Follicle diameters and hormone concentrations in the development of single versus double ovulations in mares

Relationships between double ovulations and plasma hormone concentrations were compared between 18 single ovulating and 6 double ovulating mares. The study began when the first follicle reached >or=30 mm, and ultrasound scanning and blood sampling were done every 12h to Day 3 (ovulation=Day 0). Data were analyzed for 2.5 d after the largest follicle was >or=30 mm and after Day -2.5 to encompass the mean 5-d interval between a >or=30 mm follicle and Day 0. During the 2.5 d after >or=30 mm, the increasing diameter of the largest follicle was less pronounced and plasma FSH concentrations were lower (approached significance) in the double ovulators than in the single ovulators. By Day -2.5, the largest follicle was smaller (P<0.01) and plasma FSH was lower (P<0.04) in the double ovulators. Plasma estradiol concentrations were higher (P<0.001) during the 2.5 d after >or=30 mm in the double ovulators and the correlation between estradiol and FSH was negative (r=-0.39, P<0.0001). In double ovulators, compared to single ovulators, the largest follicle was smaller, FSH was lower and estradiol was higher on most occasions between Days -2.5 and -0.5 (P<0.05), but plasma concentrations of LH and ir-inhibin were not significantly different. In conclusion, smaller preovulatory follicles in double ovulators were a response to lower FSH concentrations, due to higher estradiol concentrations from two preovulatory follicles; preovulatory differences in hormone concentrations between single and double ovulators were an effect rather than a cause of the double ovulations.     

Effects of bromocriptine administration during the follicular phase of the oestrous cycle on prolactin and gonadotrophin secretion and follicular dynamics in merino monovular ewes

Two experiments using Spanish Merino ewes were conducted to investigate whether the secretion of prolactin during the follicular phase of the sheep oestrous cycle was involved in the patterns of growth and regression of follicle populations. In both experiments, oestrus was synchronized with two cloprostenol injections which were administered 10 days apart. Concurrent with the second injection (time 0), ewes (n = 6 per group) received one of the following treatments every 12 h from time 0 to 72 h: group 1: vehicle injection (control); group 2: 0.6 mg bromocriptine (0.03 mg per kg per day); and group 3: 1.2 mg bromocriptine (0.06 mg per kg per day). In Expt 1, blood samples were collected every 3 h from 0 to 72 h, and also every 20 min from 38 to 54 h to measure prolactin, LH and FSH concentrations. In Expt 2, transrectal ultrasonography was carried out every 12 h from time 0 until oestrus, and blood samples were collected every 4 h to measure prolactin, LH and FSH concentrations. Ovulation rates were determined by laparoscopy on day 4 after oestrus. Bromocriptine markedly decreased prolactin secretion, but did not affect FSH concentrations, the mean time of the LH preovulatory surge or LH concentrations in the preovulatory surge. Both doses of bromocriptine caused a similar decrease in LH pulse frequency before the preovulatory surge. The highest bromocriptine dose led to a reduction (P < 0.01) in the number of 2-3 mm follicles detected in the ovaries at each time point. However, bromocriptine did not modify the total number or the number of newly detected 4-5 mm follicles at each time point, the number of follicles > 5 mm or the ovulation rate. In conclusion, the effects of bromocriptine on gonadotrophin and prolactin secretion and on the follicular dynamics during the follicular phase of the sheep oestrous cycle indicate that prolactin may influence the viability of gonadotrophin-responsive follicles shortly after luteolysis.     

Effects of unilateral ovariectomy on follicular development and ovulation in cattle

In a study of 4 cyclic dry cows (Trial I) and 6 cyclic puberal heifers (Trial II), unilateral ovariectomy increased the number of ovulatory follicles, did not alter the hormone profile, cycle length or the number of follicular waves. Ovarian follicular development in all 4 cows was monitored daily using transrectal ultrasonography until the day of ovulation, during which period daily blood samples were also taken from the tail vein for determination of plasma FSH, LH and P4 concentrations. Unilateral ovariectomy was performed on the day after ovulation and ovarian activity was again monitored daily (ultrasonography and blood sampling for FSH, LH and P4) for 2 consecutive cycles (8 cycles in all). Estrus in all 6 heifers was synchronized using 2 injections of PGF2 alpha given 12 d apart. Similarly, ovarian activity in the 6 puberal heifers was monitored daily using ultrasonography and blood sampling for 1 complete control cycle. Following estrus and ovulation the left ovary was removed in all the animals, and thereafter 1 complete cycle was followed. Mean cycle length, FSH, LH and P4 concentrations before and after unilateral ovariectomy were compared using paired sample t-test. The results show that unilateral ovariectomy neither altered the cycle length nor the number of follicular waves in the cows, but it increased the number of ovulatory follicles (2 follicles developed and ovulated in 6 of the 8 cycles). The mean diameter of the largest follicle was 16.1 +/- 0.9 mm and the second largest 12.5 +/- 0.9 mm. No significant (P > 0.05) differences were observed in FSH (0.72 +/- 0.09 vs 0.71 +/- 0.07), LH (0.42 +/- 0.1 vs 0.37 +/- 0.07) and P4 (2.8 +/- 0.6 vs 2.6 +/- 0.4) levels before and after unilateral ovariectomy. Of the 6 heifers, 5 had 2 waves and 1 heifer had 3 waves of follicular growth during the control cycle, and this pattern did not change after the procedure. Mean cycle length (20.7 +/- 0.9 vs 21 +/- 0.9) did not differ before and after unilateral ovariectomy, and 4 of the 6 heifers ovulated twin follicles following ovariectomy. The mean diameter of the largest follicle was 14.5 +/- 0.7 mm and second largest measured 12.1 +/- 0.8 mm. No significant (P > 0.05) differences were observed in FSH (0.16 +/- 0.09 vs 0.21 +/- 0.07), LH (0.11 +/- 0.1 vs 0.15 +/- 0.07) and P4 levels (3.6 +/- 0.26 vs 3.8 +/- 0.29) before and after unilateral ovariectomy. Based on these results, we conclude that unilateral ovariectomy is an ideal method for obtaining twin ovulations in cows and heifers.     

Follicular and hormonal dynamics during the first follicular wave in heifers

A few days after the first follicular wave emerges as 4-mm follicles, follicular deviation occurs wherein 1 follicle of the wave continues to grow (dominant follicle) while the others regress. The objectives of this study were to characterize follicle growth and associated changes in systemic concentrations of gonadotropins and estradiol at 8-h intervals encompassing the time of follicle deviation. Blood samples from heifers (n = 11) were collected and the ovaries scanned by ultrasound every 8 h from 48 h before to 112 h after the maximal value for the preovulatory LH surge. The follicular wave emerged at 5.8 +/- 5.5 h (mean +/- SEM) after the LH surge, and at this time the future dominant follicle (4.2 +/- 0.8 mm) was larger (P < 0.001) than the future largest subordinate follicle (3.6 +/- 0.1 mm). There was no difference in growth rates between the 2 follicles from emergence to the beginning of the deviation (0.5 mm/8 h for each follicle), indicating that, on average, the future dominant follicle maintained a size advantage over the future subordinate follicle. Deviation occurred when the 2 largest follicles were 8.3 +/- 0.2 and 7.8 +/- 0.2 mm in diameter, at 61.0 +/- 3.7 h after wave emergence. Diameter deviation was manifested between 2 adjacent examinations at 8-h intervals. Mean concentrations of FSH decreased, while mean concentrations of LH increased 24 and 32 h before deviation, respectively, and remained constant (no significant differences) for several 8-h intervals encompassing deviation. In addition to the increase and decrease in circulating estradiol concentrations associated with the preovulatory LH surge, an increase (P < 0.05) occurred between the beginning of deviation and 32 h after deviation. The results supported the hypotheses that deviation occurs rapidly (within 8 h), that elevated systemic LH concentrations are present during deviation, and that deviation is not preceded by an increase in systemic estradiol.     

Concentrations of steroids and gonadotropins in follicular fluid from normal heifers and heifers primed for superovulation

The concentrations of six steroids and of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured in follicular fluid from preovulatory and large atretic follicles of normal Holstein heifers and from preovulatory follicles of heifers treated with a hormonal regimen that induces superovulation. Follicular fluid from preovulatory follicles of normal animals obtained prior to the LH surge contained extremely high concentrations of estradiol (1.1 +/- 0.06 micrograms/ml), with estrone concentrations about 20-fold less. Androstenedione was the predominant aromatizable androgen (278 +/- 44 ng/ml; testosterone = 150 +/- 39 ng/ml). Pregnenolone (40 +/- 3 ng/ml) was consistently higher than progesterone (25 +/- 3 ng/ml). In fluid obtained at 15 and 24 h after the onset of estrus, estradiol concentrations had declined 6- and 12-fold, respectively; androgen concentrations had decreased 10- to 20-fold; and progesterone concentrations were increased, whereas pregnenolone concentrations had declined. Concentrations of LH and FSH in these follicles were similar to plasma levels of these hormones before and after the gonadotropin surges. The most striking difference between mean steroid levels in large atretic follicles (greater than 1 cm in diameter) and preovulatory follicles obtained before the LH surge was that estradiol concentrations were about 150 times lower in atretic follicles. Atretic follicles also had much lower concentrations of LH and slightly lower concentrations of FSH than preovulatory follicles. Hormone concentrations in follicles obtained at 12 h after the onset of estrus from heifers primed for superovulation were similar to those observed in normal preovulatory follicles at estrus + 15 h, except that estrogen concentrations were about 6-40 times lower and there was more variability among animals for both steroid and gonadotropin concentrations. Variability in the concentrations of reproductive hormones in fluid from heifers primed for superovulation suggests that the variations in numbers of normal embryos obtained with this treatment may be due, at least in part, to abnormal follicular steroidogenesis.     

Perturbation of estradiol-feedback control of luteinizing hormone secretion by immunoneutralization induces development of follicular cysts in cattle

We used immunoneutralization of endogenous estradiol to investigate deficiencies in the estradiol-feedback regulation of LH secretion as a primary cause of follicular cysts in cattle. Twenty-one cows in the prostaglandin (PG) F(2alpha)-induced follicular phase were assigned to receive either 100 ml of estradiol antiserum produced in a castrated male goat (n = 11, immunized group) or the same amount of castrated male goat serum (n = 10, control group). The time of injection of the sera was designated as 0 h and Day 0. Five cows in each group were assigned to subgroups in which we determined the effects of estradiol immunization on LH secretion and follicular growth during the periovulatory period. The remaining six estradiol-immunized cows were subjected to long-term analyses of follicular growth and hormonal profiles, including evaluation of pulsatile secretion of LH. The remaining five control cows were used to determine pulsatile secretion of LH on Day 0 (follicular phase) and Day 14 (midluteal phase). The control cows exhibited a preovulatory LH surge within 48 h after injection of the control serum, followed by ovulation of the dominant follicle that had developed during the PGF(2alpha)-induced follicular phase. In contrast, the LH surge was not detected after treatment with estradiol antiserum. None of the 11 estradiol-immunized cows had ovulation of the dominant follicle, which had emerged before estradiol immunization and enlarged to more than 20 mm in diameter by Day 10. Long-term observation of the six immunized cows revealed that five had multiple follicular waves, with maximum follicular sizes of 20-45 mm at 10- to 30-day intervals for more than 50 days. The sixth cow experienced twin ovulations of the initial persistent follicles on Day 18. The LH pulse frequency in the five immunized cows that showed the long-term turnover of cystic follicles ranged from 0.81 +/- 0.13 to 0.97 +/- 0.09 pulses/h during the experiment, significantly (P < 0.05) higher than that in the midluteal phase of the control cows (0.23 +/- 0.07). The mean LH concentration in the immunized cows was also generally higher than that in the luteal phase of the control cows. However, the LH pulse and mean concentration of LH after immunization were similar to those in the follicular phase of the control cows. Plasma concentrations of total inhibin increased (P < 0.01) concomitant with the emergence of cystic follicles and remained high during the growth of cystic follicles, whereas FSH concentrations were inversely correlated with total inhibin concentrations. In conclusion, neutralization of endogenous estradiol resulted in suppression of the preovulatory LH surge but a normal range of basal LH secretion, and this circumstance led to an anovulatory situation similar to that observed with naturally occurring follicular cysts. These findings provide evidence that lack of LH surge because of dysfunction in the positive-feedback regulation of LH secretion by estradiol can be the initial factor inducing formation of follicular cysts.     

Effect of the metabolic environment at key stages of follicle development in cattle: focus on steroid biosynthesis

Cellular mechanisms that contribute to low estradiol concentrations produced by the preovulatory ovarian follicle in cattle with a compromised metabolic status are largely unknown. To gain insight into the main metabolic mechanisms affecting preovulatory follicle function, two different animal models were used. Experiment 1 compared Holstein-Friesian nonlactating heifers (n = 17) and lactating cows (n = 16) at three stages of preovulatory follicle development: 1) newly selected dominant follicle in the luteal phase (Selection), 2) follicular phase before the LH surge (Differentiation), and 3) preovulatory phase after the LH surge (Luteinization). Experiment 2 compared newly selected dominant follicles in the luteal phase in beef heifers fed a diet of 1.2 times maintenance (M, n = 8) or 0.4 M (n = 11). Lactating cows and 0.4 M beef heifers had higher concentrations of β-hydroxybutyrate, and lower concentrations of glucose, insulin, and IGF-I compared with dairy heifers and 1.2 M beef heifers, respectively. In lactating cows this altered metabolic environment was associated with reduced dominant follicle estradiol and progesterone synthesis during Differentiation and Luteinization, respectively, and in 0.4 M beef heifers with reduced dominant follicle estradiol synthesis. Using a combination of RNA sequencing, Ingenuity Pathway Analysis, and qRT-PCR validation, we identified several important molecular markers involved in steroid biosynthesis, such as the expression of steroidogenic acute regulatory protein (STAR) within developing dominant follicles, to be downregulated by the catabolic state. Based on this, we propose that the adverse metabolic environment caused by lactation or nutritional restriction decreases preovulatory follicle function mainly by affecting cholesterol transport into the mitochondria to initiate steroidogenesis.     

Minor FSH surge,minor follicular wave,and resurgence of preovulatory follicle several days before ovulation in heifers

Blood samples were collected and follicle diameters were determined daily beginning on Day 12 (Day 0 = ovulation) in 35 interovulatory intervals (IOIs) in heifers. A minor follicular wave with maximal diameter (6.0 ± 0.3 mm) on Day −4 was detected in six of seven IOIs that were scanned for follicles 4 mm or greater. The number of IOIs with a CV-identified minor FSH surge toward the end of the IOI was greater (P < 0.03) in two-wave IOIs (10/17) than in three-wave IOIs (4/18). The 17 two-wave IOIs were used for study of the temporal relationships among preovulatory follicle, FSH, LH, and estradiol. Daily growth rate of the preovulatory follicle was maximum on Days −11 to −7, minimum (P < 0.05) on Days −7 to −4, and increased (resurged, P < 0.05) on Days −4 to −3. A transient increase in FSH was maximum on mean Day −4, and the peak of a minor FSH surge occurred on Day −4.5 ± 0.2. Concentration of LH and estradiol increased between Days −5 and −4. Results demonstrated resurgence of the preovulatory follicle apparently for the first time in any species. Resurgence seemed more related temporally to the minor FSH surge than to the LH increase, but further study is needed. Results supported the novel hypotheses that a minor FSH surge near the end of the IOI is temporally associated with (1) the emergence of a minor follicular wave and (2) the resurgence in growth rate of the preovulatory follicle.     

Effects of follicle-stimulating hormone with and without luteinizing hormone on serum hormone concentrations, follicle growth, and intrafollicular estradiol and aromatase activity in gonadotropin-releasing hormone-immunized heifers

To evaluate the roles of FSH and LH in follicular growth, GnRH-immunized anestrous heifers (n = 17) were randomly assigned (Day 0) to one of three groups (n = 5 or 6). Group 1 received i.m. injections of 1.5 mg porcine FSH (pFSH) 4 times/day for 2 days; group 2 received i.v. injections of 150 microg pLH 6 times/day for 6 days; group 3 received both pFSH and pLH as described for groups 1 and 2. After slaughter on Day 6, measurements were made of follicle number and size, and follicular fluid concentrations of progesterone (P(4)), estradiol (E(2)), and aromatase activity. Injection of pFSH increased (P: < 0.01) the serum concentrations of FSH between 12 and 54 h. Infusion of pLH increased (P: < 0.05) mean and basal concentrations of LH and LH pulse frequency. Serum E(2) concentrations were higher (P: < 0.05) for heifers given pFSH + pLH than those given either pFSH or pLH alone. There was no difference (P: > or = 0.24) between treatments in the number of small follicles (<5 mm). Heifers given pFSH or pFSH + pLH had more (P: < or = 0.02) medium follicles (5.0-9.5 mm) than those that were given pLH alone (none present). Heifers given pFSH + pLH had more (P: = 0.04) large follicles (> or =10 mm) than those given either pLH or pFSH alone (none present). Overall, only 1 of 35 small follicles and 2 of 96 medium follicles were E(2)-active (i.e., E(2):P(4) >1.0), whereas 18 of 21 large follicles (all in the pFSH + pLH treatment) were E(2)-active; of these, 8 of 18 had aromatase activity. Concentrations of E(2) and E(2) activity in follicular fluid were correlated (r > or = 0.57; P: < 0.0001) with aromatase activity in heifers given pLH + pFSH. In conclusion, pLH failed to stimulate follicle growth greater than 5 mm; pFSH stimulated growth of medium follicles that were E(2)-inactive at slaughter and failed to increase serum E(2) concentrations; whereas pFSH + pLH stimulated growth of medium follicles and E(2)-active large follicles, and a 10- to 14-fold increase in serum E(2) concentrations.     

Ultrasonographic and endocrine aspects of follicle deviation, and acquisition of ovulatory capacity in buffalo (Bubalus bubalis) heifers

The objectives of this study were to determine the interval from ovulation to deviation and the diameter of the dominant (DF) and largest subordinate (SF) follicles at deviation in buffalo (Bubalus bubalis) heifers. Two methods of evaluation (observed vs. calculated) were used. FSH and LH profiles encompassing follicle deviation (Experiment 1), and the follicular diameter when the DF acquired ovulatory capacity (Experiment 2) were also determined. The time of deviation and the diameter of the DF and the largest SF at deviation did not differ between observed and calculated methods. Overall, follicle deviation occurred 2.6 ± 0.2d (mean ± SEM) after ovulation, and the diameters of the DF and SF at deviation were 7.2 ± 0.2 and 6.4 ± 0.2mm, respectively. No changes in plasma levels of FSH or LH were observed (P=0.32 and P=0.96, respectively). Experiment 2 was conducted in two phases according to the diameter of the DF during the first wave of follicular development at the time of LH challenge (25mg of pLH). In the first phase, follicles ranging from 5.0 to 6.0mm (n=7), 6.1 to 7.0mm (n=11), or 7.1 to 8.0mm (n=9) were used, and in the second phase, follicles ranging from 7.0 to 8.4mm (n=10), 8.5 to 10.0mm (n=10), or 10.1 to 12.0mm (n=9) of diameter were used. After the pLH treatment, the DF was monitored by ultrasonography every 12h for 48h. No ovulations occurred in heifers in the first phase. However, in the second phase, an effect of follicular diameter was observed on ovulation rate [7.0-8.4mm (0.0%, 0/10), 8.5-10.0mm (50.0%, 5/10), and 10.0-12.0mm (55.6%, 5/9)]. In summary, follicle deviation occurred 2.6d after ovulation in buffalo (B. bubalis) heifers, when the diameters of the DF and SF were 7.2 and 6.4mm, respectively. No significant changes in plasma concentrations of FSH or LH were detected. Finally, the acquisition of ovulatory capacity occurred when the DF reached 8.5mm in diameter.     

Selection of the dominant follicle in cattle: role of two-way functional coupling between follicle-stimulating hormone and the follicles

The functional coupling between the declining portion of the FSH surge and the growing follicles of a wave was studied by treating heifers with a minimal dose of estradiol to decrease FSH concentrations without an associated change in LH concentrations. Estradiol treatment when the largest follicle reached >/= 6.0 mm (Hour 0) resulted in depression of both FSH concentrations and diameter of the largest follicle by Hour 8. The smaller follicles were also inhibited. These results supported the hypothesis that FSH continues to be needed by the growing follicles even when the FSH concentrations are decreasing during the declining portion of the FSH surge. Estradiol treatment when the largest follicle was >/= 8.5 mm (expected time of follicular deviation) also resulted in a transient decrease in both FSH concentrations and diameter of the largest follicle, but the diameters of the smaller follicles were not affected. These results supported the hypothesis that the low concentrations of FSH at the expected time of deviation, although inadequate for the smaller follicles, were required for continued growth of the largest follicle. In another study, ablation (Hour 0) of the largest follicle was done at >/= 7.5 mm vs. >/= 8.5 mm. The mean FSH concentrations for the 8.5-mm groups were greater for the ablation group than for the control group at Hours 8 and 12, but there was no difference between the 7.5-mm groups at any hour. These results supported the hypothesis that by the time the largest follicle reaches the expected beginning of deviation it has developed a greater capacity for suppressing FSH. It is postulated that the essence of the selection of a dominant follicle is a close two-way functional coupling between changing FSH concentrations and follicular growth.     

Bovine model of reproductive aging: response to ovarian synchronization and superstimulation

The responsiveness of the hypothalamo-pituitary axis to steroid treatments for ovarian synchronization and the ovarian superstimulatory response to exogenous FSH was compared in 13-14 year old cows and their 1-4 year old young daughters. We tested the hypotheses that aging in cattle is associated with: (1) decreased follicular wave synchrony after estradiol and progesterone treatment; (2) delayed LH surge and ovulation in response to exogenous preovulatory estradiol treatment; (3) reduced superstimulatory response to exogenous FSH. Higher plasma FSH concentrations (P<0.01), and a tendency (P=0.07) for fewer 4-5 mm follicles at wave emergence were observed in old cows (n=10) than in young cows (n=9). The suppressive effect of estradiol/progesterone treatment on FSH was similar between old and young cows. Although the preovulatory LH surge in response to estradiol treatment was delayed in old than young cows (P=0.01), detected ovulation times were not different. No difference in ovarian superstimulatory response was detected between age groups, but old cows (n=8) tended (P=0.10) to have fewer large follicles (>or=9 mm) 12 h after last FSH treatment than in young cows (n=7). We concluded that pituitary and ovarian responsiveness to estradiol/progesterone synchronization treatment was similar between old and young cows, but aging was associated with a delayed preovulatory LH surge subsequent to estradiol treatment. Old cows tended to have fewer large follicles after superstimulatory treatment than young cows.     

Follicle selection in monovular species

Follicle deviation is proposed to be the eminent event in follicle selection in monovular species. At deviation, the largest follicle establishes dominance apparently before the second-largest follicle can reach a similar diameter. In cattle, based on diameters of the two follicles at the beginning of deviation, the mechanism becomes established in <8 h. An FSH:follicle-coupling hypothesis has been supported as the essence of follicle selection. According to the hypothesis, the growing follicles cause the FSH decline from the peak of the wave-stimulating FSH surge until deviation, even though the follicles continue to require FSH (two-way functional coupling involving multiple follicles). During multiple-follicle coupling, inhibin is the primary FSH suppressant. Near the beginning of deviation, the largest follicle secretes increased estradiol, and apparently both estradiol and inhibin contribute to the continuing FSH decline; only the more-developed largest follicle is able to utilize the low FSH concentrations (single-follicle coupling). Deviation is encompassed by a transient elevation in LH in heifers and by a component, often distinct, of the long ovulatory LH surge in mares. In heifers, receptors for LH appear in the granulosa cells of the future dominant follicle about 8 h before the beginning of deviation. The LH stimulates the production of estradiol and insulin-like growth factor-1. These intrafollicular factors and perhaps others account for the responsiveness of the largest follicle to the low concentrations of FSH. The smaller follicles have not reached a similar developmental stage and because of their continued and close dependency on FSH become susceptible to the low concentrations. Thereby, follicle selection is established.     

Follicular and hormonal response to experimental suppression of FSH during follicle deviation in cattle

A near steroid-free fraction of bovine follicular fluid was used to suppress FSH concentrations at the expected time of follicle deviation or when the largest follicle of Wave 1 reached > or = 8.0 mm (actual mean diameter, 8.4 mm; Hour 0). It was hypothesized that the low concentrations of FSH associated with deviation are inadequate for the smaller follicles but are needed for continued growth of the largest follicle. Control heifers (n=8) received 10 mL of saline, and treated heifers (n=16) received either 8.8 mL or 13.3 mL of the follicular-fluid fraction at Hours 0, 12, and 24. Between Hours -48 and 0, FSH concentrations decreased (P<0.05) and diameters of the 4 largest follicles increased (Hour effect, P<0.0001) similarly between groups. Concentrations of LH in the controls increased (P<0.05) between Hours -24 and -12 and decreased (P<0.05) between Hours 8 and 36, demonstrating a transient LH surge encompassing the expected beginning of deviation. In the treated group, a comparable increase in LH occurred before deviation but a decrease did not occur until after Hour 48. By Hour 4.5, the FSH concentrations in the treated group decreased (P<0.05) to below the concentrations in the controls. Suppressed diameter (P<0.001) of the largest follicle was detected at the first post-treatment examination (Hour 12; 7.5 h after FSH suppression) and was accompanied by reduced (P<0.04) systemic estradiol concentrations. The mean growth rates of the 3 smaller follicles in both the treated and control groups began to decrease at Hours -12 to 24 and were not different between groups during Hours 0 to 36. Concentrations of FSH in the treated group returned to control concentrations by Hour 24 (hour of last treatment). A rebound (P<0.05) in concentrations of FSH to >100% above control concentrations occurred by Hour 48 and was accompanied by resumed growth of the largest follicle in 75% of the heifers between Hours 48 and 72. The results demonstrated that the low concentrations of FSH associated with deviation can be further reduced by treatment with a nonsteroidal factor of follicular origin. Transient reduction of FSH concentrations to below the already low control concentrations inhibited the largest follicle but did not further inhibit the smaller follicles. These results support the hypothesis that the low FSH concentrations associated with follicle deviation are below the minimal requirements of the smaller or subordinate follicles but are needed for continued growth of the largest or dominant follicle in cattle.     

Timing of the onset and duration of ovulation in superovulated beef heifers

Thirty-two beef heifers were induced to superovulate by the administration of follicle stimulating hormone-porcine (FSH-P). All heifers received 32 mg FSH-P (total dose) which was injected twice daily in decreasing amounts for 4 d commencing on Days 8 to 10 of the estrous cycle. Cloprostenol was administered at 60 and 72 h after the first injection of FSH-P. Heifers were observed for estrus every 6 h and were slaughtered at known times between 48 to 100 h after the first cloprostenol treatment. The populations of ovulated and nonovulated follicles in the ovaries were quantified immediately after slaughter. Blood samples were taken at 2-h intervals from six heifers from 24 h after cloprostenol treatment until slaughter and the plasma was assayed for luteinizing hormone (LH) concentrations. The interval from cloprostenol injection to the onset of estrus was 41.3 +/- 1.25 h (n = 20). The interval from cloprostenol injection to the preovulatory peak of LH was 43.3 +/- 1.69 h (n = 6). No ovulations were observed in animals slaughtered prior to 64.5 h after cloprostenol (n = 12). After 64.5 h, ovulation had commenced in all animals except in one animal slaughtered at 65.5 h. The ovulation rate varied from 4 to 50 ovulations. Approximately 80% of large follicles (> 10 mm diameter) had ovulated within 12 h of the onset of ovulation. Onset of ovulation was followed by a dramatic decrease in the number of large follicles (> 10 mm) and an increase in the number of small follicles (相似文献   

正常月经周期妇女卵泡液中激素水平的变化

本文测定了24例正常月经妇女在不同时相、不同大小卵泡的卵泡液中雌二醇(E_2)、孕酮(P_0)、雄烯二酮(A)、睾酮(T)、卵泡刺激素(FSH)、黄体生成素(LH)和催乳素(PRL)的含量,并分析其与外周血中相应激素浓度的关系。测定结果显示:小卵泡的卵泡液中E_2、Po,FSH,LH水平低于大卵泡中水平,而A和T水平则相反。排卵前大卵泡中E_2(9815nmol/L),P_0(3316nmol/L),FSH(1.34IU/L)和LH(3.9lIU/L)达最高值。A(280nmol/L)和T(137nmol/L)却较小卵泡中水平低(相应为692nmol/L和176nmol/L)。PRL水平在大小卵泡中无显著性差异。卵泡液中甾体激素水平高于外周血7—20.000倍,FSH、LH水平为外周血的10—80％,PRL水平为60％—3倍。     

Association between surges of follicle-stimulating hormone and the emergence of follicular waves in heifers.

The effects of ablation of a dominant follicle and treatment with follicular fluid on circulating concentrations of follicle-stimulating hormone (FSH) were studied and the temporal relationships between surges of FSH and follicular waves were studied in heifers with two or three follicular waves/interovulatory interval. Cauterization of the dominant follicle on Day 3 or Day 5 (ovulation on Day 0) (six control and six treated heifers/day) resulted in a surge (P less than 0.05) in FSH beginning the day after cautery. The FSH surge prior to wave 2 (first post-treatment follicular wave) occurred 4 days (Day 3 cautery) and 2 days (Day 5 cautery) before the surge in control groups, corresponding to a 4-day and a 2-day advance in emergence of wave 2 compared with controls. It was concluded that the dominant follicle on Day 3 and Day 5 was associated with the suppression of circulating FSH concentrations. Heifers (n = 4/group) were untreated or treated intravenously with a proteinaceous fraction of bovine follicular fluid on Days 0-3, 3-6, or 6-11. Concentrations of FSH were suppressed (P less than 0.05) for the duration of treatment, regardless of the days of treatment. Cessation of treatment was followed within 1 day by the start of a surge in FSH. The FSH surge prior to wave 2 occurred 2 days earlier (treatment on Days 0-3), 1 day later (treatment on Days 3-6), and 6 days later (treatment on Days 6-11) than in controls, corresponding to an equivalent advance or delay, respectively, in the emergence of wave 2 compared with controls. The results suggest that the effects of exogenous follicular fluid on follicular development were mediated, in whole or in part, by altering plasma FSH concentrations. Control heifers combined for the two experiments were separated into those with 2-wave (n = 11) or 3-wave (n = 5) interovulatory intervals. Two-wave heifers had two FSH surges and 3-wave heifers had three apparent FSH surges during the interovulatory interval. Results of the cautery and follicular fluid experiments indicated that a surge in FSH necessarily preceded the emergence of a wave. The FSH surges in treated and control heifers began 2-4 days before the detectable (ultrasound) emergence of a follicular wave (follicles of 4 and 5 mm), peaked 1 or 2 days before emergence and began to decrease approximately when the follicles of a wave begin to diverge into a dominant follicle and subordinate follicles (follicles 6-7 mm).     

The ovarian follicle and fertility

The precise roles of follicle stimulating hormone (FSH) and luteinizing hormone (LH) in the control of preovulatory follicle growth has been re-examined. Suppression of both pulsatile LH secretion and FSH or specific suppression of FSH results in an inhibition of preovulatory follicle growth beyond 2.5 mm dia. Infusion of sheep FSH alone in physiological amounts in the presence of basal, non-pulsatile LH results in the growth of preovulatory follicles. Co-infusion of large amplitude pulses of LH reduced or abolished this effect of FSH. It is suggested that: (1) FSH controls the number of follicles which develop; (2) selection of the large follicle destined to ovulate is directly related to the decline in the plasma concentration of FSH occurring during the period of follicle selection--thus, only the follicle(s) which can withstand this withdrawal of FSH will continue to develop; and (3) pulses of LH may directly affect the action of FSH on the follicle and play an important, hitherto unrecognized role in the selection of the ovulatory follicle by actively inducing atresia.     

Ram-induced growth of ovarian follicles and gonadotrophin inhibition in anoestrous ewes

Southdown ewes in mid-seasonal anoestrus were exposed to rams for 0 h (control group), 2 h, 24 h, 40 h, 3 days, 10 days or 20 days. Serial blood samples were then taken to determine LH and FSH levels. Ewes with greater than 24 h ram exposure were ovariectomized immediately after bleeding, and all follicles greater than 1 mm diameter were dissected from the ovaries and measured. LH basal concentrations and pulse frequency increased significantly within 2 h of ram introduction, but by 24 h fell, and then remained low. FSH concentrations fell within 2 h of ram introduction and remained low. Control group ewes (isolated) had no follicles greater than 4 mm diameter, whereas all ewes exposed to rams had large follicles, with CL or preovulatory follicles present at 40 h after ram introduction. Ram introduction was also associated with follicle recruitment (antrum formation to less than 2 mm). Follicular recruitment and development to the large follicle stage therefore occurred during a period of low plasma gonadotrophin levels and suppressed LH pulsing.     

Effects of monoclonal antibody against PMSG administered shortly after the preovulatory LH surge on time and number of ovulations in PMSG/PG-treated cows

Normally cyclic heifers received 2500 i.u. PMSG i.m. at Day 10 of the oestrous cycle and 15 mg prostaglandin (PG) i.m. 48 h later. From 30 h after PG the LH concentration in the peripheral blood was estimated every hour using a rapid RIA method which allowed the LH concentration to be known within 4 h. Monoclonal antibody against PMSG was injected in the jugular vein of 29 heifers at 4.8 h after the maximum of the preovulatory LH peak; 28 heifers were not treated with anti-PMSG (controls). Peripheral blood concentrations of PMSG, LH, progesterone and oestradiol were compared. Ovaries were collected by ovariectomy at fixed times, 22-30 h after the LH peak, and numbers were counted of small (2-10 mm), large (greater than 10 mm) and ovulated follicles, and of follicles with a stigma. In anti-PMSG-treated cows, the PMSG concentration fell sharply to non-detectable levels within 2 h of the treatment, indicating that PMSG was neutralized in these cows at the onset of final follicular maturation. In all cows, the concentration of oestradiol showed a significant decrease at about 8 h after the LH peak. After anti-PMSG treatment ovulations took place from 24 until 30 h after the LH peak, whereas in control cows follicles had already ovulated at or before 22 h and ovulations continued until 30 h. At 30 h 90% of the follicles had ovulated in anti-PMSG-treated cows vs 72% in the controls, resulting in 15 and 8 ovulations per cow respectively (P less than 0.05). Also, administration of monoclonal antibody against PMSG synchronized final follicular maturation and shortened the period of multiple ovulations. In conclusion, neutralization of PMSG shortly after the preovulatory LH peak suppresses adverse effects of PMSG on final follicular maturation, leading to an almost 2-fold increase of the ovulation rate.