Decline In Progesterone Concentrations Research Articles

Use of Intravaginal Progesterone-Releasing Device Results in Similar Pregnancy Rates and Losses to Long-Acting Progesterone to Synchronize Acyclic Embryo Recipient Mares.

The objectives of this study were: (1) to assess uterine features and serum progesterone concentrations of acyclic mares synchronized and resynchronized with intravaginal progesterone release device (IPRD), and (2) to compare pregnancy rates and losses of cyclic and acyclic embryo recipient mares treated with different synchronization protocols. In Experiment 1, mares (n = 12) received estradiol for 3 days (E2-3d), and then 24 h after the last injection, an IPRD was inserted and kept in place for 9 days. Three days after IPRD removal, mares were treated with E2-3d, and then a new IPRD was inserted and maintained for three days. Serum progesterone concentrations were assessed 2, 6, and 12 h after insertion and removal of IPRD, and then daily from the insertion of the first IPRD to one day after removal of the second IPRD. Experiment 2 was conducted with embryo recipient mares randomly assigned to four groups: (1) Cyclic: mares (n = 75) had ovulation confirmed after receiving a single dose of histrelin when a periovulatory follicle was first detected, (2) LAP4: acyclic mares (n = 92) were treated with E2-3d and then administered a single dose of LAP4 24 h after the last estradiol injection, (3) IPRD: acyclic mares (n = 130) were treated with E2-3d and an IPRD for 4–8 days, and (4) RE-IPRD: acyclic mares (n = 32) were synchronized as in the IPRD group but not used for embryo transfer (ET), then 8 to 15 days later, the mares were resynchronized with E2-3d and an IPRD for 4–8 days. In vivo-produced Day-8 embryos were collected and transferred 4–8 days after ovulation or progesterone treatments. Mares in IPRD and RE-IPRD groups had the intravaginal device removed immediately before ET, and then a new IPRD was inserted right after ET. Pregnancy diagnosis was performed at 5, 30, and 60 days after ET. Once pregnancy was confirmed, mares in the three acyclic groups received weekly injections of LAP4 (1.5 g) until 120 days of pregnancy. Mares in IPRD and RE-IPRD groups had the device removed three days after the first pregnancy diagnosis. In Experiment 1, progesterone concentrations increased rapidly starting 2 h after insertion of IPRD (p < 0.05); then, concentrations plateaued well above pregnancy maintenance until removal on days 9 and 3, respectively. Progesterone concentrations were reduced to baseline 24 h after IPRD removal (p < 0.05). For experiment 2, there was no difference in pregnancy rates across groups (65–74%) or pregnancy losses by 60 days of gestation (7–12%) (p > 0.05). In conclusion, the IPRD used herein resulted in a rapid increase and a sharp decline in progesterone concentrations upon its insertion and removal, respectively. Finally, our results demonstrated that IPRD could be a compatible alternative to LAP4 to synchronize and resynchronize acyclic embryo recipient mares.

Gonado-hypophyseal lesions and reproductive hormonal changes in Brucella melitensis-infected mice and its lipopolysaccharides (LPSs)

Gonado-hypophyseal lesions and reproductive hormonal changes in Brucella melitensis-infected mice and its lipopolysaccharide (LPS) were investigated. Forty-eight mice (24 males and 24 females) were used as infection models in this study, and they were divided into three equal separate groups of eight mice based on their sex: M1, M2, and M3 and F1, F2, and F3 (M = Male, F = Female). Groups M1 and F1 were orally inoculated with sterile phosphate-buffered saline (PBS) and served as the negative control. Groups M2 and F2 were orally inoculated with 0.4 ml of 109 colony-forming units (cfu) of B. melitensis, while groups M3 and F3 were orally inoculated with 0.4 ml of LPSs from 109 cfu of B. melitensis. All the groups were observed for 10 days for changes in clinical signs or signs of mortality and then euthanized. Whole blood was collected via cardiac puncture, while tissues were fixed in 10 % formalin for histopathological processing. Histopathological lesions in the male and female reproductive tracts ranged from mild to moderate degenerative, inflammatory, and necrotic lesions. These changes were moderate in M2 than in M3 in males and in F3 than in F2 groups in females. Lesions in the pituitary gland ranged from mild to moderate inflammation and necrosis with astrogliosis. F2 and M2 groups had more lesion distribution in the pituitary gland than F3 and M3 groups. There was a 13 % decline in progesterone concentration in F2 and a 44 % decline in F3. Estradiol level declined by 33 % in F2 and slightly increased by 4.2 % in F3. Progesterone-estrogen ratio (P/E) increased by 31 % in F2 and declined by 46 % in F3. Testosterone concentration increased by 74 % in M2 and decreased by 56 % in M3. The study showed that oral administration of B. melitensis affects the pituitary gland and may alter the hypothalamic-pituitary-gonadal axis.

Experimental infection of early pregnant cows with bovine viral diarrhea virus: Transmission of virus to the reproductive tract and conceptus

The objective of this study was to chronologically investigate the effect of bovine viral diarrhea virus (BVDV) infection on early pregnant cows before placenta formation. Six cows were intravenously inoculated with either BVDV (treated, n = 4) or growth medium (control, n = 2) (day 0) at day 26 of pregnancy. Two treated cows and one control cow were euthanized on day 3 post-infection and the remaining animals were euthanized on day 6. BVDV was isolated from maternal tissues such as lymphoid or reproductive tissues of treated animals on days 3 and 6 post-infection. Additionally, one treated cow autopsied on day 6 post-infection had evidence of infectious BVDV in the allantoic membranes, allantoic fluid and embryos. In three treated cows, a significant decline in progesterone concentration was also observed post-infection while in control cows they remained constant. Therefore, BVDV can infect bovine embryos before placenta formation and may affect progesterone profiles in cows during early pregnancy.

Uterine Vein Infusion of Interferon Tau (IFNT) Extends Luteal Life Span in Ewes1

Interferon tau (IFNT) from the ovine conceptus has paracrine actions on the endometrium that alter release of prostaglandin F(2alpha) (PGF) and protect the corpus luteum (CL). Antiviral activity in uterine vein blood and expression of interferon-stimulated genes (ISGs) in CL is greater in pregnant than in nonpregnant ewes. We hypothesized that IFNT contributes to antiviral activity in uterine vein blood and has endocrine actions on the CL. Preadsorption of IFNT with antiserum against recombinant ovine (ro) IFNT revealed that antiviral activity in uterine vein blood from pregnant ewes was mediated by IFNT. Endocrine actions of IFNT were examined after infusing either roIFNT or bovine serum albumin (BSA; 200 microg/24 h; mini-osmotic pump) into the uterine vein of nonpregnant ewes from Day 10 to Day 11 postestrus. The abundance of ISG15 mRNA and protein was greater in CL (P < 0.05) from ewes receiving 24-h roIFNT infusion compared to that from ewes receiving 24-h BSA infusion. Injection of PGF at 12 h following insertion of mini-osmotic pumps resulted in a decline in serum progesterone concentrations 6 through 12 h later in BSA-infused ewes; however, in roIFNT-infused ewes, a similar decline in progesterone concentrations at 6 h was followed by recovery to control values at 12 h. Ewes then received infusions (200 microg/day) of either roIFNT or BSA for 7 days beginning on Day 10 of the estrous cycle. All BSA-infused ewes returned to estrus by Day 19, whereas 80% of roIFNT-infused ewes maintained luteal-phase concentrations of progesterone through Day 32. In conclusion, IFNT is released from the uterus into the uterine vein and acts through an endocrine mechanism to induce ISGs in the CL and delay luteolysis.

Efficacy of an injection of dinoprost tromethamine when given subcutaneously on luteal regression in lactating Holstein cows

The objectives of these studies were to evaluate the efficacy of a PGF 2α (PGF) analog given through different routes on causing luteal regression in lactating dairy cows. In Experiment 1, lactating Holstein cows ( n = 118) at random stages of lactation were blocked by parity and days in milk (DIM) and, within each block, randomly assigned to receive PGF as an intra-muscular (IM) injection in the semimembranous/semitendinous muscle (CON), subcutaneous (SC) injection in the cervical area (SCN), or SC injection in the ischio-rectal fossa (IRF). Blood was sampled at 0, 12, 24, 36, and 48 h after treatment for assessment of progesterone concentration. In Experiment 2, a total of 379 lactating Holstein cows, 46 ± 7 DIM, were blocked by DIM and, within each block, randomly assigned to receive treatment similar to CON or IRF groups from Experiment 1. Blood was sampled 0 and 48 h after treatment for assessment of progesterone concentration. Cows were classified as experiencing luteal regression when progesterone concentration was <1.0 ng/mL or <40% of initial concentration (0 h = 100%). In Experiment 1, there was no effect of route of PGF treatment on decline in progesterone concentration and on the proportion of cows experiencing luteal regression by 12, 24, 36, and 48 h after treatment. Similarly, in Experiment 2, route of treatment did not affect either the decline in progesterone concentration or the proportion of cows that had luteal regression by 48 h after treatment. Treatment of lactating dairy cows with 25 mg of PGF given SC in the ischio-rectal fossa did not affect either the decline in progesterone concentration or the proportion of cows that experienced luteal regression by 12, 24, 36, and 48 h after PGF treatment.

Hormonal Profiles during Periparturient Period in Single and Twin Fetus Bearing Goats

The effect of fetal number (single or twin) on plasma concentrations of progesterone, estradiol 17β, cortisol, prolactin, growth hormone, triiodothyronine, thyroxine and insulin around parturition (periparturient period) were studied on ten Alpine × Beetle crossbred goats in their first to third lactation. The hormone profiles were studied on days -20, -15, -10, -5, -4, -3, -2, -1 prior to kidding and on day 0 and +1, +2, +3, +4, +5, +10, +15, +20 days postkidding. Plasma progesterone levels were significantly (p<0.01) higher in twin bearing goats comparison to single bearing goats during all the days of sampling. The decline in progesterone concentration from day 20 to day 1 before kidding was 56% in twin and 42% in single bearing goats. In single bearing goats plasma estradiol 17β was significantly (p<0.01) higher during prekidding days compared to twin bearing goats. The level of estradiol 17β was highest on the day of kidding in both the groups. The plasma prolactin level in twin bearing goats from day 10 to day 1 prepartum was higher as compared to single fetus bearing goats. However there was abrupt increase in prolactin level on the day of kidding in both the groups. The plasma growth hormone levels were significantly (p<0.01) higher in twin compared to single bearing goats. On the day of kidding growth hormone levels were significantly (p<0.01) higher in twin as compared to single bearing goats (1.40 vs. 0.95 ng/ml). In twin bearing goats plasma cortisol values from day 5 till the day of kidding remained elevated and the levels on the day of kidding was significantly highest in both the groups. The levels of triiodothyronine (T3) were significantly higher (p<0.01) during all the periods of sampling in single compared to twin bearing goats. Plasma thyroxine (T4) was significantly (p<0.01) lower in twin compared to single bearing goats. In single bearing goats plasma insulin levels were significantly (p<0.01) higher than twin bearing goats during prepartum period however during post partum period the levels in both the groups remained similar. It can be concluded that number of fetuses is having significant influence on the hormone profile during periparturient period. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 3 : 346-351)

Effects of oestrous cycle control on reproductive efficiency

Abstract Original methods for controlling the oestrous cycle of cattle were based on extending or reducing the luteal phase to produce a synchronised decline in concentrations of progesterone or a synthetic progestagen. Modifications with GnRH or oestradiol at treatment initiation can alter patterns of ovarian follicle development to synchronise the emergence of a new dominant follicle. Otherwise, dominance can persist and the synchronised oestrus may be associated with reduced fertility. Avoiding this effect may increase variation in the duration of pro-oestrus and complicate inseminating animals at a prescribed post-treatment interval (timed insemination). Using oestradiol, GnRH or hCG during pro-oestrus can reduce variation in the interval to ovulation. Timing of these pro-oestrous treatments is important if the effects of inducing premature ovulations are to be avoided. Oestradiol has also been shown to be more effective than eCG as a pro-oestrous treatment with anoestrous dairy cows, allowing them to be included in synchrony programmes initially using progesterone supplementation. Current trials are investigating techniques for processing semen for use with inseminations made during pro-oestrus. Finally, concepts of oestrous cycle control to improve reproductive efficiency should be extended to include re-synchronisation of returns to service and the further development of treatments which increase the probability of conceptus recognition. Effective oestrous cycle control to improve reproductive efficiency may require modifications to ovarian follicle patterns when the treatment is initiated, as well as during pro-oestrus and at a specified period in the cycle following insemination.

Concentrations of Progesterone During Storage of Whole Blood from Llama (Lama glama): Effects of Anticoagulants, Storage Time and Temperature

Reproductive studies usually utilizes measurement of progesterone in various fluids such as plasma, serum or milk. It has been shown that progesterone concentrations in bovine whole blood decrease proportionally to: i) the time elapsed between the collection of the sample and the separation of plasma or serum from the erythrocytes and ii) the temperature of storage during this period (Breuel et al, 1988, Pulido et al. 1991). The addition of anticoagulants cause a more rapid decline in progesterone concentrations (Wiseman et al. 1982). In equine, porcine and canine blood samples storage time and temperature has a negligible effect on progesterone concentrations (Wiseman et al. 1982; Oltner & Edqvist 1982). Cordero et al. (1991) working with llama and alpaca whole blood, treated with EDTA as anticoagulant, reported a slight progesterone metabolization in alpaca plasma, but not in llama plasma.

Luteolytic and antiluteolytic effect of the antiprogestagen RU486 in pseudopregnant rats.

To study the effects of the antiprogestagen RU486 on luteal activity in pseudopregnant rats, adult female rats made pseudopregnant by sterile copulation were given daily injections with oil vehicle or with RU486 (2 mg/day) either during the entire period of pseudopregnancy (day 1 till day 14) or during the second half of pseudopregnancy (day 8 till day 14). Blood was taken every other day to measure serum concentrations of progesterone. At autopsy, on day 15, the weights of ovaries, isolated corpora lutea and pituitary glands were recorded. In a second study using the same experimental protocol, blood was taken via a jugular vein cannula on days 8, 9, 10 and 11 after induction of pseudopregnancy; on each of these days blood samples were taken at 0700, 0800 and 0900 h, and at 1700, 1800 and 1900 h to measure plasma concentrations of prolactin, LH and progesterone. Administration of RU486 from day 1 of pseudopregnancy onwards had no effect on the increasing concentrations of serum progesterone during the first half of pseudopregnancy. Thereafter progesterone concentrations of serum progesterone during the first half of pseudopregnancy. Thereafter progesterone concentrations increased further in RU486-treated rats whereas they decreased in oil-treated pseudopregnant rats. Administration of RU486 from day 8 of pseudopregnancy onwards resulted in a decline in progesterone concentrations in serum on day 10 followed by ovulation on day 11. Plasma LH concentrations in rats treated with RU486 from day 1 of pseudopregnancy were higher than those in oil-treated rats on days 8, 9, 10 and 11.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of PGF 2α-induced luteolysis in early pregnant and estrogen-treated ‘pseudopregnant’ gilts

Conceptus estrogen clearly plays a major role in luteal maintenance in the pig; however, other conceptus-derived substances or conceptus-induced uterine secretory products appear to have a local luteotrophic/anti-luteolytic effect on the corpora lutea (CL) and likely may play a key role in maternal recognition of pregnancy in the pig. The objective of these studies was to compare PGF 2α-induced luteolysis in estrogen-treated ‘pseudopregnant’ gilts versus pregnant gilts during the period of maternal recognition of pregnancy. In Experiment 1, doses of PGF 2α ranging from 1 to 100 μg were administered via intraluteal silastic implants to pseudopregnant gilts to determine the dose necessary to cause functional (progesterone) and structural (weight) luteal regression similar to that observed during the natural estrous cycle. Luteal sensitivity to this minimally effective luteolytic dose of PGF 2α was then determined for both pseudopregnant and pregnant gilts in Experiment 2. Experiment 3 investigated whether Day 13 porcine conceptus tissue could directly prevent PGF 2α-induced luteolysis at the level of the CL. The minimally effective luteolytic dose of PGF 2α (100 μg) determined in the pseudopregnant pig caused a similar decline in progesterone concentration and weight of CL in pregnant gilts, suggesting that the susceptibility of CL of pregnant and pseudopregnant pigs to PGF 2α is similar. However, luteal weight was greater ( P<0.05) for the pregnant gilts than for pseudopregnant gilts, suggesting that estrogen treatment alone cannot mimic the conceptus effects on CL growth and development. Experiment 3 demonstrated that lyophilized Day 13 conceptus tissue implanted directly into individual CL could partially inhibit PGF 2α-induced luteolysis, providing for the first time direct evidence that porcine conceptuses as early as Day 13 contain factors which can directly (i. e. at the level of the CL) prevent luteal regression.

Possible mechanisms for reduction of circulating concentrations of progesterone by interferon-alpha in cows: effects on hyperthermia, luteal cells, metabolism of progesterone and secretion of LH.

Experiments were performed to determine the mechanism by which recombinant bovine interferon-alpha I1 (rbIFN-alpha) causes an acute reduction in plasma concentrations of progesterone. In experiment 1, administration of a prostaglandin synthesis inhibitor blocked rbIFN-alpha-induced hyperthermia but did not prevent the decline in plasma concentrations of progesterone. The decline in progesterone concentrations caused by rbIFN-alpha was, therefore, not a direct consequence of the associated hyperthermia or of pathways mediated through prostaglandin synthesis. It is also unlikely that rbIFN-alpha acts to increase the clearance of progesterone since injection of rbIFN-alpha did not decrease plasma concentrations of progesterone in ovariectomized cows given an intravaginal implant of progesterone (experiment 2). In experiment 3, rbIFN-alpha did not affect basal and LH-induced release of progesterone from cultured luteal slices, indicating that rbIFN-alpha is unlikely to affect luteal function directly. Injection of rbIFN-alpha did, however, cause a decrease in plasma concentrations of LH in ovariectomized cows (experiment 4) that coincided temporally with the decrease in progesterone concentrations seen in cows having a functional corpus luteum. The present results strongly suggest that rbIFN-alpha acts to reduce secretion of progesterone by interfering with pituitary support for luteal synthesis of progesterone. The finding that rbIFN-alpha can inhibit LH secretion implies that interferon-alpha molecules should be considered among the cytokines that can regulate hypothalamic or pituitary function.

Analyses of ovine corpora lutea for tumor necrosis factor mRNA and bioactivity during prostaglandin-induced luteolysis

It has been suggested that tumor necrosis factor (TNF) participates in the mechanism of regression of the corpus luteum. We measured luteal expression of TNFα mRNA and biological activity during prostaglandin-induced luteolysis in sheep. Initiation of functional luteolysis was marked by a sharp decline in concentrations of progesterone in luteal tissue beginning 4 h after administration of luteolysin. Structural regression of corpora lutea was manifested by a reduction in glandular weight at 16 h. A luteal cytotoxic factor with TNFα-like bioactivity was isolated after the decrease in tissue progesterone had occurred, but before evidence of luteal resorption. We were unable to detect temporal alterations in TNFα mRNA in luteal samples by classical Northern blot or in situ hybridization analyses. These results imply that luteal TNFα is derived primarily as a preformed entity from an extraovarian source, such as infiltrating leukocytes. These results raise the possibility that this cytokine might not be involved in the early stages of luteal regression in the ewe, yet could play a secondary role, perhaps in the subsequent opsonization and removal of degenerating cells.

Variable Ovarian Response to Gonadotropin-Releasing Hormone Antagonist-Induced Gonadotropin Deprivation during Different Phases of the Menstrual Cycle

The gonadotropin dependence of ovarian follicular maturation and corpus luteum function can now be examined in women using antagonistic analogs of GnRH. We studied the responses of three groups of women throughout a control cycle and during the administration of a potent GnRH antagonist, detirelix ([N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10++ +] GnRH, Syntex Research). Detirelix (10 mg, sc) was administered for 3 consecutive days during the midfollicular phase (n = 4), preovulatory phase (n = 4), and early luteal phase (n = 4). The pituitary response to detirelix was similar throughout the three phases of the menstrual cycle. Immunoreactive LH concentrations decreased to 35% (mean +/- SEM) of pretreatment values within 8 h after the initial injection and remained suppressed for 72 h after discontinuance of treatment. Immunoreactive FSH concentrations decreased to 73 +/- 3% of pretreatment levels within 8 h and returned to baseline within 24 h after the third injection. In contrast, the ovarian response to detirelix varied markedly during different phases of the cycle. Midfollicular phase treatment was associated with a decline in estradiol (E2) levels from pretreatment values of 246 +/- 48 to 81 +/- 15 pmol/L within 24 h of the last injection. Vaginal bleeding ensued in three of four women. Follicular recruitment was then reinitiated, and an ovulatory LH surge occurred 18.2 +/- 2.9 days after the last injection. Similarly, treatment during the early luteal phase produced a decline in E2 concentrations from 286 +/- 29 to 70 +/- 7 pmol/L and a decline in progesterone concentrations from 20 +/- 1.6 to 1.9 +/- 0.3 nmol/L within 24 h after the last injection. Luteolysis was associated with menstrual bleeding in all four women. The subsequent ovulatory LH surge occurred 16.5 +/- 1.0 days after discontinuance of treatment. In contrast, treatment during the preovulatory phase resulted in a decline in E2 concentrations from 844 +/- 66 to 429 +/- 132 pmol/L during the first 48 h of treatment. Gonadotropin and E2 concentrations subsequently recovered from suppression, growth of the dominant follicle resumed, and a LH surge occurred 5.8 +/- 1.4 days after the last injection. These data indicate that the GnRH antagonist detirelix produces rapid and consistent suppression of pituitary gonadotropin secretion. The magnitude of suppression and preferential suppression of LH vs. FSH are similar throughout the cycle. In contrast, the ovarian response to gonadotropin deprivation varies during the menstrual cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Variable Ovarian Response to Gonadotropin-Releasing Hormone Antagonist-Induced Gonadotropin Deprivation during Different Phases of the Menstrual Cycle*

The gonadotropin dependence of ovarian follicular maturation and corpus luteum function can now be examined in women using antagonistic analogs of GnRH. We studied the responses of three groups of women throughout a control cycle and during the administration of a potent GnRH antagonist, detirelix ([N-Ac-D-Nal(2)1,D-pCl-Phe2,D-Trp3,D-hArg(Et2)6,D-Ala10++ +] GnRH, Syntex Research). Detirelix (10 mg, sc) was administered for 3 consecutive days during the midfollicular phase (n = 4), preovulatory phase (n = 4), and early luteal phase (n = 4). The pituitary response to detirelix was similar throughout the three phases of the menstrual cycle. Immunoreactive LH concentrations decreased to 35% (mean +/- SEM) of pretreatment values within 8 h after the initial injection and remained suppressed for 72 h after discontinuance of treatment. Immunoreactive FSH concentrations decreased to 73 +/- 3% of pretreatment levels within 8 h and returned to baseline within 24 h after the third injection. In contrast, the ovarian response to detirelix varied markedly during different phases of the cycle. Midfollicular phase treatment was associated with a decline in estradiol (E2) levels from pretreatment values of 246 +/- 48 to 81 +/- 15 pmol/L within 24 h of the last injection. Vaginal bleeding ensued in three of four women. Follicular recruitment was then reinitiated, and an ovulatory LH surge occurred 18.2 +/- 2.9 days after the last injection. Similarly, treatment during the early luteal phase produced a decline in E2 concentrations from 286 +/- 29 to 70 +/- 7 pmol/L and a decline in progesterone concentrations from 20 +/- 1.6 to 1.9 +/- 0.3 nmol/L within 24 h after the last injection. Luteolysis was associated with menstrual bleeding in all four women. The subsequent ovulatory LH surge occurred 16.5 +/- 1.0 days after discontinuance of treatment. In contrast, treatment during the preovulatory phase resulted in a decline in E2 concentrations from 844 +/- 66 to 429 +/- 132 pmol/L during the first 48 h of treatment. Gonadotropin and E2 concentrations subsequently recovered from suppression, growth of the dominant follicle resumed, and a LH surge occurred 5.8 +/- 1.4 days after the last injection. These data indicate that the GnRH antagonist detirelix produces rapid and consistent suppression of pituitary gonadotropin secretion. The magnitude of suppression and preferential suppression of LH vs. FSH are similar throughout the cycle. In contrast, the ovarian response to gonadotropin deprivation varies during the menstrual cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Concentrations of 13, 14-dihyro-15-keto prostaglandin F 2α after pulsatile progesterone administration at the time of luteolysis of heifers

Progesterone was administered in pulses to 12 dairy heifers from days 17.5 to 22.5 post-estrus in order to determine its ability to modify secretion of PGF 2a around the time of luteolysis. Control heifers exhibited pulses of PGFM concomitant with a sharp decline in progesterone concentrations and thus these pulses were temporally associated with luteolysis. Additional pulses of PGFM were observed in heifers receiving exogenous progesterone, but these were not statistically predictable by either dose of progesterone (50 or 100 ug) or time of administration (3 or 6 hour intervals). However, all heifers ( 4 4 ) treated with progesterone at 3 hour intervals had additional pulses of PGFM as compared to only one heifer ( 1 4 ) treated at 6 hour intervals. When pulses of PGFM were induced by exogenous progesterone there was a substantial lag time between the initiation of progesterone treatment and their occurence. The limited response to progesterone administration and the lack of synchrony is not consistent with an ability of exogenous progesterone to directly stimulate secretion of PGF 2a at the time of luteolysis.

Effects of ACTH and cortisol on luteolysis in the ewe

Daily administration of 100 IU adrenocorticotrophic hormone (ACTH) on days 12–16 of the oestrous cycle was found to delay oestrus and induce formation of follicular cysts; daily cortisol infusions on days 12–16 did not have these effects. In the ACTH-treated ewes release of 13,14-dihydro-15-keto-prostaglandin F 2α was depressed on days 13–16, and decline in progesterone concentrations was delayed. Intramuscular administration of ACTH (25 IU) significantly raised plasma concentrations of progesterone in ovariectomized ewes, relative to saline-treated controls. Peak value of progesterone were between 0.76 and 1.1. ng.ml −1. In ovariectomized ewes primed with first progesterone (20 mg.day −1 × 6 days) and then oestradiol-17β (500 μg.day −1 × 3 days). ACTH (25 IU) significantly reduced the ability of oxytocin to release 13,14-dihydro-15-keto-prostaglandin F 2α into the peripheral circulation. Both these effects may contribute to the ability of ACTH to delay oestrus in intact ewes.

Release of prostaglandin F-2 alpha and the timing of events associated with luteolysis in ewes with oestrous cycles of different lengths.

Ewes (N = 32) were bled every 2 h from 5 days before expected oestrus until the end of oestrus. Plasma concentrations were determined for progesterone to monitor luteal activity and for the prostaglandin F-2 alpha (PGF-2 alpha) metabolites, 15-keto-13,14-dihydro-PGF-2 alpha and 11-ketotetranor-PGF to determine uterine synthesis and release of PGF-2 alpha. Most of the variation in cycle length was associated with the time of onset of luteolysis, the timing of events after luteolysis being constant and not related to cycle length. The time of occurrence of the first PGF-2 alpha pulse and the interval between this pulse and the start of luteolysis were the two main determinants responsible for oestrous cycle length. Several PGF-2 alpha pulses with interpulse intervals of 15.9 h occurred before the onset of functional luteolysis compared with 7.7 h for pulses associated with luteolysis. The numbers of PGF-2 alpha pulses and interpulse intervals were similar for oestrous cycles of different lengths. While a gradual decline in progesterone concentrations was observed before functional luteolysis in the ewes with longer cycles, this did not appear to be an integral part of the stimulus which initiates the pulse frequency of PGF-2 alpha required for luteolysis. We therefore suggest that differences in oestrous cycle length in the ewe are determined by the time of the onset of PGF-2 alpha pulsatile release, and especially by the time of increased pulse frequency.

Involvement of prostaglandin A1 in interrupting early pregnancy in Syrian golden hamsters.

The effects of a single administration of authentic prostaglandin A1 intravaginally in early pregnant hamsters were investigated. A single dose of 1 mcg/animal given on day 4 of pregnancy inhibited the appearance of embryonic swellings when observed on day 8 of pregnancy. A significant fall (p less than 0.01) in FSH with a rise (p less than 0.03) in prolactin concentration in the serum and no change in LH levels were observed. The pituitary content of prolactin showed a significant decrease (p less than 0.0006) with no change in FSH and LH contents. Progesterone concentration in the serum was markedly reduced (p less than 0.002), along with that of the ovaries (p less than 0.01). The decline in progesterone concentration coincided with the absence of corpora lutea and the embryos. However, no change in ovarian weights was observed. These results indicate the contragestive potential of prostaglandin A1. It appears to act as a luteolytic agent by disrupting the luteotropic complex (FSH:prolactin ratio).

Changes in Muskox Blood Progesterone Concentration between Collection and Centrifugation

Jugular blood was collected from 4 muskoxen (Ovibos moschatus) during late pregnancy, in either heparinized or untreated tubes. The tubes were either refrigerated (4 C) or kept at room temperature (21 C) for periods of 6, 12, or 24 hours. The samples were then centrifuged and the serum or plasma was frozen (-18 C) prior to radioimmunoassay for progesterone. Samples designated Time 0 were handled identically but were centrifuged within 1 hour of collection. A significant decline in progesterone concentration had occurred in all samples between collection and centrifugation, and this was more rapid at 21 than at 4 C. Heparinization had no effect on the rate of decline. These results indicate that care should be taken to minimize the effects of handling on progesterone levels, particularly when blood is collected in the field. J. WILDL. MANAGE. 51(4):901-903 Radioimmunoassay (RIA) of circulating steroid hormones is being applied with increasing frequency to the study of wild species, such as Rocky Mountain bighorn sheep (Ovis canadensis) (Ramsay and Sadlier 1979, Whitehead and McEwan 1980), white-tailed deer (Odocoileus virginianus) (Plotka et al. 1977a,b, 1980) and roe deer (Capreolus capreolus) (Sempere 1977, Hoffman et al. 1978). RIA techniques are subject to strict controls, but few standards exist for handling blood samples between collection and centrifugation. This is of particular importance in relation to field collections for progesterone assay, since it is known that in some species, notably cattle, progesterone is rapidly degraded in whole blood. This degradation is slower in sheep (Wiseman et al. 1982) and goats (Fahmi et al. 1985) than in cattle and it is negligible in horses and pigs (Wiseman et al. 1982). As might be expected, the amount of progesterone lost increases with the time and temperature of storage and may be influenced by the anticoagulant used. In ewes Wiseman et al. (1982) found that blood stored in heparinized tubes at 22 C for 24 hours showed a significant decrease in plasma progesterone but blood without anticoagulant did not. In goats a significant progesterone decline occurred in samples stored at room temperature (22 C), regardless of anticoagulant, but this decline was not significant if the tubes were kept at 5 C (Fahmi et al. 1985). In cattle progesterone concentrations decline dramatically with time, regardless of the technique used. The decline is greatest in heparinized samples held at 22 C, in which progesterone concentrations are reduced to 5% of their original value after 12 hours (Wiseman et al. 1982, Vahdat et al. 1984). The decline in progesterone concentration in whole blood is greatly reduced if the red blood cells are removed shortly after collection (Vahdat et al. 1984). Although Lesniewski et al. (1984) found a 17% decrease in assayable progesterone in stored plasma, this only occurred after prolonged incubation (48 hours) at a relatively high temperature (35 C). This suggests that, in addition to rapid plasma separation, plasma should be immediately frozen to prevent further progesterone decline. Muskoxen, cattle, and sheep all belong to the Bovidae and have many common characteristics. We, therefore, felt that it was necessary to investigate the behavior of progesterone in whole muskox blood stored under various conditions, in order to optimize our techniques of sample collection in field and laboratory situations. This study was supported by Natl. Sci. and Eng. Res. Counc. Can., operating grant A2759 and infrastructure grant A2793. Samples were assayed by Reprod. Endocrine Assay Systems, Reprod. Endocrine Lab. West. Coll. Vet. Med., Saskatoon. We especially thank S. Cooke for advice regarding the assay and C. Stevens for skilled and dedicated care of the animals.

Effects of furazolidone on some reproductive hormones during oestrous cycle in the goat

1. In non-pregnant goat luteolysis is characterized by a decline in peripheral plasma progesterone level and increased peripheral plasma concentrations of testosterone (T) and 5 α-dihydrotesosterone (DHT). 2. Daily oral doses of furazolidone (80 mg/kg) between days 10 and 16 delayed luteolysis and suppressed both the decline in progesterone concentrations and the increase in T and DHT level.