induced CCL2 expression. IL8 treatment did not alter basal or LH-stimulated progesterone synthesis. IL8 did not activate AKT or ERK signaling pathways in steroidogenic cells, endothelial cells or fibroblasts. However, IL8 rapidly stimulated neutrophil degranulation as shown by cell surface expression of CDIIB. Cytokines are rapidly induced during luteal regression and IL8 stimulates neutrophil degranulation and chemotaxis, suggesting that luteolysis may be a controlled inflammatory response.

Relationship of vascular perfusion of the wall of the preovulatory follicle to in vitro fertilisation and embryo development in heifers

The effect of the extent of vascular perfusion of the wall of the preovulatory follicle on in vitro cleavage rate of the recovered oocyte and embryo development to >8 cells was studied in 52 heifers. Heifers received a luteolytic dose of prostaglandin F2alpha (PGF2alpha) when the largest follicle was > or =11 mm. An ovulation-inducing injection of GnRH was given 36 h later (hour 0), and collection of follicular fluid and the oocyte was done at hour 26. Vascular perfusion of the follicular wall was assessed by colour Doppler ultrasonography at hours 0 and 26. Each of the recovered oocytes (41/52; 79%) was mature (extruded polar body). Cleavage and embryo development were assessed at 48 h and 120 h respectively, after in vitro fertilisation (IVF). The percentage of cleaved oocytes and >8 cell embryos was 80% (31/39) and 55% (17/31) respectively. Vascular perfusion of the follicular wall was greater (lower pulsatility index; P<0.001) for follicles that produced cleaved versus non-cleaved oocytes and greater (P<0.04) for follicles that produced >8 cell versus < or =8 cell embryos. Percentage of follicular wall with Doppler signals of blood flow was greater (P<0.001) for >8 cell versus < or =8 cell embryos. Follicular-fluid concentration of free IGF1 was lower for cleaved oocytes (P<0.001) and >8 cell embryos (P<0.05), and oestradiol was lower (P<0.05) for >8 cell embryos. Results supported the hypothesis that greater vascular perfusion of the wall of the preovulatory follicle was positively associated with IVF and embryo development.

Presence and regulation of messenger ribonucleic acids encoding components of the class II major histocompatibility complex-associated antigen processing pathway in the bovine corpus luteum

Luteal cells express class II major histocompatibility complex (MHC) molecules and can stimulate T lymphocyte proliferation in vitro. However, it is unknown whether luteal cells express the intracellular components necessary to process the peptides presented by class II MHC molecules. The objective of the present study was to examine the expression and regulation of three major class II-associated antigen processing components--class II MHC-associated invariant chain (Ii), DMalpha and DMbeta--in luteal tissue. Corpora lutea were collected early in the estrous cycle, during midcycle and late in the estrous cycle, and at various times following administration of a luteolytic dose of prostaglandin F(2alpha) (PGF(2alpha)) to the cow. Northern analysis revealed the presence of mRNA encoding each of the class II MHC-associated antigen processing proteins in luteal tissue. Ii mRNA concentrations did not change during the estrous cycle, whereas DMalpha and DMbeta mRNA concentrations were highest in midcycle luteal tissue compared with either early or late luteal tissue. Tumor necrosis factor-alpha (TNF-alpha) reduced DMalpha mRNA concentrations in cultured luteal cells in the presence of LH or PGF(2alpha). DMalpha and DMbeta mRNA were also present in highly enriched cultures of luteal endothelial (CLENDO) cells, and DMalpha mRNA concentrations were greater in CLENDO cultures compared with mixed luteal cell cultures. Expression of invariant chain, DMalpha and DMbeta genes indicates that cells within the corpus luteum express the minimal requirements to act as functional antigen-presenting cells, and the observation that CLENDO cells are a source of DMalpha and DMbeta mRNA indicates that non-immune cells within the corpus luteum may function as antigen-presenting cells.

Induction of Short Ovulatory Cycle in Shiba-Goats by Repeated Treatments with Prostaglandin F2.ALPHA..

Follicular growth of ruminant species occurs more than once during an estrous cycle either resulting in ovulation (ovulatory follicular wave) or not resulting in ovulation (latent follicular wave). Using Shiba-goats, we examined if ovulation could be induced from every latent follicular wave and if the resulting ova were fertile. Ovarian follicular development was monitored daily by transrectal ultrasonographic examination in 20 female goats for 2 consecutive estrous cycles. After the second spontaneous ovulation (day 0 = ovulation), all animals were each treated with a luteolytic dose of prostaglandin F2α (PGF 2α) on days 3 and 4,which resulted in ovulation from the first latent wave. Fertile males goats (n=2) were immediately introduced to the first group of animals (n=5), resulting in 4 pregnancies. For the second group of goats (n=9), 4 consecutive short estrous cycles were induced by the PGF2 α treatment at a mean interval of 6.5 ± 1.2 days with a range of 4-9 days. Five of 9 goats were allowed to mate following 4 consecutive short ovulatory cycles; normal behavioral estrus was observed at each estrus, and four of five animals became pregnant. The third group of goats (n=6), in addition to PGF2α treatment, received exogenous progesterone supplement which allowed latent follicular development to occur, but prevented ovulation until the effect of progesterone supplement subsided. These results suggest that female Shiba-goats possess physiological mechanisms for the final steps of follicular maturation and subsequent ovulation at short intervals when progesterone production from the newly developed corpus luteum is terminated.

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.

Response of Dairy Cows Treated with Bovine Somatotropin to a Luteolytic Dose of Prostaglandin F2α

The objective of this study was to evaluate the timing of follicular waves in cows treated with bovine somatotropin (bST) by measuring ovarian responses to a luteolytic dose of PGF2α on d 12 of the estrous cycle. Thirty lactating cows (26 Holstein and 4 Guernsey) were assigned to receive bST (500mg; n=18) or saline (control; 1.5ml; n=12) every 14 d for three injection cycles. On d 12 of a synchronized estrous cycle, cows were injected with PGF2α to induce luteolysis. Following PGF2α, 9 cows ovulated from the dominant follicle during the first follicular wave (4 cows treated with bST and 5 control cows), and 14 cows ovulated from the dominant follicle during the second follicular wave (8 cows treated with bST and 6 control cows). Of the cows that ovulated during the second follicular wave, cows treated with bST had more class 3 follicles (≥ 10mm) than did control cows. Concentrations of estradiol rose earlier after PGF2α injection in cows treated with bST than in control cows. This rise in estradiol was parallel to the development of dominant follicles. Serum concentrations of FSH were decreased in cows treated with bST. During the first and second estruses, equivalent numbers of cows treated with bST and control cows ovulated, but fewer cows treated with bST expressed estrus. These results are consistent with the hypothesis that cows treated with bST have reduced FSH, a faster turnover of dominant follicles, and differences in the timing of follicular waves. Treatment of cows with bST also increased the incidence of undetected estrus.

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