Steroid hormones in uterine washings and in plasma of gilts between days 9 and 15 after oestrus and between days 9 and 15 after coitus

Between Days 9 and 15 after oestrus, concentrations of pregnenolone, pregnenolone sulphate, dehydroepiandrosterone (DHEA), DHEA sulphate, androstenedione, oestrone and oestrone sulphate in free uterine fluid collected from non-pregnant gilts were greater than respective values in plasma (P less than 0.05). The total contents of pregnenolone, progesterone, DHEA, testosterone, oestrone and oestradiol in washings from pregnant uteri exceeded (P less than 0.05) respective non-pregnancy levels during this same period. Concentrations of pregnenolone, pregnenolone sulphate, DHEA, DHEA sulphate, androstenedione, oestrone, oestrone sulphate and oestradiol in free uterine fluid recovered from gravid uteri were also higher (P less than 0.05) than respective plasma values. By contrast, the progesterone concentration in uterine fluid from pregnant animals was lower (P less than 0.001) than the plasma value. Concentrations of DHEA, DHEA sulphate, androstenedione and oestrone sulphate in plasma of pregnant gilts between Days 9 and 15 after mating exceeded (P less than 0.05) the respective concentrations in unmated gilts between Days 9 and 15 after oestrus. Plasma levels of pregnenolone sulphate were lower (P less than 0.05) in the pregnant animals. We therefore suggest that the endometrium of the pig can concentrate steroid hormones in uterine fluid and that increases in steroid levels in this milieu between Days 9 and 15 after coitus reflect steroidogenesis by embryonic tissues and modification of enzyme activities within uterine tissues under the influence of progestagens. The pool of steroid sulphoconjugates present in uterine fluid between Days 9 and 15 post coitum could serve as an important precursor source for progestagen, androgen and oestrogen synthesis by tissues of pig embryos before implantation.     

Concentrations of oestradiol-17β and progesterone in the plasma of dairy heifers before and after cloprostenol-induced and natural luteolysis and during early pregnancy

Plasma oestradiol-17β and progesterone levels were measured in seven nulliparous, dairy heifers (British Friesian breed) that were administered cloprostenol (a synthetic analogue of prostaglandin F_2α) between days 8 and 14 of the oestrous cycle and inseminated (AI) 72 and 96 h later, and in seven heifers inseminated (AI) at natural oestrus.In both treated and untreated heifers, the beginning of the progesterone fall and the oestradiol-17β rise associated with luteolysis appeared to be synchronous but, whereas the rate of fall in progesterone level was greater for the treated heifers, that of the oestradiol-17β rise did not differ between treated and untreated heifers. Mean pre-ovulatory peaks of oestradiol-17β were 8 pg/ml and 10 pg/ml for treated and untreated heifers respectively.A post-ovulatory peak of oestradiol-17β in plasma 5–6 days after the pre-ovulatory peak occurred in all heifers whether or not conception had taken place. It is suggested that 7 days after the initiation of oestradiol-17β secretion by the pre-ovulatory follicle, another follicle begins to mature and secrete oestradiol-17β and that the progress of the latter towards full maturation and potential ovulation is stopped by rising progesterone levels from the corpus luteum; as a result in normal, non-pregnant cattle an interval of about 21 days elapses before another ovulation (of another follicle) takes place. In the event of premature luteolysis (in the present study induced between the 8th and 14th day) there is no evidence that the timing of this luteolysis influences the time taken for a follicle to enter the final stages of pre-ovulatory maturation, when increasing amounts of oestradiol-17β are secreted. Thus the interval between ovulations may not be less than 7 days but, depending on corpus luteum survival, may vary between 7 and 21 days.In one heifer after natural luteolysis a normal plasma oestradiol-17β peak followed but this was not associated with ovulation and corpus luteum formation. The second oestradiol-17β peak 6 days after the first, however, evidently assumed the ovulatory role; presumably the secreting follicle concerned, not being subject to inhibition by progesterone rising to luteal levels, matured fully and ovulated. Thus the second, normally post-ovulatory, oestradiol-17β peak in cattle can, in the event of failure of ovulation at the normal time, itself assume the ovulatory function, the oestrous cycle length then being about 28 days.     

Attainment of puberty in female pigs: Clinical appearance and patterns of progesterone,oestradiol-17β and LH

The object of the study was to investigate the clinical and endocrine patterns of progesterone, oestradiol-17β and LH during the peripubertal period in female pigs. Crossbred gilts were penned in groups at an age of 10–12 weeks and boars were kept in adjacent pens during the entire experimental period. Daily oestrous checks started at 4.5 months of age and the gilts were slaughtered after their third heat. At the age of 4.5–5 months a permanent catheter was inserted in the cephalic vein and blood samples were collected from the gilts once daily until either the first or second oestrus. In three gilts hourly blood samples were taken during their first and second oestrus, beginning at early pro-oestrus.The gilts showed their first oestrus at the average age of 183 days. No corpora lutea from earlier ovulations were observed in gilts laparoscoped after their first detected oestrus. During the 30-day period before first oestrus the mean daily progesterone levels varied between 32 and 329 pmol/l. The average levels of oestradiol-17β varied between 15.6 and 30.8 pmol/l. There was no tendency for the oestradiol-17β level to rise before onset of first pro-oestrus. The average levels of LH varied between 0.15 and 0.94 μg/l. The statistical analyses revealed no significant relationship between the level of the hormones studied and onset of first oestrus. The mean progesterone levels during the first and second oestrous cycles were almost identical, however. Oestradiol-17β increased gradually during pro-oestrus, reaching maximum levels before onset of oestrus and thereafter decreasing sharply to values around 30 pmol/l. The oestradiol-17β levels were higher at the second than at the first pro-oestrous period. The concentrations of plasma LH rose sharply with declining plasma levels of oestradiol-17β. The duration of elevated plasma LH levels (> 1 μg/l) was, on average, 26 h and the LH levels were higher during the first oestrus than during the second oestrus. The first rise in progesterone was observed 11–29 h after the LH levels had decreased to concentrations below 1 μg/l.     

Prolonged interovulatory interval after oestradiol treatment in mares.

This study was designed to test if oestradiol treatment would prevent or delay luteolysis in mares. Mares (5/group) received 0, 0.1, 1.0 or 10.0 mg oestradiol-17 beta daily from the day of ovulation until the next ovulation or for a maximum of 32 days. This treatment did not prevent luteolysis which occurred 15.8, 16.8, 15.8 and 17.3 days after the previous ovulation for the mares treated with 0, 0.1, 1.0 and 10.0 mg oestradiol respectively. Although oestradiol treatment failed to alter oestrous behaviour after luteolysis, daily treatment with 10.0 mg oestradiol prevented follicular growth and inhibited ovulation.     

Bovine Steroid Hormone and SHBG Concentrations Postpartum and during the Oestrous Cycle

Changes in consecutive estimates of milk progesterone concentrations and serum steroid hormone and sex hormone-binding globulin (SHBG) concentrations in the postpartum period were examined in Finnish Ayrshire and Friesian dairy cows which were divided according to feeding into a hay group and a silage group. Milk progesterone concentrations rose above 10 nmol/1, indicating the start of ovarian luteal activity, slightly earlier in the silage group (28.4 ± 8.7 (S.D.) days, n = 19) than in the hay group (33.4 ± 10.3, n = 28) after calving. Likewise, the first normal oestrous cycles began slightly earlier in cows fed with silage. On the other hand, no differences in the beginning of ovarian luteal activity were observed between the breeds. Serum oestradiol-17β, oestrone, testosterone, 5α-dihydrotestosterone (5α-DHT), pregnenolone and progesterone concentrations were fairly unchanged during postpartum anoestrus after uterine involution and before ovarian cyclic activity. After first ovulation, considerable increases in milk and serum progesterone concentrations were observed. The increase was accompanied by elevations in serum pregnenolone and 5α-DHT concentrations. In the late luteal phase, progesterone, 5α-DHT and pregnenolone concentrations rapidly declined, leading to low hormone levels in pro-oestrus. Thereafter, serum pregenolone and 5α-DHT concentrations slightly increased during the follicular phase. On the other hand, oestradiol-17β concentrations were elevated in pro-oestrus and decreased after that, being lowest at met-oestrous. Serum testosterone concentrations appeared to be unchanged during postpartum anoestrus and over the oestrous cycle. Serum SHBG concentrations were unchanged during postpartum anoestrus and over the oestrous cycle, as well as in pregnant animals. The serum SHBG concentrations were about double those found in women with normal menstrual cycles, whereas oestradiol concentrations were much lower. At present, it cannot be explained how the biological effects of oestradiol become evident under such conditions.     

Bactericidal activity of peripheral blood neutrophils during the oestrous cycle and early pregnancy in the mare

The oestrous cycles of 20 mixed-breed mares were synchronized with daily injections of 10 mg oestradiol-17 beta and 150 mg progesterone given i.m. for 10 days. On the 10th day, 10-15 mg prostaglandin F-2 alpha was administered i.m. to induce oestrus. Neutrophils were isolated from jugular blood on the 2nd or 3rd day of oestrus, Days 5 and 7 after ovulation or during early pregnancy (Days 18-34 of pregnancy). Neutrophils were challenged with Staphylococcus aureus and their bactericidal activity examined after 30 and 120 min of incubation for a reduction of colony forming units. Bactericidal activity increased with the time of incubation (P less than 0.01) but did not differ for the oestrous cycle or pregnancy (P greater than 0.05).     

Use of bovine follicular fluid to increase ovulation rate or prevent ovulation in sheep

Romney ewes were injected intramuscularly once or twice daily for 3 days with 0, 0.1, 0.5, 1 or 5 ml of bovine follicular fluid (bFF) treated with dextran-coated charcoal, starting immediately after injection of cloprostenol to initiate luteolysis on Day 10 of the oestrous cycle. There was a dose-related suppression of plasma concentrations of FSH, but not LH, during the treatment period. On stopping the bFF treatment, plasma FSH concentrations 'rebounded' to levels up to 3-fold higher than pretreatment values. The mean time to the onset of oestrus was also increased in a dose-related manner by up to 11 days. The mean ovulation rates of ewes receiving 1.0 ml bFF twice daily (1.9 +/- 0.2 ovulations/ewe, mean +/- s.e.m. for N = 34) or 5.0 ml once daily (2.0 +/- 0.2 ovulations/ewe, N = 25) were significantly higher than that of control ewes (1.4 +/- 0.1 ovulations/ewe, N = 35). Comparison of the ovaries of ewes treated with bFF for 24 or 48 h with the ovaries of control ewes revealed no differences in the number or size distribution of antral follicles. However, the large follicles (greater than or equal to 5 mm diam.) of bFF-treated ewes had lower concentrations of oestradiol-17 beta in follicular fluid, contained fewer granulosa cells and the granulosa cells had a reduced capacity to aromatize testosterone to oestradiol-17 beta and produce cyclic AMP when challenged with FSH or LH. No significant effects of bFF treatment were observed in small (1-2.5 mm diam.) or medium (3-4.5 mm diam.) sized follicles. Ewes receiving 5 ml bFF once daily for 27 days, from the onset of luteolysis, were rendered infertile during this treatment period. Oestrus was not observed and ovulation did not occur. Median concentrations of plasma FSH fell to 20% of pretreatment values within 2 days. Thereafter they gradually rose over the next 8 days to reach 60% of pretreatment values where they remained for the rest of the 27-day treatment period. Median concentrations of plasma LH increased during the treatment period to levels up to 6-fold higher than pretreatment values. When bFF treatment was stopped, plasma concentrations of FSH and LH quickly returned to control levels, and oestrus was observed within 2 weeks. The ewes were mated at this first oestrus and each subsequently delivered a single lamb.     

The control of oestrous behaviour in the mare.

Using a range of positive and negative sexual behaviour components, proceptivity of cycling, non-lactating mares and postpartum, lactating Pony mares was quantified around ovulation. Behavioural observations were compared to plasms concentrations of progesterone, total oestrogens and androstenedione. In addition, in cycling mares, comparison with plasma testosterone concentrations was carried out. Overall rejection behaviour by the mare was apparent both during dioestrus and during periods of basal plasma progesterone concentrations. Within cycling, non-lactating mares, and between postpartum ovulation associated with silent as opposed to overt oestrus, no consistent relationship existed between net behavioural scores and the circulating concentrations of oestrogens or androgens. The findings are taken to suggest that regulation of the signs of oestrus occurs to a large extent independently of circulating steroid concentrations.     

Ovarian morphology and the concentration of steroids, and of gonadotrophins during the breeding season in ewes actively immunized against oestradiol-17 beta or oestrone

Ewes were actively immunized against oestrone-6-(O-carboxymethyl)-oxime-bovine serum albumin, 17 beta-oestradiol-6-(O-carboxymethyl)oxime-bovine serum albumin or bovine serum albumin (controls). All 4 control ewes, 1 of 5 oestradiol-immunized ewes and 1 of 5 oestrone-immunized ewes had regular oestrous cycles. The other animals displayed oestrus irregularly or remained anoestrous. The plasma concentrations of LH and, to a lesser degree, FSH were increased relative to those in control ewes on Days 11-12 after oestrus or a similar total period after progestagen treatment in ewes not showing oestrus. The ovaries were examined and jugular venous blood, ovarian venous blood and follicular fluid were collected at laparotomy on Days 9-10 of the oestrous cycle. The ovaries of immunized ewes were heavier than those of control ewes. There were no CL in 5 of the immunized ewes but in the other 5 there were more CL than in the control ewes. Ovaries from 4 of 5 oestrone-immunized ewes contained luteinized follicles, while ovaries from 4 of 5 oestradiol-immunized ewes contained very large follicles with a degenerated granulosa and a hyperplastic theca interna. Both types of follicles produced progesterone, detectable in ovarian venous plasma and production of other steroids, particularly androstenedione, was also increased. The steroid-binding capacity of plasma was increased in the immunized ewes. The binding capacity of follicular fluid for oestradiol-17 beta and oestrone was similar to that of jugular venous plasma from the same ewes. These results suggest that immunization against oestrogens disrupts reproductive function by interfering with the feedback mechanisms controlling gonadotrophin secretion.     

Reproductive performance of heifers induced to oestrous asynchrony by suprabasal plasma progesterone levels

Suprabasal progesterone concentrations around oestrus have induced disturbances in oestrous behaviour and ovulation. To determine whether fertility in such an altered oestrus can be maintained at normal levels with additional inseminations (AI) until ovulation, fertility was compared in heifers (n = 11) inseminated in normal oestrous cycles and thereafter in cycles in which the animals were treated with progesterone in order to create suprabasal concentrations after luteolysis. The treatment consisted of silicone implants containing 10.6 mg kg⁻¹ of progesterone inserted subcutaneously on Day 8 of the oestrous cycle (day of ovulation designated Day 0) and removed on Day 25. Both in control oestrous cycles and oestrous cycles under progesterone treatment, growth of the ovulatory follicle and ovulation were determined by frequent ultrasound scanning. Blood was collected frequently for further analysis of progesterone, oestradiol-17β and luteinising hormone (LH). Insemination was performed 12 h after onset of standing oestrus. if ovulation did not occur 24 h after AI, heifers were inseminated again until ovulation. Pregnancy was diagnosed by ultrasound 25 days after ovulation.In control oestrous cycles, plasma progesterone decreased to 0.3 ± 0.3 nmol 1⁻¹. Duration of oestrus was 22.9 ± 2.0 h, the interval from onset of oestrus to ovulation was 32.4 ± 2.3 h and the interval from LH peak to ovulation was 28.6 ± 1.4 h. The interovulatory interval was 20.7 ± 0.6 days. In oestrous cycles in treated heifers, progesterone decreased to 1.0 ± 0.3 nmol l⁻¹ (P > 0.10) and the interovulatory interval was prolonged to 23.5 ± 1.0 days (P < 0.05). Standing oestrus lasted 47.2 ± 12.0 h (P = 0.09, n = 7). The interval from the onset of oestrus to ovulation was 59.4 ± 13.0 h (P = 0.08) and the interval from LH peak to ovulation 25.8 ± 1.3 h (P > 0.10). The prolonged oestrus was associated with increased (P < 0.05) growth of the ovulatory follicle and higher (P < 0.05) release of oestradiol-17β. Conception rates were 90% and 46% (P < 0.05), and the numbers of AI per heifer were 1.1 ± 0.1 and 3.4 ± 0.6 (P < 0.01) for control oestrous cycles and after treatment, respectively.The induction of suprabasal concentrations of progesterone caused asynchronies similar to those observed in cases of repeat breeding. The repeated AI did not maintain fertility at normal levels. It is suggested that the extended growth of the ovulatory follicle may cause impaired oocyte maturation or it may alter the maternal milieu owing to the prolonged release of oestradiol.     

Changes in equine endometrial oestrogen receptor alpha and progesterone receptor mRNAs during the oestrous cycle, early pregnancy and after treatment with exogenous steroids

Two experiments were performed to determine changes in the abundance of oestrogen and progesterone receptor (ER alpha and PR) mRNAs in equine endometrium during the oestrous cycle and early pregnancy, and under the influence of exogenous steroids. In Expt 1, endometrial biopsies were obtained from non-mated mares during oestrus and at days 5, 10 and 15 after ovulation, and from pregnant mares at days 10, 15 and 20 after ovulation. There were overall effects of day on the abundance of ER alpha (P = 0.0001) and PR (P = 0.0014) mRNAs. The amount of ER alpha mRNA decreased at day 10 of pregnancy, and PR mRNA was reduced at day 5 in non-mated mares and at day 15 of pregnancy, compared with oestrous values. Experiment 2 was conducted to determine the effects of exogenous steroids on endometrial ER alpha and PR mRNAs. Endometrial biopsies were obtained from 19 anoestrous mares that had been treated with vehicle, oestradiol, progesterone, or oestradiol followed by progesterone for either a short or a long duration. The steroid treatment affected the abundance of ER alpha mRNA (P = 0.0420), which was higher (P < 0.05) in the oestradiol group than in the group treated with oestradiol followed by long duration progesterone. The steroid treatment did not affect the abundance of PR mRNA. These results demonstrate that the amount of steroid receptor mRNA changes with the fluctuating steroid environment in the uterine endometrium of cyclic and early pregnant mares, and that the duration of progesterone dominance may affect ER alpha gene expression. In addition, factors other than steroids may regulate ER alpha and PR gene expression in equine uterine endometrium.     

Plasma concentrations of progesterone, oestrogens, testosterone and LH-like activity during the oestrous cycle of the camel (Camelus dromedarius)

Peripheral plasma concentrations of progesterone, total oestrogens and testosterone (measured by RIAs) and LH (monitored by the mouse Leydig cell bio-assay) were measured in 8 female camels for a complete oestrous cycle (23.1 +/- 1.2 days). The absence of an LH surge and a low concentration of progesterone (less than 1 ng/ml) during oestrus (5 days) and throughout the cycle indicated a failure of spontaneous ovulation and absence of a subsequent luteal phase in this species. High concentrations of testosterone and oestrogens indicated that the oestrous cycle in the camel is mostly follicular and that the increasing values of the two hormones during follicular development (5 days) is probably the stimulus to behavioural oestrus.     

Relationships between sexual behaviour, dominant follicle area, uterus ultrasonic image and pregnancy rate in mares of two breeds differing in reproductive efficiency

Weak or equivocal expression of oestrous behaviour, related to different level of mares' reactivity, may cause problems in oestrus detection and thus influence the reproductive efficiency. The aim of the study was to test whether a breed characterised by low pregnancy rate and high emotional reactivity (Thoroughbreds) differs in oestrous behaviour from a primitive breed with higher reproductive efficiency (Koniks). Additionally, the follicle size was examined to determine how it influences the intensity of oestrus and uterine ultrasonic image and whether the pregnancy rate differs in relation to the intensity of oestrous behaviour and the size of the dominant follicle(s) area on day preceding ovulation in both breeds. During four reproductive seasons the behaviour of 20 Konik polski (K) and 37 Thoroughbred (T) was observed during daily teasing. Simultaneously, the ultrasonic examinations of the reproductive system were carried out. The behaviour of mares was quantified by scoring on an 8-point scale (behavioural score, BS), according to increasing sexual receptivity. Cross-sectional follicular area (FA) was taken as a product of the two largest perpendicular follicular diameters and mean values for each breed were estimated on 1693 and 1982 mm2 for K and T mares, respectively (P < 0.05). Mares were classified according to the pooled area of dominant follicle (FA) during the preovulatory period: group A (FA < or = breed mean) and group B (FA > breed mean). Uterus image (UI) was scored (1-5) according to the increasing uterine echogenicity. The BS was higher (P < 0.01) in K mares (BS = 5.19) than in T mares (BS = 4.04). The BS was significantly related to increasing follicular area (FA). There was no breed difference in uterus image (UI) score. However, significant regression of UI on FA was found in K mares. The intensity of oestrus was positively related with UI (r = 0.29; P < 0.01) only in K mares, no such relationship was found in T mares. The pregnancy rate was significantly higher for K mares (88.5%) than for T mares (46.0%) and lower for T mares with less intense oestrous behaviour (29.4%) as compared to T mares with more intense oestrus (60.0%). No differences in pregnancy rate was found in mares belonging to A or B group of follicular area. The ascertained weaker oestrous behaviour in Thoroughbred was related to lower pregnancy rate. It is hypothesised that oestrus intensity may be the result of breed differences in the response of the neural system to follicular secretions, or may be an effect of higher incidence of multiple non-synchronic ovulation and/or higher sensitivity to stress in Thoroughbred mares.     

Effects of recombinant human follicle stimulating hormone on follicle development and ovulation in the mare

The only gonadotrophin preparation shown to stimulate commercially useful multiple ovulation in mares is equine pituitary extract (EPE); even then, the low and inconsistent ovulatory response has been ascribed to the variable, but high, LH content. This study investigated the effects of an LH-free FSH preparation, recombinant human follicle stimulating hormone (rhFSH), on follicle development, ovulation and embryo production in mares. Five mares were treated twice-daily with 450 i.u. rhFSH starting on day 6 after ovulation, coincident with PGF(2alpha) analogue administration; five control mares were treated similarly but with saline instead of rhFSH. The response was monitored by daily scanning of the mares' ovaries and assay of systemic oestradiol-17beta and progesterone concentrations. When the dominant follicle(s) exceeded 35 mm, ovulation was induced with human chorionic gonadotrophin; embryos were recovered on day 7 after ovulation. After an untreated oestrous cycle to 'wash-out' the rhFSH, the groups were crossed-over and treated twice-daily with 900 i.u. rhFSH, or saline. At the onset of treatment, the largest follicle was <25 mm in all mares, and mares destined for rhFSH treatment had at least as many 10-25 mm follicles as controls. However, neither dose of rhFSH altered the number of days before the dominant follicle(s) reached 35 mm, the number of follicles of any size class (10-25, 25-35, >3 mm) at ovulation induction, the pre- or post-ovulatory oestradiol-17beta or progesterone concentrations, the number of ovulations or the embryo yield. It is concluded that rhFSH, at the doses used, is insufficient to stimulate multiple follicle development in mares.     

Fertility, ovulation and maturation of eggs in mares injected with HCG

Pony mares were observed from January to August for incidence of oestrus, duration of oestrus, length of the oestrous cycle and for ovulation and fertility after injection of HCG. From January to 15 May most mares showed oestrus but the duration of oestrus was quite variable and few mares ovulated in response to HCG. From 15 May to 17 August oestrous cycles were more regular and ovulation was induced within 40-50 h by an intramuscular injection of 1500-5000 i.u. HCG. Pregnancy was established by one mating at a fixed time after HCG in 20 of 69 mares. Degenerate eggs were recovered from the oviducts of anoestrous recently ovulated, mated, unmated and pregnant mares. The first polar body was formed before ovulation in 2 eggs and had not formed in 2 recently ovulated eggs flushed from the oviduct. The second polar body formed after sperm penetration 10-12 h after ovulation. After formation of pronuclei, the first cleavage division occurred at 20 h and the second at 32 h after ovulation. Oestrus was inhibited by progesterone administered by vaginal devices but occurred within 1-3 days in 12 of the 20 mares after withdrawal of the devices.     

Intratesticular steroid levels and their hormonal control

Litter-mate adult male rats were treated with daily intramuscular injections of ACTH (10.5 micrograms), dexamethasone (2.0 mg), ethynyl estradiol (1.7 micrograms) and hCG (5 IU) for three consecutive days. The animals were sacrificed on the fourth day and the intratesticular and peripheral plasma steroid levels were analyzed. The steroids measured by radioimmunoassay included pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone, progesterone, 17-hydroxyprogesterone, androstenedione, testosterone and dihydrotestosterone. In addition, the sulphoconjugated forms of pregnenolone, dehydroepiandrosterone, testosterone and dihydrotestosterone were estimated in the peripheral blood. The administration of ACTH diminished the intratesticular levels of all steroids studied. Also dexamethasone and ethynyl estradiol treatment suppressed all intratesticular steroid levels, except that of pregnenolone (the former) and of 17-hydroxyprogesterone (the latter). The suppressive effect of ethynyl estradiol was strongest on the levels of the delta 5-steroids and that of dexamethasone on the delta 4-steroids; the latter was significantly stronger than the effect of ACTH. The stimulatory effect of hCG was limited to the metabolism of progesterone and was restricted to the sequence: 17-hydroxyprogesterone----androstenedione----testosterone---- dihydrotestosterone. Dexamethasone-suppression, and hCG-stimulation of the intratesticular levels of delta 4-steroids, was mirrored by corresponding changes in the peripheral plasma levels, with the exception of the plasma levels of androstenedione which were not influenced by any of the treatments studied. Also the suppression of intratesticular testosterone and dihydrotestosterone levels by ACTH, dexamethasone, or ethynyl estradiol was closely reflected by their plasma levels both in the unconjugated and sulphoconjugated forms. On the hand, the administration of ACTH diminished the intratesticular levels of pregnenolone and progesterone but significantly increased those in the plasma. Moreover, both ACTH and ethynyl estradiol reduced the levels of all delta 5-steroids in testicular tissue, but not in the peripheral plasma, although they decreased the circulating levels of pregnenolone sulphate and dehydroepiandrosterone sulphate. The data are interpreted as suggesting that the hormonal agents studied interfere with testicular steroidogenesis through different mechanisms.     

Plasma levels of oestradiol-17 beta in the pre-puberal heifer treated to induce superovulation

The plasma concentrations of oestradiol-17β have been measured by radioimmunoassay in pre-puberal calves following treatments used to induce superovulation (PMSG/HCG and PMSG/FGA/HCG). Before treatment, in almost all animals, the concentrations of oestradiol-17β were different from zero (2 to 8 pg/ml). The highest concentrations were measured around 130 h. after the beginning of treatment, before ovulation (150 to 2050 pg/ml). The curves showing the changes in hormonal levels have the same form as those of follicular growth measured using morphological criteria. The two hormonal treatments resulted in similar oestradiol-17β concentrations.     

Administration of pregnenolone and dehydroepiandrosterone to guinea pigs and rats causes the accumulation of fatty acid esters of pregnenolone and dehydroepiandrosterone in plasma lipoproteins.

Steroids were administered continuously to guinea pigs and rats using subcutaneously applied silastic tubing implants, and the effects on circulating steroid and steroid conjugate levels were monitored. Using implants filled with pregnenolone, we observed that pregnenolone had a marked effect on increasing the levels of its fatty acid-esterified derivative, while dehydroepiandrosterone-releasing implants produced a rise in circulating nonconjugated dehydroepiandrosterone, androst-5-ene-3 beta,17 beta-diol, androstenedione, testosterone, and lipoidal derivatives of both dehydroepiandrosterone and androst-5-ene-3 beta,17 beta-diol. Implants filled with androstenedione produced a 20-fold increase in plasma androstenedione levels relative to untreated controls and a corresponding five-fold increase over control testosterone levels. No fatty acid-esterified derivative of testosterone could be detected within the plasma. Lipoproteins were isolated from both rats and guinea pigs treated with implants filled with pregnenolone or dehydroepiandrosterone. The steroid and steroid fatty acid esters present in each fraction were analyzed, revealing that approximately 75% of all the fatty acid esters of pregnenolone recovered in the lipoproteins was localized within the high-density lipoprotein (HDL) fraction of both guinea pig and rat plasma. Similarly, lipoidal dehydroepiandrosterone was found associated predominantly with the low-density lipoprotein and HDL fractions in the guinea pig, while in the rat this steroid conjugate was exclusively within the HDL fraction. High-density lipoprotein-incorporated tritiated pregnenolone fatty acid esters and dehydroepiandrosterone fatty acid esters were injected into castrated male guinea pigs to study the fate of these complexes.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of trenbolone acetate on the bovine oestrous cycle

The anabolic steroid, trenbolone acetate, affected the bovine oestrous cycle in different ways depending on the timing of administration relative to oestrus and the plasma concentration of trenbolone achieved. Administration before oestrus caused failure of ovulation and a high incidence of a syndrome similar to cystic ovarian disease. High plasma concentrations of trenbolone during the luteal phase of the oestrous cycle prevented luteolysis and maintained progesterone secretion for up to 42 days. Subsequent cycles were not affected.     

Steroid concentrations in follicular fluid aspirated repeatedly from transitional and cyclic mares

The objectives of the present study were to determine follicular progesterone (P4) and estradiol-17beta (E2) in transitional mares and to compare follicular steroid concentrations between transitional and cyclic mares. Follicles > 8 mm were aspirated under transvaginal ultrasound-guidance 4 times at 3 to 4 day intervals (T1-T4) in Norwegian pony mares during vernal transition. During the breeding season, follicular aspirations were conducted in each mare on Day 6, Day 14 and Day 18 after ovulation of 3 separate estrous cycles (Day of ovulation = Day 0). Plasma and follicular fluids were analyzed for P4 and E2 with ELISA and RIA, respectively. Plasma P4 concentrations remained below 1 ng/mL throughout T1-T4, while the follicular P4 concentrations increased significantly to cyclic levels after the first transitional aspiration. Plasma E2 concentrations similarly remained at low levels during the course of the transitional aspirations, while the follicular E2 concentrations increased gradually over the 4 aspirations to cyclic concentrations. The mares ovulated on average 9.8 +/- 1.6 (mean +/- SEM) days after the last transitional aspiration, and 16.6 +/- 0.2, 11.3 +/- 1.5 and 23.2 +/- 4.4 days after aspirations conducted on Day 6, 14 and 18, respectively. The present study demonstrates that in the transitional mare newly developing follicles exhibit biosynthesis of P4 and E2. Furthermore, an increase in follicular steroid concentrations is not necessarily reflected in the peripheral steroid concentrations.