Concentrations of ovarian and pituitary hormones following prostaglandin F2 alpha-induced luteal regression in ewes varies with day of the estrous cycle at treatment

Prostaglandin F2 alpha (PGF2 alpha) was injected on d 5, 8 or 11 postestrus in ewes to determine how stage of the estrous cycle would affect PGF2 alpha-induced changes in concentrations of ovarian and pituitary hormones and intervals to the onset of estrus and the preovulatory surge of luteinizing hormone (LH). Initial concentrations of progesterone and average values during the 12 h after PGF2 alpha were related positively to the day of cycle on which PGF2 alpha was administered. Patterns of decline in progesterone after injection of PGF2 alpha were similar among the 3 d. Concentrations of LH in plasma increased in a similar manner from 0 to 12 h in all ewes. After 12 h LH continued to increase, plateaued or declined in ewes treated on d 5, 8 or 11, respectively. Initial concentrations of follicle stimulating hormone (FSH) in plasma were related positively to day of treatment. After treatment with PGF2 alpha, FSH increased within 2 h on d 5 but declined by that time on d 8 or 11. Concentrations of estradiol following treatment did not vary with day. The onset of estrus and the preovulatory surge of LH occurred at 36 and 35, 40 and 45, and 48 and greater than 48 h in ewes treated on d 5, 8 or 11, respectively. It is concluded that: 1) the initial increase in LH is dependent on a decrease in plasma progesterone and 2) differences in patterns of secretion of gonadotropins before the preovulatory surge of LH might be caused by differences in progesterone or progesterone:-estradiol ratio when luteal regression is induced on different days of the estrous cycle.     

Regulation of pulsatile LH secretion by ovarian steroids in the heifer

Two experiments were conducted to evaluate relationships among luteinizing hormone (LH), estradiol-17 beta (E2) and progesterone secretion during the preovulatory period in the heifer after prostaglandin F2 alpha (PGF2 alpha)-induced regression of the corpus luteum. A second objective was to elucidate the effects of E2 in regulating LH secretion. In Exp. 1, LH, E2 and progesterone concentrations were determined in serial samples collected during the preovulatory period after PGF2 alpha-induced luteal regression in five Red Angus X Hereford heifers. Progesterone declined to 1 ng/ml by 12 h after the second injection of PGF2 alpha. Frequency of LH pulses increased linearly (P less than .01), whereas no change in amplitude of LH pulses was detected before the preovulatory LH surge. This resulted in a linear increase (P less than .01) in mean LH concentrations. Estradiol also increased in a linear manner (P less than .01), and the rise in E2 was parallel to the increase in mean LH concentrations. In Exp. 2, 12 Angus X Hereford heifers were ovariectomized and administered either 13.5- or 27-cm silastic implants containing E2 at ovariectomy. Four heifers served as nonimplanted controls. Thirty-one days after ovariectomy all heifers were bled at 12-min intervals for 6 h. Frequency of LH pulses declined linearly (P less than .03) while mean LH (P less than .09) and pulse amplitude (P less than .01) increased linearly as E2 dose increased. These results indicate that a reduction in progesterone increases the frequency of LH pulses during the follicular phase of the estrous cycle in cattle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prostaglandin F2 alpha on the adenylate cyclase and phosphodiesterase activity of ovine corpora lutea

The objective of the present study was to determine the temporal relationships among luteal adenylate cyclase activity, luteal phosphodiesterase activity, luteal progesterone concentration and plasma progesterone concentration during prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis in ewes. Corpora lutea (CL) were removed from cycling ewes on d 9 (d 0 = first day of estrus) at 0, 2, 4, 6, 12 and 24 h (seven to eight ewes/group) after PGF2 alpha administration (im). Jugular blood samples were collected at the time of enucleation of CL and analyzed for progesterone. Plasma and luteal progesterone concentrations were decreased (P less than .05) by 4 and 12 h after PGF2 alpha injection, respectively. Basal adenylate cyclase, luteinizing hormone (LH)-activated adenylate cyclase, guanylylimidodiphosphate [Gpp(NH)p]-activated adenylate cyclase and LH plus Gpp(NH)p-activated adenylate cyclase activities were decreased (P less than .05) by 2 h after PGF2 alpha injection. The decrease in adenylate cyclase activity paralleled the decrease in plasma progesterone concentration over time. Luteinizing hormone stimulated (P less than .05) adenylate cyclase activity relative to basal activity at 0, 2, 12 and 24 h post-PGF2 alpha; whereas, Gpp(NH)p stimulated (P less than .01) adenylate cyclase activity relative to basal activity at each time point. In contrast to the decrease in adenylate cyclase activity, phosphodiesterase activity was increased (P less than .05) at 2 and 4 h post-PGF2 alpha. These results suggest that a decrease in adenylate cyclase activity coupled with an increase in phosphodiesterase activity may decrease the intracellular adenosine 3',5' cyclic monophosphate (cAMP) concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of feed restriction on reproductive and metabolic hormones in ewes

The goal of this study was to determine the effects of short-term feed withdrawal on reproductive and metabolic hormones during the luteal phase of the estrous cycle in mature ewes. Mature ewes observed in estrus were assigned randomly to control and fasted groups (n = 10 per group Trials 1 and 2). For Trials 1 and 2, control ewes had ad libitum access to feed, whereas fasted ewes were not fed from d 7 through 11 of their estrous cycle; on d 12, all ewes were treated with 10 mg of PGF2alpha, and fasted ewes were gvien ad libitum access to feed. For Trial 1, blood samples were collected daily through fasting and at 2-h intervals following PGF2alpha for 72 h. Serum concentrations of insulin (P < or = 0.002) and IGF-I (P < or = 0.01), but not GH (P > or = 0.60), were decreased during fasting compared with fed ewes. Serum concentrations of 29 (P = 0.02) and 34 kDa (P = 0.04) IGFBP were greater in fasted ewes at 96 h after initiation of fasting than in control ewes. Two control and four fasted ewes in Trial 1 did not exhibit a preovulatory surge release of LH by 72 h. Therefore, Trial 2 was conducted so that the timing of the LH surge could be predicted following the collection of blood samples at 2-h intervals for 112 h and then at 6-h intervals until 178 h following PGF2alpha administration and realimentation. The magnitude of the preovulatory LH surge in Trial 2 was decreased (P = 0.009) and delayed (P = 0.04), and serum concentrations of estradiol were diminished (P < or = 0.03) 12 h before the LH surge in fasted ewes. Ovulation rates were not influenced (P > or = 0.32) by fasting in Trials 1 and 2. Serum concentrations of progesterone in both Trials 1 and 2 were, however, greater (P < 0.001) in fasted than in control ewes. A third trial with ovariectomized ewes was conducted to determine whether the increased serum concentrations of progesterone observed in fasted ewes during Trials 1 and 2 were ovarian-derived. Ovariectomized ewes were implanted with progesterone-containing intravaginal implants and allotted to control (n = 5) or fasted (n = 5) treatment groups and fed as described for Trials 1 and 2. Similar to intact ewes, serum concentrations of progesterone were approximately twofold greater (P < 0.001) in fasted than in control implanted ovariectomized ewes. In summary, feed withdrawal for 5 d during the luteal phase of the estrous cycle increased serum concentrations of progesterone and evoked endocrine changes that could perturb the subsequent estrous cycle.     

FSH injections and intrauterine insemination in protocols for superovulation of ewes

In Exp. 1, five injections of crude FSH (20 mg total), starting 36 h before removal of progestin pessaries or injection of prostaglandin F2 alpha (PGF2 alpha), were found to be as effective for superovulation of ewes as seven injections starting 72 h before removal of pessaries. Seven injections caused superovulation (more than three ovulations) in 13 of 15 ewes with an average (all ewes) of 12 +/- 2.3 ovulations. Five injections caused superovulation in 17 of 19 ewes with an average of 11.5 +/- 1.6 ovulations after pessary-regulated estrus in 12 of 16 ewes with an average of 12.4 +/- 2.2 ovulations after PGF2 alpha injection. In Exp. 2, intrauterine artificial insemination (IUAI) of naturally mated ewes provided ovum fertilization rates of 75.3% with an embryo recovery rate of 39.4%, whereas mating alone (MATED) provided fertilization rates of 64.2% with an embryo recovery rate of 72.1%. However, subsequent replications of the MATED protocol (MATED2) resulted in a low fertilization rate (34.2%). In Exp. 3, surgical IUAI at 22 h after removal of pessaries resulted in a low rate of superovulation (5 of 12 ewes), presumably as the result of pentobarbital anesthesia. Conducting IUAI at 46 h after removal of pessaries resulted in a high rate of superovulation (14 of 16 ewes) but a low embryo recovery rate (30.7%). In two subsequent trials, IUAI at 40 h after removal of pessaries resulted in most ewes superovulating (33 of 35 in April/May and 16 of 17 in September) with acceptable embryo recovery (65.2% and 71.3%) and high fertilization rates (82.8% and 96.4%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Maintenance of the corpus luteum of early pregnancy in the ewe. IV. Changes in luteal sensitivity to prostaglandin F2 alpha throughout early pregnancy

Two experiments were conducted to examine the temporal aspects of luteal resistance to the luteolytic effect of prostaglandin (PG) F2 alpha during early pregnancy. In Exp. 1, 14 pregnant and 12 nonpregnant ewes were treated with PGF2 alpha either on d 10 or 13 post-estrus. Jugular venous blood samples were collected at -30 min, 0, 6, 12, 18, 24, 30 and 36 h post-injection for quantification of progesterone. The difference (delta P) between pre-treatment and post-treatment concentrations of progesterone was calculated for each ewe. There was a significant interaction between pregnancy status and day of treatment on delta P (P less than .05). Pregnant and nonpregnant ewes treated on d 10 showed a large delta P. A large delta P also was observed in nonpregnant ewes treated on d 13 post-estrus. However, delta P in pregnant ewes treated on d 13 was smaller than in the other three groups (P less than .05). The temporal patterns of concentrations of progesterone in serum were different among treatment groups (P less than .05). A suppression in the concentration of progesterone was observed by 24 h post-injection in all four treatment groups. Progesterone returned to pre-treatment levels only in pregnant ewes treated on d 13. In Exp. 2, 47 pregnant ewes were treated with PGF2 alpha on d 10, 13, 16, 19, 22, 26 or 30 postestrus. Blood samples were collected and data were analyzed as described for Exp. 1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of domperidone and thyrotropin-releasing hormone on secretion of luteinizing hormone and prolactin during the luteal phase and following induction of luteal regression in sheep

Effects of domperidone, a peripheral dopamine receptor antagonist, on secretion of LH and prolactin were studied during the luteal phase and following administration of PGF2 alpha. Since hyperprolactinemia has been reported to inhibit secretion of LH in ewes, effects of thyrotropin-releasing hormone (TRH) also were examined. Ewes 8-10 days post-estrus were assigned to be treated with: 1) vehicle (n = 5); 2) 0.3 mg domperidone (n = 6); 3) 1.0 mg domperidone (n = 6); 4) 3 micrograms TRH (n = 6); or 5) 10 micrograms TRH (n = 6) every 4 hours for 60 hr. Luteal regression was induced with PGF2 alpha at 12 hr after initiation of treatments. During the luteal phase, pulses of LH were more frequent (P less than .05) and the amplitudes of these were higher (P less than .05) in ewes treated with domperidone or TRH than in control ewes. These changes in LH occurred even though each treatment elevated markedly concentrations of prolactin in plasma. After induction of luteal regression, mean of LH and frequency of LH discharges were similar in all groups. However, in ewes treated with the 1.0 mg/4 hr dose of domperidone the pulse amplitude was greater than in the other groups (2.3 vs 1.1 ng/ml). Dose-response relationships and the magnitude of the prolactin release following domperidone or TRH varied with time. Treatments did not affect the timing of the LH surge or the increase in progesterone associated with the subsequent cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum concentrations of IGF-I in postpartum beef cows

Four experiments assessed changes in serum IGF-I under various physiologic conditions in postpartum cows. In Exp. 1, anestrous suckled cows (n = 25) were infused for 6 d with either saline or glucose at two different infusion rates. In Exp. 2, anestrous cows (n = 29) received either a saline (weaned and suckled controls) or 3 g/d phlorizin (weaned phlorizin) infusion for 3 d. Calves from the weaned groups were removed from 15 h before and throughout infusions. In Exp. 3, cycling suckled cows (n = 20) received prostaglandin F2 alpha (PGF2 alpha) when the 5-d saline or phlorizin infusion began. In Exp. 4, suckled cows (n = 20) had ad libitum access to feed or received 50% of control feed consumption from 30 to 40 d postpartum. Increasing glucose availability (Exp. 1) increased (P less than .05) serum IGF-I by 30 to 35%. IGF-I remained stable after weaning (Exp. 2) in phlorizin-infused cows (128.8 +/- 12.7 ng/ml), but increased (P less than .05) by 3 d after calf removal in weaned control cows (152.2 +/- 7.5 ng/ml). IGF-I also remained stable in phlorizin-infused cows following PGF2 alpha injection (Exp. 3), but increased in control cows by 2 d after PGF2 alpha (156.8 +/- 18.3 on d 2 vs. 133.7 +/- 9.8 ng/ml pre-injection; P less than .05) and remained elevated (P less than .05) during the periovulatory period. In cows receiving restricted feed intake (Exp. 4), IGF-I decreased by approximately 50% within 4 d of feed restriction (71.3 +/- 9.4 vs 137.4 +/- 16.6 ng/ml; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Acquisition of luteolytic capacity involves differential regulation by prostaglandin F2alpha of genes involved in progesterone biosynthesis in the porcine corpus luteum

Luteolytic capacity is defined as the ability of corpora lutea (CL) to undergo luteolysis after prostaglandin (PG) F2alpha treatment. The mechanisms causing acquisition of luteolytic capacity are not yet identified but CL without luteolytic capacity have PGF2alpha receptors and respond to PGF2alpha with some changes in gene expression. Inhibition of progesterone biosynthesis is a key feature of luteolysis and therefore we postulated that genes involved in progesterone biosynthesis would be regulated by PGF2alpha differently in CL with or without luteolytic capacity. Gilts on day 9 after estrus (lack luteolytic capacity) or day 17 of pseudopregnancy (with luteolytic capacity) were treated with saline or a PGF2alpha analog (cloprostenol) and CL were collected 0.5 (Experiment I) or 10 h (Experiment II) later. In Experiment III, large luteal cells from CL on day 9 or 17 were cultured for 1, 12 and 24h with or without PGF2alpha. PGF2alpha decreased LDL receptor mRNA (27%), steroidogenic acute regulatory protein (StAR) mRNA (41%), StAR protein (75%), LH receptor mRNA (55%), and LH receptor protein (45%) at 10 h after treatment in day 17 but not day 9 CL. PGF2alpha increased DAX-1 mRNA at 0.5 h (43%) and 10 h (46%) after PGF2alpha in day 17 but not day 9 CL but decreased 3betaHSD mRNA ( approximately 20% at 10 h) in both days 9 and 17 CL. In vitro, PGF2alpha decreased StAR mRNA at 12 h only in day 17 luteal cells; however, continuous treatment with PGF2alpha for 24 h decreased StAR mRNA in both days 9 and 17 luteal cells. Thus, luteolytic capacity involves a critical change in responsiveness of DAX-1, StAR, and LH receptor to PGF2alpha that results in inhibition of luteal progesterone biosynthesis.     

Effects of LH and PGF2alpha in equine dominant follicles observed by MDS

Microdialysis System (MDS) is a novel technique used for investigation of molecule secretion between different cell populations. Local hormonal secretion at follicular wall has been still unclear. This MDS study was used to determine progesterone (P4), androstenedione (A4), estradiol-17beta (E2) and Prostaglandin F2alpha (PGF2alpha) release in mare pre-ovulatory follicles. Follicles larger than 30 mm were isolated from the ovary and follicular fluid aspirated for hormone assay. Follicular fluid collected from small, middle and large follicles were analyzed by EIA. The concentrations of P4 and PGF2alpha were similar among the different sizes of follicles. The release of A4 was observed in middle and large follicles. E2 concentration was observed in middle follicles and was higher in large follicles compared with middle follicles. Follicular wall was cut and incubated for MDS and when LH was infused, there was an increase in P4 and A4 release. PGF2alpha release was considerably high after LH infusion compared to the control group. Infusion of PGF2alpha increased P4 and A4 release but there was no change in E2 release. This results suggest that in pre-ovulatory follicles, LH stimulates theca interna cells and also PGF2alpha seemed to have a mediator role to induce steroid hormone production and luteinization of follicular cells. The nature of the mechanisms involved in selection of large follicles is still a perplexing research problem in reproduction.     

Supplemental norgestomet,progesterone, or melengestrol acetate increases pregnancy rates in suckled beef cows after timed inseminations

In Exp. 1, 187 lactating beef cows were treated with injections of GnRH 7 d before and 48 h after prostaglandin F2alpha (PGF2alpha; Cosynch) or with Cosynch plus a 7-d treatment with an intravaginal progesterone (P4)-releasing insert (CIDR-B; Cosynch + CIDR). In Exp. 2, 183 lactating beef cows were treated with the Cosynch protocol or with Cosynch plus a 7-d treatment with norgestomet (Cosynch + NORG). In Exp. 1 and 2, blood samples for later P4 analyses were collected on d -17, -7 (first GnRH injection), 0 (PGF2alpha injection), and at timed artificial insemination (TAI; 48 h after PGF2alpha). In Exp. 3, 609 lactating beef cows were treated with the Cosynch + CIDR protocol or were fed 0.5 mg of melengestrol acetate (MGA) per day for 14 d before initiating the Cosynch protocol 12 d after the 14th d of MGA feeding (MGA + Cosynch). Blood samples were collected as in Exp. 1 and 2, plus additional samples on d -33 and -19 before PGF2alpha. In Exp. 4, 360 lactating beef cows were treated with a Cosynch + CIDR protocol, with TAI occurring at either 48 or 60 h after PGF2alpha, while receiving either GnRH or saline to form four treatments. Blood samples were collected as in Exp. 1 and 2. In Exp. 1, addition of P4 reduced the ability of the first GnRH injection to induce ovulation in anestrous cows with low P4 before PGF2alpha but improved (P = 0.06) pregnancy rates (61 vs 66%). In Exp. 2, the addition of NORG mimicked P4 by likewise increasing (P < 0.01) pregnancy rates (31 vs 51%) beyond those after Cosynch. In Exp. 3, the Cosynch + CIDR protocol increased (P < 0.001) pregnancy rates from 46 to 55% compared to the MGA + Cosynch protocol. In Exp. 4, administration of GnRH at TAI improved (P < 0.05) pregnancy outcomes (50 vs 42%), whereas timing of TAI had limited effects. We conclude that a progestin treatment concurrent with the Cosynch protocol improved pregnancy outcomes in all experiments, but pretreatment of cows with MGA was not as effective as the CIDR insert or NORG implants in this Cosynch-TAI model. Most of the improvement in pregnancy rates was associated with the increase in pregnancy rates of anestrous cows, regardless of whether ovulation was successfully induced in response to GnRH 7 d before PGF2alpha. Injection of GnRH at TAI following the Cosynch + CIDR protocol increased pregnancy rates in cycling cows with high P4 before the PGF2alpha injection and in anestrous cows with low P4 before PGF2alpha injection.     

Plasma luteinizing hormone and progesterone concentrations in goats with estrous cycles of normal or short duration after prostaglandin F2 alpha administration during diestrus or pregnancy

Plasma luteinizing hormone (LH) and progesterone concentrations were compared in does experiencing short-duration estrous cycles and in does with estrous cycles of normal duration. The short-duration estrous cycles were observed immediately after induction of abortion in pregnant does by use of prostaglandin (PG) F2 alpha. Intramuscular administration of 5 mg of PGF2 alpha was accomplished in 8 does that were 52 to 63 days into gestation and in 9 cycling does at 7 to 10 days after estrus. In both groups, the mean plasma concentration of progesterone decreased from a luteal phase concentration immediately before to less than 1 ng/ml by 24 hours after PGF2 alpha administration. Of the 8 does that aborted, 6 experienced short-duration estrous cycles, and 4 of these 6 had an LH surge during the time of blood sample collection. The mean time from PGF2 alpha administration to the LH surge was significantly (P less than 0.05) longer in does with short-duration estrous cycles (71 hours) than that in does with estrous cycles of normal duration (58 hours). The mean area under the LH concentration curve was significantly (P less than 0.005) less for does with short-duration estrous cycles. Short-duration estrous cycles were associated with delayed preovulatory LH surges of reduced magnitude.     

Maintenance of the corpus luteum of early pregnancy in the ewe. III. Differences between pregnant and nonpregnant ewes in luteal responsiveness to prostaglandin F2 alpha

The effects of pregnancy and number of corpora lutea on luteal regression induced with prostaglandin F2 alpha (PGF2 alpha) were examined in 93 ewes. Bred and nonpregnant ewes were assigned randomly to receive a single im injection of PGF2 alpha: 0, 2, 4, 6, 8 or 10 mg/58 kg body weight. Injections were given on d 13 postestrus. The concentration of progesterone in serum 24 h after PGF2 alpha injection was affected by dose (P less than .001). The effect of pregnancy and the interaction of pregnancy with number of corpora lutea on levels of progesterone in serum were significant (P less than .05); therefore, data were partitioned according to pregnancy status and analyzed separately. There was an effect of number of corpora lutea on serum concentration of progesterone in pregnant (P less than .01) but not nonpregnant ewes (P greater than .10). Similar relationships among groups were observed for the concentration of progesterone in luteal tissue. In nonpregnant ewes the minimum dose of PGF2 alpha to produce a significant suppression of progesterone in serum (P less than .05) was 4 mg/58 kg body weight. In pregnant ewes with one or two corpora lutea, the minimum effective doses were 6 and 10 mg/58 kg body weight, respectively. The concentration of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum was related to the dose of PGF2 alpha injected. There were no differences in the concentration of PGFM in serum between pregnant and nonpregnant ewes either before or after injection. Corpora lutea of early pregnancy appear to be resistant to the luteolytic effect of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prostaglandin F2alpha on ovarian, adrenal, and pituitary hormones and on luteal blood flow in mares

The effect of a single injection of prostaglandin F2alpha (PGF) during mid-diestrus on systemic concentrations of progesterone, LH, FSH, estradiol, and cortisol and on blood flow to the corpus luteum was studied in 10 controls and 10 PGF-treated mares. Blood flow was assessed by estimating the percentage of corpus luteum with color-Doppler signals of blood flow during real-time scanning of the entire structure and by the diameter of the vascular pedicle near its attachment to the ovary. Treatment was done 8 days after ovulation and 0 h was immediately before the treatment. Examinations and collection of blood samples were done at 0 h, every 5 min until 1h, and then at 1.5, 2, 4, 8, 12, 24, 48, and 72 h. The concentrations of estradiol did not change, but progesterone, LH, FSH, and cortisol increased significantly within 5 min. Concentrations of LH and FSH in the PGF group remained elevated until a temporarily lower concentration at 8 or 4h, respectively, rebounded to 12h, and then slowly decreased. Cortisol remained elevated, until a decrease between 1 and 4h. Progesterone in the PGF group increased significantly until 10 min after 0 h and then decreased by 40 min to below the concentrations in controls. Within the PGF group, progesterone decreased significantly by 45 min to below the concentrations at 0 h. The values for each of the two indicators of blood flow did not differ significantly between the PGF and control groups until a decrease at 24h in the PGF group. Results did not support the hypothesis that the immediate transient post-PGF increase in progesterone was associated with an increase in luteal blood flow. Luteolysis, as indicated by decreasing progesterone, began well before the beginning of a decrease in luteal blood flow.     

Ovarian 3'5'-cyclic adenosine monophosphate and prostaglandins: a sequential comparison of gonadotropin-stimulated events in small and large ovine follicles

Luteinizing hormone (LH) stimulates a cascade of ovarian hormonal events that culminate in ovulation. This study was designed to investigate, in sheep, sequential changes in prostaglandin (PG) E2, PGF2 alpha, 6-keto-PGF1 alpha, and cyclic adenosine monophosphate (cAMP) in the theca, granulosa and follicular fluid of large preovulatory follicles and small nonovulatory follicles in response to LH. On d 15 postestrus, preovulatory or nonovulatory follicles were injected intrafollicularly with saline or LH. Ewes were then ovariectomized at 0, 2, 4, or 8 h postinjection. Injected follicles were excised; theca, granulosa and fluid were separated, weighed and assayed for cAMP and PG. Contents of cAMP in the theca, granulosa and fluid of preovulatory follicles increased (P less than .01) 2 to 4 h after injection of LH. Increases (P less than .05) in contents of PGE2 and PGF2 alpha in the theca and fluid of preovulatory follicles were observed between 4 and 8 h after injection of LH. The time courses of LH-induced synthesis of PGE2 and PGF2 alpha in preovulatory follicles were parallel. Luteinizing hormone had no effect on PGE2, PGF2 alpha or cAMP in any compartment of small follicles. Contents of 6-keto-PGF1 alpha varied with time in both theca and granulosa of large and small, saline- and LH-injected follicles. Although specific increases in cAMP and PG followed an injection of LH only in large follicles, the parallel temporal relationship of PGE2 and PGF2 alpha did not explain the dichotomous functions ascribed to PGE2 and PGF2 alpha during the periovulatory period.     

Preovulatory changes in follicular prostaglandins and their role in ovulation in cattle.

Indomethacin (INDO, n = 5) or vehicle (CONTROL, n = 4) was injected into superovulated heifers at 48 and 60 h following a luteolytic cloprostenol injection (0 h). One heifer from each group was ovariectomized (OVX) at 48, 56, 64 and 72 h. The fifth heifer of the INDO group was OVX at 80 h. Blood samples were collected at 0 h, every 2 h between 37 and 47 h, and at the time of each OVX to monitor plasma progesterone (P4) and luteinizing hormone (LH) concentrations. Following each OVX, the number and size of follicles were recorded and the incidence of ovulation determined. Follicular fluid (FF) was aspirated from follicles greater than or equal to 8 mm to determine the concentration of prostaglandins E2 (PGE2) and F2 alpha (PGF2 alpha). The highest PG concentrations were measured in both groups at 24-25 h following the preovulatory LH surge and the PGF2 alpha concentration at this time was significantly greater (p less than 0.01) in the CONTROL group compared to the INDO group. By 35-36 h after the LH surge, 75% (25/34) of the CONTROL follicles had ovulated, whereas there were no ovulations (0/50) on either ovary of the INDO treated heifer. These preliminary results suggest that the preovulatory rise of PGs in FF, particularly PGF2 alpha, is essential for ovulation and that suppression of this rise with indomethacin will inhibit ovulation in heifers.     

Follicular, hormonal, and pregnancy responses of early postpartum suckled beef cows to GnRH, norgestomet, and prostaglandin F2alpha.

ABSTRACT: Cycling (n = 16) and noncycling (n = 24), early postpartum, suckled beef cows of three breeds were assigned randomly to three treatments: 1) 100-microg injection of GnRH plus a 6-mg implant of norgestomet administered on d -7 before 25 mg of PGF2alpha and implant removal on d 0 (GnRH+NORG); 2) 100 microg of GnRH given on d -7 followed by 25 mg of PGF2alpha on d 0 (GnRH); or 3) 2 mL of saline plus a 6-mg implant of norgestomet administered on d -7 followed by 25 mg of PGF2, and implant removal on d 0 (NORG). All cows were given 100 microg of GnRH on d +2 (48 h after PGF2alpha). Blood sera collected daily from d -7 to d +4 were analyzed for progesterone and estradiol-17beta, and ovaries were monitored daily by transrectal ultrasonography to assess changes in ovarian structures. Luteal structures were induced in 75% of noncycling cows in both treatments after GnRH, resulting in elevated (P < .01) progesterone on d 0 for GnRH+NORG-treated cows. Concentrations of estradiol-17beta (P < .01) and LH (P < .05) were greater on d +2 after GnRH for cows previously receiving norgestomet implants. Pregnancy rates after one fixed-time AI at 16 h after GnRH (d +2) were greater (P < .05) in GnRH+NORG (71%) than in GnRH (31%) and NORG (15%) cows. Difference in pregnancy rate was due partly to normal luteal activity after AI in over 87% of GnRH+NORG cows and no incidence of short luteal phases. The GnRH+NORG treatment initially induced ovulation or turnover of the largest follicle, induction of a new follicular wave, followed later by increased concentrations of estradiol-17beta and progesterone. After PGF2alpha, greater GnRH-induced release of LH occurred in GnRH+NORG cows before ovulation, and pregnancy rates were greater after a fixed-time AI.     

Hormone secretion and characteristics of estrous cycles after treatment of heifers with human chorionic gonadotropin or prostaglandin F2 alpha during corpus luteum formation

Fertility in cattle is related positively to concentrations of progesterone in blood during the estrous cycle preceding insemination. This study determined whether treatment of heifers with prostaglandin F2 alpha (PGF2 alpha) or human chorionic gonadotropin (hCG) during d 2 to 4 of an estrous cycle affected progesterone during that cycle and whether hormone secretion during the cycle and onset of subsequent estrus were related to progesterone secretion. Nine Holstein heifers were assigned to an experiment designed as a triplicate Latin square, and each heifer received each of three treatments during three consecutive estrous cycles. Treatments were: saline (control, 1 ml) on d 2, 3 and 4 after estrus; hCG, 1000 IU on d 2, 3 and 4; and PGF2 alpha, 25 mg on d 3 with repeated doses 12 and 24 h later. Progesterone throughout the estrous cycle was higher in heifers given hCG than in those given saline. Progesterone during the first week of the cycle was lower in heifers given PGF2 alpha than those given saline, but means for these two groups were similar thereafter. Number of peaks of 15-keto,13,14-dihydro-PGF2 alpha (PGFM) during 24 h after onset of luteolysis was lower in heifers given hCG than in those given saline or PGF2 alpha. Patterns of secretion of luteinizing hormone and estradiol at subsequent estrus were not affected by treatment. Temporal relationships among hormone secretion and onset of estrus were unaffected by treatment.     

Gonadotropin concentrations, follicular development, and luteal function in pituitary stalk-transfected ewes treated with bovine follicular fluid.

Two experiments, each arranged as a 2 x 2 factorial, were conducted in ewes to examine direct effects of bovine follicular fluid (bFF) on follicular development and luteal function and to further characterize follicular development and luteal function after pituitary stalk transection (SS). In Exp. 1, ewes were sham-operated or SS on d 6 of an estrous cycle and received 5 ml of saline or bFF three times daily on d 5 through 11 of the same cycle. In Exp. 2, all ewes were SS on d 6 of an estrous cycle and treated with saline or bFF three times daily on d 5 through 11 and with ovine FSH (60 micrograms; NIADDK-oFSH-16) or saline (1.2 ml) from d 7 to 11. In Exp. 2, ewes were ovariectomized on d 11 to assess effects of treatments on follicular development and luteal function. In both experiments, concentrations (ng/ml) of FSH on d 7 were suppressed (P less than or equal to .005) by bFF compared with saline (.50 +/- .17 vs 1.63 +/- .15) and remained suppressed (P less than or equal to .005) through d 11 (.46 +/- .12 vs 1.54 +/- .12). Replacement therapy (oFSH) restored concentrations of FSH. Concentrations of LH were not affected by bFF but were elevated (P less than or equal to .05) 1 d after SS (d 7; .88 +/- .09 vs .56 +/- .09) and remained elevated (P less than or equal to .05; 1.31 +/- .20 vs .65 +/- .11) from d 6 through 11. Concentrations of progesterone were unaffected by SS.(ABSTRACT TRUNCATED AT 250 WORDS)