Timing of ovulation in relation to onset of estrus and LH peak in yak (Poephagus grunniens L.)

The objective of the study was to determine the timing of ovulation in relation to onset of estrus and the preovulatory LH peak in yaks. For this purpose, a sensitive LH enzymeimmunoassay previously established in buffaloes was successfully validated for measuring the hormone in yak plasma. Plasma LH and progesterone were estimated from blood samples collected from eight non-lactating cycling yaks at 2 h intervals after estrus onset until 6 h after ovulation (ovulation was confirmed by palpation of ovaries per rectum). The mean+/-S.E.M. preovulatory plasma LH peak was 10.11+/-0.35 ng/ml with the values ranging from 8.75 to 11.51 ng/ml in individual yaks. The mean+/-S.E.M. duration of the LH surge was 7.25+/-0.55 h with a range of 6-10 h. Onset of LH surge (mean+/-S.E.M.) occurred 3.0+/-0.65 h after the onset of estrus. Mean plasma progesterone stayed low (<0.25 ng/ml) during the entire duration of sampling. Ovulation occurred 30.5+/-0.82 h (range, 28-34 h) after the onset of estrus and 20.25+/-1.03 h after the end of LH surge. The occurrence of the LH peaks within a narrow time frame of 4-8h post estrus onset in yaks could have contributed to the animals ovulating within a narrow time interval.     

Neuroendocrine control of luteinizing hormone secretion and reproductive function in spontaneously persistent-estrous aging rats

Middle-aged female rats cease to display estrous cycles and exhibit a state of persistent estrus (PE). Under PE and chronic anovulatory conditions, there is a lack of spontaneous luteinizing hormone (LH) surges, but ovulations often occur after the females are caged with males. This study examined the effects of caging and mating with male rats on LH release in PE females, and assessed their reproductive capacity. Young cyclic rats received intra-atrial cannulae, and subsequently were sampled every 90 min during 1400-2130 h on proestrus for plasma LH measurement. PE females were similarly cannulated and sampled. Two days later, these PE rats received an s.c. injection of estradiol benzoate (EB) and were sampled on the following day. While young females exhibited the proestrous LH surge, PE rats maintained low plasma LH levels persistently and were unable to increase LH release after EB administration. On the other hand, when cannulated PE females were caged with fertile males, 92% displayed lordotic responses, and 75% of those sexually receptive PE females exhibited LH surges followed by ovulation. The initiations of the lordotic response and the LH surge both were more rapid in PE females caged with males beginning at 1500 h than at 1400 h. In contrast, when individual PE rats were placed in clean boxes without males, only one of 13 females showed an increase in LH release followed by ovulation. Separate groups of PE rats were mated with fertile males, and subsequently used for counting the number of blastocysts in the uteri on Day 5 of pregnancy and the number of pups delivered at term.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exogenous GnRH induces ovulation in seasonally anoestrous lactating goats (Capra hircus)

A specific sheep LH radioimmunoassay was validated for the measurement of goat LH, and used to monitor luteal-phase LH episodes and the preavulatory LH surge in progestagen sponge-synchronized cycling goats. No luteal-phase LH episodes were detected during 12 h of frequent (15-min) blood sampling in 2 goats. A preovulatory LH surge was recorded in 5/5 goats, with a mean amplitude of 45.4 +/- 7.2 ng/ml and a mean time of onset of 38.4 +/- 1.2 h after removal of a progestagen-impregnated sponge. In anoestrous goats, single i.v. injections of 1000 and 2000 ng GnRH induced LH episodes with a mean amplitude of 2.04 +/- 0.11 and 3.67 +/- 0.06 ng/ml respectively, but injections of 250 or 500 ng did not consistently elevate LH concentrations. Progestagen-primed, seasonally anoestrous lactating goats were treated with repeated injections of 1500 ng GnRH (every 2 h for 52 or 78 h) in May 1985 or 1986. All 10 had kidded in March of the same year, and were consequently at peak lactation at the time of GnRH treatment. A preovulatory LH surge was detected in 9 goats with a mean time of onset of 59.5 +/- 2.9 h (1985) or 39.6 +/- 3.3 h (1986) after vaginal sponge removal. All animals displayed oestrus and ovulated, and 9 of the goats were mated: in 5 of these animals pregnancies were successfully carried to term. The results show episodic LH release in response to GnRH and indicate that ovulation can be induced in seasonally anoestrous goats, even at peak lactation, and normal pregnancies may result.     

Opiate antagonist treatment reinstates estrous cycles in middle-aged persistent-estrous rats

Middle-aged female rats display luteinizing hormone (LH) surge deficits and cycle irregularity followed by the onset of persistent estrus (PE). The central nervous system has been identified as a primary locus of failure in PE rats, but the particular neural elements involved have not been determined. The goal of the present study was to identify a role for endogenous opioid peptides (EOP) in age-related acyclicity by evaluating the effect of opiate antagonist treatment on vaginal cytology in PE rats. PE rats were administered, s.c., saline (SAL), naloxone (NAL) or naltrexone (NTX) once daily for 20 days, or repetitively on Day 1 and on successive proestrus days if cyclicity was resumed. Single NTX (50 mg/kg), but not NAL (2 mg/kg), treatment interrupted the PE state in almost half of treated animals. Daily or repetitive proestrus NTX (10 mg/kg) treatment interrupted PE more frequently, and many animals displayed repeated estrous cycles and ovulation. Afternoon LH surges were observed after initial NTX treatment in animals displaying PE interruption. This demonstration that LH surges and ovulatory cycles can be reinitiated in PE rats with NTX suggests that dysfunction in the 'brake' on EOP secretion during proestrus may be one of the neuroendocrine impairments mediating acyclicity in aging female rats.     

The variability in the interval between estrus and ovulation in cattle and its determinants

Fertility of Holstein cows has been decreasing for years and, to a lesser extent, the fertility of heifers too but more recently. A hypothesis to explain this phenomenon may be that the chronology of events leading to ovulation is different for those animals bred nowadays when compared to what was reported previously; this would result in an inappropriate time of insemination. Therefore, two experiments were designed to investigate the relationships among estrus behavior, follicular growth, hormonal events and time of ovulation in Holstein cows and heifers. In the first experiment, the onset of estrus, follicular growth, patterns of estradiol-17beta, progesterone and LH, and the time of ovulation were studied in 12 cyclic Holstein heifers that had their estrus synchronized using the Crestar method; this was done twice, 3 weeks apart. The intervals between estrus and ovulation, estrus and the LH peak, and between the LH peak and ovulation were, respectively, 38.5 h +/-3.0, 9.1 +/- 2.0 and 29.4 h +/-1.5 (mean+/- S.E.M). The variation in the interval between estrus and the LH peak explained 80.6% of the variation in the interval between estrus and ovulation. The intervals between estrus and the LH peak, and estrus and ovulation were correlated with estradiol-17beta peak value (r=-0.423, P <0.04 and r=-0.467, P<0.02, respectively). Positive correlation coefficients for the number of follicle larger than 5 mm, and negative correlation coefficients for the size of the preovulatory follicle with the intervals between estrus and LH peak, LH peak and ovulation, and estrus and ovulation suggest an ovarian control of these intervals. In respect to its role to explain the variation in the interval between estrus and ovulation, the variation in the interval between estrus and the LH peak was evaluated further in a second set of experiments utilizing 12 pubertal Holstein heifers and 35 Holstein cows. The duration of the interval between the beginning of estrus and the LH peak was longer in heifers than in cows (4.15 h versus -1.0 h; P <0.002); the variation for this interval was higher in cows than in heifers (S.E.M.= 1.2 h versus 0.8 h; P=0.01). According to the results of these studies it can be proposed that estradiol and other product(s) of ovarian origin regulate not only the duration of intervals between the onset of estrus and the LH surge but also between the LH surge and ovulation. From the results obtained in the first experiment, it may be postulated that differences observed between cows and heifers for the duration of the interval between onset of estrus and the LH surge as well as for the variation of this interval would be observed also for the interval between the onset of estrus and ovulation. Therefore, on a practical point of view, the long interval between the onset of estrus and ovulation and the high variation of this interval, especially in cows, may be a source of low fertility and should be considered when analysing reproductive disorders.     

Preovulatory secretion of progesterone, luteinizing hormone, and prolactin in 4-day and 5-day cycling rats

Timing of ovulation and changes in plasma progesterone, luteinizing hormone (LH), and prolactin (PRL) during periovulatory stages were determined in Holtzman rats exhibiting regular 4- or 5-day cycles under a daily artificial illumination from 0500 to 1900 h. The 5-day cycling rats ovulated between 0130 and 0930 h on estrus, whereas some of the 4-day cycling animals ovulated as early as about 0130 h and others as late as 1130 h on estrus. Onset time of preovulatory LH and progesterone surges was about 1500 h on proestrus in both the 4- and the 5-day cycling rats. Peak levels of plasma LH and progesterone were measured at 1700 to 1900 h on proestrus, while the first rises and peak values of plasma PRL were evident a few hours earlier than those of plasma LH in the rats with two cycle lengths. Plasma LH levels at 1900 h on proestrus as well as plasma progesterone levels at 1600 and 2300 h on proestrus and at 0130 and 0330 h on estrus were significantly lower in the 5-day cycling rats than in the 4-day cycling animals (p less than 0.05). In contrast, PRL levels from 1500 through 2300 h on proestrus remained consistently higher in 5-day cycling rats than in 4-day cycling rats, and significant differences in PRL levels between these rats were apparent at 1500, 1600, and 2100 h (p less than 0.05-0.01). Thus, these results demonstrate that the 5-day cycling rats exhibit the attenuated magnitude of LH surge accompanied by the augmented preovulatory PRL release, and that plasma progesterone levels reflect the magnitude of LH surge. A tentative working hypothesis concerning the etiology of the 5-day cycle has been proposed.     

Effect of age and time of day on the timing of the surge in luteinizing hormone, behavioural oestrus and mating in red deer hinds (Cervus elaphus).

The oestrous cycles of fourteen red deer hinds (six yearling; eight more than 2 years old) were synchronized during the early breeding season by removal of a progesterone-containing intravaginal device and blood samples were taken at intervals of 3 h commencing 13 or 25 h later and continued for 54 h. The controlled internal drug release devices (CIDRs) were removed at 08:00 h (group 1; three yearlings and four adults) or 12 h later at 20:00 h (group 2; three yearlings and four adults). There was no significant effect of time of removal of CIDR on the interval to the onset of oestrus (group 1, 34.5 +/- 4.05 h; group 2, 42.14 +/- 7.8 h) on the time of peak concentration (group 1, 41.81 +/- 5.69 h; group 2, 41.71 +/- 7.81 h) or on duration of the luteinizing hormone (LH) surge (group 1, 15.00 +/- 0.95 h; group 2, 14.57 +/- 0.78 h). The six yearling animals exhibited oestrus and LH surge significantly later than the adults (55 +/- 4.2 versus 32 +/- 6.3 h for the LH surge for yearling and adult females, respectively). In a further experiment, 20 hinds were synchronized during the breeding season by removal of CIDR at two times of day 12 h apart and placed with a stag. Mating took place at a mean time of 42.1 +/- 2.4 h and 37.0 +/- 1.3 h later in the two groups. There was no significant effect of time of removal of CIDR upon time to onset of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Sulawesi Crested Black Macaque (Macaca nigra) menstrual cycle: changes in perineal tumescence and serum estradiol, progesterone, follicle-stimulating hormone, and luteinizing hormone levels.

Events in the normal menstrual cycle of the endangered Sulawesi Crested Black Macaque (Macaca nigra) were characterized. Daily blood samples were obtained during 10 menstrual cycles from five M. nigra demonstrating regular cycles. The amount of perineal tumescence was scored daily. Serum levels of estradiol and progesterone were determined by RIA, serum LH levels were determined by the mouse Leydig cell bioassay, and serum FSH levels were determined by the rat granulosa cell aromatase bioassay. Cycle length was 39.8 +/- 1.0 days (mean +/- SEM) with an LH surge occurring 25 +/- 1.5 days from the onset of menses. After menses, both LH and estradiol were initially depressed, with estradiol first exceeding 50 pg/ml 8 days before the LH surge. In five cycles, peak estradiol levels (340 +/- 44 pg/ml) occurred on the day of the LH surge (637 +/- 58 ng/ml) and in the other five cycles, on the day before the LH surge. There was a broad increase of FSH in midcycle without a well-defined surge corresponding to the LH surge. Progesterone began increasing on the day of the LH surge and reached peak levels (6.8 +/- 0.96 ng/ml) 8 days later. Maximal perineal tumescence was generally associated with the time of the LH surge, but variation between animals made it impossible to predict accurately the day of the LH surge by perineal tumescence scores alone.     

Photoperiodic modification of negative and positive feedback effects of oestradiol on LH secretion in ovariectomized goats

Ovariectomized Shiba goats carrying an oestradiol implant (4-10 pg/ml) were kept under a short-day light regimen (10L:14D; Group 1, N = 4) or a long-day regimen (16L:8D; Group 2, N = 4). Plasma LH concentrations were lower (P less than 0.05) in Group 2 than in Group 1 between Days 40 and 200, suggesting an enhanced negative feedback effect of oestradiol on LH secretion under a long-day regimen. On Days 30, 60, 100, 149 and 279, an LH surge was induced by i.v. infusion of oestradiol for 48 h; the infusion rate was gradually increased from 0.5 (0 h) to 4.1 (48 h) micrograms/h, thereby mimicking the preovulatory increase of oestradiol secretion. The duration and magnitude of the induced LH surge were indistinguishable between the groups. The latency from the onset of oestradiol infusion to the LH surge was relatively constant in Group 1, 41.1 +/- 0.9 h (mean +/- s.e.m., n = 17) but was shorter in Group 2 (19.7 +/- 3.7 h, P less than 0.05) on Day 149; less oestradiol was therefore required for induction of the LH surge (27.4 vs 89.7 micrograms, P less than 0.01), suggesting an increased sensitivity to the oestradiol positive feedback under a long-day regimen. These results might be interpreted to indicate that the hypothalamic-pituitary axis of the goat becomes hypersensitive to the positive as well as the negative feedback effect of oestradiol under long-day conditions.     

Comparison of the rate of decline in plasma progesterone concentrations at a natural and progesterone-synchronized oestrus and its effect on tonic LH secretion in the ewe

The pattern of change in plasma progesterone and LH concentrations was monitored in Clun Forest ewes at a natural oestrus and compared to that observed after removal of progesterone implants. The rate of decline in plasma progesterone concentrations after implant withdrawal (1.8 +/- 0.2 ng/ml h-1) was significantly greater (P less than 0.001) than that observed at natural luteolysis (0.2 +/- 0.1 ng/ml h-1), and this resulted in an abnormal pattern of change in tonic LH secretion up to the time of the preovulatory LH surge. This more rapid rate of progesterone removal was also associated with a shortening of the intervals from the time that progesterone concentrations attained basal values to the onset of oestrus (P less than 0.05) and the onset of the preovulatory LH surge (P less than 0.01). However, there were no significant differences in the duration of the LH peak, preovulatory peak LH concentration, ovulation rate or the pattern of progesterone concentrations in the subsequent cycle. It is suggested that the abnormal patterns of change in progesterone and tonic LH concentrations may be one factor involved in the impairment of sperm transport and abnormal patterns of oestradiol secretion known to occur at a synchronized oestrus.     

Behavioral and endocrine responses of hair sheep ewes exposed to different mating stimuli around estrus

Hair sheep ewes were used to evaluate the influence of various levels of mating stimuli on the duration and timing of estrus and LH concentrations around estrus. Ewes were treated with PGF2alpha (15 mg, im) 10 d apart. At the time of the second PGF2alpha treatment (Day 0) ewes were placed in groups and exposed to different types of mating stimuli. One group of ewes (n = 16) was exposed to an epididymectomized ram (RAM), a second group of ewes (n = 16) was exposed to an epididymectomized ram wearing an apron to prevent intromission (APRON) and a third group of ewes (n = 17) was exposed to an androgenized ovariectomized ewe (T-EWE). Jugular blood samples were collected from ewes at 6-h intervals through Day 5. Plasma was harvested and LH concentration was determined by RIA. The ewes were observed at 6-h intervals to detect estrus. A ewe was considered to be out of estrus when she no longer stood to be mounted by the teaser animal. There was no difference (P > 0.10) in the proportion of ewes expressing estrus (79.6%) or having an LH surge (85.7%) among the treatments. Neither the time to estrus nor the duration of estrus were different (P > 0.10) among APRON, RAM or T-EWE groups (41.6+/-3.8 vs 43.6+/-3.6 vs 46.1+/-3.6 h, respectively, and 26.5+/-2.2 vs 24.8+/-2.3 vs 30.5+/-2.2 h, respectively). The time to LH surge was similar (P > 0.10) among APRON, RAM and T-EWE groups (51.2+/-4.5 vs 51.2+/-4.7 vs 52.7+/-4.5 h, respectively). The magnitude of the LH surge was similar (P > 0.10) in the T-EWE, APRON and RAM ewes (99.7+/-4.9 vs 87.2+/-4.9 vs 85.8+/-5.0 ng/mL, respectively). The time from estrus to the LH surge was not different (P > 0.10) among APRON, RAM or T-EWE ewes (10.1+/-2.2 vs 9.8+/-2.3 vs 11.6+/-2.3 h, respectively). These results show that the expression and duration of estrus are not influenced by different types of mating stimuli in hair sheep ewes. In addition, the timing and the magnitude of LH release does not appear to be influenced by mating stimuli around the time of estrus.     

Male stimulation of luteinizing hormone surge, progesterone secretion and ovulation in spontaneously persistent-estrous, aging rats

In aging, persistently estrous (PE) female rats, there are no estrous cycles or cyclic increases in luteinizing hormone (LH) secretion, but the sexual receptivity to the male is consistently maintained. We recently reported that caging and mating with fertile males elicits an LH surge followed by ovulation in aging PE rats. The present study examined the relationship between the LH surge, the increase in progesterone (P) secretion and ovulation in PE females exposed to males, and assessed whether intromission was essential for the male-induced pre-ovulatory LH surge. PE rats were implanted with intra-atrial cannulae. Six to eight days later, these females were individually caged with a fertile male and repeatedly sampled (once every 30 or 60 min) between 1400 and 1900 h for assays of plasma LH and P. Sexual behavior of the female was recorded and correlated with the changes in plasma LH and P values. Similar experiments were also performed on cannulated PE rats with their vaginal orifice blocked with adhesive tape during the caging and sampling session. In both experiments, over 90% of the PE females displayed a high degree of lordosis response to mounting by the male, and over 60% of those sexually receptive PE females exhibited an LH surge followed by ovulation. The male-induced preovulatory LH surge occurred in PE females without actual intromission. Caging with fertile males also elicited a marked increase in plasma P concentrations in PE rats and in PE females prevented from experiencing intromission.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stag exposure advances the LH surge and behavioral estrus in Eld's deer hinds after CIDR device synchronization of estrus

The impact of male presence or absence on the timing of the preovulatory LH surge and estrus was studied in 3 experimental groups (n = 6/group) of Eld's deer hinds pretreated with intravaginal progesterone-releasing devices (CIDR-type G) as follows: Group 1 = indirect male contact barn; Group 2 = direct male contact barn; and Group 3 = male isolation barn. For all hinds, the duration of the preovulatory LH surge averaged 2.5+/-0.5 h, whereas mean peak preovulatory and basal LH concentrations were 2.9+/-0.2 ng mL(-1) and 0.27+/-0.03 ng mL(-1), respectively. Nine of 12 male-exposed hinds exhibited a preovulatory LH surge within 24 to 32 h postCIDR device withdrawal, whereas 0 of 6 male-isolated hinds exhibited a preovulatory LH surge during the same time period. Onset of behavioral estrus (45.2+/-2.3, 52.7+/-5.7 and 66.3+/-1.8 h, respectively) was significantly advanced (P<0.05) after CIDR device withdrawal in male exposed hinds (Groups 1 and 2) compared with male isolated hinds (Group 3). These data suggest that stag exposure is important for modulating the timing of the preovulatory LH surge and behavioral estrus after synchronization of estrus with exogenous progestagens.     

Influence of CIDR treatment during superovulation on embryo production and hormonal patterns in cattle

One of the major sources of success in embryo transfer is timing of AI relative to the LH surge and ovulation. The aim of this study was to compare the embryo production following superovulation during a PGF2alpha (control cycle) or a CIDR-B synchronized cycle (CIDR-B cycle). CIDR-B (CIDR-B ND, Virbac, Carros, France) was inserted on Day 11 of a previously synchronized cycle and left for 5 days. A total dose of 350 microg FSH was administered (eight injections i.m. for 4 days; first on Day 13, decreasing doses) and PGFalpha analog (750 microg i.m.: Uniandine ND, Schering-Plough, Levallois-Perret, France) injected at the time of third FSH injection. Artificial inseminations were performed 12 and 24 h after standing estrus (Day 0). Embryos were collected on Day 7. Luteinizing hormone was measured by EIA (Reprokit Sanofi, Libourne, France) from blood samples collected every 3 h for 36 h, starting 24 h after PGF2alpha (control cycle) or 12 h after CIDR-B removal (CIDR-B cycle). The effects of treatment group and interval between the LH peak and AI (two classes, < 10 and > or = 10 h) on embryo production and quality were analyzed by ANOVA. No effect of treatment was observed on embryo production variables. The intervals between the end of treatment and onset of estrus and between end of treatment and LH surge were greater in heifers treated during a control than a CIDR-B cycle, respectively (45.5 +/- 1.4 versus 31.9 +/- 0.7; 42.0 +/- 1.6 versus 31.0 +/- 1.5; P < 0.05), but maximal LH and estradiol concentrations, at the preovulatory surge were similar in control and CIDR-B synchronized heifers. The numbers of viable and Grade I embryos were significantly increased (P < 0.01) when animals had an interval from LH peak to first AI > or = 10 h (7.2 +/- 0.9 and 3.5 +/- 0.6) when compared to shorter intervals (4.2 +/- 1.1 and 2.0 +/- 0.7) whereas total number of embryos was unchanged (11.8 +/- 1.4 versus 10.3 +/- 1.8). It is concluded that late occurrence of LH peaks in relation to estrous behavior is associated with a lower embryo quality when first AIs are performed systematically 12 h after standing estrus. Further studies are needed to know if results may be improved when making AI at a later time after standing estrus or if LH assays are useful to better monitor AI time.     

Human chorionic gonadotropin and luteinizing hormone-releasing hormone reverse the blockade of ovulation in pregnant mare's serum gonadotropin-primed immature rats by the anti-androgenic drug, hydroxyflutamide

The present study was designed to examine mechanism(s) of the anti-ovulatory action of the anti-androgen, hydroxyflutamide (OH-F). Prepubertal rats were treated with 4 IU pregnant mare's serum gonadotropin (PMSG) (day -2) to induce first estrus and ovulation. They received OH-F in sesame oil or oil alone at 08:00 and 20:00 h on day 0 (the day of proestrus) and ovulations were assessed on the morning of day 1. Eighty-three percent of control animals ovulated with a mean of 7.7 +/- 1.1 corpora lutea per rat. Hydroxyflutamide blocked ovulation in all but 2 of the 12 rats receiving this drug alone. All of OH-F treated rats that received 5 and 25 IU human chorionic gonadotropin (hCG) ovulated with means +/- SEM of 9.1 +/- 0.1 and 7.3 +/- 1.4 corpora lutea per rat, respectively. The dose of 0.2 IU hCG was essentially ineffective, while the effect of 1.0 IU hCG was intermediate. At the dose of 20 ng and above (100 and 500 ng) luteining hormone-releasing hormone (LHRH) completely overcame the ovulation blockade in the OH-F treated animals, while a 4-ng dose was ineffective. At 18:00 h on the day of proestrus, serum LH levels in control animals were 17.56 +/- 2.60 ng/mL, which were 920% above basal levels (1.90 +/- 0.13) indicating a spontaneous LH surge. This surge was suppressed in OH-F treated rats. Injection of LHRH, at the dose of 20 ng and above, reinstated the LH release in OH-F treated animals. Thus, the anti-androgen, OH-F, inhibits ovulation in PMSG-treated immature rats through its interference with the preovulatory LH surge; the inhibition can be reversed by hCG or LHRH. Hydroxyflutamide does not appear to interfere at the level of the pituitary, but may have direct action at the hypothalamic and (or) extrahypothalamic sites involved in the generation of positive feedback signals that control LH release.     

Improved in vitro embryo development using in vivo matured oocytes from heifers superovulated with a controlled preovulatory LH surge

In bovine in vitro embryo production, the IVM step is rather successful with 80% of the oocytes reaching the MII stage. However, the extent to which the process limits the yield of viable embryos is still largely unknown. Therefore, we compared embryonic developmental capacity during IVC of IVF oocytes which had been matured in vitro with those matured in vivo. In vitro maturation was carried out for 22 h using oocytes (n = 417) obtained from 2- to 8-mm follicles of ovaries collected from a slaughterhouse in M199 with 10% fetal calf serum (FCS), 0.01 IU/mL LH, and 0.01 IU/mL FSH. In vivo matured oocytes (n = 219) were aspirated from preovulatory follicles in eCG/PG/anti-eCG-superovulated heifers 22 h after a fixed time GnRH-induced LH surge; endogenous release of the LH surge was suppressed by a Norgestomet ear implant. This system allowed for the synchronization of the in vitro and in vivo maturation processes and thus for simultaneous IVF of both groups of oocytes. The in vitro developmental potential of in vivo matured oocytes was twice as high (P < 0.01) as that of in vitro matured oocytes, with blastocyst formation and hatching rates 11 d after IVC of 49.3 +/- 6.1 (SEM; n = 10 heifers) vs 26.4 +/- 1.0% (n = 2 replicates), and 39.1 +/- 5.1% vs 20.6 +/- 1.4%, respectively. It is concluded that IVM is a major factor limiting in the in vitro production of viable embryos, although factors such as the lack of normal preovulatory development of IVM oocytes contributed to the observed differences.     

Pulsatile nature of luteinizing hormone release is maintained during luteinizing hormone-releasing hormone stimulation in normal male rats

The plasma LH concentration is believed to be reasonably steady in normal male rats. We found that LH is released in a regular pulsatile fashion. The overall mean concentration of plasma LH in normal male rats was 46.6 +/- 4.4 (mean +/- SEM) ng/ml. The normal male rats showed periodic LH pulses: the mean pulse amplitude was 144.4 +/- 25.5 ng/ml and the inter-peak interval was 22.5 +/- 2.0 min. Each pulse lasted 9.7 +/- 0.8 min. When LH-RH (1 microgram/kg) was injected as a bolus, the peak concentration was attained in 10-30 min reaching a peak concentration of 279.4 +/- 39.6 ng/ml. Distinct pulsatile bursts of plasma LH were discernible during the period of elevated plasma LH concentration. When a higher dose of LH-RH (5 micrograms/kg) was administered, the LH concentration slowly increased to a peak concentration of 400.2 +/- 38.7 ng/ml in 20-40 min. The pulsatile nature of the LH concentration was recognizable with distinct bursts. We have observed that: (a) normal male rats release LH in a pulsatile fashion with an approximate 20-min inter-peak interval; (b) mean LH pulses last less than 10 min, and (c) the LH pulses are visible even with elevated LH and LH-RH concentrations in the general circulation.     

Relationship between the onset of oestrus, the preovulatory surge in luteinizing hormone and ovulation following oestrous synchronization and superovulation of farmed red deer (Cervus elaphus).

The timing of ovulation relative to the onset of oestrus and the preovulatory surge in luteinizing hormone (LH) was studied in red deer following treatments to synchronize oestrus and induce either a monovulatory or superovulatory response. Mature hinds (n = 36) were allocated randomly to two mating groups (n = 16 + 20), with respective treatments staggered by 4 weeks during the 1990 rut (March-April). Each hind was treated with an intravaginal controlled internal drug releasing (CIDR)-type S device for 14 days. Treatments to induce a monovulatory response included CIDR device alone (treatment A; n = 4 + 8) and additional injection of 200 iu pregnant mares' serum gonadotrophin (PMSG) at device removal (treatment B; n = 4 + 4). Treatments to induce a superovulatory response included injections of 200 iu PMSG and 0.5 units ovine follicle-stimulating hormone (FSH) at about time of removal of CIDR devices (treatment C; n = 4 + 4) and further treatment with gonadotrophin-releasing hormone (GnRH) analogue 18 h after removal of CIDR devices (treatment D; n = 4 + 4). The hinds were run with crayon-harnessed stags from insertion of CIDR devices (12 March or 9 April) and blood samples were taken every second day to determine plasma progesterone. Further blood samples were collected for determination of plasma LH and progesterone via indwelling jugular cannulae every 2 h for 72 h from removal of CIDR devices. Hinds were allocated randomly to an initial ovarian examination by laparoscopy at either 16 or 20 h (A and B), or 12 or 16 h (C and D) after the onset of oestrus, with laparoscopy repeated at intervals of 8 h until either ovulation was recorded (A and B), or for four successive occasions (C and D). All hinds received cloprostenol injections 15 days after device removal. A total of 28 hinds (78%) exhibited oestrus and a preovulatory LH surge, with mean (+/- SEM) times to onset of oestrus of 44.6 +/- 1.0 h (A; n = 7), 37.4 +/- 2.0 h (B; n = 7), 16.3 +/- 1.7 h (C; n = 6) or 14.0 +/- 1.7 h (D; n = 8). Failure to exhibit oestrus or LH surge was most prevalent among hinds in treatment A early in the rut.(ABSTRACT TRUNCATED AT 400 WORDS)     

Restoration of the luteinizing hormone surge in middle-aged female rats by altering the balance of GABA and glutamate transmission in the medial preoptic area

Hypothalamic glutamate and gamma-aminobutyric acid (GABA) neurotransmission are involved in the ovarian hormone-induced GnRH-LH surge in rodents. We previously reported that middle-aged rats have significantly less glutamate release in the medial preoptic area than young rats on the day of the LH surge. The present study tested the hypothesis that the delayed and attenuated LH surge in ovariohysterectomized middle-aged rats primed with ovarian steroids results from reduced hypothalamic glutamate and increased GABA(A) neurotransmission. Microdialysis results show that middle-aged rats with attenuated LH surges had reduced extracellular glutamate and increased extracellular GABA levels in the medial preoptic area compared with young rats. Blocking GABA(A) receptors with bicuculline or inhibiting synaptic glutamate reuptake with L-trans-pyrrolidine-2,4-dicarboxylic acid increased extracellular Glu in the medial preoptic area and partially restored LH surge amplitude in middle-aged rats without altering LH surge onset. Complete recovery of LH surge amplitude was observed in middle-aged rats treated with the combination of bicuculline and L-trans-pyrrolidine-2,4-dicarboxylic acid. This treatment also restored the extracellular glutamate:GABA ratio in the medial preoptic area of middle-aged rats to the level of young rats. Immunoblot analysis revealed that estradiol and progesterone treatment reduced SLC32A1(formerly known as vesicular GABA transporter) levels and increased SLC17A6 (formerly known as vesicular glutamate transporter 2) levels in the anterior hypothalamus of ovariohysterectomized young but not middle-aged rats. These data suggest that both reduced availability of glutamate and increased activation of GABA(A) receptors under estrogen-positive feedback conditions contribute to the age-related delay in onset and attenuated amplitude of the LH surge.