Further investigation of the antiovulatory effects of the antiprogestational steroid RMI 12,936 in the rat.

Inhibition of ovulation by RMI 12,936 was associated with suppression of the pro-oestrous peak of hypothalamic dopamine. The antiovulatory effect was not reversed by administration of oestrogen, was partly reversed by progesterone and was fully reversed by oestrogen and progesterone. Hypophysial sensitivity to LH-RH, known to be reduced by RMI 12,936, remained low when ovulation was restored by steroid treatment. Administration of oestrogen did not restore the pro-oestrous peak of hypothalamic dopamine and ovulation was not induced following administration of L-DOPA in RMI 12,936-treated animals. It was concluded that RMI 12,936 is antioestrogenic as well as antiprogestational, that oestrogen is necessary for induction of full hypothalamic-hypophysial responsiveness to progesterone and that a hypothalamic dopaminergic pathway may have a non-essential role in the control of ovulation possibly associated with increasing hypophysial sensitivity to LH-RH.     

Androgenic effects of the antiprogestagen RMI 12,936

RMI 12,936 (7alpha-methyl-17beta-hydroxy-androst-5-en-one) was tested for androgenic activity in mouse kidney and for antiprogestational activity in guinea-pig uterus. RMI 12,936 stimulated an increase in kidney weight and in the activity of the androgen-responsive renal enzymes, beta-glucuronidase, alcohol dehydrogenase and arginase. RMI 12,936 was bound by the renal androgen receptor with a relative affinity approximately one-third that of testosterone. Although RMI 12,936 did not stimulate glycogen accumulation in guinea-pig endometrium in vivo, it was active in endometrial organ culture. When RMI 12,936 was combined with progesterone, glycogen accumulation in vitro was partly inhibited. RMI 12,936 was bound by the guinea-pig uterine progesterone receptor with a relative affinity of less than 1%. It is concluded that RMI 12,936 is an androgenic steroid with antifertility actions and in-vitro antiglycogenic activity.     

Effect of RMI 12,936, an antiprogestational steroid on decidual cell reaction and embryos in rat.

Subcutaneous administration of RMI 12,936 at a dose level of 2 mg/rat on day 5 of unilaterally pregnant rat having trauma-induced decidual cell reaction (DCR) in the contralateral uterine horn, suppresses DCR, induces resorption of implanted embryos and leads to decrease in the plasma level of progesterone. Progesterone replacement (D 5-8) in this situation reverses DCR suppressive effect of RMI 12,936 but fails to prevent resorption of implanted embryos. It is concluded that possibly the drug simultaneously exerts embryotoxic as well as luteolytic effects, but these effects are independent.     

Effects of gonadotropin-releasing hormone treatment on ovarian steroid production during midpregnancy

During the second half of pregnancy, ovarian testosterone (T) through its conversion to estradiol (E) promotes progesterone (P) synthesis by the ovary which maintains the pregnancy. To determine if the administration of gonadotropin-releasing hormone (GnRH) disrupts pregnancy by suppressing ovarian production of T or its conversion to E, rats were treated from Day 11 through Day 18 of pregnancy with 50 or 100 micrograms/day of GnRH or 1, 5, or 10 micrograms/day of a GnRH agonist (GnRH-Ag; WY-40972) using an osmotic minipump. Rats were bled daily from the jugular vein under light ether anesthesia and on Days 14 or 18 of pregnancy both jugular and ovarian blood samples were obtained. While the GnRH-Ag treatment at the dose of 5 or 10 micrograms/day terminated pregnancy within 48 hr as indicated by vaginal bleeding, 1 microgram/day terminated pregnancy more slowly. Neither dose of GnRH was effective in terminating pregnancy through Day 18. By Day 14, peripheral levels of plasma P in rats treated with 0, 1, 5, or 10 micrograms of GnRH-Ag were 97 +/- 9, 24 +/- 1, 13 +/- 3, and 8 +/- 1, respectively. In the same groups, levels in the ovarian vein were 3205 +/- 633, 1317 +/- 273, 360 +/- 113, and 228 +/- 73 ng/ml. By Day 18, serum P levels in the peripheral circulation and in the ovarian vein were declining even more dramatically. Daily administration of P (4 mg) and E (0.5 micrograms) simultaneously with GnRH-Ag at the dose of 5 micrograms/day from Days 11 through 14 reversed the abortifacient effect of GnRH-Ag and maintained pregnancy indicating that the GnRH-Ag effect is not directly on the uterus. Ovarian vein levels of T on Days 14 or 18 of pregnancy were either not different from controls at 1407 +/- 163 or 1476 +/- 122 pg/ml, respectively, or increased dramatically in certain groups. Ovarian vein levels of E were either not different from controls at 292 +/- 13 pg/ml on Day 14 or increased significantly in rats treated at the dose of 1 microgram/day of GnRH-Ag. However by Day 18, treatment with GnRH-Ag at all doses suppressed ovarian secretion of E. These results suggest that while the GnRH-Ag induces abortion in rats by suppressing ovarian production of P, this abortifacient effect is not due to a fall in ovarian T levels nor to its aromatization to E in the ovary.     

Effects of prostaglandins on peripheral progesterone and uterine diamine oxidase in the pregnant hamster

Serum progesterone and uterine levels of diamine oxidase (DAO) activity were determined during pregnancy in hamsters. Progesterone was elevated on Day 1 of pregnancy, had a transient peak on Day 5, remained relatively constant on Days 6–10, and then increased on Days 13 and 14. Uterine DAO activity could not be detected until Day 7 of pregnancy, approximately 1 $\text{1}\text{2}$ days after the initiation of implantation. DAO activity was associated with placental tissue, and more than 90% of the activity was localized in the maternal placenta. The temporal relationship between changes in serum concentrations of progesterone and uterine levels of DAO activity following PG administration also was studied. Serum progesterone was significantly depressed by 6 hr after treatment with PGs on Day 7 of pregnancy. However, uterine levels of DAO activity at 6 hr in the treated animals were not different from those in control animals. In contrast, both the serum progesterone concentrations and uterine levels of DAO activity were significantly lower at 24 hr after PG treatment. The effects of PG treatment on uterine DAO activity were completely blocked by concomitant administration of progesterone. However, concomitant administration of Provera® only blocked the effect of one PG analog that was tested (9-deoxo-9-methylene-16,16-dimethyl0-PGE₂). The data indicate that changes in uterine DAO activity following treatment with the PGs used here are primarily a consequence of a decrease in peripheral progesterone (i.e. a luteolytic effect of the PG).     

Effects of RMI 12,936, a synthetic antiprogestational steroid, on the oestrous cycle and ovulation in the rat.

RMI 12,936 inhibited the vaginal cycle and ovulation in the rat. This effect was not mimicked by oestrogen and was partly reversed by progesterone. Ovulation was restored by injection of hCG and the inhibition was associated with reduced cyclic and tonic LH secretion while hypophysial LH levels were generally unaffected. Hypophysial sensitivity to LH-RH was reduced compared with that when ovulation was blocked with sodium pentobarbitone. It is concluded that RMI 12,936 blocks ovulation by causing a reduction in hypophysial sensitivity to LH-RH and that this is probably an antiprogestational effect.     

Effect of a deslorelin implant in a timed artificial insemination protocol on follicle development, luteal function and reproductive performance of lactating dairy cows

This study examined the influence of a GnRH agonist containing either 450 or 750 microg of deslorelin in an implant form or a gonadorelin injection (control) to induce ovulation in the Ovsynch protocol on pregnancy rates (PR), embryonic loss, and ovarian function in 593 lactating Holstein cows. Cows were given two injections of PGF2alpha 14 days apart, followed 14 days later by the Ovsynch protocol, and were timed artificially inseminated (TAI) at 68 +/- 3 days postpartum. Blood samples for determination of plasma progesterone concentrations were collected at 24 and 10 days prior to and 11 days after TAI. Pregnancy was diagnosed on Day 27 and reconfirmed on Day 41 after TAI. Non-pregnant, not re-inseminated cows at Day 27 had their ovaries examined by ultrasonography, and the number and size of follicles and presence of luteal tissue were determined. Simultaneously, these cows were re-synchronized with the Ovsynch protocol. Pregnancy during the re-synchronization period was determined between 35 and 41 days after insemination. On Day 27, PR were higher for control (39.0%) and deslorelin 450 microg (DESLORELIN 450) implant (41.3%) than for those receiving the deslorelin 750 microg (DESLORELIN 750) implant (27.5%; P<0.05). Pregnancy losses tended to decrease for DESLORELIN 450 compared with control (5.0% versus 12.7%; P<0.13). Plasma progesterone concentrations did not differ significantly among treatments. Deslorelin suppressed ovarian activity and decreased PR during the re-synchronization period compared with control. The percentage of non-pregnant animals that were re-inseminated by Day 27 was less for deslorelin compared with control. In conclusion, incorporation of an implant of the GnRH agonist deslorelin to induce ovulation in the Ovsynch protocol has the potential to reduce pregnancy losses, but the response was dependent upon implant concentration. Evaluation of lower doses to minimize the negative effects on subsequent fertility is warranted.     

Rat placental luteotropin: initial secretion and luteolytic quality

The secretion of placental lactogen begins early in pregnancy. Previous studies indicate that rat placental lactogen (rPL) is secreted from Day 8 of pregnancy and that it is luteolytic as well as luteotrophic. This study establishes the onset of both the luteotrophic and the luteolytic effects of placental lactogen in pregnant rats subject to timed hypophysectomy. Pregnancy was preserved in all groups with the administration of dydrogesterone (9 beta, 10 alpha-pregna4,6-diene-3, 20 dione), a progesterone analog, and diethylstilbestrol, an estrogen analog. Plasma progesterone and 20 alpha-hydroxypregn-4-ene-3-one (20-OHP) were measured in serial serum samples by RIA. The data indicate that rPL is secreted as early in pregnancy as the seventh day. Rats hypophysectomized on Day 6 of pregnancy or later had ovaries that contained corpora lutea that secreted increasing quantities of progesterone during pregnancy. On Day 16 serum progesterone values were lowest in animals operated on Days 4 and 5 compared to animals operated on Days 6 or 8. The 20-OHP serum values from animals operated on Days 4 and 5 declined steadily from Day 8 to Day 16. These findings indicate progestational incompetency, which was confirmed morphologically. Thus, rPL secretion begins by Day 7 and it is both luteotrophic and luteolytic.     

Effectiveness of administration of gonadotropin-releasing hormone at Days 11, 14 or 15 after anticipated ovulation for increasing fertility of lactating dairy cows and non-lactating heifers

One strategy for improving fertility in cattle is mid-cycle administration of GnRH to increase progesterone secretion and delay luteolysis. This strategy might be especially useful during hot weather because heat stress increases uterine prostaglandin release and reduces development of the elongating embryo. A series of experiments was conducted to test the efficacy of GnRH for increasing fertility. There was no effect of administration of 100 microg GnRH at Day 11 after anticipated ovulation on pregnancy rates in virgin heifers subjected to timed artificial insemination (TAI) during the summer. Similarly, there was no beneficial effect of administration of GnRH at Day 11 after anticipated ovulation on pregnancy rates of lactating cows subjected to TAI in summer and winter. Three experiments tested effects of injection of GnRH at Days 14 or 15 after anticipated ovulation on pregnancy rates of lactating cows. The first experiment used 477 lactating cows subjected to TAI. Cows receiving GnRH at Day 14 had higher pregnancy rates in both summer and winter than cows receiving vehicle (20.3 versus 12.7%, P<0.02). When this experiment was repeated during summer with 137 cows, there was a negative effect of GnRH treatment at Day 14 on pregnancy rate. In the third experiment, lactating cows during summer were inseminated at detected estrus and cows were assigned to treatment with either GnRH or vehicle at Days 14 or 15 after insemination. Pregnancy rates were 25.6% (32/125) for cows receiving vehicle, 20.7% (19/92) for cows receiving GnRH at Day 14, and 20.3% (16/79) for cows receiving GnRH at Day 15. In conclusion, GnRH administration at Days 11-15 after anticipated ovulation or estrus did not consistently increase pregnancy rates in either cool or warm seasons.     

Pregnancy failure in hypophysectomized rats following LH-RH administration.

Daily LH-RH administration induced a dose related increase in fetal resorption in rats following hypophysectomy on Day 11 or Day 12 of pregnancy. Ovarian and adrenal weights, as well as serum progesterone levels, were significantly decreased by Day 18. Serum progesterone was also significantly lower than control in those animals that remained pregnant after receiving LH-RH post-hypophysectomy. These observations suggest that LH-RH exerts an anti-pregnancy effect via a placental:ovarian axis in this species.     

Effect of timing of prostaglandin administration, controlled internal drug release removal and gonadotropin releasing hormone administration on pregnancy rate in fixed-time AI protocols in crossbred Angus cows

Two experiments were conducted to investigate the effects of timing of prostaglandin F2(alpha) (PGF2(alpha)) administration, controlled internal drug release device (CIDR) removal and second gonodotropin releasing hormone (GnRH) administration on the pregnancy outcome in CIDR-based synchronization protocols. In Experiment 1, suckled Angus crossbred beef cows (n = 580) were given 100 microg of GnRH+a CIDR on Day 0. Cows in Group 1 (modified Ovsynch-P) received 25 mg of dinoprost (PGF2(alpha)) and CIDR device removal on Day 8 (AM), 100 microg of GnRH 36 h later on Day 9 (p.m.), and fixed-time AI (FTAI) 16 h later on Day 10 (47.5+/-1.1 h after PGF2(alpha)). Cows in Group 2 (Ovsynch-P) received 25mg of PGF2(alpha) and CIDR device removal on Day 7 (p.m.), 100 microg of GnRH 48 h later on Day 9 and FTAI 16 h later on Day 10 (66.6+/-1.2 h after PGF2(alpha)). Pregnancy rates were 56.5% (170/301) for Group 1 and 55.6% (155/279) for Group 2, respectively (P = 0.47). In Experiment 2, beef cows (n=734) were synchronized with 100 microg of GnRH+CIDR on Day 0, 25 mg of PGF2(alpha) and CIDR device removal on Day 7 and either 100 microg of GnRH 48 h later on Day 9 (Ovsynch-P) and FTAI 16 h later on Day 10 (64.9+/-3.3 h from PGF2(alpha)) or 100 microg of GnRH on Day 10 (CO-Synch-P) at the time of AI (63.2+/-4.2 h from PGF2(alpha)). Pregnancy rates were 48.8% (180/369) for Ovsynch-P and 44.7% (163/365) for CO-synch-P groups, respectively (P = 0.11). In both experiments, there was a locationxtreatment interaction (P<0.05); pregnancy rates between locations were different (P < 0.05) in the Ovsynch-P group. In conclusion, in a CIDR-based Ovsynch synchronization protocol, delaying administration of prostaglandin and CIDR removal by 12 h, or timing of the second GnRH by 16 h, did not affect pregnancy rates to FTAI. Therefore, there may be an opportunity to make changes in synchronization protocols with out adversely affecting FTAI pregnancy rates.     

Changes in pituitary prolactin responsiveness to TRH during pregnancy

Prolactin plasma concentration during pregnancy was determined in rats treated with thyrotropin-releasing hormone (TRH). Day 0 of pregnancy was defined as the day sperm were first found in the vagina. All blood samples were obtained in unanesthetized rats which had previously received a cannula in the right common carotid. On Day 8 of pregnancy, plasma prolactin concentrations reached a peak between 2400 and 0800 hr (lights on from 0600 to 1800 hr). Injection of TRH (1 microgram/kg body wt) via the carotid artery increased plasma prolactin levels within 5 min. The largest increase occurred when TRH was given during the prolactin surge, whereas much smaller effects were found when TRH was given at the beginning or after the end of the surge period. Thus, the sensitivity of the prolactin cell to TRH appears to be the greatest when the secretory activity of the cell is high. It was then determined whether there was any change in the sensitivity of the prolactin cell to TRH after the prolactin surges had disappeared at midpregnancy. Injection of TRH between 1100 and 1200 hr increased prolactin less on Day 12 than on Day 8 of pregnancy. Since placental lactogen (PL) levels in the plasma are high on Day 12 compared to Day 8, and are inhibitory to prolactin secretion, it was reasoned that PL may be the factor which caused the reduced sensitivity to TRH. However, hysterectomy on Day 11 failed to increase the pituitary responsiveness to TRH the next day. In summary, these data indicate that the pituitary responsiveness to factors that stimulate prolactin, such as TRH, varies with relation to the time of pregnancy or presence of the nocturnal surge. What cellular mechanism is responsible for these sensitivity changes is not known.     

Comparison of synchronization of ovulation with timed insemination and exogenous progesterone as therapeutic strategies for ovarian cysts in lactating dairy cows

The objective of this study was to compare the effectiveness of the Ovsynch and controlled internal drug releasing (CIDR) protocols under commercial conditions for the treatment of cystic ovarian disease in dairy cattle. A total of 401 lactating dairy cows with ovarian cysts were alternatively allocated to two treatment groups on the day of diagnosis. Cows in the Ovsynch group were treated with GnRH on Day 0, PGF2alpha on Day 7, GnRH on Day 9, with timed insemination 16-20 h later. Cows in the CIDR group were treated with a CIDR insert on Day 0 for 7 days; on Day 7, the CIDR was removed, and cows were treated with PGF2alpha. All cows in the CIDR group were observed for estrus and cows exhibiting estrus within 7 days following removal of the CIDR and PGF2alpha administration were inseminated. The outcomes of interest for this experiment were the likelihood to be inseminated, return to cyclicity (determined by a CL on Day 21), conception and pregnancy rates. Data for these variables were analyzed using logistic regression. The percentage of cows inseminated in the Ovsynch and CIDR groups were 82 and 44%, respectively. Cows in the Ovsynch group were 5.8 times more likely to be inseminated than cows in the CIDR group. Cows with a low BCS were 0.48 times less likely to be inseminated than cows with a high BCS. The percentage of cows with a CL on Day 21 for the Ovsynch and CIDR groups was 83 and 79%, respectively (P > 0.05). Cows with a low BCS were 0.49 times less likely to have CL on Day 21 than cows with a high BCS. Conception and pregnancy rates for cows in the Ovsynch group were 18.3 and 14.4%, respectively. Conception and pregnancy rates for cows in the CIDR group were 23.1 and 9.5%, respectively. There was no significant differences between conception or pregnancy rates in cows in both groups. Primiparous cows were 2.6 times more likely to conceive than multiparous cows. In conclusion, the results of this study suggested that fertility was not different between cows with ovarian cysts treated with either the Ovsynch or the CIDR protocols in this dairy herd. In addition, primiparous cows had an increased likelihood for conception compared to multiparous cows, and cows with a low BCS were less likely to be inseminated or have a CL on Day 21, regardless of treatment.     

Follicular development during early pregnancy and the estrous cycle of the sow

The objective of this study was to monitor and compare follicle populations and follicular development in pregnant and nonpregnant sows from Day 3 to Day 20 after breeding. Twenty-four sows were paired within parity on the day of artificial insemination and were randomly allocated within pair for insemination with either killed (n=12) or live spermatozoa (n=12). All the sows were artificially inseminated with the pooled ejaculate of the same boar. From Day 3 through Day 20 post estrus, ovarian follicles were scanned daily by ultrasonography. Ultrasound images were recorded on videotape and were retrospectively analyzed. Follicles were mapped to indentify the existence of follicular waves. The follicles were then classified as small (< 3 mm), medium (3-5 mm), or large (>/=5 mm). Pregnancy diagnosis was performed on Day 21 by ultrasonography. Pregnant sows maintained a constant proportion of the follicle population in the small, medium and large follicle categories. However, in the nonpregnant sows, the proportion of follicles in the various size categories remained constant until Day 15. Thereafter, the proportion of small follicles decreased (P < 0.05) from Day 15 to 20, and the proportions of medium and large follicles increased (P < 0.05). The predictability of pregnancy status on Day 20 based on follicle populations in any of the 3 follicle categories was low. Moreover, there was no evidence of follicular waves during the estrous cycle or early pregnancy. In conclusion, the proportion of small follicles decreased while medium and large follicle increased from Day 15 through Day 20 of the estrous cycle, but not during a similar stage of pregnancy. This latter finding concurs with follicle recruitment from the pool of small follicles for ovulation following PGF2alpha secretion to induce luteolysis, which reduces progesterone concentrations and thereby allows for the stimulation of the pool of small follicles by gonadotropins.     

Estrus synchronization in beef cows: comparison between GnRH+PGF2alpha+GnRH and PRID+PGF2alpha+eCG

The aim of this study was to compare two protocols for estrus synchronization in suckled beef cows over a 2 years period. The population studied consisted of 172 Charolais and 168 Limousin cows from 12 and 14 beef herds, respectively. In each herd, cows were allotted to groups according to parity, body condition score and calving difficulty. Cows in Group 1 (n=174) received PRID on Day-8 with estradiol benzoate (10mg, vaginal capsule), dinoprost on Day-4 (25mg i.m.), eCG on Day 2 (500 IU i.m.). The PRID was removed on Day-2 and cows were inseminated on Day 0, 56 h after PRID was removed. Cows in Group 2 (n=166) received GnRH on Day-10 (100 microg i.m.), dinoprost on Day-3 (25mg i.m.) and GnRH on Day-1 (100 microg i.m.), and were inseminated on Day 0, 16-24h after the last GnRH treatment. Plasma progesterone concentrations were measured to determine cyclicity prior to treatment (Days-20 and -10), to confirm the occurrence of ovulation (Days 0 and 10) and to determine the apparent early pregnancy rate (Days 0, 10 and 24). Pregnancy diagnosis was performed by ultrasonography between Days 35 and 45. The effects of various factors on ovulation, apparent early pregnancy and pregnancy rates were studied using logistic mixed models. There was no significant difference between Groups 1 and 2, respectively, for the cyclicity rate before treatment (80.5% versus 80.1%), for apparent pregnancy rate on Day 24 (62.1% versus 54.8%, P=0.09) and for pregnancy rate on Days 35-45 (53.8% versus 46.3%, P=0.16). Ovulation rate was higher (P<0.01) in Group 1 (90.8%) than in Group 2 (77.1%) and was affected by cyclicity prior to treatment in Group 2 but not in Group 1 (Group 1: 88.2% in anestrous cows versus 91.4% in cyclic cows; Group 2: 45.5% in anestrous cows versus 85.0% in cyclic cows, P interaction=0.05). Apparent pregnancy rates on Day 24 were influenced by the year of study (52.4% versus 68.8%, OR=2.12, P<0.01) and by the cyclicity before treatment (anestrous cows 46.3% versus cyclic cows 61.5%, OR=1.86, P<0.05). Pregnancy rates at 35-45 days were influenced by the year of study (44.2% versus 59.8%, OR=1.92, P<0.01). In conclusion, although pregnancy rates were similar for the two treatments, the combination of GnRH+PGF2alpha+GnRH in suckled beef cows induced a lower rate of ovulation than treatment with PRID+PGF2alpha, particularly in anestrous cows.     

Effect of embryo age and recipient asynchrony on pregnancy rates in a commercial equine embryo transfer program

In the present study, 809 uterine flushes and 454 embryo transfers performed in mares over a 4-yr interval were examined to evaluate the effects of: (1) the day of embryo collection on recovery rates; (2) the degree of synchrony between donor and recipient mares on pregnancy rates; (3) the recipient day post ovulation on pregnancy rates; and (4) the age of the embryo at recovery on pregnancy rates at 60 days. Uterine flushes were performed on Days 6, 7, 8, 9, and 10 (Day 0 = ovulation) and embryos were transferred to recipients with degrees of synchrony varying between +1 to −6 (recipient ovulated 1 day before through 6 days after the donor). Recipient mares ranged from 2 to 8 days post ovulation. Embryo recovery rates were similar for flushes performed on Day 7 (61%), Day 8 (66%), Day 9 (59%), and Day 10 (56%), but the embryo recovery rate was lower (P < 0.03) for flushes performed on Day 6 (42%) compared with all other days. Pregnancy rates for various degrees of synchrony were as follows: +1 (71%), 0 (77%), −1 (68%), −2 (63%), −3 (66%), −4 (76%), −5 (61%), and −6 (27%). The −6 day of degree of synchrony had the lowest (P < 0.05) pregnancy rate compared with all other days, but there was no significant difference among +1 to −5 days. There was a lower (P < 0.05) pregnancy rate for embryos transferred to recipient mares on Day 2 (33%) compared with mares on Day 3 (66%), Day 4 (66%), Day 5 (62%), Day 6 (55%), Day 7 (58%), and Day 8 (56%). Pregnancy rate was higher (P < 0.05) for Day 7 (76%) embryos compared with Day 6 (50%), Day 8 (64%), and Day 9 (44%) embryos; Day 9 embryos resulted in lower (P < 0.05) pregnancy rates than Days 7 or 8 embryos. In conclusion, this study demonstrated that: (1) embryo recovery rates between Days 7 and 10 were similar and acceptable (e.g., 63% 488/771); (2) the degree of synchrony between donor and recipient mares does not need to be as restricted as previously reported in horses. Acceptable pregnancy rates (e.g., 70%, 99/142) were obtained even when recipient mares ovulated 4 to 5 days after the donors; (3) similar pregnancy rates were obtained when recipient mares received embryos within a large range of days post ovulation (Days 3 to 8); and (4) Day 7 embryos produced higher pregnancy rates when compared with Days 8 and 9 embryos. In clinical terms, the application of these new findings will be beneficial to large equine embryo transfer operations in producing more pregnancies per season.     

Effect of resynchronization with GnRH on day 21 after artificial insemination on pregnancy rate and pregnancy loss in lactating dairy cows

The objectives of the present study were to determine the effects of resynchronization with GnRH on Day 21 after artificial insemination (AI) on pregnancy rate and losses of pregnancy in lactating dairy cows. Holstein cows (n=585) on two dairy farms were assigned to one of two treatments in a randomized complete block design. On Day 21 after a pre-enrollment AI, animals assigned to the resynchronization (RES) group received 100 microg of GnRH i.m., whereas animals in the control (CON) group received no treatment. All animals were examined ultrasonographically on Days 21 and 28 after AI, and blood samples were taken for progesterone measurement on Day 21. Pregnancy was diagnosed on Day 28 and reconfirmed 14 days later. Nonpregnant cows on Day 28 were inseminated using timed AI after the completion of the Ovsynch protocol 10 and 17 days after enrollment in the study for RES and CON groups, respectively. Progesterone concentration > or =2.35 ng/ml was used as an indicator of pregnancy on Day 21. For RES and CON cows, pregnancy rate at Days 21 (70.9% versus 73.0%, P<0.56), 28 (33.1% versus 33.6%; P<0.80) and 42 (27.0% versus 26.8%; P<0.98) after the pre-enrollment AI did not differ. Administration of GnRH on Day 21 after AI had no effect on pregnancy loss in RES and CON groups from days 21 to 28 (53.2% versus 53.5%; P<0.94) and days 28 to 42 (17.9%; P<0.74) after AI. Pregnancy rate after the resynchronization period was similar for both treatment groups. Resynchronization with GnRH given on Day 21 after AI for initiation of a timed AI protocol prior to pregnancy diagnosis does not affect pregnancy rate and pregnancy loss in lactating dairy cows.     

Changes and localization of ovarian carbonyl reductase during pseudopregnancy and pregnancy in rats

The present study investigates changes in the activity and enzyme content of ovarian carbonyl reductase (CR), which catalyzes the reduction of 9-keto and 15-ketoprostaglandins in rats during pseudopregnancy and pregnancy. The activity of ovarian CR decreased from the onset of pseudopregnancy and pregnancy, reaching 20-30% of the Day 1 value by Day 12 of pseudopregnancy and 50-60% of the Day 1 value by Day 14 of pregnancy. In the case of pregnant rats, the enzyme activity maintained a minimal level between Day 14 of pregnancy and Day 22 of parturition. An acute increase of the enzyme activity was found on the morning after parturition. The CR content in the ovary maintained a constant level from Day 1 to Day 12 of pseudopregnancy and to Day 18 of pregnancy. In pregnant rats, there was a gradual decrease after 18 days and then a surge during parturition. CR was primarily localized in interstitial gland cells and in theca interna cells but was not found in corpora lutea cells in the ovary during the estrous cycle. Additional immunostaining was also observed in corpora lutea cells during pseudopregnancy and pregnancy. The changes in ovarian CR activity, i.e. the rapid decrease with progressing pseudopregnancy and pregnancy, correlated with the increase in progesterone and the decrease in LH. These results indicate that rat ovarian CR may be regulated via the hypothalamo-pituitary-ovarian axis and may also be involved in luteal function.     

Regulation of placental villous angiopoietin-1 and -2 expression by estrogen during baboon pregnancy

We recently showed an increase in vascular endothelial growth factor (VEGF), decrease in angiopoietin-1 (Ang-1) and unaltered Ang-2 expression by the villous placenta with advancing baboon pregnancy. Moreover, placental VEGF expression was increased by estrogen in early pregnancy. In the present study, we determined whether placental Ang-1 and Ang-2 are regulated by estrogen. Ang-1 and Ang-2 mRNA and protein were determined by RT-PCR and immunocytochemistry in the placenta of baboons on Day 60 of gestation (term is 184 days) after administration of estrogen precursor androstenedione on Days 25-59 or on Day 54 after acute estradiol administration. Chronic androstenedione treatment increased serum estradiol levels three-fold (P < 0.001) and decreased (P < 0.05) villous cytotrophoblast Ang-1 mRNA to a level (0.36 +/- 0.08 relative to 18S rRNA) that was one-third of that in untreated animals (0.98 +/- 0.26). Within 2 hr of estradiol administration, cytotrophoblast Ang-1 mRNA was decreased to a level (0.24 +/- 0.05) one-fifth (P < 0.05) of that in untreated animals (1.14 +/- 0.23). However, Ang-2 mRNA levels were unaltered. Ang-1, Ang-2 and estrogen receptors alpha and beta protein were localized within villous cytotrophoblasts providing a mechanism for estrogen action at this site. In summary, estrogen increased VEGF, decreased Ang-1, and had no effect on Ang-2 expression within placental cytotrophoblasts during early baboon pregnancy. We propose that the estrogen-dependent differential regulation of these angioregulatory factors underpins the unique pattern of neovascularization established within the villous placenta during primate pregnancy.     

Progesterone supplementation during the early fetal period reduces pregnancy loss in high-yielding dairy cattle

It was hypothesized that sub-optimal progesterone concentrations during the late embryo and early fetal period may act to compromise conceptus development in dairy cattle. The aim of the present study was to test this hypothesis by supplementing pregnant cows with exogenous progesterone following pregnancy diagnosis. The study population consisted of 1098 pregnant lactating cows. Pregnancy was diagnosed by transrectal ultrasonography between 36 and 42 days after insemination. Animals found to be pregnant were randomly assigned to the Control (untreated cows, n = 549) or Treatment (n = 549) groups. Cows in group Treatment were fitted at pregnancy diagnosis with a progesterone releasing intravaginal device (PRID) containing 1.55 g of progesterone, for 28 days. Cows were then subjected to a further diagnosis by palpation per rectum on Day 90 of gestation. Pregnancy loss was registered in 95 (8.7%) cows on Day 90 of pregnancy: 66 (12%) in group Control and 29 (5.3%) in group Treatment. Logistic regression analysis indicated that there were no significant effects of herd, bull, milk production, service number, days in milk at pregnancy and lactation number. Based on the odds ratio, treated cows were 2.4 (1/0.41) times less likely to miscarry, whereas the risk of pregnancy loss was 1.6 times higher in cows that became pregnant during the warm period in comparison to the cool period. These results support the hypothesis that sub-optimal progesterone concentrations in high producer dairy cows may compromise conceptus development. Under these conditions, intra-vaginal progesterone supplementation has the potential to reduce the incidence of pregnancy loss during the early fetal period.