Biomedical subjects

J G Gong

Publications and source records attributed to J G Gong.

At least 19 recordsLinked to original sources

PubMed2003

Mechanisms regulating follicular development and selection of the dominant follicle.

Reproductive function is an integrated process encompassing both extra-ovarian signals, such as gonadotrophins, and intrafollicular factors, such as locally produced growth factors. Initiation of primordial follicle growth and the early stages of folliculogenesis can occur without gonadotrophins. However, in vivo and in vitro studies indicate that FSH may stimulate the rate of preantral follicle growth and that it can take only 3 months for a primordial follicle to reach the ovulatory stage. Antral follicle development from 2 and 4 mm in diameter in sheep and cattle, respectively, is gonadotrophin dependent. During the oestrous cycle a transient increase in circulating FSH precedes the recruitment of a group of follicles. Recruited follicles are characterized by induction of expression of mRNAs encoding a range of steroidogenic enzymes, gonadotrophin receptors and local regulatory factors. As follicles continue to mature, there is a transfer of dependency from FSH to LH, which may be part of the mechanism involved in selection of follicles for continued growth. The mechanism of selection of the ovulatory follicle seems to be linked to the timing of mRNA expression encoding LHr and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in granulosa cells. Locally produced growth factors, such as the insulin-like growth factors (IGFs) and members of the transforming growth factor beta (TGFbeta) superfamily (inhibins, activins and bone morphogenetic proteins (BMPs)), work in concert with gonadotrophins throughout the follicular growth continuum. The roles of growth factors in follicular development and survival are dependent on gonadotrophin status and differentiation state, including morphology. In conclusion, it is the integration of extraovarian signals and intrafollicular factors that determine whether a follicle will continue to develop or be diverted into atretic pathways, as is the case for most of the follicles in monovulatory species, such as cattle.

Animals↗

PubMed2003

Interactions between nutrition and ovarian activity in cattle: physiological, cellular and molecular mechanisms.

The effects of acute changes in dietary intake on ovarian activity can be correlated with changes in circulating concentrations of metabolic hormones including insulin, insulin-like growth factor I (IGF-I), growth hormone and leptin. There is no corresponding change in circulating gonadotrophin concentrations and it is proposed that the dietary induced changes in ovarian activity, resulting from acute changes in dietary intake, are a result of direct actions of these metabolic hormones on the ovary. Changes in the peripheral concentrations of insulin, IGF-I and leptin were also associated with the initiation of a synchronized wave of follicle growth and it is hypothesized that oestrogen secreted by the developing follicle is involved in regulating the secretion of these metabolic hormones. At the cellular level, physiological concentrations of insulin and IGF-I interact to stimulate oestradiol production by granulosa cells. In contrast, leptin inhibits FSH-stimulated oestradiol production by granulosa cells and LH-stimulated androstenedione production by theca cells. At the molecular level, dietary energy intake affects the expression of mRNA encoding components of the ovarian IGF system and these changes can directly influence the bioavailability of intrafollicular IGF. This, in turn, can increase the sensitivity or response of follicles to FSH and is one mechanism through which nutrition can directly affect follicle recruitment. Dietary induced increases in intrafollicular IGF bioavailability also have a negative effect on oocyte quality, and diets that are optimal for follicle growth may not necessarily be optimal for oocyte maturation.

Animal Nutritional Physiological Phenomena↗

PubMed2002

The effect of increased dietary intake on superovulatory response to FSH in heifers.

We have previously shown that the number of ovarian follicles <4 mm in diameter can be increased by enhanced dietary intake in heifers. This study investigated the effect of the same dietary treatment on superovulatory response. The estrous cycles of 24 mature Hereford x Friesian heifers were synchronized by a standard progesterone plus prostaglandin protocol. The animals were fed with either 100% (group M, n = 12) or 200% (group 2M, n = 12) maintenance requirements for a 3-week period. Starting from day 4 of the synchronized estrous cycle, all the animals were superovulated using a standard 4-day FSH regime followed by an injection of GnRH analogue (GnRHa) to induce ovulation. Rectal ultrasound scanning was carried out to assess ovarian follicular populations at the start of FSH treatment and on the day of GnRHa injection, and to determine the number of corpora lutea 5 days after GnRHa injection. The body weight (BW) and body condition score (BCS) were recorded weekly and plasma samples were collected throughout the experimental period. There were no differences in either BW or BCS between two groups at the start of the experiment. The BW and BCS were maintained during the experiment in the group M, whilst animals in the group 2M showed a non-significant (P > 0.05) increase in BW and BCS. Circulating concentrations of insulin were significantly (P < 0.01) higher in heifers from the group 2M throughout the controlled feeding period. The group 2M had significantly (P < 0.05) more follicles 2-4 mm in diameter at the start of FSH treatment and more (P < 0.01) follicles >9 mm in diameter on the day of GnRHa injection, when compared with the group M. Similarly, 5 days after GnRHa injection there were significantly (P < 0.01) more corpora lutea in the group 2M (18.1+/-2.2) than in the group M (10.6+/-3.0). In addition, plasma progesterone concentrations following GnRHa injection were significantly (P < 0.01) higher in heifers from the group 2M. In conclusion, these results confirm that increased dietary intake can enhance the recruitment of ovarian follicles in heifers. This treatment may provide a valuable approach to improving superovulatory response in cattle.

Animals↗

PubMed2002

Influence of metabolic hormones and nutrition on ovarian follicle development in cattle: practical implications.

Nutrition has long been known to have a profound influence on reproductive performance of female cattle, but the underlying mechanism remains poorly understood. Whilst early investigations focused on the modulation of nutrition on hypothalamic-pituitary axis, more recent studies have tested the hypothesis that metabolic hormones as nutritional signals exert a direct effect at the ovarian level. In cattle, treatment with recombinant bovine somatotrophin (rGH) significantly increases the population of small ovarian follicles. This is associated with increases in circulating concentrations of insulin and insulin-like growth factor-I (IGF-I). Subsequent studies, both in vitro and in vivo, have highlighted the importance of IGF-I and/or insulin acting in synergy with FSH and LH. More recently, we demonstrated that feeding heifers with 200% maintenance requirements for a short period significantly increases circulating insulin concentrations and population of small ovarian follicles. Based on these findings, our recent work has aimed at addressing some practical problems in cattle production. Firstly, we showed that both rGH pretreatment and increased dietary intake significantly enhance the response to standard superovulatory regimes. Secondly, we have demonstrated that feeding a diet to increase circulating insulin concentrations during the early lactation can advance the first ovulation postpartum and increase conception rate to the first service in dairy cows. In summary, nutrition influences ovarian follicle development in cattle possibly through changes in metabolic hormones. These interactions can be manipulated to improve reproductive performance.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Steroidogenesis in bovine granulosa cells: the effect of short-term changes in dietary intake.

The nutritional status of a cow is a key factor in the regulation of both follicle growth and oocyte quality. In this study, the effect of diets designed to increase circulating insulin and insulin-like growth factor I (IGF-I) concentrations on steroid production by granulosa cells in vitro was examined to analyse the mechanisms through which these changes occur. Hereford x Friesian heifers (n = 24) were offered maintenance or twice maintenance diets during the experimental period (17 days). Circulating concentrations of FSH did not differ between the two dietary groups, whereas insulin and IGF-I concentrations showed significant diet x day of oestrous cycle interactions. Ovaries were collected on day 3 of the first follicle wave after synchronization of oestrus. Granulosa cells were isolated from small (1-4 mm) and medium-sized (4-8 mm) follicles and cultured in the presence of long R3-IGF-I or bFSH or both. After 4 days in culture, granulosa cells isolated from small follicles, but not medium-sized follicles, collected from cattle offered the twice maintenance diet secreted significantly higher (P < 0.05) amounts of oestradiol compared with granulosa cells collected from cattle offered the maintenance diet. The effect was apparent in either the presence or absence of FSH and long R3-IGF-I. This nutritional effect on aromatase activity in granulosa cells was not apparent after day 6 of culture. There was no effect of diet on progesterone production by granulosa cells after 4 or 6 days of culture. These results support the hypothesis that dietary-induced changes in circulating insulin and IGF-I concentrations have a direct effect on the steroidogenic potential of bovine granulosa cells from small follicles. The dietary-induced increases in aromatase activity in small follicles combined with the increased concentration of metabolic hormones are possible mechanisms through which short-term changes in nutrition may affect follicle dynamics.

Animal Nutritional Physiological Phenomena↗

PubMed2002

Effect of dietary-induced increases in circulating insulin concentrations during the early postpartum period on reproductive function in dairy cows.

Although it has become increasingly clear that fertility in modern dairy cattle is declining in association with increased milk yields, the underlying mechanism is poorly understood. The first ovulation post partum is delayed in dairy cows undergoing selection for genetic merit for milk yield in association with lower circulating insulin concentrations. The aim of this study was to investigate whether feeding a diet to increase circulating insulin concentrations can overcome this delay in the first ovulation post partum. The experiment was a 2 x 2 factorial design (n = 10 per group) involving diet and genetic merit for milk yield. The dietary treatment started on the day of calving and lasted for 50 days. Plasma samples were collected each day and ovarian ultra-sonography was performed three times a week during the experimental feeding period. Milk yield was recorded each day, and body weight and body condition score were determined each week. Milk samples were collected three times a week from day 50 to day 105 post partum, and reproductive performance data were recorded for all the cows as part of the routine farm practice. The dietary treatment induced significant differences in plasma insulin concentrations in both high and low genetic merit cows. Although high genetic merit cows produced more milk, lost more body weight and had lower body condition scores during the experiment, no significant effect of diet was observed on these measurements. The high insulin inducing diet increased the proportion of cows ovulating within 50 days of calving and reduced the intervals from calving to first ovulation, and tended to reduce the intervals from calving to first service and to conception. These fertility parameters were also more favourable in low than in high genetic merit cows, but no interaction between diet and genetic merit was observed for any of these parameters. Genetic merit, but not diet, also affected the number of services required per conception and the conception rate. In conclusion, these results have confirmed that genetic selection for high milk yield is associated with a decrease in reproductive performance in dairy cows. More importantly, this study has demonstrated that it is possible to alleviate this problem by nutritional manipulation.

Analysis of Variance↗

PubMed1999

The tyrosine kinase c-Abl regulates p73 in apoptotic response to cisplatin-induced DNA damage.

Cancer chemotherapeutic agents such as cisplatin exert their cytotoxic effect by inducing DNA damage and activating programmed cell death (apoptosis). The tumour-suppressor protein p53 is an important activator of apoptosis. Although p53-deficient cancer cells are less responsive to chemotherapy, their resistance is not complete, which suggests that other apoptotic pathways may exist. A p53-related gene, p73, which encodes several proteins as a result of alternative splicing, can also induce apoptosis. Here we show that the amount of p73 protein in the cell is increased by cisplatin. This induction of p73 is not seen in cells unable to carry out mismatch repair and in which the nuclear enzyme c-Abl tyrosine kinase is not activated by cisplatin. The half-life of p73 is prolonged by cisplatin and by co-expression with c-Abl tyrosine kinase; the apoptosis-inducing function of p73 is also enhanced by the c-Abl kinase. Mouse embryo fibroblasts deficient in mismatch repair or in c-Abl do not upregulate p73 and are more resistant to killing by cisplatin. Our results indicate that c-Abl and p73 are components of a mismatch-repair-dependent apoptosis pathway which contributes to cisplatin-induced cytotoxicity.

3T3 Cells↗

PubMed1999

Molecular mechanisms regulating follicular recruitment and selection.

Ovarian follicular growth and development is an integrated process encompassing both extraovarian signals, such as gonadotrophins and metabolic hormones, and intraovarian factors. Follicular development has been classified into gonadotrophin-independent and -dependent phases. In the latter, FSH provides the primary drive for follicular recruitment and LH is required for continued development of follicles to the preovulatory stage. A transient increase in circulating FSH precedes the recruitment of a group of follicles, and these recruited follicles are characterized by expression of mRNAs encoding P450scc and P450arom in granulosal cells. As follicles mature, there is a transfer of dependency from FSH to LH, which may be part of the mechanism(s) involved in selection of follicles for continued growth. Indeed, changes in the pattern of expression of mRNA for gonadotrophin receptors and steroid enzymes within follicular cells appear to be closely linked to changes in peripheral concentrations of gonadotrophins. The mechanism of selection of dominant follicles still requires clarification, but seems to be linked to the timing of mRNA expression encoding LHr and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in granulosal cells. Additional intraovarian systems, including the ovarian IGF and activin/inhibin systems, also exert a role. For example, it appears that the development of follicular dominance in cows is associated with the FSH-dependent inhibition of the expression of mRNA encoding insulin-like growth factor binding protein 2 (IGFBP-2) in granulosal cells. In conclusion, the integration of these endocrine signals and intraovarian factors within follicles determines whether follicles continue to develop and become dominant or are diverted into apoptotic pathways leading to atresia.

3-Hydroxysteroid Dehydrogenases↗

PubMed1997

Ultra-structural characteristics of bovine granulosa cells associated with maintenance of oestradiol production in vitro.

We investigated whether the maintenance of oestradiol production by bovine granulosa cells (GC) in vitro was related to GC ultra-structure, and studied the effects of inclusion of serum as a cell attachment factor on oestradiol secretion, cell morphology and ultra-structure. Bovine granulosa cells from medium-sized follicles (4-8 mm diameter), in a serum-free (SF) culture system, maintained oestradiol production for 6 days, whereas oestradiol secretion by cells cultured in serum-coated (SC) wells declined rapidly with time, in culture. SF cells formed clumps consisting of two types of cells. Cells within clumps presented a phenotype similar to GC in vivo, being spherical, tightly joined by extensive gap junctions and interdigitated pseudopodia/microvilli, had abundant rough and smooth endoplasmic reticulum (ER) and mitochondria with trabecular cristae. In contrast, cells cultured in either SC wells or in the flattened base of cell clumps from SF cultures were enlarged, containing less rough ER, had fewer mitochondria (which tended to be round) and contained endosome-like structures, morphological characteristics suggestive of early luteinisation.

Animals↗

PubMed1997

Enhancement of ovarian follicle development in heifers by treatment with recombinant bovine somatotrophin: a dose-response study.

Treatment with recombinant bovine somatotrophin (bST) can enhance the development of ovarian antral follicles in cattle. The underlying mechanism was examined further by performing a dose-response study to investigate the effects of bST on peripheral concentrations of somatotrophin, insulin-like growth factor I (IGF-I), insulin, FSH and LH, and ovarian follicle development. Twenty mature heifers were randomly divided into five groups and injected s.c. at 6 h intervals for 7 days with 25% of one of the following daily doses of bST: 0, 3.13, 6.25, 12.5 or 25.0 mg. Ovarian follicular dynamics were monitored by real-time ultrasonography. Blood samples were collected daily during the experiment, and every 15 min for 8 h on days 1 and 5 of bST treatment. Treatment with bST increased (P < 0.01) peripheral concentrations of somatotrophin in a dose-dependent manner. Serum concentrations of both IGF-I and insulin were significantly (P < 0.01) increased in all heifers given 12.5 or 25.0 mg bST per day. Peripheral concentrations of IGF-I and insulin in all animals in the group given 3.13 mg bST and two heifers in the group given 6.25 mg bST were not different from those in the control group, while concentrations in the other two heifers given 6.25 mg bST were significantly (P < 0.01) higher. The number of ovarian follicles < 5 mm in diameter was increased (P < 0.05) in response to bST, but only in heifers (n = 10) with significantly increased serum concentrations of IGF-I and insulin. There were no effects of treatment on peripheral concentrations of FSH, LH and progesterone, and on the numbers of follicles > 5 mm in diameter. In conclusion, this study has demonstrated in vivo that the effect of treatment with bST on ovarian follicle development appears to be mediated through an increase in circulating IGF-I or insulin concentrations, rather than via an alteration in the secretion of pituitary gonadotrophins or a direct effect of bST on ovarian follicles.

Animals↗

PubMed1997

The recruitment of ovarian follicles is enhanced by increased dietary intake in heifers.

The objective of this study was to determine whether dietary-induced changes in growth hormone (GH), insulin, and IGF-I alter the pattern of ovarian follicular development in heifers. Twenty-eight 2- to 3-yr-old Hereford-Friesian heifers were equally allocated (n = 7) to one of four dietary treatments: 1) Control (C) fed a maintenance diet as two meals per day; 2) twice maintenance (2M2) given as two meals per day; 3) twice maintenance (2M6) given as six meals per day; 4) feed-deprived (F) fed maintenance requirements as for C, changed to straw ad libitum for 3 d from a synchronized estrus. On d 4 (estrus = d 0) heifers were transferred to grass silage (ad libitum access) until the end of the experiment. Blood samples were collected hourly for 10 h on d 1 and 3 and daily for an additional 14 d. Follicular development was monitored daily by ultrasonography until d 14. The number of small follicles (< 4 mm) was increased (P < .05) by 37% on d 1 and 2 in 2M2 and 2M6 heifers, with no carryover effect of nutrition to the second follicular wave. Number of medium-sized (4 to 8 mm) and large (> 8 mm) follicles did not vary (P > .05) among treatments. The FSH concentrations were not different (P > .05) among treatments. Insulin concentrations were higher (P < .05) in 2M2 and 2M6 heifers than in C or F heifers, with no carryover after the diet was changed. Increase in number of small follicles was independent of changes in FSH and IGF-I, negatively associated with GH, but positively associated with circulating insulin. These results indicate that a short-term increase in nutritional plane can affect follicular recruitment in cycling heifers.

Animal Nutritional Physiological Phenomena↗

PubMed1996

Pretreatment with recombinant bovine somatotropin enhances the superovulatory response to FSH in heifers.

One of the primary limiting factors to superovulation and embryo transfer in cattle has been the large variability in response, both between and within animals. It appears that the primary source of this problem is the variability in the population of gonadotropin-responsive follicles present in ovaries at the time of stimulation. We have shown that treatment of heifers with recombinant bovine somatotropin (rbGH) increases the number of small antral follicles (2 to 5 mm) and, therefore, enhances the subsequent superovulatory response to eCG. To investigate further the potential of using this approach to improve superovulatory regimens in cattle, the effect of rbGH pretreatment on the response to pituitary FSH was studied. The estrous cycles of 16 heifers were synchronized using PGF2alpha. On Day 7 of the synchronized cycle, half of the animals were injected with 320 mg sustained-release formulated rbGH, while the other half received 10 ml saline. Five days later, all heifers were given a decreasing-dose regimen of twice daily injections of oFSH for 4 d, incorporating an injection of PGF2alpha with the fifth FSH treatment, to induce superovulation. All animals were artificially inseminated twice with semen from the same bull during estrus. Ova/embryos were recovered nonsurgically on Days 6 to 8 of the following estrous cycle, and the ovulation rate assessed on Day 9 by laparoscopy. Using the same animals as described above, the experiment was repeated twice, 3 and 6 mo later, with no laparoscopy in the third experiment. The animals were randomized both between experiments and for the day of ova/embryo collection. Pretreatment of heifers with rbGH significantly (P < 0.01) increased the number of ovulations, total number of ova/embryos recovered and the number of transferable embryos. The percentage of transferable embryos was significantly (P < 0.05) increased by rbGH pretreatment. In addition, the incidence (2/16) of follicular cysts with a poor ovulatory response (< 6 ovulations) for the rbGH-pretreated heifers was significantly lower (P < 0.05) when compared with the incidence (7/16) in the control animals. It is concluded that pretreatment with rbGH may provide a useful approach for improving superovulatory response in cattle.

Journal Article↗

PubMed1996

Suppression in the secretion of follicle-stimulating hormone and luteinizing hormone, and ovarian follicle development in heifers continuously infused with a gonadotropin-releasing hormone agonist.

A novel experimental model was developed in cattle to investigate the requirement for FSH and LH during ovarian follicle growth and development. On Day 5 of the estrous cycle, 7 heifers were each implanted with an osmotic minipump containing a GnRH agonist (GnRHa), Buserelin (release rate, 2.5 micrograms/h). Another 7 heifers served as controls. Each minipump was replaced 28 days later with a second pump, which was left in place for a further 20 days. Blood samples were collected daily throughout the experimental period, and frequent samples were also collected on both days of minipump insertion and at 10 days after insertion of the second pump. The ovaries of all heifers were scanned daily by real-time ultrasonography to monitor follicular dynamics. All controls displayed 2 or 3 waves of FSH and follicular development per estrous cycle during the experiment. Insertion of the first minipump produced a large LH and FSH surge and induced ovulation in all 7 animals. Within 8 days of the start of treatment, serum LH concentrations fell to basal levels; they then remained constant at this level throughout the infusion period, only beginning to recover 4-5 days after the termination of infusion. After the initial increase, FSH returned to basal levels before showing a normal wave that was coincident with the emergence, growth, and regression of a dominant follicle. However, despite the peak levels of FSH, dominant follicles from the next wave failed to grow beyond 7-9 mm; they remained at this size for 3 wk until 3-4 days after insertion of the second minipump, when FSH fell precipitously to reach low levels that were maintained throughout the remainder of the infusion. After this fall in FSH concentrations, these follicles regressed rapidly, and no antral follicles > 4 mm were detected until after the termination of treatment. Thereafter, FSH concentrations increased significantly; the increase was accompanied by the emergence of a follicular wave and development of a dominant follicle, with estrus observed 8-11 days later. In conclusion, this study has demonstrated clearly that in cattle the early stages of follicle development (< or = 4 mm) are not dependent on acute support by gonadotropins. However, FSH is required for further growth of follicles up to 9 mm, while LH pulses are indispensable for follicle development beyond 9 mm in diameter. The model developed in this study should be valuable for studying the control of ovarian follicle development and atresia in vivo.

Animals↗

PubMed1995

Effects of chronic treatment with a gonadotrophin-releasing hormone agonist on peripheral concentrations of FSH and LH, and ovarian function in heifers.

The effect of chronic treatment with a gonadotrophin-releasing hormone agonist (GnRHa) on ovarian function in cattle was investigated by injecting heifers i.m. twice a day with saline, 5 micrograms GnRHa (Buserelin) or 10 micrograms GnRHa (n = 7) for 21 days. Blood samples were taken twice a day during the treatment period, and then three times a day for 7 days and once daily for a further 4 days. Frequent samples were also collected on day 1, day 10 and day 21 of treatment. The ovaries of all heifers were examined daily using real-time ultrasonography throughout the experimental period. No significant differences in the response were observed between two doses of GnRHa. The first GnRHa injection produced a large LH and FSH surge and this acute response was still present by day 21 of treatment, but both the magnitude and duration of response were significantly attenuated (P < 0.01). After an initial increase, LH returned to the basal concentration, which was maintained until the termination of treatment, when concentrations increased significantly, with a preovulatory surge occurring approximately 6 days later. Peripheral FSH concentrations during the oestrous cycle in control animals displayed a pattern of three waves, each of which closely preceded a wave of follicular development. Concentrations of FSH in GnRHa-treated heifers showed a normal pattern for the first wave after the start of treatment. During the next wave, concentrations increased and remained at the peak values until about 4 days after the end of treatment. An additional ovulation was induced in 11 of 14 GnRHa-treated heifers within 2-3 days of the start of treatment, and a significant (P < 0.05) increase in serum progesterone concentrations was detected 2 days later. All GnRHa-treated heifers then showed a normal follicular wave, with the development and regression of a dominant follicle. The dominant follicles from the next wave grew to only 7-9 mm in diameter and remained at this size until the end of treatment, when they resumed growth, ovulated approximately 7 days later and formed corpora lutea. We conclude that chronic treatment of heifers with GnRHa for 3 weeks suppresses pulsatile secretion of LH and blocks the development of dominant follicles beyond 9 mm in diameter, preventing the preovulatory LH surge and ovulation. However, GnRHa did not suppress the secretion of FSH within the 3 week treatment period. The maintenance of the dominant follicles for an extended period should provide an ideal model to study the control of follicular atresia in cattle in vivo.

Animals↗

PubMed1994

Effects of recombinant bovine somatotrophin, insulin-like growth factor-I and insulin on bovine granulosa cell steroidogenesis in vitro.

Our previous studies have demonstrated that physiological concentrations of metabolic hormones, including recombinant bovine somatotrophin (BST), insulin-like growth factor-I (IGF-I) and insulin, can significantly stimulate the proliferation of bovine granulosa cells cultured under serum-free conditions. In this study we investigated the effects of these factors on bovine granulosa cell steroidogenesis using the same culture system. Bovine granulosa cells were obtained from antral follicles classified into three size classes: small, < 5 mm; medium-sized, 5-10 mm and large, > 10 mm in diameter. Whilst not affecting steroidogenesis by granulosa cells from small and medium-sized follicles, BST (10-1000 ng/ml) stimulated the secretion of both oestradiol and progesterone by granulosa cells from large follicles in a dose-dependent manner. Insulin (1-1000 ng/ml) and IGF-I (10-1000 ng/ml) stimulated the secretion of oestradiol and progesterone by granulosa cells from all three size categories of follicles in a dose-dependent manner. FSH (200 ng/ml) alone increased progesterone secretion by granulosa cells from all three size classes of follicles, but had no effect on oestradiol secretion by granulosa cells. Both IGF-I (200 ng/ml) and insulin (30 ng/ml) acted in synergy with FSH (200 ng/ml) to stimulate steroidogenesis by granulosa cells from all three size categories of follicles, but no such interaction was observed between BST (50 ng/ml) and FSH (200 ng/ml). In conclusion, BST, IGF-I and insulin significantly influence the steroidogenic activity of bovine granulosa cells cultured under serum-free conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effect of recombinant bovine somatotropin on the superovulatory response to pregnant mare serum gonadotropin in heifers.

Treatment of mature heifers with recombinant bovine somatotropin (BST) increases the number of ovarian follicles of 2-5 mm in diameter. This study was carried out to investigate whether the increase in the number of small follicles induced by BST treatment can enhance the superovulatory response. In the first experiment, 24 heifers were assigned, in a randomized block design, to four treatment groups: 1) control; 2) BST; 3) pregnant mare serum gonadotropin (PMSG); 4) BST+PMSG. On Day 7 of the estrous cycle, animals in groups 2 and 4 received injections of 320 mg BST (in a sustained release formulation), while heifers in groups 1 and 3 received 10 ml saline. Five days later heifers in groups 3 and 4 were treated with a single dose of 2000 IU PMSG to induce superovulation. Embryos were recovered nonsurgically on Days 6-8 of the following cycle, and all heifers underwent laparoscopy on Day 9 to assess ovulation rate. In a second experiment, 24 heifers were assigned randomly to four treatment groups: 1) PMSG (1000 IU); 2) BST (320 mg) + PMSG (1000 IU); 3) PMSG (2000 IU); 4) BST (320 mg) + PMSG (2000 IU), and then treated as for experiment I. In both experiments, all heifers were scanned daily using real-time ultrasound from the day before BST injection until the day of ovulation to monitor dynamics of ovarian follicular growth and development, and blood samples were collected daily throughout the experimental period for measurement of peripheral progesterone, estradiol-17 beta, growth hormone (GH), and insulin-like growth factor-I (IGF-I).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

The effect of recombinant bovine somatotrophin on ovarian follicular growth and development in heifers.

The effects of recombinant bovine somatotrophin (BST) on the dynamics of ovarian follicular growth and development and peripheral insulin concentrations were investigated. Initially, studies were carried out in a population of Hereford x Friesian heifers to validate the ultrasound technique. In the first experiment, 12 heifers were injected daily with either 25 mg BST or vehicle for two oestrous cycles, and the effects on follicular dynamics and peripheral insulin were determined. In a second experiment, 12 heifers were given a single injection of 10 ml saline or 320 mg BST in a sustained-release formulation to examine the temporal relationships between growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin and the number of follicles. The validation studies demonstrated that small follicles (< 5 mm in diameter) could be clearly detected by real-time ultrasound, and that 75% (9 of 12) of heifers showed three waves of dominant follicle development during the oestrous cycle, whereas the remainder had only two waves. The changes in the numbers of follicles of the three size categories (< 5 mm, small; 5-10 mm, medium-sized and > 10 mm, large) also displayed a wave pattern similar to that of the dominant follicle, with a marked reduction in the number of subordinate follicles as the dominant follicle grew and reached its maximum size. In Expt 1, BST treatment increased the number of small follicles and caused a rise in peripheral insulin concentrations (P < 0.01) throughout the treatment period.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Effects of recombinant bovine somatotrophin, insulin-like growth factor-I and insulin on the proliferation of bovine granulosa cells in vitro.

Treatment of heifers with recombinant bovine somatotrophin (BST) significantly increases the population of small ovarian follicles and peripheral concentrations of somatotrophin, insulin-like growth factor-I (IGF-I) and insulin. To investigate the possible mechanism(s) involved in the action of BST on ovarian follicles, the effects of BST, IGF-I and insulin, given alone or in combination with either FSH or LH, on the proliferation of bovine granulosa cells in vitro were examined using a serum-free culture system. Bovine granulosa cells were obtained from antral follicles classified into three size categories according to diameter: small < 5 mm; medium-sized 5-10 mm and large > 10 mm. The proliferation of granulosa cells was assessed by the incorporation of [3H]thymidine into the cultured cells. Both FSH and LH (1-1000 ng/ml) inhibited the proliferation of bovine granulosa cells obtained from all three size classes of follicles in a dose-dependent manner. BST, at doses ranging from 1 to 1000 ng/ml, had no effect on the proliferation of granulosa cells from small and medium-sized follicles, but inhibited the division of granulosa cells from large follicles in a dose-dependent manner. Treatment with either IGF-I (10-3000 ng/ml) or insulin (0.5-1000 ng/ml) stimulated, in a dose-dependent manner, the proliferation of granulosa cells obtained from all three size categories of follicles. No synergistic interaction between BST (30 ng/ml) and either FSH (50 ng/ml) or LH (5 ng/ml) was observed in granulosa cells from all three size classes of follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗