Estrogen-active Follicles Research Articles

Myostatin is expressed in bovine ovarian follicles and modulates granulosal and thecal steroidogenesis

Myostatin plays a negative role in skeletal muscle growth regulation but its potential role in the ovary has received little attention. Here, we first examined relative expression of myostatin (MSTN), myostatin receptors (ACVR1B, ACVR2B and TGFBR1) and binding protein, follistatin (FST), in granulosa (GC) and theca (TC) cells of developing bovine follicles. Secondly, using primary GC and TC cultures, we investigated whether myostatin affects steroidogenesis and cell number. Thirdly, effects of gonadotropins and other intrafollicular factors on MSTN expression in GC and TC were examined. MSTN, ACVR1B, TGFBR1, ACVR2B and FST mRNA was detected in both GC and TC at all follicle stages. Immunohistochemistry confirmed follicular expression of myostatin protein. Interestingly, MSTN mRNA expression was lowest in GC of large oestrogen-active follicles whilst GC FST expression was maximal at this stage. In GC, myostatin increased basal CYP19A1 expression and oestradiol secretion whilst decreasing basal and FSH-induced HSD3B1 expression and progesterone secretion and increasing cell number. Myostatin also reduced IGF-induced progesterone secretion. FSH and dihydrotestosterone had no effect on granulosal MSTN expression whilst insulin-like growth factor and tumour necrosis factor-alpha suppressed MSTN level. In TC, myostatin suppressed basal and LH-stimulated androgen secretion in a follistatin-reversible manner and increased cell number, without affecting progesterone secretion. LH reduced thecal MSTN expression whilst BMP6 had no effect. Collectively, results indicate that, in addition to being potentially responsive to muscle-derived myostatin from the circulation, myostatin may have an intraovarian autocrine/paracrine role to modulate thecal and granulosal steroidogenesis and cell proliferation/survival.

G protein-coupled receptor 34 in ovarian granulosa cells of cattle: changes during follicular development and potential functional implications

Abundance of G protein-coupled receptor 34 (GPR34) mRNA is greater in granulosa cells (GCs) of cystic vs normal follicles of cattle. The present experiments were designed to determine if GPR34 mRNA in granulosa cell [GC] changes during selection and growth of dominant follicles in cattle as well as to investigate the hormonal regulation of GPR34 mRNA in bovine GC in vitro. In Exp. 1, estrous cycles of nonlactating cows were synchronized and then ovariectomized on either day 3–4 or 5–6 after ovulation. GPR34 mRNA abundance in GC was 2.8- to 3.8-fold greater (P < 0.05) in small (1–5 mm) and large (≥8 mm) estrogen-inactive dominant follicles than in large estrogen-active follicles. Also, GPR34 mRNA tended to be greater (P < 0.10) in F2 than F1 follicles on day 3–4 postovulation. In Exp. 2–7, ovaries were collected at an abattoir and GC were isolated and treated in vitro. Expression of GPR34 was increased (P < 0.05) 2.2-fold by IGF1. Tumor necrosis factor (TNF)-α decreased (P < 0.05) the IGF1-induced GPR34 mRNA abundance in small-follicle GC, whereas IGF1 decreased (P < 0.05) GPR34 expression by 45% in large-follicle GC. Treatment of small-follicle GC with either IL-2, prostaglandin E2 or angiogenin decreased (P < 0.05) GPR34 expression, whereas FSH, cortisol, wingless 3A, or hedgehog proteins did not affect (P > 0.10) GPR34 expression. In Exp. 6 and 7, 2 presumed ligands of GPR34, L-a-lysophosphatidylserine (LPPS) and LPP-ethanolamine, increased (P < 0.05) GC numbers and estradiol production by 2-fold or more in small-follicle GC, and this response was only observed in IGF1-treated GC. In conclusion, GPR34 is a developmentally and hormonally regulated gene in GC, and its presumed ligands enhance IGF1-induced proliferation and steroidogenesis of bovine GC.

Ovarian Expression of Insulin-Like Peptide 3 (INSL3) and Its Receptor (RXFP2) During Development of Bovine Antral Follicles and Corpora Lutea and Measurement of Circulating INSL3 Levels During Synchronized Estrous Cycles

Insulin-like peptide 3 (INSL3), a major product of testicular Leydig cells, is also expressed by the ovary, but its functional role remains poorly understood. Here, we quantified expression of INSL3 and its receptor RXFP2 in theca interna cell (TIC) and granulosa cell compartments of developing bovine antral follicles and in corpora lutea (CL). INSL3 and RXFP2 mRNA levels were much higher in TIC than granulosa cell and increased progressively during follicle maturation with INSL3 peaking in large (11-18 mm) estrogen-active follicles and RXFP2 peaking in 9- to 10-mm follicles before declining in larger (11-18 mm) follicles. Expression of both INSL3 and RXFP2 in CL was much lower than in TIC. In situ hybridization and immunohistochemistry confirmed abundant expression of INSL3 mRNA and protein in TIC. These observations indicate follicular TIC rather than CL as the primary site of both INSL3 production and action, implying a predominantly autocrine/paracrine role in TIC. To corroborate the above findings, we showed that in vitro exposure of TIC to a luteinizing concentration of LH greatly attenuated expression of both INSL3 and its receptor while increasing progesterone secretion and expression of STAR and CYP11A1. Moreover, in vivo, a significant cyclic variation in plasma INSL3 was observed during synchronized estrous cycles. INSL3 and estradiol-17β followed a similar pattern, both increasing after luteolysis, before falling sharply after the LH surge. Thus, theca-derived INSL3, likely from the dominant preovulatory follicle, is detectable in peripheral blood of cattle, and expression is down-regulated during luteinization induced by the preovulatory LH surge. Collectively, these findings underscore the likely role of INSL3 as an important intrafollicular modulator of TIC function/steroidogenesis, while raising doubts about its potential contribution to CL function.

VEGFA164_B mRNA Abundance Has a Positive Relationship to AMH, BCL2 and the Ratio of E2:A4 in Mural Granulosa Cells of Estrogen Active and Inactive Follicles Prior to Ovulation.

Previously, we reported differential expression of Vascular Endothelial Growth Factor A (VEGFA) isoforms in somatic cells from bovine females of differing fertility. Thus, we sought to determine how expression of VEGFA pro and antiangiogenic isoforms were regulated after synchronization protocols that stimulated normal or persistent follicle development. Furthermore, we examined relationships between VEGFA isoforms, steroid hormones and genes that regulate follicular development in mural granulosa cells and cumulus oocyte complexes (COC). Our hypothesis was that dominant estrogen active (EA) follicles would have greater mRNA abundance of VEGFA angiogenic isoforms and genes that stimulate follicle development; while estrogen inactive (EI) follicles would contain greater mRNA expression of VEGFA antiangiogenic isoforms. Thirty-five composite beef cows [75% MARC III (1/4 Angus, 1/4 Hereford, 1/4 Pinzgauer, 1/4 Red Poll) and 25% Red Angus] were treated with either 1) a modified Co-Synch protocol (CIDR) or 2) injected with prostaglandin and offered Melengesterol Acetate (MGA) for 14 days. Dominant follicle aspirations were performed 18, 36, and 60 hours after the last PGF2a injection utilizing transvaginal ultrasound guided ovum pickup. Follicular fluid steroid hormone concentrations were determined via RIA (E2 and P4) or ELISA (A4). Follicles were then classified as EA (E2:P4 > 1) or as EI (E2:P4 = 1). There was no effect of time on gene expression or steroid hormone levels, thus animals were grouped based on treatment and follicle E2-activity. CIDR and MGA EI follicles had a greater (P = 0.02) concentrations of progesterone compared to CIDR EA follicles. Although A4 concentration was similar among groups, CIDR EA follicles had greater E2:A4 ratio compared to EI follicles suggesting reduced efficiency in conversion of A4 to E2.To determine if the reduced E2:A4 ratio in EI follicles alters the mRNA abundance of VEGFA isoforms in the COC or mural granulosa cells quantitative, real-time RT-PCR was performed. There was no difference in VEGFA_164 gene expression among groups. However, abundance of VEGFA_164B mRNA was 7-fold and 2-fold greater (P < 0.01) in the mural granulosa cells of MGA EI and CIDR EI, respectively, compared to CIDR EA follicles. Furthermore, there was a trend (P = 0.06) for an increased ratio of VEGFA_164/ VEGFA_164B in mural granulosa of CIDR EA follicles. Follicles classified as MGA EI had greater (7-fold; P = 0.02) mRNA abundance of AMH compared to CIDR EA follicles in granulosa cells. Furthermore, BCL2 mRNA expression tended to be increased (P = 0.07) in MGA EI follicles. In contrast to the mural granulosa cells, VEGFA_164B mRNA abundance was not different in COC. In mural granulosa cells, there was a positive correlation between VEGFA_164B and BCL2; VEGFA_164B and AMH; VEGFA_164B and the ratio of E2:P4; and the ratio of VEGFA_164/VEGFA_164B and BCL2.Taken together these data suggest a tendency for increased levels of anti-apoptotic factors and reduced efficiency of conversion of A4 to E2 in granulosa cells of EI follicles. Furthermore, there is a positive correlation between the antiangiogenic VEGFA isoform and BCL2 and AMH which play a role in regulating follicle development. USDA is an equal opportunity provider and employer.

Follicular characteristics and intrafollicular concentrations of nitric oxide and ascorbic acid during ovarian acyclicity in water buffalo (Bubalus bubalis)

The objective of this study was to examine the follicular characteristics and intrafollicular concentrations of nitric oxide and ascorbic acid during ovarian acyclicity in buffaloes. Ovaries were collected from 56 acyclic and 95 cyclic buffaloes at slaughter, surface follicle number was counted and follicles were classified into small (5.0-6.9 mm), medium (7.0-9.9 mm), and large (≥ 10.0 mm) size categories based on their diameter. Follicular fluid was aspirated and assayed for nitric oxide, ascorbic acid, estradiol, and progesterone. Acyclic buffaloes had a higher (P<0.05) number of medium-sized follicles and a lower (P<0.001) number of large follicles than the cyclic ones. In acyclic animals, the number of large follicles was lower (P<0.01) than in medium size category which in turn was lower (P<0.001) than the number of small follicles. In contrast, the number of medium and large follicles was not different (P>0.05) in the cyclic control. However, the number of small-sized follicles was higher (P<0.001) compared to the other two categories. The incidence of large-sized follicles was lower (P<0.05) in acyclic buffalo population compared to the cyclic control. Evaluation of estrogenic status demonstrated that all the follicles of acyclic buffaloes are estrogen-inactive (E (2)/P (4) ratio<1). Small- and medium-sized follicles of acyclic buffaloes had higher concentrations of nitric oxide (P<0.05 and P<0.001, respectively) and lower concentrations of ascorbic acid (P<0.05 and P<0.01, respectively) than the corresponding size estrogen-active follicles of their cyclic counterparts. In conclusion, this study indicates that follicular development continues during acyclicity in buffaloes. Although follicles in some acyclic buffaloes attain a size corresponding to morphological dominance, they are unable to achieve functional dominance, perhaps due to an altered balance of intrafollicular nitric oxide and ascorbic acid and, as a result, these follicles instead of progressing to ovulation undergo atresia.

Follicular fluid nitric oxide and ascorbic acid concentrations in relation to follicle size, functional status and stage of estrous cycle in buffalo

The objective of this study was to evaluate the changes in follicular fluid nitric oxide (NO) and ascorbic acid (AA) concentrations with varying follicle size and functional status, and stage of estrous cycle in buffalo. The main effect of follicle size on NO concentration and size-by-status interaction were statistically significant ( P < 0.05). Small follicles had a higher ( P < 0.05) NO concentration compared to medium and large follicles. Further, estrogen-active (EA) small follicles showed increased ( P < 0.05) NO concentrations than the corresponding estrogen-inactive (EI) follicles. Within EA category, higher ( P < 0.01) concentrations were recorded in small compared to medium and large follicles. There was no significant main effect of stage ( P > 0.1) on NO concentration but the stage-by-size interaction was significant ( P < 0.05) with medium follicles showing a higher ( P < 0.05) concentration during late luteal stage compared to the mid luteal stage. During early and mid luteal stages, higher ( P < 0.05) NO concentrations were recorded in small than in medium follicles. A significant ( P < 0.01) main effect of size on AA concentration was observed with higher values in medium than in small and large follicles. Size-by-status interaction for AA approached statistical significance ( P < 0.06) with higher ( P < 0.05) concentrations recorded in medium than in large EA follicles. The main effect of stage on AA concentration was, however, non-significant ( P > 0.1) but the stage-by-size interaction approached statistical significance ( P < 0.06) with lower ( P < 0.05) levels recorded in large compared to medium size follicles during the follicular stage. In conclusion, the present study demonstrates that the concentrations of follicular fluid NO and AA vary according to the follicle size, functional status and stage of estrous cycle suggesting their possible role in process of follicular development during estrous cycle in buffalo.

Evidence Supporting a Role for Cocaine- and Amphetamine-Regulated Transcript (CARTPT) in Control of Granulosa Cell Estradiol Production Associated with Dominant Follicle Selection in Cattle

We demonstrated previously a negative association of granulosa cell cocaine- and amphetamine-regulated transcript (CARTPT) expression with follicle health status and inhibitory effects of the mature CARTPT peptide (CART) on follicle-stimulating hormone (FSH) signal transduction in vitro, resulting in reduced bovine granulosa cell CYP19A1 mRNA and estradiol production. The objectives of this study were to investigate temporal regulation of granulosa cell CARTPT expression (granulosa cell mRNA and follicular fluid CART peptide concentrations) during follicular waves, CART regulation of androstenedione production (precursor for estradiol biosynthesis) by thecal tissue collected at specific stages of a follicular wave, FSH regulation of granulosa cell CARTPT mRNA expression, and the ability of CART to inhibit granulosa cell estradiol production and CYP19A1 mRNA expression when administered in vivo. CART concentrations in healthy, estrogen-active follicles (estradiol greater than progesterone in follicular fluid) decreased after dominant follicle selection, and CARTPT mRNA was lower in healthy, estrogen-active versus estrogen-inactive atretic follicles (progesterone greater than estradiol) collected at the predeviation and early dominance stages. CART treatment reduced luteinizing hormone-induced androstenedione production by thecal tissue collected at predeviation and early dominance stages but not at later stages of a follicular wave. The FSH or insulin-like growth factor 1 treatment in vitro reduced granulosa cell CARTPT mRNA in a dose-dependent fashion. Administration of CART in vivo into follicles at the early dominance stage reduced follicular fluid estradiol concentrations and granulosa cell CYP19A1 mRNA. Collectively, results support a potential stage-specific regulatory role for CART in negative regulation of estradiol production associated with selection of the dominant follicle.

Estrogen to progesterone ratio affects hormonal and lipid follicular fluid profiles in dairy cows.

Aim: The present study described hormonal and lipids concentrations of follicles that develop under high progesterone plasmatic levels, mimicking the second follicular wave. Methods: All follicles were removed by aspiration in order to generate a new follicular wave. Follicular fluid was then obtained from either 3day old follicles (F3) or 6dayold follicles (F6). This experimental protocol was carried out at 20days and 90days post-partum on Frisian dairy cows that had already returned to cyclicity. Results: Estrogen active follicles (ratio of estrogen to progesterone in follicular fluid higher than 1) have higher levels of VEGF, IGF-I and linoleic acid, and have lower levels of NEFA, oleic and arachidonic acid. Non-estrogen active follicular fluid concentrations of IGF-I and NEFA were similar to plasma concentrations. In contrast, estrogen active follicles showed higher IGF-I and lower NEFA levels than plasmatic ones that could be used to sustain follicular growth. Conclusions: The results show that estrogen active follicles might have their own metabolism. (Reprod Med Biol 2007; 6: 45-51).

Follicular development and maturation in gilts selected for an index of high ovulation rate and high prenatal survival1

Seventy-one 10th-generation gilts from White Line-1 (WL-1 = randomly selected control line) and White Line-2 (WL-2 = selected for an index of ovulation rate and prenatal survival rate) were used to compare the pattern of follicular development and atresia during the follicular phase of the estrous cycle. Gilts were treated with PGF(2alpha)on d 13 of the estrous cycle (d 0 of induced follicular development) to induce luteolysis and assigned randomly within line and sire for ovary recovery on d 0, 2, 3, 4, 5, and the day after estrus. Ovaries were evaluated for numbers of corpora albicantia and small (2 to 2.9 mm), medium (M1 = 3 to 4.9 mm; M2 = 5 to 6.9 mm), and large (>or=7 mm) follicles. The concentration of estradiol-17beta in follicular fluid was used to classify individual M2 and large follicles as estrogen-active (>or=100 ng of estradiol-17beta/mL) or inactive (<100 ng of estradiol-17beta/mL). The WL-2 gilts had a greater ovulation rate than WL-1 gilts at their pre-treatment estrus (20.4 vs. 13.8 corpora albicantia; P < 0.001). The small and M1 follicle populations decreased rapidly in both lines over time (P < 0.001). The M2 follicle population increased in both lines between d 0 to 4 and then decreased. Mean estradiol concentration of M2 follicles increased in both genetic lines over time (P < 0.02). All large follicles were estrogen-active in both lines; the number of large follicles increased with day (P < 0.001) and was similar in both lines. The number of estrogen-active M2 follicles was similar in both lines, increasing to d 3 and 4 and then decreasing (P < 0.01) thereafter. However, the total number of estrogen-active follicles (sum of estrogen-active M2 and large follicles) was greater in WL-2 than in WL-1 gilts (P < 0.04), increasing to the ovulatory potential by d 3 in WL-1 gilts, but continuing to increase through d 4 in WL-2 gilts. Selection of an additional six ovulatory follicles from the estrogen-active M2 follicle pool after d 5 was required in both lines to achieve the projected ovulation rate, and after estrus, the number of large follicles remained insufficient to attain the ovulatory potential of each line.

Development and Validation of a Short-Term, Serum-Free Culture System for Bovine Granulosa Cells: Evaluation of the Effects of Somatotropin and Growth Hormone-Releasing Factor on Estradiol Production

The objective of this study was to develop and validate a short-term, serum-free culture system to determine whether recombinant bovine somatotropin (rbST) or recombinant bovine growth hormone-releasing factor (rbGRF) altered the estradiol-producing capacity of bovine granulosa cells isolated from dominant or subordinate follicles of the first follicular wave. Thus, ovaries were obtained at an abattoir from cows that were between d 2 to 5 or 6 to 10 of the estrous cycle. Three size classes of follicles were isolated from each cow's ovaries: small (2 to 5mm in diameter), medium (6 to 14mm), or the largest (6 to 19mm). In vivo steroid-producing capacity of follicles was assessed by measuring concentration of estradiol, progesterone, androstenedione and 5α-dihydrotestosterone in each follicle. In vitro steroid-producing capacity was assessed by culturing granulosa cells from the different follicle sizes for 48h in serum-free media with 19-OH androstenedione and measuring the estradiol and progesterone concentrations in media at the end of culture. The effect of different doses of FSH, rbST, or rbGRF on estradiol and progesterone production by granulosa cells from each follicle size class during d 2 to 5 or 6 to 10 was also evaluated. A high percentage (91.7%) of the largest follicles obtained on d 2 to 5 was estrogen-active (estradiol>progesterone) compared with other follicle classifications (d 2 to 5, small = 0%, medium = 13.8%; d 6 to 10, small = 0%, medium = 3.3%, largest = 33.3%). Estradiol was highest (P<0.05) in the largest follicle on d 2 to 5 and correlated positively with follicle diameter. The pattern of in vitro production of estradiol by granulosa cells from the different follicle size classes reflected the original in vivo capacity of follicles to produce estradiol. However, only granulosa cells from the largest estrogen-active follicle on d 2 to 5 produced more estradiol than progesterone in vitro. Progesterone production by granulosa cells from all follicle classifications was increased by FSH, but FSH only enhanced estradiol production by granulosa cells from the largest estrogen-active follicles on d 2 to 5. Recombinant bST blocked the FSH-induced increase in estradiol by granulosa cells from the largest estrogen-active follicles on d 2 to 5, whereas rbGRF had no effect on steroid production. Based on these results, we concluded that short-term, serum-free culture of bovine granulosal cells obtained from first-wave follicles at an abattoir could be used to reflect reliably the original in vivo estradiol-producing capacity of granulosal cells, and that neither rbST nor rbGRF enhance basal or FSH-induced estradiol production by bovine granulosa cells from first-wave follicles.

A potential role for insulin-like growth factor binding protein-4 proteolysis in the establishment of ovarian follicular dominance in cattle.

A critical transition in ovarian follicular development is the selection of a dominant follicle, capable of ovulating, from a cohort of synchronously growing antral follicles. However, little is known about mechanisms and factors that regulate the selection and growth of dominant ovarian follicles. We have investigated whether a component of the insulin-like growth factor (IGF) system, namely IGFBP-4 protease, is associated with the establishment of follicular dominance in cattle. IGFBP proteases degrade IGFBPs, freeing IGFs to interact with their receptors. In experiment 1, follicular fluid from preovulatory follicles (n = 4) degraded about 80% of the added recombinant human (rh) IGFBP-4 within 18 h of incubation. The IGFBP-4 protease exhibited optimal activity at neutral/basic pH and its sensitivity to various protease inhibitors suggested a metalloprotease. The decline in the intensity of the band corresponding to intact rhIGFBP-4 was accompanied by the appearance of immunoreactive fragments of molecular weights approximately 18 and 14 kDa, which were not detectable by ligand blot analysis. In experiment 2, follicular fluid samples were collected from dominant and subordinate follicles on Day 2 or 3 of the first follicular wave, after ovariectomy (experiment 2a, n = 3/day) or by ultrasound-guided follicular aspiration (experiment 2b, n = 4-5/day). Estradiol concentrations in follicular fluid from dominant vs. subordinate follicles confirmed their identities and indicated that the dominant follicle had been selected by Day 2 of the follicular wave. In both experiments 2a and 2b, IGFBP-4 proteolytic activity was 2- to 3.5-fold (P < 0.05) and 5-fold (P < 0.01) higher in follicular fluid from dominant than subordinate follicles on Days 2 and 3 of the follicular wave, respectively. The finding that IGFBP-4 proteolytic activity is higher in dominant, estrogen-active follicles than in subordinate follicles of the same cohort, as early as Day 2 of the follicular wave, strongly suggests a role for IGFBP-4 protease in the establishment of ovarian follicular dominance.

Estrogen and progesterone receptors in the ovine cervix during the postpartum period

Cervical estrogen (E) and progesterone (P) receptors were characterized and quantified during the postpartum period in Corriedale ewes lambing in the late breeding season. Cervices and uteri were collected after ovariohysterectomy at 1 d (n=2), 5 d (n=4), 17 d (n=2) or 30 d (n=2) post partum. The estrogen and progesterone receptors were measured using binding assays with tritiated hormones, dextran charcoal separation and inverse Scatchard analysis. Similar kinetic parameters in cytosolic binding sites for both hormones were found in all cervical and uterine samples, indicating that the binding protein in both tissues is of the same nature. Receptor concentrations (fmol/mg cytosolic protein) in the cervix of early (1 to 5 d, n=6) and late (17 to 30 d, n=4) postpartum ewes were 348 ± 66 vs 994 ± 145 (P<0.05) for E and 618 ± 126 vs 1170 ± 201 (P<0.05) for P, respectively. These data suggest an increased synthesis of receptors, probably due to the presence of ovarian estrogen-active follicles. Cervical E and P receptor concentrations were similar or higher than those in the uterus (1.40 ± 0.15, n=10 and 1.51 ± 0.19, n=10; for E and P respectively), and these receptor ratios did not differ between the early and late postpartum period. The high ratio between cervical/uterine receptors suggests that the ovine cervix may be a very sensitive to steroid action. In conclusion, it was shown that restoration of steroid receptors during the postpartum period in the ovine cervix is similar to receptor dynamics in the uterus, and is probably associated with the recovery of ovarian cyclicity.

Effect of long-term infusion with recombinant growth hormone-releasing factor and recombinant bovine somatotropin on development and function of dominant follicles and corpora lutea in Holstein cows.

The objective of this study was to evaluate the effects of recombinant bovine growth hormone-releasing factor (rGRF) or recombinant bovine somatotropin (rbST) on growth and function of the first-wave dominant follicle and corpus luteum. Primiparous Holstein cows (117 d postpartum) were infused with 12 mg/d of rGRF (n = 10) or 29 mg/d of rbST (n = 10) for 63 d, and non-infused cows (n = 10) were controls. At slaughter on d 5 of an estrous cycle, blood and ovaries were collected and data from cows with a corpus luteum were analyzed (control, n = 8; rGRF, n = 5; rbST, n = 6). Treatment with rGRF or rbST increased somatotropin (ST) and IGF-I in serum similarly compared with controls. In contrast, rbST-treated cows had higher concentrations of ST in follicular fluid (FF) compared with rGRF-treated and control cows. In addition, rbST, but not rGRF, increased the number and decreased the size of estrogen-active follicles (EA; estradiol > progesterone concentrations in FF), increased the abundance of IGF binding proteins-2, -3, and -4 in FF from EA follicles, and increased the number but decreased the size of corpora lutea and decreased concentration of progesterone in serum compared with controls. Based on these results, we concluded that long-term infusion of rbST alters growth and function of the first-wave dominant follicle and the corpus luteum in cattle.

Selection of the dominant follicle in cattle occurs in the absence of differences in the expression of messenger ribonucleic acid for gonadotropin receptors.

Mechanisms that allow selection of a dominant ovarian follicle from a cohort of growing follicles are unknown. Large healthy, estrogen-active follicles contain more LH receptors than atretic estrogen-inactive follicles, and levels of messenger RNA (mRNA) for LH receptor increase in the granulosa cells of dominant follicles as growth progresses. The aim of the present study was to test the hypothesis that changes in the temporal pattern of expression of mRNA for LH and FSH receptors are associated with selection of dominant follicles in cattle. Based on size, the dominant and two largest subordinate follicles were collected from the ovaries of heifers on days 2 (n = 3) or 3 (n = 3) of a follicular wave. On day 2, the dominant follicle was 1 mm larger than the largest subordinate follicle, but by day 3 of the wave the dominant follicle was 2-4 mm larger than the largest subordinate. Follicular fluid concentrations of estradiol and estradiol secretion in vitro by pieces of follicle wall (granulosa and theca cells) were greatest by the dominant compared with the subordinate follicles (P < 0.05). These data indicate that selection of a dominant follicle had occurred by the second day of the follicular wave. By in situ hybridization, mRNAs for LH and FSH receptors, P450 aromatase and P450 17alpha-hydroxylase (17alpha-OH) were localized in frozen sections from each follicle. The expression of mRNA for LH receptor in granulosa cells was always at or near background and was not different between days or follicle types (P = 0.63). In contrast, the expression of mRNA for LH receptor in theca cells of the same sections was readily detectable; there was no difference between follicle types on the second day of the follicular wave, but by the third day expression in the subordinate follicles had decreased (P < 0.05). The expression of mRNA for FSH receptor was highest in granulosa cells of dominant follicles collected on day 3 of the follicular wave (P < 0.05) and was not different between dominant and subordinate follicles on day 2 of the wave (P > 0.05). The expression of mRNA for aromatase in granulosa cells was similar (P > 0.05) between the dominant follicles on days 2 and 3 and the largest subordinate follicle on day 2 of the follicular wave and was much lower in the remaining follicles (P < 0.01). On day 2 of the wave, the expression of mRNA for 17alpha-OH was not different between the dominant and subordinate follicles, but by day 3 the dominant follicles had more mRNA for 17alpha-OH than the subordinate follicles (P < 0.05). These data show that the dominant follicle had been selected by the second day of the follicular wave (based on diameter and estradiol secretion) and that selection occurred in the absence of detectable levels of mRNA for LH receptor in the granulosa cells or differences between dominant and subordinate follicles in mRNA for LH receptor in theca cells or FSH receptor in granulosa cells. However, the divergent pattern of growth between dominant and subordinate follicles (after follicle selection) was associated with higher levels of mRNA for gonadotropin receptors and steroidogenic enzymes in dominant compared with subordinate follicles. Therefore, selection of the dominant follicle in cattle does not appear to involve the regulation of expression of mRNA for gonadotropin receptors, although such regulation may be important at other stages of differentiation of the dominant follicle.

Selection, dominance and atresia of follicles during the oestrous cycle of heifers.

This study examined the correlation between measurement of follicle growth by ultrasound, and measurement of intrafollicular ratios of oestradiol and progesterone concentrations and the serum concentrations of FSH during selection, dominance and atresia or ovulation of dominant follicles in heifers. Heifers were ovariectomized on days 0 (before LH surge), 1 (after LH surge, preovulation), 1 (postovulation), 3, 6 and 12 of the oestrous cycle. Blood samples were collected at 4-6 h intervals. After ovariectomy all follicles > or = 5 mm were measured and follicular fluid was aspirated. Follicles were classified by size according to ultrasound (F1, largest; F2, second largest; F3, all remaining follicles > or = 5 mm) and by the ratio of oestradiol:progesterone concentrations. During the follicular phase, a single dominant oestrogen-active follicle increased in diameter while serum concentrations of LH increased and FSH decreased (P < 0.05). On day 1 (after LH surge, preovulation), serum LH and FSH decreased to pre-surge concentrations (P < 0.0001), while follicle size and intrafollicular progesterone concentration increased and oestradiol concentration decreased (P < 0.05). A dominant nonovulatory follicle, classified as oestrogen-active on days 1, 3 and 6 and oestrogen-inactive on day 12, increased in size from day 1 to day 7 and lost dominance during days 10-12, coincident with the growth of multiple oestrogen-active follicles. The serum FSH concentration increased transiently (P < 0.05) before each new wave of dominant follicular growth. The overall correlation of ultrasound measurements of follicle diameter with measures of follicle size after ovariectomy was high.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of FSH-P induced follicular growth in cows

Because cow ovaries do not contain a dominant follicle before Day 3 of the estrous cycle, we hypothesized that gonadotropin treatment early in the estrous cycle would induce growth of multiple follicles and could be used to induce superovulation. In Experiment 1, when 16 cows were treated with FSH-P beginning on Day 2 of the estrous cycle and were slaughtered on Day 5, all cows responded to gonadotropin treatment by exhibiting a large number ( approximately 19) of estrogenactive follicles >/= 6 mm. In Experiment 2, in response to FSH-P treatment from Day 2 to Day 7, and fenprostalene treatment on Day 6, 11 of 15 cows exhibited estrus and had a mean ovulation rate of 23.7 +/- 1.5. In Experiment 3, an FSH-P treatment regimen identical to that used in Experiment 2 was administered to cows beginning either on Day 2 (Day-2 cows; n=14) or Day 10 (Day-10 cows; n=11) of the estrous cycle. Twelve of 14 Day-2 cows and all Day-10 cows exhibited estrus after fenprostalene treatment. Day-2 cows exhibited 34.3 +/- 7.0 ovulations, which was less (P < 0.05) than that exhibited by Day-10 cows (48.3 +/- 4.4). However, the proportion of embryos recovered per corpus luteum was about 2-fold greater (P < 0.05) for Day-2 cows than for Day-10 cows (0.49 +/- 0.08 vs 0.27 +/- 0.06). These data indicate that beginning gonadotropin treatment early in the estrous cycle, when a dominant follicle is not present, provides an efficacious means to induce growth of multiple follicles and superovulation in cows. However, when FSH was administered for 6 d, beginning the treatment on Day 10 also resulted in a consistent and efficacious response.

Expression of Messenger Ribonucleic Acid for Inhibin Subunits and Ovarian Secretion of Inhibin and Estradiol at Various Stages of the Sheep Estrous Cycle1

The relationship between expression of inhibin mRNA and ovarian secretion of estradiol (E2) and immunoactive inhibin was investigated at midluteal phase and throughout the follicular phase of the sheep estrous cycle. At laparotomy, timed samples of ovarian blood were collected and ovaries were removed from 39 Scottish Blackface ewes (ovulation rate 1.3 +/- 0.1) on Day 10 of the luteal phase or 24, 48, 60, 72, or 84 h after injection of cloprostenol (PG; 100 micrograms) on Days 10-12. Ovaries were removed and fixed for in situ hybridization using 35S-labeled antisense riboprobes transcribed from inhibin alpha, beta A, and beta B cDNAs. LH, E2, and inhibin concentrations were determined by RIA. On the basis of peripheral LH levels and the presence of estrogen-active follicles (E-A; > or = 3 mm in diameter secreting > 1 ng/min E2) or recent ovulations, animals were grouped as follows: presurge (24 or 48 h post-PG; LH < 5 ng/ml; n = 7), midsurge (with E-A; LH > 5 ng/ml; n = 6), late surge (large follicle not E-A; LH > 5 ng/ml; n = 4), postsurge (large follicle not E-A; LH < 5 ng/ml; n = 7), and postovulation (n = 10). As expected, E2 secretion by the "active" ovary (containing preovulatory follicle) tended to increase with follicular development such that secretion was maximal at midsurge and then declined. E2 secretion by the "inactive" ovary was low at all stages. Immunoactive inhibin, in contrast, was secreted in substantial quantities by both ovaries, although secretion from active ovaries was higher at all stages (p < 0.05). Effects of stage on secretion were not significant, but immunoactive inhibin secretion from active ovaries was high in postsurge animals when E2 secretion was very low. Hybridization for inhibin mRNA was specific for granulosa cells of antral follicles. While most sheep in the luteal (4 of 5), presurge (2 of 3), and midsurge groups (5 of 5) had at least one inhibin-positive large follicle (expressing both alpha- and beta-subunit mRNA), none were present between the LH surge and ovulation (late and postsurge groups). Inhibin mRNA was undetectable in midcycle CL, but 4 of 10 recent ovulations hybridized weakly with the alpha probe and one very weakly with the beta A probe. The mean number of inhibin-positive large follicles per animal (in those having at least one) was 1.3 +/- 0.15 (n = 15 ewes).(ABSTRACT TRUNCATED AT 400 WORDS)

Ovarian follicular characteristics, embryo recovery, and embryo viability in heifers fed high-fat diets and treated with follicle-stimulating hormone.

Postpubertal beef heifers (n = 55) were used to examine the effects of high-fat diets, independently of energy intake, on nonesterified fatty acid and lipoprotein metabolic patterns, ovarian follicular dynamics, and embryo recovery/viability after FSH superstimulation. High-lipid (HL) diets (5.4% added fat) increased (P < .01) serum concentrations of cholesterol, but not of nonesterified fatty acids, during the 35-d period before FSH treatment. Development of medium-sized (5 to 9.9 mm) follicles was enhanced (P < .05) during this period in heifers fed the HL diet. The HL diet increased total cholesterol (P < .05) and progesterone (P = .14) concentrations in follicular fluid obtained at ovariectomy (n = 10) 60 h after the onset of FSH treatment, but neither estradiol-17 beta nor androstenedione was affected. Granulosa cells recovered from FSH-induced, estrogen-active follicles in heifers fed the HL diet produced greater quantities of progesterone (P = .06) and less estradiol-17 beta (P < .05) in vitro than did granulosa cells from heifers fed the normal lipid diet. Dietary treatment did not influence FSH-stimulated recruitment of medium and large follicles, number of ovulations, embryo recovery, or embryo viability. Data suggest that increments in dietary fat intake can alter specific aspects of ovarian steroidogenic potential and can increase the population of medium-sized follicles theoretically available for maturation and harvest during the estrous cycle. However, conditions that limited the latter process in the current experiment are not understood and require further investigation.

Effect of FSHp on day 1 of the estrous cycle on follicle number and concentrations of inhibin in follicular fluid in heifers

The objectives of this experiment were to determine 1) the effect of a single injection of porcine follicle stimulating hormone (FSHp) on Day 1 of the estrous cycle on the number of estrogen-active (EA dominant) follicles present on Days 3, 5 and 7 of the same cycle, and 2) the relationship between concentrations of estradiol and inhibin in these follicles. Cyclic beef heifers (n=38) were treated with a synthetic analogue of prostaglandin F2α (Luprostiol, 15 mg) to synchronize estrus (Day 0). On Day 1, heifers were randomly assigned to one of two treatments: 7 mg FSHp (Folltropin, n=18); or controls (n=20). Heifers were slaughtered on Days 3, 5 or 7 and the number of follicles ≥5mm was recorded. Follicular fluid from each follicle ≥5mm was aspirated, quantified, centrifuged and frozen for subsequent determination of estradiol 17β (E2), progesterone (P4) and inhibin concentrations. Follicles were classified as estrogen-active if the concentration of estradiol 17β exceeded that of progesterone in follicular fluid. A single injection of FSHp on Day 1 had no significant effect (P>0.05) on the overall number of follicles on Days 3, 5 and 7; FSHp treatment possibly increased the number of large follicles on Day 3 (P=0.04). There were more estrogen-active follicles on Day 3 than on Day 5 or Day 7 irrespective of treatment. The FSHp treatment had a significant effect on the proportion of estrogen-active follicles when all follicles were considered together (94% estrogen-active for control, 50% for FSHp treatments; P=0.025) or when only medium follicles were assessed (92% for control, 28% for FSHp treatments; P=0.0001); this effect was not significant when only the large follicles were considered. No significant correlations were found between concentrations of inhibin, estrogen or progesterone in medium or large follicles. In conclusion, a single injection of FSHp on Day 1 did not significantly affect the total number of follicles, and it possibly increased the number of large follicles on Day 3 and decreased the percentage of estrogen-active follicles on Day 3.

Effect of dietary intake on concentrations of insulin-like growth factor-I in plasma and follicular fluid, and ovarian function in heifers

The objective of this study was to determine if alterations in dietary intake of heifers can influence IGF-I concentrations in plasma and(or) follicular fluid (FFL), size of follicles, and steroid concentrations in FFL (as an indicator of steroidogenic capacity). Cyclic heifers [n=23; mean ± SE body weight (BW) = 373 ± 7 kg were individually fed for 10 weeks either: a) 1.8% of BW in dry matter (DM) per d (GAIN; n=7), b) 1.1% of BW in DM per d (MAINT; n=8) or c) 0.7% of BW in DM per d (LOSE; n=8). After 10 wk of treatment, heifers were ovariectomized 36–40 hr after the second injection of prostaglandin F2α analog (2 injections 11 d apart), and plasma and ovaries were collected. Heifers weighed 444 ± 13, 387 ± 8 and 349 ± 9 kg in the GAIN, MAINT and LOSE groups, respectively, at time of ovariectomy. Mean diameter of follicles ≥ 10 mm was greater (P<.05) for GAIN (15.6 mm) than for MAINT (11.0 mm) or LOSE (12.5 mm) heifers. Numbers of follicles and concentrations of IGF-I in plasma and FFL did not differ (P>.20) between LOSE, MAINT and GAIN heifers. Progesterone concentrations were greater (P<.05) in small and medium follicles of GAIN than MAINT or LOSE heifers, but were unaffected by diet in large follicles. Estradiol concentrations in FFL in small, medium and large follicles were unaffected (P>.20) by dietary treatment. However, estradiol concentrations in estrogen-active follicles were two-fold greater (P<.05) in GAIN heifers than either MAINT or LOSE heifers. In conclusion, IGF-I, of ovarian and(or) systemic origin, was unlikely the primary mediator of dietary alterations in ovarian follicular function of heifers in the present study.