Intrafollicular concentrations of steroids and steroidogenic enzymes in relation to follicular development in the mare

The objective of the present study was to determine the changes in follicular fluid steroid concentrations and in granulosa cell steroidogenic enzyme expression during the follicular phase, in relation to follicular size and physiological status in the mare. Follicular fluid and follicular cells were recovered by ultrasound-guided follicular punctures either around the time of emergence of the dominant follicle, at the end of the dominant follicle growth, or at the preovulatory stage, after injection of gonadotropin to induce ovulation. Cellular relative amounts of steroidogenic acute regulatory protein (StAR), P450-side chain cleavage (P450(scc)), 3beta-hydroxysteroid dehydrogenase (3betaHSD), 17alpha-hydroxylase, and aromatase were assessed by semiquantitative Western blot and densitometry. Follicular fluid was assayed for cholesterol concentrations by colorimetric assay and for progesterone, testosterone, and estradiol-17beta concentrations by RIA. Intrafollicular concentrations of progesterone and estradiol-17beta significantly increased in the dominant follicle during growth. After injection of gonadotropin, follicular maturation was characterized by a decrease in estradiol-17beta concentrations and a further increase in progesterone concentrations. Granulosa cells from dominant follicles had increased levels of StAR, P450(scc), 3betaHSD, and aromatase during growth, but decreased levels during maturation. Levels of StAR, P450(scc), 3betaHSD, and aromatase, as well as progesterone and estradiol-17beta, were lower in granulosa cells from subordinate than from dominant follicles. We did not observe a relationship between the steroidogenic activity of follicles and the capacity of their enclosed oocytes to complete meiosis in vitro.     

Estradiol-induced blockade of ovulation in the cow: effects on luteinizing hormone release and follicular fluid steroids

Administration of 10 mg estradiol valerate (EV) to nonlactating Holstein cows on Days 16 of the estrous cycle prevented ovulation in 7 of 8 cows for 14 days post-injection. In these 7 cows, the timing of luteolysis and the luteinizing hormone (LH) surge was variable but within the normal range. At 14 days post-treatment, each of these cows had a large (greater than 10 mm) follicle, with 558 +/- 98 ng/ml estradiol-17 beta, 120 +/- 31 ng/ml testosterone, and 31 +/- 2 ng/ml progesterone in follicular fluid (means +/- SE). A second group of animals was then either treated with EV as before (n = 22), or not injected (control, n = 17) and ovariectomized on either Day 17, Day 18.5, Day 20, or Day 21.5 (24, 60, 96, or 132 h post-EV). Treatment with EV did not influence the timing of luteolysis, but surges of LH occurred earlier (59 +/- 8 h post-EV vs. 100 +/- 11 h in controls). The interval from luteolysis to LH peak was reduced from 44 +/- 6 h (controls) to 6.9 +/- 1.5 h (treated). Histologically, the largest follicle in controls tended to be atretic before luteolysis, but nonatretic afterwards, whereas the largest follicle in treated animals always tended to be atretic. Nonatretic follicles contained high concentrations of estradiol (408 +/- 59 ng/ml) and moderate amounts of testosterone (107 +/- 33 ng/ml) and progesterone (101 +/- 21 ng/ml), whereas atretic follicles contained low concentrations of estradiol (8 +/- 4 ng/ml) and testosterone (12 +/- 4 ng/ml), and either low (56 +/- 24 ng/ml) or very high (602 +/- 344 ng/ml) concentrations of progesterone. This study suggests that EV prevents ovulation by inducing atresia of the potential preovulatory follicle, which is replaced by a healthy large follicle by 14 days post-treatment.     

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.     

Carry-over effect of summer thermal stress on characteristics of the preovulatory follicle of lactating cows

Low fertility of cattle during the cool autumn is mostly associated with exposure to thermal stress in the previous summer. This study examined carry-over effects of summer heat stress and induction of enhanced follicular turnover, on the characteristics of preovulatory follicles during autumn. Holstein cows were treated with PGF₂ and GnRH to induce six successive 9-day follicular waves during autumn. Intact cows served as controls. Follicular fluid concentrations of androstenedione were higher in treated cows, but those of IGF-I and progesterone did not differ between groups. The concentration of estradiol at the end of the treatment was higher, and the content per follicle increased with time and was numerically higher in treated cows. The volume of follicular fluid increased during the autumn and was greater in treated cows. A delayed effect of heat stress on preovulatory follicles was noted, and induction of follicular waves by GnRH was able to improve follicular characteristics in autumn.     

Comparison of oocyte developmental competence and follicular steroid content of nulliparous heifers and cows at different stages of lactation

Reduced reproductive performance and lower conception rates of lactating cows are closely associated with genetic progress for high milk production. In contrast, the fertility of nulliparous Holstein heifers has remained fairly stable over the years and appears to be markedly higher than that of mature lactating cows. Possible differences in oocyte quality and follicular steroid levels, which could be associated with the low fertility of high-lactating cows, were examined in 13-month-old heifers, cows around the time of first AI (60-95 d post-partum, yielding 49+/-2.4 kg/d) and cows at mid-lactation (120-225 d post-partum, yielding 37+/-2.1 kg/d). Estrus was synchronized by two doses of PGF2alpha and follicles (5-8 mm) were aspirated on days 4, 8, 11 and 15 of the cycle by an ultrasound-guided procedure. Oocytes were morphologically examined, matured in vitro, chemically activated and cultured for 8d. Cleavage rate and the proportion of developing parthenogenetic blastocysts were determined on days 3 and 8 post-activation, respectively. On day 17, heifers and cows received additional PGF2alpha and follicular fluids from preovulatory follicles were collected on day 19 perior to the expected estrus. Follicular-fluid volumes were similar in cows and heifers, as were estradiol, progesterone and androstenedione concentrations in the follicular fluid. Percentages of high-grade oocytes, proportions of cleaved oocytes and developed blastocysts did not differ between the groups. Results suggest that the fertility gap between nulliparous heifers and high-lactating cows is not directly related to steroid content in the preovulatory follicular fluid or oocyte developmental competence.     

The effect of short-term nutritional supplementation of ewes with lupin grain (Lupinus luteus), during the luteal phase of the estrous cycle on the number of ovarian follicles and the concentrations of hormones and glucose in plasma and follicular fluid

An experiment was conducted using 16 cyclic, Welsh Mountain ewes during the luteal phase of the estrous cycle to determine the effect of a 5-day period of feeding a high-energy high-protein diet (lupin grain; 500 g/day) on folliculogenesis and on the plasma concentrations of glucose, insulin, follicle stimulating hormone (FSH) and estradiol-17beta, and on the follicular fluid concentrations of glucose, inhibin A, estradiol-17beta, androstenedione and progesterone. Average weight did not differ between lupin-fed and control groups during the experiment. There was a trend for the number of small and large follicles to increase in the lupin-fed group. The plasma concentrations of glucose (P=0.012) and insulin (P=0.007) were higher during the feeding period in lupin-fed ewes. The plasma concentrations of FSH and estradiol-17beta were not significantly different. The mean follicular fluid concentration of glucose (small follicles; <3.5 mm) from lupin-fed ewes was elevated (P=0.010) and progesterone lowered (P=0.034) compared to controls. The follicular fluid concentrations of estradiol-17beta, androstenedione and inhibin A were not significantly different. The follicular fluid concentration of estradiol-17beta was positively correlated with androstenedione (r=-0.241; P=0.001) and inhibin A (r=0.734; P< or =0.001) and glucose was negatively correlated with inhibin (r=-0.241; P=0.01), but not estradiol (r=0.075; P=0.410) or androstenedione (r=0.050; P=0.564). The lupin grain supplement increased the number of follicles as expected, but this increase was not significant. These changes were reflected in follicular fluid where lupin feeding increased the concentration of glucose and decreased the concentration of progesterone in follicles less than 3.5mm in diameter. These data suggest that the local ovarian actions of nutrients have a role in the mediation of nutritional influences on folliculogenesis.     

Structural and endocrine aspects of equine oocyte maturation in vivo

The objectives were to describe the ultrastructure of equine oocytes aspirated from small and preovulatory follicles, and to relate the ultrastructural features to follicle size and follicular fluid steroid concentrations. Mares were examined every second day by transrectal ultrasonography, and follicles measuring ≤30 mm were aspirated (in vivo) using a 20-cm-long 12-gauge needle through the flank. Following slaughter, both large and small follicles were aspirated (in vitro) from six mares. The oocytes were isolated under a stereomicroscope and processed for transmission electron microscopy, and the follicular fluid was assayed for progesterone (P4) amd estradiol-17β (E2). A total of 29 oocytes (32% recovery rate) were aspirated in vivo, and 15 oocytes were recovered in vitro. According to the stage of nuclear maturation, the oocytes could be divided into the following six categories: 1) the central oocyte nucleus (CON) stage, 2) the peripheral spherical oocyte nucleus (PON-I) stage, 3) the peripheral flattened oocyte nucleus (PON-II) stage, 4) the oocyte nucleus breakdown (ONBD) stage, 5) the metaphase I (M-I) stage, and 6) the metaphase II (M-II) stage. The maturation of the preovulatory follicle was reflected by alterations in the follicular fluid concentrations of steroid hormones. E2 was high in all preovulatory follicles, whereas P4 concentration exhibited a 10-fold increase during follicle maturation, particularly associated with the progression from M-I-to M-II-stage oocytes. The nuclear oocyte maturation included flattening of the spherical oocyte nucleus, followed by increasing undulation of the nuclear envelope, formation of the metaphase plate of the first meiotic division, and, finally, the extrusion of the first polar body and the subsequent formation of the metaphase plate of the second meiotic division. The cytoplasmic oocyte maturation changes comprised breakdown of the intermediate junctions between the cumulus cell projections and the oolemma, enlargement of the perivitelline space, the formation and arrangement of a large number of cortical granules immediately beneath the oolemma, the rearrangement of mitochondria from a predominantly peripheral distribution to a more central or semilunar domain, and the rearrangement of membrane-bound vesicles and lipid droplets from an even distribution to an often semilunar domain, giving the ooplasm a polarized appearance. It is concluded that the final equine oocyte maturation includes a series of well-defined nuclear and cytoplasmic changes that are paralleled by an increase in P4 concentration in the follicular fluid, whereas E2 concentration remains constantly high. © 1995 wiley-Liss, Inc.     

Dominant bovine ovarian follicular cysts express increased levels of messenger RNAs for luteinizing hormone receptor and 3 beta-hydroxysteroid dehydrogenase delta(4),delta(5) isomerase compared to normal dominant follicles

The objective was to compare ovarian steroids and expression of mRNAs encoding cytochrome P450 side-chain cleavage, cytochrome P450 17 alpha-hydroxylase, cytochrome P450 aromatase, 3 beta-hydroxysteroid dehydrogenase Delta(4),Delta(5) isomerase, LH, and FSH receptors and estrogen receptor-beta in ovaries of cows with dominant and nondominant ovarian follicular cysts and in normal dominant follicles. Estradiol-17 beta, progesterone, and androstenedione concentrations were determined in follicular fluid using specific RIAs. Dominant cysts were larger than young cysts or dominant follicles, whereas nondominant cysts were intermediate. Estradiol-17 beta (ng/ml) and total steroids (ng/follicle) were higher in dominant cysts than in dominant follicles. Expression of LH receptor and 3 beta-hydroxysteroid dehydrogenase mRNAs was higher in granulosa cells of dominant cysts than in dominant follicles. Nondominant cysts had higher follicular concentrations of progesterone, lower estradiol-17 beta concentrations, and lower expression of steroidogenic enzyme, gonadotropin receptor, and estrogen receptor-beta mRNAs than other groups. In summary, increased expression of LH receptor and 3 beta-hydroxysteroid dehydrogenase mRNAs in granulosa and increased follicular estradiol-17 beta concentrations were associated with dominant cysts compared to dominant follicles. Study of cysts at known developmental stages is useful in identifying alterations in follicular steroidogenesis.     

Steroid hormone concentrations in the fluid of bovine follicles relative to size, quality and stage of the oestrus cycle

Eight hundred and seven bovine antral follicles from 2 mm to 20 mm in diameter were dissected free of stromal tissue, measured, qualified and divided into 36 groups according to size, quality and stage of cycle. The follicular fluid was collected and assayed by RIA for oestradiol-17beta, testosterone and progesterone. The steroid hormone concentrations vary with follicular size, degree of atresia and stage of the cylce. Non-atretic follicles of less than 8 mm are generally androgen-dominated and non-atretic follicles of more than 11 mm are oestrogen-dominated. Follicles betwen 8 mm and 11 mm are intermediate in this respect. Degeneration leads to a gradual decrease of oestradiol-17beta and testosterone concentration and increase of progesterone. It is suggested that the ratio of oestradiol-17beta/testosterone and oestradiol- 17beta/progesterone and oestradiol-17beta/testosterone + progesterone cannot generally be used to discriminate between non-atretic and atretic follicles. Large follicles present during the early luteal stage contain as much oestradiol-17beta in the follicular fluid as large follicles during the follicular stage, whereas large follicles of the luteal stage contain only 15% of the maximal amount of the latter's. This and other presented data support the statement that follicles present during the early luteal, late luteal and follicular stages of the cycle belong to different groups of growing follicles. It has been concluded that groups of macroscopically qualified follicles can be distinguished from each other by the steroid hormone concentration in the follicular fluid. It is therefore possible to predict the hormonal environment of the oocyte in any individual follicle of a defined size and quality.     

Long-term follicular dynamics and biochemical characteristics of dominant follicles in dairy cows subjected to acute heat stress

The objective of this study was to examine the quality of successive dominant follicles (DFs) after induced heat stress. Non-lactating dairy cows expressing estrus at normal intervals were allocated randomly to heat stress (HS; n=8) and control (C; n=8) groups. Cows received GnRH (100 microg, i.m.) on Day 0, a progesterone CIDR-B device on Day 4 and prostaglandin (PGF(2alpha); 25mg, i.m.) on Day 7 upon removal of the CIDR device. The DF and follicles >5mm were aspirated on Day 8, and GnRH (100 microg) injected following aspiration, to initiate a new follicular wave. In this manner, a DF was aspirated every 8 days (one "follicular cycle") for 10 cycles. After the first follicular cycle, HS cows were placed in environmental chambers for 7 days during the second follicular cycle (8h per day at 43.3 degrees C set point and 16h per day at 24 degrees C for 4 days, and 8h per day at 43.3 degrees C set point and 16h per day at 32.2 degrees C set point for 3 days; relative humidity, 40%) and thereafter maintained outdoors with control cows at a mean ambient temperature (18.5 degrees C; range 12.7-26 degrees C). Rectal temperature increased (P<0.001) in HS as compared with C cows (39.28+/-0.01 degrees C versus 38.78+/-0.01 degrees C). Concentrations of estradiol (E(2); 1662+/-189 versus 1493+/-188ng/ml) and progesterone (P(4); 44.7+/-5 versus 54.1+/-5.1ng/ml) in follicular fluid (FF) of DF did not differ between C and HS treatments, respectively. Total FF protein concentration was greater (P<0.05) in HS (99.7+/-2.3mg/ml) than in C (92.7+/-2.3mg/ml). Heat shock protein 90 (Hsp 90) in FF was not altered by heat stress. IGF-II ligand blots were conducted with FF samples (n=79) from four HS and four C cows. There was a predominance of IGFBP-3 in 76 of 79 FF samples, indicating healthy follicular status, and only three FF samples had the lower molecular weight IGFBP-2 indicative of a poor quality follicle. Plasma P(4) and E(2) concentrations did not differ between C and HS groups. The number of class 1 and 3 follicles increased during and just after heat stress, but the number of class 2 follicles did not differ between C and HS cows. Heat stress appeared to induce a decrease in follicular dominance, but GnRH-induced follicular cycles resulted in development of healthy preovulatory follicles in both groups.     

Endocrine and ovarian responses associated with the first-wave dominant follicle in cattle.

To examine endocrine and biochemical differences between dominant and subordinate follicles and how the dominant follicle affects the hypothalamic-pituitary-ovarian axis in Holstein cows, the ovary bearing the dominant follicle was unilaterally removed on Day 5 (n = 8), 8 (n = 8), or 12 (n = 8) of synchronized estrous cycles. Follicular development was followed daily by ultrasonography from the day of detected estrus (Day 0) until 5 days after ovariectomy. Aromatase activity and steroid concentrations in first-wave dominant and subordinate follicles were measured. Intact dominant and subordinate follicles were cultured in 4 ml Minimum Essential Medium supplemented with 100 microCi 3H-leucine to evaluate de novo protein synthesis. Five days after unilateral ovariectomy, cows were resynchronized and the experiment was repeated. Follicular growth was characterized by the development of single large dominant follicles, which was associated with suppression of other follicles. Concentrations of estradiol-17 beta (E2) in follicular fluid and aromatase activity of follicular walls were higher in dominant follicles (438.9 +/- 45.5 ng/ml; 875.4 +/- 68.2 pg E2/follicle) compared to subordinate follicles (40.6 +/- 69.4 ng/ml; 99.4 +/- 104.2 pg E2/follicle). Aromatase activity in first-wave dominant follicles was higher at Days 5 (1147.1 +/- 118.1 pg E2/follicle) and 8 (1028.2 +/- 118.1 pg E2/follicle) compared to Day 12 (450.7 +/- 118.1 pg E2/follicle). Concentrations of E2 and androstenedione in first-wave dominant follicles were higher at Day 5 (983.2 +/- 78.2 and 89.5 +/- 15.7 ng/ml) compared to Days 8 (225.1 +/- 78.6 and 5.9 +/- 14.8 ng/ml) and 12 (108.5 +/- 78.6 and 13.0 +/- 14.8 ng/ml). Concentrations of progesterone in subordinate follicles increased linearly between Days 5 and 12 of the estrous cycle. Plasma concentrations of FSH increased from 17.9 +/- 1.4 to 32.5 +/- 1.4 ng/ml between 0 and 32 h following unilateral removal of the ovary with the first-wave dominant follicle. Increases in plasma FSH were associated with increased numbers of class 1 (3-4 mm) follicles in cows that were ovariectomized at Day 5 or 8 of the cycle. Unilateral ovariectomy had no effects on plasma concentrations of LH when a CL was present on the remaining ovary. First-wave dominant follicles incorporated more 3H-leucine into macromolecules and secreted high (90,000-120,000) and low (20,000-23,000) molecular weight proteins that were not as evident for subordinate follicles at Days 8 and 12.(ABSTRACT TRUNCATED AT 400 WORDS)     

Follicular 17β-estradiol and progesterone concentrations and degree of cumulus cell expansion as predictors of in vivo-matured oocyte developmental competence in superstimulated heifers

The quality of an oocyte is crucial for successful generation of offspring, but few selection parameters have been identified that reliably predict oocyte developmental competence. The objective of the present study was to determine whether the developmental competence of in vivo-matured oocytes derived from superstimulated heifers could be predicted by 17β-estradiol and progesterone concentrations in follicular fluid, degree of cumulus cell expansion, and follicular diameter. Cumulus oocyte complexes were individually collected from follicles ≥8 mm 22 hours after an induced LH peak and individually fertilized and cultured in vitro. Only oocytes that originated from follicles with 17β-estradiol ≤0.25 μM and progesterone ≥0.26 μM developed into blastocysts. When a combination of these cutoff values was evaluated as a predictor of oocyte competence, the sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 75%, 49%, and 100%, respectively. Hormone concentrations in follicular fluid were also associated with the degree of cumulus cell expansion and only cumulus oocyte complexes with full expansion developed into blastocysts; sensitivity, specificity, positive predictive value, and negative predictive value were 100%, 71%, 45%, and 100%, respectively, when full expansion was used as the predictive criterion for blastocyst production. Follicular diameter was not a good predictor of oocyte competence. In conclusion, concentrations of 17β-estradiol and progesterone in the preovulatory follicle and the degree of cumulus cell expansion are predictors of blastocyst production in superstimulated heifers and can be used as selection markers for oocyte developmental competency.     

Serum estradiol-17beta concentrations during spontaneous silent estrus and after prostaglandin treatment in the mare

Serum estradiol-17beta concentrations were determined during silent estrus in the mare. Relationships between serum estradiol-17beta concentration, corpus luteum regression, follicular development, ovulation, prostaglandin treatment and behavioral estrus were investigated. The expression of behavioral estrus was found to be related to the patterns of progesterone and estradiol-17beta secretion during the periovulatory period. When compared to normal estrous cycles, silent estrus was accompanied by a significantly lower maximum serum estradiol-17beta concentration (47.8 vs 34.6 pg/ml), a significantly longer interval from maximum estradiol-17beta concentration to ovulation (1.7 vs 4.0 days), and a significantly shorter interval from corpus luteum regression to ovulation (5.3 vs 2.8 days). Silent estrus following prostaglandin treatment was related to a significantly shorter interval from prostaglandin treatment to ovulation (3.6 +/- 0.4 days) than from normal corpus luteum regression to ovulation (5.3 +/- 0.3 days). Silent estrus appeared to be related to changes in follicular estradiol-17beta secretion and to the pattern of its secretion as related to regression of the corpus luteum. There appeared to be not only less estradiol-17beta present, but also less time available after luteal regression for it to interact with the central nervous system to elicit the changes necessary to cause behavioral estrus. There fore, unusual relationships between luteal function and folliculogenesis can result in one type of silent estrus. Significant correlations (P<0.05) were found between follicle size and serum estradiol-17beta concentration whenever behavioral estrus occurred [follicle diameter in mm = 0.96 (serum estradiol-17beta in pg/ml) + 6.08 and 0.73 (serum estradiol-17beta + 13.32 for control and normal estrus following prostaglandin treatment groups, respectively]. During silent estrus, however, no significant correlations between follicle size and serum estradiol-17beta concentration were observed.     

Relationship of morphology and follicular fluid environment of bovine oocytes to their developmental potential in vitro

Morphology of bovine cumulus oocyte complexes (BCOC) and follicular fluid parameters were examined as potential criteria for selecting in vitro developmentally competent oocytes. Immature BCOC, from antral follicles, exhibiting similar morphological characteristics were grouped and the blastocyst development for oocytes in each group was examined. In a second experiment, follicles were individually aspirated to recover BCOC with their associated follicular fluid. Each oocyte was categorized and individually matured, fertilized and cultured. Radioimmunoassays for follicular progesterone, estradiol-17beta and insulin-like growth factor-I (IGF-1) concentrations were performed. The BCOC were categorized into 9 groups based on the homogeneity of the ooplasm, compactness of the cumulus investment, color and size. Oocytes classified into Groups 1, 2 and 3 demonstrated the highest rates of development to the blastocyst stage at 13, 16 and 20%, respectively. Therefore, Groups 1, 2 and 3 were pooled and designated as the enhanced developmental potential (EDP) group, and the remaining groups were designated as the reduced developmental potential (RDP) group. The progesterone concentration (+/- SEM) in follicles containing EDP oocytes (27.54 +/- 5.08 ng/ml) was significantly lower than the RDP group (72.72 +/- ng/ml; P < 0.001). Follicles containing oocytes that developed to the blastocyst stage (28.65 +/- 7.18 ng/ml) possessed significantly lower progesterone levels than all remaining follicles (52.9 +/- 7.51 ng/ml; P < 0.05). No significant differences were found for estradiol-17beta or IGF-I concentrations between the EDP and RDP groups or developmental stages. These results indicate that morphological criteria and follicular fluid progesterone concentration may be used to select BCOC for high potential of blastocyst development.     

The effect of an acute energy deficit on the hormone profile of dominant follicles in dairy cows

The effect of an acute energy deficit on the hormone balance of dominant follicles was studied in six normally-cycling, high-yielding Italian Friesian cows at 60 and 90 days after calving. At 60 days after calving, the cows, which had been fed according to their maintenance and production requirements, were synchronized and follicular fluid was collected from the dominant follicles under ultrasound guidance. At 90 days after calving, the same protocol was used on the same cows, which had been subjected to an acute dietary restriction since the day of the second prostaglandin treatment for synchronization. At the follicular level, the dietary restriction caused a significant reduction (P < 0.05) in the concentration of estradiol-17beta and a significant increase (P < 0.05) in NEFA. There were no significant differences in follicular diameter, follicular concentrations of progesterone, and Insulin-like Growth Factor-I (IGF-I). The amount of IGFBP2 and IGFBP3 in follicular fluid increased. The results suggest that an acute dietary restriction induces substantial changes at the dominant follicle level, despite the fact that the recruitment and selection phase occurred before the cows' diet was restricted.     

Inhibition of mouse oocyte cyclic AMP phosphodiesterase by steroid hormones: a possible mechanism for steroid hormone inhibition of oocyte maturation

Testosterone, progesterone, and estradiol-17 beta each inhibit cAMP phosphodiesterase activity of mouse oocyte extracts in a concentration-dependent manner. This finding provides an explanation for the inhibitory effect of steroid hormones on germinal vesicle breakdown (GVBD) of mouse oocytes in vitro. Furthermore, it raises the possibility that steroid hormones present in follicular fluid participate in maintaining meiotic arrest in vivo by acting in a nonclassical manner.     

Oxytocin and bovine parturition: a steep rise in endometrial oxytocin receptors precedes onset of labor.

Oxytocin receptors were measured in myometrium and intercaruncular endometrium of cows during pregnancy and parturition. Concentrations of estradiol-17 beta, estrone, and progesterone in peripheral blood were also measured. Receptor concentrations in the endometrium rose almost 200-fold from Day 20 to term (p < 0.0001, ANOVA), from 40 +/- 11 to 7300 +/- 1430 fmol/mg protein. Myometrial receptor concentrations increased 10-fold from 180 +/- 36 fmol/mg on Day 20 to 1850 +/- 360 fmol/mg protein at term (p < 0.0001, ANOVA). During labor, endometrial receptors (6600 +/- 1300 fmol/mg) remained at prelabor values, whereas myometrial receptor concentrations had decreased to 1190 +/- 316 fmol/mg (not significant) and declined further postpartum. Plasma concentrations of progesterone declined from 4-5 ng/ml to about 2 ng/ml between Days 250 and 282 and dropped to < 0.2 ng/ml shortly before delivery. Plasma concentrations of estrone and estradiol-17 beta were below 10-20 pg/ml until Day 230. Estrone concentrations were significantly (p < 0.05) increased by Day 250 and estradiol-17 beta by Day 270, and then both rose rapidly. During labor, plasma estrone was 1135 +/- 245 pg/ml and plasma estradiol-17 beta was 226 +/- 131 pg/ml. The molar ratio of estrone and estradiol-17 beta to progesterone rose from less than 0.01 to 4.4 during labor, and was correlated with oxytocin receptor concentrations in endometrium (r = 0.5160, p < 0.001), but not those in myometrium (r = 0.0122). The regulation of oxytocin receptors by ovarian hormones in the two tissues may therefore differ.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of a GnRH analogue on the dynamics of follicular development and synchronization of estrus in lactating cyclic dairy cows

A GnRH analogue was used to synchronize ovarian follicular development prior to an injection of PGF(2alpha) for the synchronization of estrus in lactating Holstein cows. On Day 12 (estrus = Day 0) of the experimental cycle, cows (n = 8) were injected with 8 mug Buserelin (BUS group), followed by 25 mg PGF(2alpha) 7 d later (Day 19). Control cows (n = 7) received PGF(2alpha) on Day 12 (PGF group). Ovaries were scanned daily via ultrasonography, and plasma progesterone and estradiol concentrations were determined. Sizes of all visible follicles were recorded. Follicles were classified as small (3 to 5 mm), medium (6 to 9 mm), or large (>/= 10 mm). Between Days 12 and 16 of the cycle, the number of large follicles in PGF cows remained unchanged (1.2), whereas in the BUS group, the number of large follicles decreased from 1.3 on Day 12 to 0.5 on Day 15. Only 4 of 7 PGF cows ovulated a second-wave dominant follicle. In the BUS group, 7 of 8 cows ovulated a GnRH analogue induced dominant follicle that was first identified on Day 15. During the follicular phase (last 5 d prior to estrus), plasma progesterone declined in association with CL regression in both groups, and estradiol concentrations increased, reaching higher (P<.0.05) preovulatory peak concentration in BUS cows than in PGF cows (14.0 +/- 1.0 vs 10.4 +/- 1.1 pg/ml). The number of medium-size follicles was smaller and the number of small-size follicles tended to be higher in BUS cows than in the PGF-treated group. On the day of estrus, the size of the ovulatory follicle (16.1 vs 13.3 mm) and the size difference between the ovulatory and second largest follicle (11.4 vs 6.2 mm) were both larger in BUS cows than in PGF-treated cows, suggesting a more potent dominance effect of the ovulatory follicle in the BUS cows. This study suggests that a GnRH analogue can alter follicular development prior to synchronization of estrus with an injection of PGF(2alpha) in lactating dairy cows.     

Ovarian follicular wave synchronization and induction of ovulation in postpartum beef cows

An experiment was designed to evaluate a) the effect of a progesterone-estradiol combined treatment on ovarian follicular dynamics in postpartum beef cows, and b) ovulation and the subsequent luteal activity after short-term calf removal and GnRH agonist treatment. Multiparous Angus cows (25 to 40 d after calving) were assigned to the following treatments: untreated (Control, n = 9); short term calf removal (CR, n = 8); progesterone (CIDR, n = 9) and progesterone plus estradiol-17 beta (CIDR + E-17 beta, n = 9). Progesterone treatment (CIDR) lasted 8 d and the day of device insertion was considered as Day 0. Cows in the CIDR + E-17 beta group also received an i.m. injection of 5 mg of E-17 beta on Day 1. On Day 8, calves were removed for 48 h (CR, CIDR and CIDR + E-17 beta groups) and 6 h before the end of calf removal these cows also received an i.m. injection of 8 micrograms of Busereline (GnRH). Anestrus was confirmed in all cows by the absence of luteal tissue and progesterone concentrations below 1 ng ml-1 at the beginning of the experiment. Although mean (+/- SEM) interval from the beginning of the experiment (Day 0) to wave emergence did not differ (P > 0.05) among treatment groups (Control, 1.9 +/- 1.0, range -2 to 7 d; CR, 3.9 +/- 0.7, range 0 to 6 d; CIDR, 2.8 +/- 0.5, range 0 to 4 d and CIDR + E-17 beta, 4.1 +/- 0.2, range 3 to 5), the variability was less (P < 0.05) in the CIDR + E-17 beta group. The proportion of cows ovulating 24 to 48 h after GnRH administration tended (P = 0.08) to be higher in cows from CIDR + E-17 beta group (8/9) than in those of CR (5/8) or CIDR (6/9) groups, respectively and was associated with a higher proportion (P < 0.05) of CIDR + E-17 beta treated cows (9/9) that had a dominant follicle in the growing/early static phase at the time of GnRH treatment compared to the other GnRH treated groups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows ovulated 0-24 h after GnRH and only one Control cow ovulated the day before the time of GnRH administration. Cows pretreated with progesterone had longer (P < 0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR + E-17 beta, 13.9 +/- 0.6 d) than those not treated with CIDR (Control, 5, CR, 4.0 +/- 0.4). We conclude that progesterone plus estradiol treatment results in tightly synchronized wave emergence and high GnRH-induced ovulation rate with normal luteal activity in postpartum beef cattle.