Plasma insulin-like growth factor-I concentrations increase during the estrous phase in goats

Insulin-Like Growth Factor 1 Increases GABAergic Neurotransmission to GnRH Neurons via Suppressing the Retrograde Tonic Endocannabinoid Signaling Pathway in Mice

INTRODUCTION

Hypophysiotropic gonadotropin-releasing hormone (GnRH) neurons orchestrate various physiological events that control the onset of puberty. Previous studies showed that insulin-like growth factor 1 (IGF-1) induces the secretion of GnRH and accelerates the onset of puberty, suggesting a regulatory role of this hormone upon GnRH neurons.

METHODS

To reveal responsiveness of GnRH neurons to IGF-1 and elucidate molecular pathways acting downstream to the IGF-1 receptor (IGF-1R), in vitro electrophysiological experiments were carried out on GnRH-GFP neurons in acute brain slices from prepubertal (23-29 days) and pubertal (50 days) male mice.

RESULTS

Administration of IGF-1 (13 nM) significantly increased the firing rate and frequency of spontaneous postsynaptic currents and that of excitatory GABAergic miniature postsynaptic currents (mPSCs). No GABAergic mPSCs were induced by IGF-1 in the presence of the GABAA-R blocker picrotoxin. The increase in the mPSC frequency was prevented by the use of the IGF-1R antagonist, JB1 (1 µM), or the intracellularly applied PI3K blocker (LY294002, 50 µM), showing involvement of IGF-1R and PI3K in the mechanism. Blockade of the transient receptor potential vanilloid 1, an element of the tonic retrograde endocannabinoid machinery, by AMG9810 (10 µM) or antagonizing the cannabinoid receptor type-1 by AM251 (1 µM) abolished the effect.

DISCUSSION/CONCLUSION

These findings indicate that IGF-1 arrests the tonic retrograde endocannabinoid pathway in GnRH neurons, and this disinhibition increases the release of GABA from presynaptic terminals that, in turn, activates GnRH neurons leading to the fine-tuning of the hypothalamo-pituitary-gonadal axis.

Plasma IGF1 and 17β-Estradiol Concentrations During the Follicular Wave in Llamas

The aim of this study was to characterize the temporal association between follicular waves and circulating concentrations of 17β-estradiol (E2) and IGF1 in llamas. Follicular waves could be clearly divided in three phases: growth, plateau and regression; with a mean duration of 18.8 ± 0.32 days. All follicular waves showed overlapping, so that as one dominant follicle was regressing, another one was growing. E2 plasma concentration showed a wavelike pattern, similar to that followed by the dominant follicle; reaching its maximum concentration at the end of the growth phase and decreasing at the end of the plateau phase. IGF1 also showed variations during the follicular wave. It tended to increase during the growth phase and decreased toward Days 14 and 16. IGF1 reached its maximum concentration before E2 did (5 ± 0.8 vs. 7.2 ± 0.5 days after wave emergence) and before the maximum follicular diameter was attained (10.2 ± 0.46 days after wave emergence). Both hormones started to rise again in coincidence with the development of a new follicular wave. The observed profiles allow to suggest that IGF1 could have a role on folliculogenesis and ovarian steroideogenesis in llamas, as reported for other species.

Relationship between insulin-like growth factor-1 (IGF-1) concentrations and body trait measurements and climatic factors in prepubertal goat kids

This study aimed to investigate relations between insulin-like growth factor-1 (IGF-1) concentrations and some body trait measurements (body weight, withers height, rump height, body length, chest depth, chest width, chest girth and cannon bone circumference) and climatic factors in prepubertal male and female White (75 % Saanen and 25 % Kilis goat) and Angora goat kids. For this purpose, blood samples were regularly taken from the vena jugularis, and body trait measurements were regularly carried out (every 15 d for 5 months) on each kid. The IGF-1 analysis on the blood serum was performed using the enzyme immunoassay (EIA) method. Climatic values and the length of the photoperiod were obtained from the Turkish State Meteorological Service for the experimental period, and the temperature-humidity index (THI) was calculated using these values. Statistical analysis showed that the IGF-1 concentrations were higher ( P < 0.05 ) in female White goat kids. Furthermore, differences in IGF-1 concentrations were found ( P < 0.05 ) between periods and between the gender groups for both the White and the Angora goat kids. Moreover, the difference between the IGF-1 concentrations between genders was higher ( P < 0.05 ) in White goat kids. Additionally, positive and significant correlations were found between IGF-1 concentrations and some body trait measurements in prepubertal kids, except for in female White goat kids. In summary, it was found that there was a significant relationship between IGF-1 concentrations and growth characteristics of the goat kids. Furthermore, IGF-1 concentrations in the goat kids were significantly influenced by climatic factors such as photoperiod, temperature and the temperature-humidity index, with the release of IGF-1 increasing due to increases in the photoperiod and the environmental temperature.

The onset of puberty in Cameroon Dwarf goats kept as pets in northwestern Croatia

The aim of this study was to determine onset of puberty in Cameroon Dwarf goats (CDGs) kept as pets in northwestern Croatia by determining progesterone (PGS) and insulin-like growth factor-I (IGF-I) levels in the blood by RIA methods. The first cyclic ovarian activity was estimated according to hormone profiles as determined in CDG in a moderate climate environment. Sixteen female CDG kids were kept in stables with access to pasture which provided space for exercise. The goat kids born in winter (December-January-February), spring (March-April-May), summer (June-July-August) and autumn (September-October-November) were assigned into four groups according to the season of the year of birth (n = 4 in each group). At 75 days of age at the initiation of the study, they weighed between 3.2 and 5.1 kg (4.24 ± 0.53 kg). The onset of ovulatory activity was determined by PGS and IGF-I serum concentrations every 10 days starting from 75 days to 155 days of age. The onset of puberty in CDG kids occurred on average at 141.15 ± 2.66 days of age, but varied depending on the season of birth. All CDG kids born during summer were in heat by 155 days of age. In the other groups (kids born in autumn, winter or spring), one goat in each group was not in heat. Changes in blood serum PGS and IGF-I concentrations during prepubertal and pubertal periods could aid in the evaluation of reproductive status and determination of the onset of puberty in CDG during all seasons of the year in a moderate climate region.

Effects of hypothalamic dopamine on growth hormone-releasing hormone-induced growth hormone secretion and thyrotropin-releasing hormone-induced prolactin secretion in goats

The aim of the present study was to clarify the effects of hypothalamic dopamine (DA) on the secretion of growth hormone (GH) in goats. The GH-releasing response to an intravenous (i.v.) injection of GH-releasing hormone (GHRH, 0.25 μg/kg body weight (BW)) was examined after treatments to augment central DA using carbidopa (carbi, 1 mg/kg BW) and L-dopa (1 mg/kg BW) in male and female goats under a 16-h photoperiod (16 h light, 8 h dark) condition. GHRH significantly and rapidly stimulated the release of GH after its i.v. administration to goats (P < 0.05). The carbi and L-dopa treatments completely suppressed GH-releasing responses to GHRH in both male and female goats (P < 0.05). The prolactin (PRL)-releasing response to an i.v. injection of thyrotropin-releasing hormone (TRH, 1 μg/kg BW) was additionally examined in male goats in this study to confirm modifications to central DA concentrations. The treatments with carbi and L-dopa significantly reduced TRH-induced PRL release in goats (P < 0.05). These results demonstrated that hypothalamic DA was involved in the regulatory mechanisms of GH, as well as PRL secretion in goats.

Insulin-like growth factor-1 promotes wound healing in estrogen-deprived mice: new insights into cutaneous IGF-1R/ERα cross talk

Although it is understood that endogenous IGF-1 is involved in the wound repair process, the effects of exogenous IGF-1 administration on wound repair remain largely unclear. In addition, the signaling links between IGF-1 receptor (IGF-1R) and estrogen receptors (ERs), which have been elucidated in other systems, have yet to be explored in the context of skin repair. In this study, we show that locally administered IGF-1 promotes wound repair in an estrogen-deprived animal model, the ovariectomized (Ovx) mouse, principally by dampening the local inflammatory response and promoting re-epithelialization. Using specific IGF-1R and ER antagonists in vivo, we reveal that IGF-1-mediated effects on re-epithelialization are directly mediated by IGF-1R. By contrast, the anti-inflammatory effects of IGF-1 are predominantly via the ERs, in particular ERα. Crucially, in ERα-null mice, IGF-1 fails to promote healing, and local inflammation is increased. Our findings illustrate the complex interactions between IGF-1 and estrogen in skin. The fact that IGF-1 may compensate for estrogen deficiency in wound repair, and potentially other contexts, is an important consideration for the treatment of postmenopausal pathology.

Progesterone and insulin-like growth factor I levels in blood of Boer goats during puerperium out-of-season in a mild climate region

The aims of this study were to compare insulin-like growth factor-I (IGF-I) and progesterone concentrations as indicators of cycle activity in the blood of Boer goats during puerperium out-of-season in mild climate conditions and to investigate the influence of parity and litter size on the concentration of IGF-I and progesterone in serum during the study period. Twenty Boer (8 primiparous and 12 pluriparous) goats were examined in this study. Blood samples were taken every 4 days starting on the 3rd day and up to the 40th day of puerperium. IGF-I and progesterone (P4) blood levels were determined using radio immune assay (RIA). Results indicated cyclic ovarian activity outside the breeding season in 18 of 20 Boer goats. IGF-I levels in blood sera followed oestrus and cyclic ovarian activity. IGF-I concentrations correlated significantly with P4 concentrations. The IGF-I peak preceded the P4 peak by approximately 8 days in cycling goats. IGF-I and P4 blood levels were not influenced by parity or litter size. Changes in blood serum P4 and IGF-I concentrations levels during puerperal period can assist in the evaluation of reproductive status of goats.

The role of endocrine insulin-like growth factor-I (IGF-I) in female bovine reproduction

Insulin-like growth factor-I (IGF-I) plays a pivotal role in cattle fertility, acting as a monitoring signal that allows reproductive events to occur when nutritional conditions for successful reproduction are reached. However, endocrine IGF-I is not a predictor of reproductive events, but rather an indirect estimator of the suitability of the animal to achieve the reproductive event in question. Although measuring circulating IGF-I concentrations might not have any clinical application in the cattle industry, endocrine IGF-I screening will continue to be important for the study of interactions between nutrition and reproduction. In addition, endocrine IGF-I screening could be used as an ancillary test for the selection of cattle for high reproductive potential, especially in herds of high genetic merit for milk production, in which a decline in fertility has been identified.

Relations between Plasma IGF-I Concentrations during Treatment with CIDR-based or Ovsynch Protocol for Timed AI and Conception in Early Postpartum Japanese Black Beef Cows

We examined the relations between plasma insulin-like growth factor (IGF) -I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception and plasma steroid concentrations in early postpartum Japanese Black beef cows. Cows in the control group (Ovsynch; n = 21) underwent Ovsynch protocol (GnRH analogue on Day 0, PGF(2alpha) analogue on Day 7, and GnRH analogue on Day 9), with AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the Ovsynch+CIDR group (n = 22) received Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Cows in the further treatment group (EB+CIDR+GnRH; n = 22) received 2 mg of estradiol benzoate (EB) on Day 0 in lieu of the first GnRH treatment, followed by the same treatment as in the Ovsynch+CIDR protocol. Plasma IGF-I concentrations were determined on Days -7, 0, 7, 9 and 17. Conception rates were improved in the CIDR-combined groups (both CIDR-treated groups were combined) relative to Ovsynch group (P < 0.05) for cows with low IGF-I concentrations (<1,000 ng/ml) on Days -7, 0, and 7, but improved conception rate produced by the CIDR-based protocols did not occur in cows with a high IGF-I concentration (> or =1,000 ng/ml). Plasma estradiol-17beta concentrations increased from Day 0 to 7 (P < 0.05) and were unchanged from Day 7 to 9 in the Ovsynch group with low IGF-I concentrations on Day 0, while they were unchanged from Day 0 to 7 and increased from Day 7 to 9 (P < 0.05) in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group. Plasma progesterone concentrations in the Ovsynch group with low IGF-I concentrations on Day 0 were higher on Day 14 than in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group (P < 0.05). In conclusion, CIDR-based protocols may improve conception relative to Ovsynch in early postpartum beef cows with lower plasma IGF-I concentrations at the start of the protocols. This improvement is probably due to prevention of premature increases of estradiol-17beta and progesterone concentrations, which occurred in cows with low IGF-I concentrations treated with Ovsynch, by the CIDR treatment.

Endocrine Profiles and Growth Patterns of Cloned Goats

Two groups of goats produced by fetal somatic cell nuclear transfer (NT) were monitored to evaluate the similarities in growth patterns among cloned animals. Clone group I consisted of five Toggenburg females cloned from the same transgenic cell line and born to different recipient does. Clone group II consisted of two Saanen does born as twins to a single recipient female from a second transgenic cell line. Each cell line was constructed with a transgene (different for each clone group) that would express, producing a protein product in the milk during lactation of the does. Weight, hip height, and circulating levels of growth-related hormones were monitored at weekly and monthly intervals for comparison within the clone groups. A contemporary group (group III) consisting of seven crossbred does of similar ages and weights was also monitored for baseline endocrine values during the study. Serum samples from all groups were analyzed for growth hormone (GH), insulin-like growth factor I (IGF-I), triiodothyronine (T3), thyroxine (T4), and insulin via standard laboratory radioimmunoassay procedures. The averaged standard deviation from the mean was used to evaluate similarities within the groups of cloned does and the does in the contemporary group. The does in clone group II were less variable than the goats in clone group I for weight and hip height. This was perhaps due to a recipient effect. The two groups of cloned females were less variable than the contemporary group for circulating IGF-I and T4 concentrations. In contrast, the two groups of cloned does had at least one cloned group that was more variable than the contemporary group for GH, T3, and insulin. The animal variation, measured by the average standard deviation from the mean, of the cloned does is possibly due to environmental effects encountered in utero and/or in the postnatal period, as well as possible mitochondrial DNA differences between the cell line and donor oocytes used for NT. The variation among cloned does in this study indicates that the use of somatic cell NT to reproduce identical phenotypes may not succeed in all situations.

Origin of plasma insulin-like growth factor-I (IGF-I) during estrus in goats

The objective of this study was to clarify the origin of the increase in plasma insulin-like growth factor-I (IGF-I) during estrus in goats. Focusing on the uterus, the effect of estradiol-17 beta (E2) on the secretion of IGF-I was examined using ovariectomized and hysterectomized animals. A single 5 microg/kg BW of E2 was injected intramuscularly into ovariectomized and hysterectomized goats for 3 consecutive days, and plasma IGF-I concentrations in the two groups were compared. The concentrations of IGF-I rose after the treatments in both groups. The concentrations were significantly higher from 3 to 8 days after the treatment than before the treatment in ovariectomized goats (P<0.05), and from 1 to 3 days after the treatment than before in hysterectomized goats (P<0.05). Thus higher concentrations of plasma IGF-I tended to last longer in ovariectomized than hysterectomized goats. The area under the IGF-I response curve for the 8-day period after the first injection of E2 tended to be greater in ovariectomized than in hysterectomized goats. The results show that E2 increases plasma IGF-I concentrations in goats, and suggest that E2-stimulated IGF-I in plasma may originate mainly from the uterus.

In vivo imaging of transcriptionally active estrogen receptors

Through intracellular receptors, estrogens control growth, differentiation and function of not only reproductive tissues, but also other systems. Estrogen receptors are ligand-dependent transcription factors whose activity is modulated either by estrogens, or by alternative intracellular signaling pathways downstream of growth factors and neurotransmitters. To determine the dynamics of estrogen receptor activity and the dependence of estrogen receptor on 17beta-estradiol in vivo, we generated a transgenic mouse that expresses a luciferase reporter gene under the control of activated estrogen receptors. As expected, luciferase activity, monitored with a cooled charged coupled device camera, paralleled circulating estrogen levels in reproductive tissues and in liver, indicating that the peak transcriptional activity of the estrogen receptor occurred at proestrus. In contrast, in tissues such as bone and brain, the peak activity of estrogen receptors was observed at diestrus. These tissue-specific responses are masked when mice undergo conventional hormone treatment. We also demonstrate that estrogen receptors are active in immature mice before gonadal production of sex hormones as well as in ovariectomized adult mice. These findings emphasize the importance of hormone-independent activation of the estrogen receptor, and have implications for the therapeutic use of estrogens, such as hormone replacement therapy.

Relationship among insulin-like growth factor-I, blood metabolites and postpartum ovarian function in dairy cows

The relationship among nutritional status, systemic insulin-like growth factor-I (IGF-I) and ovarian function early postpartum were investigated. A total of 27 Holstein-Friesian cows, 10 that cycled normally within 20 days postpartum, 5 diagnosed with follicular cysts, 8 with persistent corpus luteum (CL) after the first ovulation postpartum and 4 with inactive ovaries were used for the study. Blood samples were collected 1-3 times per week, for 60 days pre- and postpartum, for IGF-I, progesterone, estradiol, free fatty acids (FFA), blood urea nitrogen (BUN), and aspartate aminotransferase (AST) determination. Inactive ovary and cystic cows had a higher body condition score before calving and lost more condition than normal or persistent CL cows. Immediately postpartum, IGF-I levels were higher and rose sharply in cows that cycled normally than in cystic, inactive ovary or persistent CL cows. At calving and early postpartum, FFA was higher in inactive ovary and cystic than in normal and persistent CL cows. There was a significant strong positive relationship between IGF-I and BUN, and strong negative relationships between IGF-I and FFA and AST in all groups. There was a positive relationship between serum IGF-I and estradiol in normal cystic and inactive ovary cows. This study found that overconditioned cows during the dry period or at calving, lost more body condition postpartum. These cows also had a deeper and longer period of negative energy balance (NEB), poor liver function and low circulating IGF-I concentrations early postpartum. Such cows were likely to have poor reproductive function as seen in development of cystic ovaries, persistent CL and inactive ovary. Changes in serum IGF-I early postpartum may help predict both nutritional and reproductive status in dairy cattle.

Insulin-like growth factor-I as a possible hormonal mediator of nutritional regulation of reproduction in cattle

The current review aims to establish insulin-like growth factor-1 (IGF-I) as the factor that signals nutritional status to the reproductive axis, and show that assessment of IGF-I in blood early postpartum during the negative energy balance (NEB) period could be used to predict both nutritional and reproductive status in dairy cattle. The review also explores the effect of nutritional status on circulating IGF-I concentrations and the endocrine role of IGF-I on the reproductive axis. IGF-I plays an important role in gonadotropin-induced folliculogenesis, ovarian steroidogenesis and corpus luteum (CL) function. It also modulates pituitary and hypothalamus function. IGF-I clearly has an endocrine role on the reproductive axis. Severe under nutrition significantly reduces plasma IGF-I concentrations. During the critical period of NEB in high yielding dairy cattle early postpartum, IGF-I concentrations are low in blood and its levels are positively correlated to energy status and reproductive function during this period. Changes in circulating IGF-I immediately postpartum may help predict both nutritional and reproductive status in dairy cattle. IGF-I is therefore one of the long sought factors that signal nutritional status to the reproductive axis.

Insulin-like growth factor I enhances gonadotropin-releasing hormone-stimulated luteinizing hormone release from bovine anterior pituitary cells

The role of insulin-like growth factor I (IGF-I) in the release of luteinizing hormone (LH) is unclear in ruminants. In the present study, the effects of IGF-I on the release of LH stimulated by gonadotropin-releasing hormone (GnRH) were examined in primary cultures of bovine anterior pituitary (AP) cells, and the interaction between estradiol-17beta (E(2)) and IGF-I was characterized. GnRH(100nM)-stimulated LH release from the cultured cells was increased (P<0.05) 12, 24 and 36h after addition of IGF-I (250ng/ml), with a maximum at 12h (48.4ng/ml media versus 35.4ng/ml media in controls). IGF-I at concentrations of 25, 250 and 500ng/ml increased the release by 18.7, 24.2 and 28.9%, respectively (P<0.05), when compared with controls (37.2ng/ml media). E(2) (10nM), IGF-I (250ng/ml) and combined treatment of E(2) plus IGF-I also induced significant increases in LH release (P<0.05). The amounts of LH release after treatment with E(2) alone was 37.3% greater than with IGF-I alone (39.0ng/ml media versus 28.4ng/ml media) (P<0.05). When E(2) and IGF-I were added together (45.6ng/ml media), the release of LH was significantly greater than with either E(2) alone or IGF-I alone (P<0.05). E(2) (10nM) significantly (P<0.05) increased the amount of GnRH bound to the cells by 51.6% when compared with controls, however, IGF-I (250ng/ml) failed to increase GnRH binding. These results show that IGF-I enhances GnRH-stimulated LH release without changing the number of GnRH receptors in cattle, and IGF-I interacts with E(2) to increase the response to GnRH.