Mechanism of the postcoital contraceptive effect of LH-RH in the rat. I. Serum hormone levels during chronic LH-RH Administration.

The mechanism of the postcoital contraceptive effect of luteinizing hormone-releasing hormone (LH-RH) was studied in the rat. 200 mcg of LH-RH administered daily over Days 1-7 of pregnancy produced a dramatic inhibition of pregnancy. This inhibition was directly correlated with induced 'surges' in serum LH over Days 1-4. Serum follicle stimulating hormone and prolactin were, in general, reduced over this same time period. A 48-hour delay in the preimplantation (Day 3) 'surge' in serum estradiol accompanied by a significant (ps less than .05 and less than .01) reduction in serum progesterone on Days 3, 4, 6, and 7 was also observed. The delayed 'surge' in serum estradiol on Day 5 and reduction in serum progesterone was correlated with an increase in folliculogenesis and luteolysis of established corpora lutea, respectively. These data suggest that in the rat LH-RH induces a rise in serum LH which is luteolytic during pregnancy and delays the serum estradiol surge necessary for normal implantation.     

The effects of luteinizing hormone releasing hormone (LH-RH) in pregnant rats. I. Postnidatory effects.

The effects of LH-RH on pregnancy in rats were investigated. A single 500 mcg injection of LH-RH on Days 9, 10, or 11 of pregnancy terminated pregnancy, whereas injection on Days 6-8 or 13-16 had little or no effect. The ED 50 on Day 10 for b.i.d. administration was 150 mcg and 550 mcg for a single injection. Administration on Day 9 was followed by a decrease in circulating progesterone levels on Days 10 and 11. The administration of large doses of progesterone reversed the effects of LH-RH administration on Days 7-12. Treatment with estradiol-17beta did not potentiate the effect of progesterone, but appeared to slightly retard fetal resorption when administered alone. The results suggest that the antifertility effect of LH-RH is mediated via functional luteolysis.     

Role of the nongravid part of the uterus in the luteolytic effects of estrogen in pregnant rats

Effects of a low dose of estradiol on the luteal function were studied in intact pregnant rats. The pregnant rats received daily sc injections of 0.1 microgram estradiol or sesame oil from day 7 to 14 of pregnancy (day 1 = day of insemination). Serum progesterone levels on day 15 were significantly lower in the estrogen-treated group than in the oil-treated group. In order to study how estrogen induced luteolysis, the pregnant rats received each of the following treatments on day 7 of pregnancy: (1) The uterus except that containing a single conceptus was removed by hysterectomy (hysterectomy group); (2) All but a single conceptus were removed by aspiration, so that rats carried only a single conceptus with the whole part of the nongravid uterus (aspiration group). Each group of rats received also sc injections of 0.1 microgram estradiol or sesame oil from day 7 to 14 of pregnancy. Estradiol treatment caused a significant decline in serum progesterone levels in the aspiration group on day 15, but this was not the case in the hysterectomy group. There was no significant difference in serum LH levels among any of the groups on day 15 of pregnancy. These results indicated that estradiol induced luteolysis in the intact pregnant rats, which would, at least in part, be mediated through the uterus.     

Estradiol-induced blockade of ovulation in the cow: effects on luteinizing hormone release and follicular fluid steroids

Administration of 10 mg estradiol valerate (EV) to nonlactating Holstein cows on Days 16 of the estrous cycle prevented ovulation in 7 of 8 cows for 14 days post-injection. In these 7 cows, the timing of luteolysis and the luteinizing hormone (LH) surge was variable but within the normal range. At 14 days post-treatment, each of these cows had a large (greater than 10 mm) follicle, with 558 +/- 98 ng/ml estradiol-17 beta, 120 +/- 31 ng/ml testosterone, and 31 +/- 2 ng/ml progesterone in follicular fluid (means +/- SE). A second group of animals was then either treated with EV as before (n = 22), or not injected (control, n = 17) and ovariectomized on either Day 17, Day 18.5, Day 20, or Day 21.5 (24, 60, 96, or 132 h post-EV). Treatment with EV did not influence the timing of luteolysis, but surges of LH occurred earlier (59 +/- 8 h post-EV vs. 100 +/- 11 h in controls). The interval from luteolysis to LH peak was reduced from 44 +/- 6 h (controls) to 6.9 +/- 1.5 h (treated). Histologically, the largest follicle in controls tended to be atretic before luteolysis, but nonatretic afterwards, whereas the largest follicle in treated animals always tended to be atretic. Nonatretic follicles contained high concentrations of estradiol (408 +/- 59 ng/ml) and moderate amounts of testosterone (107 +/- 33 ng/ml) and progesterone (101 +/- 21 ng/ml), whereas atretic follicles contained low concentrations of estradiol (8 +/- 4 ng/ml) and testosterone (12 +/- 4 ng/ml), and either low (56 +/- 24 ng/ml) or very high (602 +/- 344 ng/ml) concentrations of progesterone. This study suggests that EV prevents ovulation by inducing atresia of the potential preovulatory follicle, which is replaced by a healthy large follicle by 14 days post-treatment.     

Effects of estrogen and prostaglandin on progesterone-delayed farrowing

Effects of estradiol benzoate and prostaglandin F(2alpha) (PGF(2alpha)) on concentrations of progesterone and estrogen in serum and the percentage of live births were determined in 21 gilts treated with exogenous progesterone in late gestation. All gilts received progesterone (25mg s.c. four times daily) from Days 108 through 113 of gestation. Gilts receiving no other treatments (controls) had elevated levels of progesterone through 1800 h on Day 114 (29.2 +/- 11.4 ng/ml) and farrowed at 115.6 +/- 0.3 d of gestation with a relatively low percentage of live births (66.8 +/- 17.3). Gilts treated with PGF(2alpha) administered at 0600 h on Day 114 had less (P<0.01) progesterone by 1800 h (7.0 +/- 1.3 ng/ml) relative to that of the controls, but they had similar gestation lengths (115.5 +/- 0.3) and percentages of live births (50.0 +/- 16.2). Administration of estradiol benzoate (10 mg) to gilts at 0600 h on Day 114 did not reduce progesterone on Day 114 or the gestation length relative to that of the control gilts, but it did increase (P<0.05) the percentage of live births (100%).     

Reactivation of regressing corpora lutea by estradiol in the pregnant rat: dependence on placental lactogen

Previous investigations have clearly demonstrated that estradiol maintains corpus luteum function. However, it is unknown whether estradiol can restimulate progesterone synthesis and/or growth of corpora lutea that have already undergone luteolysis. The present study was designed to determine 1) whether estradiol can reactivate the steroidogenic capacity and/or growth of corpora lutea that are deprived of luteotropic support, 2) whether estradiol affects progesterone metabolism, and 3) whether the action of estradiol is related to levels of rat placental lactogen in the peripheral circulation. Rats were hypophysectomized and hysterectomized on Day 12 of pregnancy and were treated between Days 12 and 15 with either estradiol (100 micrograms/day) or 1-cm testosterone implants. Both treatments are known to maintain luteal concentrations of estradiol at physiological levels. In vivo treatment with either estradiol or testosterone prevented the drop in progesterone production and maintained the concentration of serum progesterone at levels found in intact pregnant rats. This action was not due to an alteration in the rate of metabolism of progesterone to 20 alpha-hydroxyprogesterone, since peripheral serum levels and in vitro production of 20 alpha-hydroxyprogesterone were unaffected by estradiol. When testosterone treatment was started 24 and 48 h after hypophysectomy and hysterectomy, at a time when progesterone production had been markedly reduced and luteal growth had ceased, a restimulation of both progesterone synthesis and luteal growth was observed. However, in all cases the ability of estradiol to stimulate progesterone was finite, and corpora lutea ceased to respond by Day 17, coincident with the time that rat placental lactogen became undetectable in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Change in responsiveness of rabbit corpus luteum to prostaglandin F-2 alpha during pregnancy and pseudopregnancy.

Previous studies have suggested that prostaglandin F-2 alpha (PGF-2 alpha) may have a role in luteolysis in rabbits. Rabbits (4-6/group) were given a single injection of saline, or 100, 500 or 2500 micrograms PGF-2 alpha (i.m.) on Day 7, 9, 12 or 15 of pregnancy or pseudopregnancy. Daily blood samples were taken via the marginal ear vein before and for 3 days after the PGF-2 alpha injection. Concentrations of serum progesterone were determined by radioimmunoassay in pseudopregnant rabbits. There were no significant differences between PGF-2 alpha-treated and control rabbits on Days 7 or 9. On Day 12 of pseudopregnancy, progesterone concentration was significantly (P less than 0.05) lower in treated than in control rabbits, the effect being dose dependent. On Day 15 of pseudopregnancy, it was not possible to distinguish between controls and treated groups because luteolysis occurred in all rabbits. In contrast, on Days 7 and 9 of pregnancy, the concentration of progesterone in treated groups was lower than in the control groups (P less than 0.05), the effect being dose dependent. This difference was maintained throughout the sampling period and resulted in termination of pregnancy. By Day 12 of pregnancy, the response to PGF-2 alpha was transient, with a significant decline in progesterone for only 2 days, followed by a return to control concentrations and normal delivery of litters. On Day 15 of pregnancy, no treatment with PGF-2 alpha significantly altered progesterone concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective release of follicle-stimulating hormone by 5 alpha-dihydroprogesterone in immature ovariectomized estrogen-primed rats

The effect of 5 alpha-dihydroprogesterone (5 alpha-DHP) on gonadotropin release was examined in the immature acutely ovariectomized (OVX) rat primed with a low dose of estradiol (E2). Treatment with various doses of 5 alpha-DHP given in combination with E2 increased levels of follicle-stimulating hormone (FSH) but had no effect on serum luteinizing hormone (LH). A single injection of a maximally stimulating dose of 5 alpha-DHP (0.4 mg/kg) stimulated increases in serum FSH at 1200 h and, 6 h later, at 1800 h. Pituitary LH and FSH content was dramatically enhanced by 1600 h and levels remained elevated at 1800 h. The administration of pentobarbital at 1200 h, versus 1400 h or 1600 h, prevented the increase in basal serum FSH levels at 1800 h, implying that the release of hypothalamic LH releasing hormone (LHRH) is modulated by 5 alpha-DHP. In addition, changes in pituitary sensitivity to LHRH as a result of 5 alpha-DHP were measured and a significant increase in the magnitude of FSH release was observed at 1200 h and 1800 h. Although the LH response to LHRH in 5 alpha-DHP-treated rats was not different from controls, the duration of LH release was lengthened. These results suggest that 5 alpha-DHP may stimulate FSH release by a direct action at the pituitary level. Together, these observations support the theory that 5 alpha-DHP mediates the facilitative effect of progesterone on FSH secretion and further suggests an action of 5 alpha-DHP in this phenomenon at both pituitary and hypothalamic sites.     

Role of luteinizing hormone-releasing factor (LH-RF) and LH on maintenance of early gestation in rats.

The role of luteinizing hormone (LH) and LH-releasing hormone (LH-RH) in the maintenance of early pregnancy in rats was studied. Serum levels of progesterone (P) and LH were measured daily in untreated pregnant rats from Day 4 through parturition. Serum levels of P and LH were determined on Days 11 and 15 of pregnancy in animals treated with antisera to LH (LH-A/S) and to LH-RH (LH-RH-A/S) on Days 8-10. Serum levels of P peaked on Days 7 and 16 in untreated animals, after which they declined sharply just before delivery. Serum LH fluctuated between 30-160 ng/ml during pregnancy but did not exhibit any distinctive peaks. Treatment with .2 ml LH-A/S on Days 8-10 reduced serum P to virtually undetectable levels on Day 11, and only a slight recovery was evident on Day 15. Lower doses of LH-A/S had no effect. Administration of 1.3 ml LH-RH-A/S had no effect on serum levels of P or LH, and did not impede fetal development. The results indicate that LH is essential to the luteotropic complex of early pregnancy in the rat, and also that LH-RH-A/S can maintain to some extent basal levels of P and LH during early pregnancy.     

Luteolytic effects of prostaglandin F2alpha on day 8 to 19 corpora lutea in the bitch

Luteolysis was induced in 5 experimental Beagle (8 cycles) and 7 client-owned bitches treated with 150 to 200 microg/kg, sc of prostaglandin F2alpha administered twice daily for 4 d, starting on Days 8 to 19 after the onset of cytological diestrus. Five experimental Beagle bitches had been mated during the estrus preceding treatment, and copulation had been confirmed in 2/7 client-owned bitches presented for termination of unwanted pregnancy. Serum progesterone concentration (mean +/- SD) declined from 26.1 +/- 66 ng/ml before treatment to 0.3 +/- 0.4 ng/ml on the fourth day of treatment One of the 7 client-owned bitches maintained her pregnancy even though serum progesterone concentrations were less than 0.5 ng/ml on the third and fourth day of treatment. Mean (+/- SEM) inter-estrous intervals before and following prostaglandin-induced luteolysis were 207.3 +/- 12.4 (n = 11 cycles in 6 bitches) and 95.5 +/- 20.0 d (n = 6 cycles in the same 6 bitches; P < 0.0001), respectively These results suggest that effective prostaglandin-induced luteolysis can be achieved with administration of 180 microg/kg during the third week of diestrus in pregnant and nonpregnant bitches.     

Quantitative changes in the metabolism of 20alpha-hydroxy-4-pregnen-3-one by rat hypothalamus and pituitary during proestrus.

The in vitro conversion of 20alpha-hydroxy-4-pregnen-3-one (20alpha-DHP) by medial basal hypothalamus and anterior pituitary was investigated throughout the day of proestrus in the 4-day cyclic rat. Reverse isotopic dilution analysis was utilized to quantitate the substrate remaining and three metabolic products: 20alpha-hydroxy-5alpha-pregnan-3-one, 5alpha-pregnane-3alpha,20alpha-diol and progesterone. Serum levels of 20alpha-DHP, progesterone, LH and FSH were measured by radioimmunoassay. Conversion of 20alpha-DHP to its 5alpha-reduced metabolites (20alpha-hydroxy-5alpha-pregnan-3-one and 5alpha-pregnane-3alpha,20alpha-diol) by the pituitary was constant throughout proestrus except for a significant decrease at 1600 h, near the end of the critical period. Although 5alpha-reduction of 20alpha-DHP by the hypothalamus fluctuated, it was relatively high at 1600 h and was lowest at 1400 h. Small amounts of progesterone (less than2%) were formed but there was not variation with time. The decrease in pituitary enzymic activity coincided with the time when serum levels of LH, FSH and progesterone were increasing but not with later times when the elevated serum levels were maintained. Thus, there may be endogenous regulation of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase activity in rat pituitary and perhaps hypothalamus on the afternoon of proestrus. The regulation and subsequent effects of quantitative changes in 5alpha-reduction of 20alpha-DHP by pituitary and hypothalamus remain to be elucidated.     

Distribution and metabolism of 20 alpha-hydroxylated progestins in the female rat

The C21 steroids, progesterone and 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-DHP) play pivotal roles in the initiation, timing and maintenance of ovulatory function and pregnancy in female mammals. They also have growth factor and central nervous system (CNS) effects; some of these are non-genomic effects mediated through 5 alpha-reduced and 3 alpha-hydroxylated derivatives. These studies examined the in vivo uptake and conversion of 20 alpha-DHP in selected CNS sites and peripheral tissues after injection of [(3)H]-20 alpha-DHP. The effects of steroid mass, time after injection, and ovariectomy, adrenalectomy and estradiol treatment were assessed in the pineal gland, preoptic area of the hypothalamus (POA), medial basal hypothalamus (MBH), midbrain, cerebellum, cerebral cortex, anterior pituitary (AP), uterus and skeletal muscle. Tissue extracts were analyzed by scintillation counting and chromatography to quantify and localize 20 alpha-DHP and its 5 alpha-reduced derivatives. Injection of increasing mass of [(3)H]-20 alpha-DHP to ovariectomized/adrenalectomized (ovx/adx) rats results in a linear increase in (3)H-steroid 10 min post injection in all tissues. (3)H-steroid content increases with time over 1 h post injection in the pineal, AP and uterus. Tissue differences in (3)H-steroid level are observed with higher levels in pineal, MBH, POA, AP and midbrain than in cerebral cortex and cerebellum, and in uterus, ovary and adrenal than in muscle. Ovariectomy, adrenalectomy and estradiol treatment affect (3)H-steroid levels in a tissue dependent manner, and the metabolites of 20 alpha-DHP in MBH and AP differ between groups. The findings demonstrate that target tissues, including areas of the CNS, are able to selectively take up and retain 20 alpha-DHP, and also support a physiological role for this progestin and its metabolites in modulation of CNS and reproductive functions.     

Binding of 5 alpha-dihydroprogesterone and other progestins to female rat anterior pituitary nuclear extracts

The specific binding of 5 alpha-dihydroprogesterone (5 alpha-DHP), progesterone and R5020 to anterior pituitary nuclear extracts was studied using ovariectomized rats treated with estradiol benzoate and progesterone. The binding equilibrium association constant for 5 alpha-dihydroprogesterone with different preparations of nuclear extract ranged from 4.0 +/- 0.54 microM-1 to 59 +/- 10 microM-1. The association constants for progesterone and R5020 were 0.39 +/- 0.81 nM-1 and 1.5 +/- 0.15 nM-1, respectively. The binding of 5 alpha-DHP was specific in that it could be competed only by R5020, progesterone and 5 alpha-DHP and not by other progesterone metabolites and other hormonal steroids tested. With [3H]-progesterone and [3H]R5020 as ligands the most efficient competitors also were R5020, progesterone and 5 alpha-DHP. Estrogen priming of ovariectomized rats consistently and significantly increased the number of binding sites for all three progestins and subsequent progesterone treatment enabled their detection at higher levels in the nuclei.     

Changes in the blood concentrations of progesterone and 20 alpha-hydroxypregn-4-en-3-one during late pregnancy in the conscious rat: a specific role for metabolic clearance rate

Near term in the rat, the blood concentration of progesterone falls while that of 20 alpha-hydroxypregn-4-en-3-one (20 alpha-DHP) increases. This is generally attributed to changes in ovarian secretion alone, but altered rates of hormone metabolism could also have a role. In the present study, therefore, metabolic clearance rate (MCR), production rate, and peripheral interconversion of progesterone and 20 alpha-DHP were measured on Day 16 of pregnancy, the time of maximal progesterone secretion, and on Day 22, one day prior to parturition. Conscious rats (n = 8 per group) were infused with either [3H]progesterone or [3H]20 alpha-DHP and the dynamics of progestin metabolism were calculated from the resultant isotopic and endogenous progesterone and 20 alpha-DHP concentrations. The blood concentration of progesterone declined by 69% between Day 16 (54 +/- 2 ng/ml) and Day 22 (17 +/- 2 ng/ml), and this was due to the combined effect of a 48% increase in the MCR and a 54% decrease in production rate of progesterone. In contrast, the production rate of 20 alpha-DHP was twofold greater on Day 22 compared to Day 16. As a result, the blood concentration of 20 alpha-DHP increased from 28 +/- 3 ng/ml on Day 16 to 40 +/- 6 ng/ml on Day 22, and this change would have been greater but for a concomitant increase (41%) in the MCR of 20 alpha-DHP. Although peripheral conversion of progesterone to 20 alpha-DHP was similar on Day 16 (transfer constant, 12.8 +/- 0.6%) and Day 22 (12.3 +/- 0.9%), the contribution of this conversion to total 20 alpha-DHP production fell from 32% to 7% between the two days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of progesterone and changes in prostaglandin F(2alpha) release during luteolysis and early pregnancy in llamas and the effect of treatment with flunixin meglumine

The secretory patterns of progesterone in relation to concentrations of 15-ketodihydro-PGF(2alpha) (PGFM) during the period of luteolysis or of maternal recognition of pregnancy were determined in the blood of llamas mated either with an intact or a vasectomized male. The ability of flunixin meglumine (FM) to postpone luteolysis in non-pregnant llamas was investigated by injecting the drug intravenously every 6 h at a dose of 2.2 mg/kg from days 6 to 12 post-copulation into a group of non-pregnant llamas. A pulsatile pattern of prostaglandin release was recorded during luteolysis in non-pregnant llamas, giving further support to the hypothesis that PGF(2alpha) is the luteolytic agent in llamas. The mean number of peaks per animal rose from 0.3 on day 7 to 3.8 on day 10 and then declined to 1.1 on day 12 with corresponding mean peak amplitude changing from 465 to 1234 and 566 pmol l(-1), respectively. In pregnant llamas, prostaglandin pulsatile release also occurred. The mean number of peaks per animal rose from 0.4 on day 7 to 0.8 on day 10 and then declined to 0.2 on day 11 and 0.6 on day 12, with corresponding mean peak amplitude changing from 494 to 676, 388 and 547 pmol l(-1), respectively. The transient decrease and subsequent recovery in progesterone concentrations was observed to occur in connection with prostaglandin release during early pregnancy. Oestradiol-17beta plasma peak concentrations attained after luteolysis were significantly higher than those recorded in early pregnant animals (around 30 pmol l(-1) and ll pmol l(-1)). Concentrations of PGFM decreased rapidly after the first administration of FM and remained low throughout the first 2 days of treatment. Thereafter, pulsatile release of prostaglandins started, and luteolysis proceeded; but a delay of 1-1.5 days in the progesterone decline was observed. Thus, it might be suggested that a higher dose and/or a more intensive injection schedule is required in llamas than in other ruminants to prevent luteolysis.     

小熊猫繁殖周期血清雌二醇和孕酮含量变化

为研究小熊猫繁殖周期血清雌二醇、孕酮含量变化规律,采用化学发光免疫分析法连续16 次测定了2只成体雌性小熊猫血清雌二醇和孕酮含量变化,历经发情间期、发情期和两次妊娠期;连续9次测定了7只小熊猫妊娠期的孕酮含量变化。结果:(1)发情间期,小熊猫血清雌二醇的水平一直维持在低水平(基础水平),进入发情前期,血清雌二醇水平明显升高,在发情期一直维持高水平,配种后迅速降至基础水平; (2)小熊猫血清孕酮含量在发情间期和发情期均维持在较低水平,直至发情期过后才出现升高,在妊娠期一直维持高水平,峰值出现在5 月;(3)发情的小熊猫不论妊娠与否,在妊娠期内血清孕酮含量均维持在高水平。研究表明:小熊猫血清雌二醇、孕酮含量变化能直接反映其繁殖规律,雌二醇对启动雌性小熊猫季节性繁殖起重要作用;在妊娠期内小熊猫血清孕酮含量升高不能作为判断小熊猫妊娠的标准;雌性小熊猫在妊娠期有假孕现象。     

Effect of continuous infusion of a GnRH agonist (Buserelin) on ovarian hormone secretion and estrous cycle length in cows

The importance of the ovarian steroid hormones estradiol and progesterone in the control of luteolysis in domestic ruminants is well established. However, there is a lack of studies specifically investigating the effect of stimulating "physiological" changes in endogenous estradiol or progesterone secretion on subsequent luteolysis. In this study we have stimulated endogenous ovarian hormone secretion by infusion of the GnRH analogue, Buserelin, and have assessed the effect of these changes on the timing of luteolysis. Concentrations of estradiol and progesterone were monitored in plasma samples collected from 6 mature, cyclic, lactating, Friesian cows during a control cycle and during a cycle in which Buserelin was infused via osmotic minipump (8.6 microg/h) for 28 days starting on Day 2 of the cycle. Buserelin infusion had little effect on progesterone secretion but did result in a marked stimulation of estradiol secretion from Days 6 to 10 of the cycle (treated cycle 4.3+/-0.2 pg/mL; control cycle 1.8+/-0.3 pg/mL; P<0.001). In addition, there was a significant advancement in the timing of luteolysis during the Buserelin -infused cycle (Day 19.3+/-0.3 compared with Day 21.3+/-0.4; P<0.01). In this study, we have found that infusion of buserelin caused both a significant stimulation of estradiol secretion from the first follicle and a significant advancement in the timing of luteolysis. We hypothesise that the increased secretion of estradiol may have been involved in causing this advancement of luteolysis.     

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).     

Estradiol production by preimplantation blastocysts and increased serum progesterone following estradiol treatment in llamas

Estradiol is a potential candidate for the blastocyst signal responsible for maternal recognition of pregnancy in the llama (Lama glama). Two experiments were conducted to determine if the llama blastocyst produces estradiol during the presumed period of maternal recognition of pregnancy and if exogenous estradiol can extend the luteal phase. In Experiment 1, llamas were superovulated with eCG and mated 7 days later (Day 0=day of mating). Blastocysts were collected nonsurgically on Days 7, 9, or 11 or at necropsy on Days 13 and 15 post-mating and cultured for 48h. Conditioned medium was recovered, replaced with fresh medium at 24-h intervals, and assayed for estradiol-17beta. Estradiol production (pg/blastocyst) over the 48-h culture increased (P<0.05) by day of gestation where more estradiol (P<0.05) was produced by Day 11 compared to Day 7 blastocysts, Day 13 compared to Days 7-11 blastocysts, and Day 15 compared to Days 7-13 blastocysts. A dramatic increase was observed between Days 11 and 13 when estradiol production by Day 13 blastocysts increased (P<0.05) more than 50-fold. In Experiment 2, 30 females were induced to ovulate with hCG (Day 0=day of hCG injection). Starting on Day 7 and continuing through Day 15, animals received daily injections i.m. of 0 (n=11), 5 (n=7), or 10mg (n=12) estradiol benzoate (EB) dissolved in isopropylmyristate. Sera were collected immediately prior to each injection and on Days 16, 17, 18, 20, and 22 and analyzed for progesterone. Progesterone concentrations were greater (P<0.05) on Days 14, 15, 16, and 17 in llamas treated with 10mg EB compared to llamas treated with 0mg EB. These results demonstrate that llama blastocysts produce estradiol and exogenous estradiol can enhance and transiently extend luteal progesterone production. Estradiol produced by the preimplantation llama blastocyst may play a role in maternal recognition of pregnancy and early luteal support.