Indirect regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase by oestradiol in the rabbit corpus luteum

Rabbits were given 50 i.u. hCG, i.v., to initiate ovulation and pseudopregnancy (Day 0) and were treated, s.c., with or without a 1-cm Silastic oestradiol implant. Serum progesterone concentrations were measured at 4-day intervals and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity was estimated by the conversion of HMG to mevalonate in microsomes from corpora lutea removed on Days 4, 8, 12, 16 and 20 of pseudopregnancy (4 rabbits/day). Total HMG-CoA reductase activity was significantly (P less than 0.05) higher in control rabbits on Days 8 and 12 (5.29 +/- 0.63 and 5.5 +/- 0.28 nmol/min/mg protein, respectively) compared to oestradiol-treated rabbits (2.57 +/- 0.25 and 4.03 +/- 0.23 nmol/min/mg protein, respectively). On Days 16 and 20, total HMG-CoA reductase activity was not different in control and oestradiol-treated animals. There was no difference in the levels of the active fraction of HMG-CoA reductase, which represented less than 20% of the total enzyme activity, in control and oestradiol-treated rabbits (less than 780 pmol/min/mg protein, Day 12). These results indicate that oestradiol does not alter the active form, but can reduce the total activity of HMG-CoA reductase in the rabbit corpus luteum without a decline in serum progesterone. Therefore, neither total nor active forms of HMG-CoA reductase are directly related to progesterone secretion. This suggests that other sources of cholesterol may contribute to progesterone production in the rabbit.     

Steroidogenic and morphological characteristics of granulosa and thecal compartments of the differentiating rabbit corpus luteum in culture

On the day after ovulation, the thecal tissue and associated mural granulosa lutein cells of the rabbit corpus luteum were separated from the granulosa lutein 'core' by dissection and these tissues were cultured separately or together (whole corpus luteum) in defined medium for 10 days on stainless-steel grids. The medium was changed completely every 24 h. Replicate tissues were cultured with testosterone (10 ng/ml), but no other hormones were added to the medium. Progesterone production increased during the first 2 days of culture for whole corpus luteum, granulosa lutein cells and the thecal compartment which also included granulosa lutein cells. After 3 days, the production of progesterone declined gradually, but was still detectable on Day 10. The production of the metabolite, 20 alpha-dihydroprogesterone, by whole corpus luteum was equal to or greater than that of progesterone. Without the addition of testosterone, the granulosa lutein cells produced little (10 pg/culture) oestradiol during 1 day of culture, but the thecal compartment and whole corpus luteum each produced about 100 pg/culture on Day 1 and declining quantities over the next 2 days. In the presence of testosterone added to the medium, the formation of oestradiol was greatly increased for all tissues for 5-6 days of culture, after which time oestradiol was no longer detectable with or without testosterone in medium. Transmission electron microscopy of cells after 10-12 days of culture revealed fine structure that is characteristic of luteal cells, including abundant smooth endoplasmic reticulum, lipid droplets, and junctions between the luteal cells. The corpus luteum in culture resembles the corpus luteum in situ in that steroidogenesis and differentiation can proceed for a period after ovulation without extrinsic hormonal stimulation.     

Effects of corpus luteum removal on progesterone, estradiol-17 beta and LH in early pregnancy of the tammar wallaby, Macropus eugenii

The quiescent corpus luteum of female tammars was reactivated by removal of the pouch young (RPY). The reactivated corpus luteum was ablated 3 days after RPY. Plasma progesterone and oestradiol concentrations were measured by radioimmunoassay in these and in sham-operated controls. Excision of the CL abolished the rise in progesterone seen at Day 5-6 in the sham-operated animals (130.7 +/- 56.6 vs 452.4 +/- 176.0 pg/ml, mean +/- s.d.). By contrast, oestradiol-17 beta values increased within 6-16 h of CL excision to 16.3 +/- 6.9 pg/ml and remained high for 1-3 days while in the sham-operated animals there were less sustained and more variable peaks of 10-20 pg/ml between Days 3 and 5 (mean 12.0 +/- 3.6 pg/ml at Day 4-5). We conclude that the early transient increase in peripheral plasma of progesterone is of luteal origin but the source of the oestradiol remains unknown.     

Development and survival of pig blastocysts after oestrogen administration on day 9 or days 9 and 10 of pregnancy

In Exp. 1, administration of 5 mg oestradiol valerate i.m. to pregnant gilts on Days 9 or 9 and 10 advanced the uterine secretion of calcium, protein, and acid phosphatase as demonstrated by levels recovered in the uterine flushings of females unilaterally hysterectomized on Day 11. Upon removal of the remaining uterine horn on Day 12, protein and acid phosphatase increased while Ca2+ decreased in oestradiol-treated gilts as did PGF. In contrast, a 4-fold increase in recoverable Ca2+ occurred from Days 11 to 12 in control gilts. Recoverable oestradiol-17 beta was increased in all 3 groups on Day 12 and plasmin inhibitor concentration increased in oestradiol-treated gilts. Two-dimensional PAGE demonstrated the appearance of a group of very acidic polypeptides in oestradiol-treated gilts. Blastocysts recovered from the second uterine horn had undergone elongation to the filamentous morphology in all 3 groups. In Exp. 2, oestradiol valerate was administered to pregnant gilts on Day 9 or Days 9 and 10 followed by total hysterectomy on Day 16. No differences in recoverable Ca2+ or protein were found, but acid phosphatase was decreased by 75% after oestradiol treatment. Recoverable oestradiol was decreased in oestradiol-treated gilts while PGF and plasmin inhibitor concentrations were unaffected. Compared with the control gilts, blastocysts recovered from oestradiol-treated gilts were fragmented and degenerating on Day 16. PAGE demonstrated greatly intensified staining of the group of acidic polypeptides in oestradiol-treated gilts. These results indicate that oestradiol treatment on Day 9 of pregnancy advances uterine secretory response, but that blastocyst elongation can occur in this uterine environment and in the presence of declining intraluminal Ca2+ levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation and role of the insulin-like growth factor I system in rat luteal cells.

The relationship between insulin-like growth factor I (IGF-I), a hormone which has potent metabolic effects and stimulates protein synthesis, and prolactin and oestradiol was examined to investigate a possible mechanism for the luteal cell hypertrophy that is responsible for the increase in size of the corpus luteum. A luteal cell line (GG-CL) derived from large luteal cells of the pregnant rat corpus luteum was used. IGF-I, IGF-I receptor and oestrogen receptor beta mRNA contents were determined by semiquantitative RT-PCR. The results revealed that prolactin upregulates the expression of IGF-I mRNA in luteal cells, but not that of its receptor. IGF-I had no effect on the expression of its receptor but caused a dose-related increase in the expression of oestrogen receptor beta. Furthermore, whereas IGF-I upregulated oestrogen receptor beta expression, oestradiol downregulated expression of mRNA for both IGF-I and its receptor. This effect of oestradiol is not mediated through progesterone which is stimulated by oestradiol in the corpus luteum. The developmental studies indicate that mRNA for IGF-I and its receptor are not expressed in tandem throughout pregnancy. Whereas the receptor mRNA is expressed at higher concentrations in early pregnancy, that of its ligand is highly expressed close to parturition. Collectively, the results indicate that prolactin stimulates luteal IGF-I production, which in turn acts on the luteal cell to stimulate expression of oestrogen receptor beta. Luteal cells with increased oestrogen receptor beta can respond fully to oestradiol, leading to cell hypertrophy.     

Effect of hCG, cAMP and FSH on steroidogenesis by human corpora lutea in vitro

Human corpora lutea of various ages were minced and incubated in the presence of hCG (10 i.u./ml), cAMP (10 mM) or FSH (20 mu/ml) and production of progesterone and oestradiol was measured. Cyclic AMP and hCG stimulated progesterone and oestradiol production during at least the mid- and late luteal phases, but FSH stimulated only oestradiol production during the early and mid-luteal phases and had no effect on progesterone production. This demonstrates that progesterone and oestradiol synthesis by the human corpus luteum can be independently controlled.     

Superoxide dismutase activity, lipid peroxide production and corpus luteum steroidogenesis during natural luteolysis and regression induced by oestradiol deprivation of the ovary in pseudopregnant rabbits.

The relationship of oxygen free radicals to corpus luteum function in rabbits was explored during various stages of pseudopregnancy, including natural and induced luteal regression. Induced luteolysis was achieved during mid-pseudopregnancy by removal of an oestradiol capsule placed at the onset of pseudopregnancy, which suppressed ovarian oestradiol production. Activity of manganese superoxide dismutase (Mn SOD) was significantly and positively correlated with ovarian progesterone production (P < 0.01) throughout pseudopregnancy and during natural regression. Oestradiol deprivation for 12, 24 or 72 h resulted in declines in Mn SOD activity and progesterone secretion, although Mn SOD rose and corpus luteum steroidogenesis was restored to normal when the capsule was replaced for 48 h before assessment, having been removed for 24 h. Lipid peroxide and progesterone concentrations were not correlated, although a significant rise in lipid peroxides in the luteal tissue was detected after deprivation of oestradiol for 72 h. Changes in progesterone production and Mn SOD activity were not associated with alterations in concentration of prostaglandin F metabolite. These data suggest that Mn SOD may be involved in regulating function of the corpus luteum during pseudopregnancy in rabbits and that oxygen free radicals may play a role in regression of corpus luteum in this species.     

Progesterone production by dispersed luteal cells of non-pregnant cows: effects of oxytocin and oestradiol

The effects of oxytocin and oestradiol on progesterone production by dispersed luteal cells of non-pregnant cows were studied. In acute incubation (3 h), oxytocin, at a concentration of 800 mIU/ml, significantly inhibited the production of progesterone induced by HCG (10 IU/ml). Suppression of basal progesterone production was evident in some corpora lutea. Lower oxytocin concentrations (4 and 40 mIU/ml) had no effect. At a concentration of 400 mIU/ml, oxytocin may be inhibitory to basal and HCG-induced progesterone production. Oestradiol (1 μkg/ml) had no effect on basal progesterone production but may suppress the production of progesterone induced by HCG. However, incubation with oxytocin (400 mIU/ml) plus oestradiol (1 μg/ml) resulted in a significant inhibition of HCG-induced progesterone production. These data provide evidence for an inhibitory effect of oxytocin on the corpus luteum of non-pregnant cows. Oestradiol may interact with oxytocin to inhibit the bovine corpus luteum function.     

Delayed effects on plasma concentration of testosterone and testicular morphology by intramuscular low-dose di(2-ethylhexyl)phthalate or oestradiol benzoate in the prepubertal boar

The immediate and delayed effects of prepubertal exposure to di(2-ethylhexyl)phthalate (DEHP) or oestradiol benzoate on the plasma concentrations of testosterone, oestradiol and LH, as well as testicular morphology were examined in prepubertal boars. In a split litter design experiment, prepubertal boars were intramuscularly exposed to DEHP, oestradiol or vehicle during five weeks, starting at six weeks of age. The dose of DEHP was 50mg/kg of bodyweight twice weekly, which is in the same range as recently used oral doses in rodents. Oestradiol-benzoate was administered at 0.25mg/kg of bodyweight twice weekly. One set of animals was examined immediately after the exposure, and the other set was examined at an age of 7.5 months. During the exposure period concentrations of LH in plasma were lower (p=0.02) in the oestradiol-treated animals than in the control group. In the group exposed to oestradiol, the relative to the body weight of the testicles tended to be lower (p=0.07) than control immediately after five weeks of exposure, and the relative to the body weight of the seminal vesicles tended to be lower (p=0.05) than control at 7.5 months of age. In the DEHP-exposed group an elevated (p=0.005) concentration of testosterone and increased (p=0.04) area of the Leydig cells in the testicles compared to the control group were seen at 7.5 months of age. These data suggest that DEHP early in life causes delayed effects on the reproductive system in the adult.     

Identification and physical mapping of genes expressed in the corpus luteum in cattle

A representational difference analysis was performed to identify genes expressed in the corpus luteum of cattle. The corpus luteum is an ovarian structure that is essential for the establishment and maintenance of pregnancy. Knowledge of gene expression and function of corpus luteum will be important to improve fertility in humans and domestic animals. Housekeeping genes were removed from the corpus luteum representation (tester) using skeletal muscle as the subtracting agent (driver). A total of 80 clones of the final subtraction product were analysed by sequencing and 11 new bovine gene sequences were identified (pBTCL1-11). The sequences were mapped to segments of 10 different chromosomes using a somatic cell hybrid panel and a radiation hybrid panel. With one exception the locations are in agreement with published comparative maps of cattle and man. Expression in corpus luteum was verified by RT-PCR for all the 11 clones.     

Regulatory effect of steroid hormones and fetal tissues on expression of oxytocin receptor in the endometrium of late pregnant ewes.

Oxytocin receptors play an important role in the establishment of pregnancy and parturition in ruminants. Previous studies in cyclic and early pregnant ewes have indicated that receptor concentrations are regulated by steroid hormones and fetal secretory products. This study investigated the effect of oestradiol and progesterone, or co-culture with placenta or corpus luteum on oxytocin receptor expression. Endometrial explants from late pregnant ewes were cultured for up to 96 h in various treatment combinations. After culture, tissues were subjected to in situ hybridization and autoradiography with 125I-labelled oxytocin receptor antagonist to localize and measure the expression of oxytocin receptor mRNA and protein. Results were quantified as absorbance units from autoradiographs. Oxytocin receptors were confined to the endometrial luminal epithelium and both mRNA and 125I-labelled oxytocin receptor antagonist binding were upregulated spontaneously in basic serum-free medium. Upregulation occurred earlier in the presence of oestradiol (0.1 mumol l-1) but the final receptor concentration was similar to that found in the basic medium. Continuous progesterone treatment (1 mumol l-1) and co-culture with corpus luteum both delayed the increase in oxytocin receptor mRNA, but a short initial (4 h) period in progesterone-free basic medium resulted in loss of the inhibitory effect. Co-culture with placental tissues had no effect. In conclusion, oxytocin receptor expression in the luminal epithelium increased immediately on removal from the maternal environment. This occurred regardless of treatment and did not require the presence of steroid hormones, but could be accelerated or delayed by oestradiol and progesterone, respectively. There may be an additional inhibitory factor present in the corpus luteum.     

Effects of the presence of a dominant follicle and exogenous oestradiol on the duration of the luteal phase of the bovine oestrous cycle.

The presence of a developing dominant follicle may be a factor in the control of the luteolytic cascade mechanism and the number of follicular waves during the bovine oestrous cycle. In this study, ovaries of all animals were examined once a day by transrectal ultrasonography. It was expected that heifers (n = 18) would have two follicular waves if the second wave occurred later than day 10 after oestrus (Expt 1) and that cows (n = 14) would have three waves if the second wave occurred on or before day 10 (Expt 2). The objective of Expt 1 was to determine if absence of a large follicle late in the luteal phase delays luteal regression in heifers that are expected to have two follicular waves. Nine heifers were injected i.v. with 10 ml charcoal-treated bovine follicular fluid three times a day for 4 days, starting on the day after initiation of the second follicular wave, to delay growth of the second wave dominant follicle. Nine heifers were injected with 0.9% NaCl as controls. The duration of the luteal phase (calculated as the number of days that serum progesterone was > 0.5 ng ml-1) was greater (P < 0.01) in the follicular fluid-treated group compared with the controls (18.7 versus 14.1 days). FSH and follicular growth were suppressed during the period of injection of follicular fluid (P < 0.01 and 0.03, respectively). The objective of Expt 2 was to determine the effect of increased oestradiol on the duration of the luteal phase in cows that were expected to have three follicular waves. Seven cows were injected i.m. three times a day for 4 days with 1 ml oestradiol (100 micrograms ml-1 in corn oil) and seven cows were similarly injected three times a day with 1 ml 0.9% NaCl (control) starting the day after cessation of growth of the second wave dominant follicle. Luteal phase duration was shorter in oestradiol-treated animals than in the controls (14.0 versus 19.0 days; P < 0.04). Serum oestradiol concentrations were higher in the oestradiol-treated group during the period of injection (P < 0.01). In summary, luteolysis was delayed when follicular growth was suppressed with follicular fluid (Expt 1). Exogenous oestradiol administration during the development of uterine oestradiol responsiveness initiated luteolysis earlier compared with control animals (Expt 2).     

Immunocytochemical evidence for the presence of oxytocin and neurophysin in the large cells of the bovine corpus luteum

Summary The presence of neurophysin, oxytocin and vasopressin in the bovine corpus luteum was examined immunocytochemically. Tissue blocks of corpora lutea from pregnant and non-pregnant animals were fixed with glutaraldehyde/paraformaldehyde fixative and immunostained by the peroxidase-antiperoxidase (PAP) method. The simultaneous presence of immunoreactive oxytocin and immunoreactive oxytocin-neurophysin was demonstrated in large luteal cells of non-pregnant animals, while no staining for vasopressin or vasopressin-neurophysin was observed. None of the peptides were detected in the corpus luteum of pregnant animals. The small luteal cells were not found to be stainable at any time.     

Seasonal and hormonal control of pulsatile LH secretion in the dairy goat (Capra hircus)

In Exp. 1, the changes in pulsatile LH secretion at the onset of the breeding season were observed in 20 intact, mature Saanen does. Blood was sampled every 20 min for 6 h each week from the beginning of August until the onset of ovulatory activity, as evidenced by cycles in plasma progesterone. The first doe ovulated at the end of August and all were cycling by the end of September. As the first ovulation approached, LH pulse frequency increased by 67% and mean levels of LH increased by 47%. These changes were progressive rather than abrupt. In Exp. 2, seasonal changes in the inhibition of pulsatile LH secretion by ovarian steroids were studied in ovariectomized Saanen does. The animals were untreated (N = 4) or given subcutaneous oestradiol implants (N = 4) and blood was sampled every 10 min for 6 h, twice during the breeding season and twice during the anoestrous season. In each season, the second series of samples was taken after the animals had been treated with progesterone, administered by intravaginal implants. Season did not significantly affect LH secretion in goats not treated with oestradiol, but LH pulse frequency was 54% lower during the anoestrous season than during the breeding season in oestradiol-treated goats. Mean LH concentrations were affected in the same manner as pulse frequency, but pulse amplitude was increased by oestradiol treatment in both seasons. Progesterone had no detectable effect on LH secretion in either season. In Exp. 3, the response to repeated melatonin injections at a set time after dawn was investigated in 11 oestradiol-treated, ovariectomized goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Levels of 15-keto-1344-dihydro-PFG2α, Progesterone and Oestradiol-17β after Induced Ovulations in Llamas and Alpacas

Six llamas and 6 alpacas were mated to vasectomized males; ovulation and corpus luteum formation followed. Progesterone in blood was elevated from day 5 and reached maximum concentrations of 10–20 nmol/1 on day 7–8. A rapid decline in progesterone levels occurred on day 9–10 in connection with repeated surge releases of prostaglandin F2α. Oestradiol-17β levels were > 100–200 pmol/1 during oestrus when the animals were mated. These high levels might have been caused by coital stimulation. A temporary increase was detected in connection with the rise in progesterone levels in the early luteal phase. With this exception levels of oestradiol stayed low, 20–40 pmol/1 during the luteal phase but rose in most animals after luteolysis to 40–60 pmol/1.     

Ovarian and placental production of progesterone and oestradiol during pregnancy in reindeer

We obtained uterine and peripheral venous plasma, and samples of luteal and placental tissues from 2- to 7-year-old, Eurasian mountain reindeer (Rangifer tarandus tarandus) from a free-living, semi-domesticated herd in northern Norway in November 1995, and February and March 1996. In November, ovarian venous blood was also collected from four animals. Plasma samples were assayed for progesterone and oestradiol. The tissue samples were examined by light and electron microscopy, steroid dehydrogenase histochemistry, and northern blot analysis for RNAs for 3beta-hydroxy-steroid dehydrogenase (3beta-HSD) and P450 (side chain cleavage (scc)). Peripheral blood was taken from non-pregnant females in the same herd on the same dates. Peripheral progesterone concentrations in pregnant reindeer (3.4 +/- 0.5 ng/ml, n = 8) clearly exceeded those in non-pregnant animals (0.40 +/- 0.14 ng/ml; P < 0.0004 , n = 10) but oestradiol levels were only marginally higher in pregnant (6.0 +/- 0.7 pg/ml) than in non-pregnant (4.8 +/- 0.5 pg/ml; P = 0.35) reindeer at the stages examined. In pregnant animals, peripheral progesterone and oestradiol concentrations rose slightly between November and March but the differences did not reach significance (progesterone, P = 0.083; oestradiol, P = 0.061). In November, progesterone concentrations in the ovarian vein (79 +/- 15 ng/ml) greatly exceeded (P < 0.03) those in the uterine vein ( 10 +/- 4 ng/ml) which in turn exceeded the levels in the peripheral blood (2.8 +/- 0.4 ng/ml; P < 0.29). Oestradiol concentrations were slightly but significantly (P < 0.05) higher in the ovarian (20 +/- 3 pg/ml) than the uterine vein (13 +/- 1 pg/ml) and, in turn, greater (P < 0.03) than in peripheral blood (4.6 +/- 0.4 pg/ml). All samples of luteal tissue consisted exclusively of normal fully-differentiated cells and stained intensely for 3beta-HSD. Isolated groups of placental cells also stained strongly for 3beta-HSD. RNA for P450 (scc) and 3beta-HSD was abundant in all corpora lutea and lower concentrations of P450 (scc) were present in the placenta. 3beta-HSD RNA in the placenta was below the limit of detection. We conclude that the corpus luteum remains an important source of progesterone throughout pregnancy in reindeer but that the placenta is also steroidogenic.     

The non-luteolytic effect of prostaglandin F2α at the beginning of the bovine oestrous cycle: The role of oestrogen?

After the preovulatory gonadotrophin surge, antral follicles ovulate or become atretic; whatever their evolution, they stop secreting oestradiol. Since it was demonstrated that oestrogens were necessary for luteolysis to occur after PGF(2)alpha treatment, their absence could explain the non-luteolytic effect of PGF(2)alpha injected early in the cycle. Thus, cyclic cows received a PGF(2)alpha analogue and oestradiol valerate together on day 3. This treatment did not affect the life span of the corpus luteum. The absence of oestrogens in the blood does not explain the failure of PGF(2)alpha to cause luteolysis in young corpora lutea.     

Influence of progesterone and oestradiol-17 beta on blastocysts of the tammar wallaby (Macropus eugenii) during seasonal diapause

Forty tammar wallabies, presumed to be carrying quiescent blastocysts, were injected with progesterone and oestradiol alone, or in combination, during seasonal quiescence when the corpus luteum is inactive. Plasma progesterone concentrations were increased to values equivalent to those of late pregnancy for the duration of the treatment in progesterone-treated groups but otherwise remained at values equivalent to seasonal quiescence. Tammars treated with low doses of oestradiol showed no measurable increase in plasma oestradiol concentrations but in those treated with high doses plasma concentrations were increased to oestrous levels. At autopsy on Day 18 after the start of treatment the embryos and reproductive tracts were assessed. While progesterone alone caused reactivation of about 50% of the embryos, blastocysts in tammars treated with oestradiol alone remained in diapause (low dose) or disappeared from the uterus (high dose): 2 blastocysts collapsed after some slight expansion. No synergistic effect on pregnancy was noted in tammars receiving both oestradiol and progesterone. We conclude that oestrogen alone is not capable of stimulating normal growth of blastocysts, and its role during early pregnancy in tammars remains unclear.     

Does exogenous progesterone and oestradiol treatment from the mid-luteal phase induce follicular cysts in goats?

The purpose of the present study was to investigate the effects of exogenous ovarian steroid treatment, which is known to induce follicular cyst experimentally in cows, on ovarian activity in goats. Eleven female Shiba goats with the length of the normal oestrous cycle (approximately 21 days) received subcutaneously either 1 ml of ethanol (control group, n=4) or 4 mg of progesterone and 2mg of oestradiol (treatment group, n=7) daily for 7 days beginning on day 14 of the oestrous cycle (day 0=ovulation). Ultrasonographic images of the ovary and blood samples were collected daily to monitor the ovarian activity. Ovulation was observed before 1 day after the end of treatment in the control group. In the treatment group, no detectable structures of follicles or corpus luteum (static ovarian condition) were found for 6.0+/-1.4 days (mean+/-S.D.) after the end of treatment. Then, detectable follicles appeared and ovulation was observed in all animals of the treatment group. There was no significant difference in the maximum diameter of the ovulatory follicle between the control and treatment group (4.7+/-0.4mm versus 5.1+/-0.7 mm). The large non-ovulatory follicles, which grew more than 10mm in diameter were observed after the static ovarian condition in one goat of the treatment group, whereas no turnover of the cystic follicular structures was found. The length of the inter-ovulatory intervals in the treatment group was significantly longer than that in the control group (38.4+/-7.4 days versus 20.3+/-0.5 days, P<0.05). The present results demonstrated that the exogenous treatment of progesterone and oestradiol, which was adapted from the follicular cyst model in cows, did not induce follicular cysts in goats, suggesting that there is/are different mechanism(s) mediating the occurrence of follicular cysts between cows and goats.     

Suppression by luteectomy of the simultaneous increase in intramammary pressure and blood oxytocin levels induced by the injection of PGF2-alpha in ewes

Seven lactating Lacaune ewes underwent either a total luteectomy on day 19 of pregnancy (D19) (compensated from that stage by a daily progesterone supplementation of 25 mg to ensure embryonic survival; group 1:4 animals) or a control laparotomy (group 2: 3 animals). Intra-jugular injection of 200 micrograms of a synthetic PGF2 alpha analogue (Dinolytic, Upjohn) caused an increase in the intramammary pressure (IMP) and a concomitant rise in oxytocinaemia only in the presence of a corpus luteum, ie in all ewes of groups 1 and 2 before D19 and only in those of group 2 after that stage. These experiments confirm that the corpus luteum, and not the other ovarian compartments, releases oxytocin when prostaglandin F2 alpha is administered.