The infusion of glucose in ewes during the luteal phase increases the number of follicles but reduces oestradiol production and some correlates of metabolic function in the large follicles

Emerging Perspectives on the Impact of Diabetes Mellitus and Anti-Diabetic Drugs on Premenstrual Syndrome. A Narrative Review

Diabetes mellitus (DM) and premenstrual syndrome (PMS) are global health challenges. Both disorders are often linked to a range of physical and psychological symptoms that significantly impact the quality of life of many women. Yet, the exact relation between DM and PMS is not clear, and the management of both conditions poses a considerable challenge. In this review, we aimed to investigate the interplay between DM, anti-diabetic drugs, and the different theories and symptoms of PMS. Female sex hormones are implicated in the pathophysiology of PMS and can also impair blood glucose control. In addition, patients with diabetes face a higher susceptibility to anxiety and depression disorders, with a significant number of patients experiencing symptoms such as fatigue and difficulty concentrating, which are reported in patients with PMS as well. Complications related to diabetic medications, such as hypoglycemia (with sulfonylurea) and fluid retention (with thiazolidinediones) may also mediate PMS-like symptoms. DM can, in addition, disturb the normal gut microbiota (GM), with a consequent loss of beneficial GM metabolites that guard against PMS, particularly the short-chain fatty acids and serotonin. Among the several available anti-diabetic drugs, those (1) with an anti-inflammatory potential, (2) that can preserve the beneficial GM, and (3) possessing a lower risk for hypoglycemia, might have a favorable outcome in PMS women. Yet, well-designed clinical trials are needed to investigate the anti-diabetic drug(s) of choice for patients with diabetes and PMS.

Dietary n-3 PUFA augments pre-ovulatory follicle turnover and prolificacy in well-fed ewes

The present study evaluated the effect of dietary supplementation with n-3 polyunsaturated fatty acids (PUFA) on preovulatory follicle (POF) turnover, prolificacy, and endocrine and metabolic milieu in Malpura sheep. Fifty cyclic ewes with 3-3.5 body condition scores on a five-point scale were allocated equally to two groups (n = 25) following estrus synchronization and were supplemented with 0.6 mL/kg body weight of n-3 PUFA-rich fish oil (FO) or palm oil (PO) as control, for 60 d following an acclimatization period of 7 d. All ewes were mated with sexually active rams at the end of the supplementation period. On ultrasonographic ovarian scanning at the last fourth estrus, the mean number of POFs was 77.8% greater (P < 0.01) in FO ewes than in the PO ewes. The proportion of ewes with multiple ovulations two months after the beginning of supplementation was 56% in the FO group as compared to 8% in the PO group. The number of fetuses was 46% higher (P < 0.01) in the FO than in the PO ewes at d 45 of gestation. At lambing, the twinning percent in the FO ewes was three times greater than in the PO ewes (27.3 vs. 9.1%). Plasma cholesterol, estradiol, and insulin concentrations were lower (P < 0.01) in ewes fed with FO than those offered PO group at the end of the feeding period. It was concluded that the dietary supplementation of n-3 PUFA-rich FO in well-fed Malpura ewes improved the number of follicles and ovulation rate which led to an increased prolificacy, accompanied by a reduction of plasma cholesterols, estradiol, and insulin.

Long Non-Coding RNA GDAR Regulates Ovine Granulosa Cells Apoptosis by Affecting the Expression of Apoptosis-Related Genes

Short-term dietary supplementation of ewes during the luteal phase can increase fertility, most probably by stimulating glucose uptake by the follicles. However, the molecular mechanism of glucose regulation of follicular development has not yet been clarified, especially the further study of long non-coding RNA (lncRNA) in determining fertility during follicular development. We generated granulosa cell (GC) models of different doses of glucose (0, 2.1, 4.2, 8.4, 16.8 and 33.6 mM), and observed that the highest cell viability was recorded in the 8.4 mM group and the highest apoptosis rates were recorded in the 33.6 mM group. Therefore, a control group (n = 3, 0 mM glucose), a low glucose group (n = 3, add 8.4 mM glucose), and a high glucose group (n = 3, add 33.6 mM glucose) of GCs were created for next whole genomic RNA sequencing. In total, 18,172 novel lncRNAs and 510 annotated lncRNAs were identified in the GCs samples. Gene Ontology indicated that differentially expressed lncRNAs associated with cell apoptosis were highly enriched. Kyoto Encyclopedia of Genes and Genomes enrichment analysis of lncRNA target genes found that the apoptosis pathway and the p53 signaling pathway were both enriched. Furthermore, we focused on the function of a lncGDAR and verified that lncGDAR could influence cell apoptosis in GC development through affecting the mRNA and protein expression of apoptosis-related markers. These results provide the basis for further study of the lncRNA regulation mechanism in nutrition on female fertility.

Insulin induces steroidogenesis in canine luteal cells via PI3K-MEK-MAPK

Glucose uptake increases in canine luteal cells under insulin treatment. We hypothesize that insulin also increases luteal cell steroidogenesis. Dogs underwent elective ovariohysterectomy from days 10-60 post ovulation and their corpora lutea (CL) and blood samples were collected. Deep RNA sequencing determined differentially expressed genes in CL; those related to insulin signaling and steroidogenesis were validated in vivo by qPCR and their respective proteins by Western blotting and immunofluorescence. Next, luteal cell cultures were stimulated with insulin with or without inhibition of MAPK14, MAP2K1 and PI3K. Studied proteins except P450 aromatase showed the same expression pattern of coding genes in vivo. The expression of HSD3B and CYP19A1 was higher in insulin-treated cells (P < 0.005). Following respective pathway blockades, the culture medium had decreased concentrations of progesterone (P4) and 17b-estradiol (E2) (P < 0.01). Our results indicate that insulin increases HSD3B and CYP19A1 expression via MAPK and PI3K, and contributes to the regulation of P4 and E2 production in canine luteal cells.

Glucose activates the primordial follicle through the AMPK/mTOR signaling pathway

Background

We have previously found that the energy level in sows affects the activation of primordial follicles. Glucose is the primary metabolic substrate of dietary energy and its effect and mechanism of action with regards to the activation and development of primordial follicle remain unclear. Studies utilizing several different animal cells have shown that energy stress, induced by glucose starvation, activates AMPK and participates in a variety of cellular processes by regulating the Hippo and mTOR signaling pathways. However, whether glucose can affect primordial follicle activation through the above pathways has not been reported.

Methods

We developed an in vitro culture system for mouse ovaries to investigate the effects of glucose on the primordial follicle activation. Protein expression of AMPK‐Hippo‐YAP and AMPK‐mTOR pathway was investigated under glucose starvation and optimal glucose level treatment. Then, ovaries were treated with AICAR or Compound C in vitro to explore the effect of AMPK activation or inhibition on primordial follicle activation, and the changes of AMPK‐Hippo‐YAP and AMPK‐mTOR signaling pathways. Finally, investigated the signaling pathways affected by glucose potentially affecting the primordial follicle activation in vivo.

Results

The glucose was an essential nutrient for primordial follicle activation and we identified 25 mM glucose as the optimal level (P < .05) for the primordial follicle activation in vitro. The glycolysis pathway was involved in primordial follicle activation (P < .05) of ovaries cultured in vitro. The glucose affected the activation of primordial follicles in vitro through AMPK/mTOR signaling pathway by AMPK activation or inhibition treatment and follicle ratio count (P < .05). Moreover, glucose affected the primordial follicle activation of ovary in vivo via mTOR signaling pathway.

Conclusions

This study demonstrates that glucose affects the primordial follicle activation through the AMPK/mTOR rather than the AMPK/Hippo signaling pathway.

Effect of short-term nutritional supplementation on hormone concentrations in ovarian follicular fluid and steroid regulating gene mRNA abundances in granulosa cells of ewes

This study was conducted to investigate effects of short-term nutritional supplementation on concentrations of reproductive hormones in follicular fluid and on mRNA abundance in granulosa cells (GCs) during the luteal phase of ewes. Eighteen ewes were randomly assigned to treatment or control groups (n = 9, each group). All the ewes were subjected to estrous synchronization using a Controlled Intravaginal Releasing Device (CIDR). From the second to the eleventh day of estrous synchronization, ewes were fed a diet with a relatively greater (treatment group) or a maintenance (control group) energy content. Samples of follicular fluid and GCs were collected from antral follicles of estrous ewes after CIDR removal. The results indicate mean FSH concentration of fluid in small follicles and mean LH concentrations of fluid in large follicles of the ewes in the treatment group were greater (P < 0.05) than that of ewes in the control group. Follicular fluid E₂ concentrations were directly related (P < 0.05) to follicular diameter. The ewes of the treatment group had greater (P < 0.05), compared with the control group, abundances of Follicle Stimulating Hormone Receptor (FSHR) in small and medium follicles, and (P<0.05) Luteinizing Hormone Receptor (LHR), Steroid Acute Regulatory Protein (STAR), cytochrome P450 (CYP17A1, CYP19A1) enzyme and Estrogen Receptor (ESR1) in large follicles. The results of this study provide evidence for a potential mechanism by which short-term nutritional supplementation improves follicular development possibly because of increased expression of steroid synthesis-regulating genes in large follicles.

Acute nutrient treatment causes alterations in intra-follicular antioxidation and AKT signaling

This study aimed to determine if short-term nutrient alteration affects (1) ovarian morphology, (2) plasma and ovarian antioxidant capability and (3) cell apoptosis and AKT signaling within the ovary. After estrus synchronization, 24 Hu sheep were assigned to three groups based on the nutrient requirement recommended for maintenance (M): 1 × M (Control), 1.5 × M (S) and 0.5 × M (R) during days 7–14 of their estrous cycle. The results indicated that undernourishment significantly increased the counts and volume of follicles <2.5 mm and decreased the counts and volume of follicles ≥2.5 mm (P < 0.05). Feed restriction altered the plasma and follicular redox balance within follicles ≥2.5 mm by inhibiting total antioxidant capacity, increasing malondialdehyde concentration (P < 0.05) and reducing the mRNA expression levels of superoxide dismutase 2 (SOD2) and glutathione peroxidase (GSH-PX), as well as the activities of total SOD and GSH-PX. Feed restriction also attenuated B-cell lymphoma-2 (BCL2) but enhanced Bcl-2-associated X protein (BAX) andBAX/BCL2transcription and translation levels in granulosa cells (P < 0.05). Uniform staining intensities of AKT and P-AKT-Ser473 were observed in each follicle stage, whereas weaker P-AKT-Thr308 staining in the antral follicle than in the pre-antral follicle suggested possible involvement of P-AKT-Thr308 during the beginning of follicle development. P-AKT-Ser473 levels in follicles ≥2.5 mm was significantly reduced in the R group (P < 0.05). The results presented in this study demonstrate that suppressed folliculogenesis caused by feed restriction might be associated with attenuated AKT signaling, reduced follicular antioxidant capacity and enhanced granulosa cells apoptosis.

Effects of different fat sources (saturated and unsaturated) on reproductive performance and biological indices of ewes during flushing period

This study was conducted to evaluate the effect of feeding different sources of fat during flushing period on the reproductive performance, lambing percent, and twin numbers of Afshari ewes. A total of 84 ewes (mean weight 48 ± 3 kg; age: 3-4 years) were divided into seven groups of 12 animals and received flushing-specific rations for 5 weeks. The control group just received a basic ration (non-flushing). Lipid sources were calcium salt of palm oil (CaP), pure palm oil (PO), calcium salt of flaxseed (CaFL), calcium salt of sunflower oil (CaSF), flaxseed oil (FLO), and sunflower oil (SFO). Estrous cycles were synchronized in all ewes using 14-day CIDRs followed by 400-IU PMSG injection at the time of CIDR removal. Fertility and lambing percent were higher in ewes fed with diets containing calcium salts of flaxseed and SFO, as compared to other treatments. Total number of lambs in flushing treatments was significantly higher than that in the control group (p < 0.01). Serum cholesterol and progesterone levels were significantly greater in omega-3 (CaFL) and omega-6 (CaSF) treatments relative to other treatments (p < 0.01). It was concluded that supplementing the flushing diet with calcium salts of fatty acids (CSFA) increased blood metabolites and hormones related to reproductive performance; and improved fertility, lambing rate and ewes of CaFL treatment have the highest number of lambs (16 lambs) between different groups. Using saturated and unsaturated fatty acids, especially in their CSFA forms during flushing period, could improve the reproduction problems induced by progesterone deficiency, lack of durability of the fetus due to hormonal instability, and abortion control factors.

Insulin signalling and glucose transport in the ovary and ovarian function during the ovarian cycle

Data derived principally from peripheral tissues (fat, muscle and liver) show that insulin signals via diverse interconnecting intracellular pathways and that some of the major intersecting points (known as critical nodes) are the IRSs (insulin receptor substrates), PI3K (phosphoinositide kinase)/Akt and MAPK (mitogen-activated protein kinase). Most of these insulin pathways are probably also active in the ovary and their ability to interact with each other and also with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signalling pathways enables insulin to exert direct modulating influences on ovarian function. The present paper reviews the intracellular actions of insulin and the uptake of glucose by ovarian tissues (granulosa, theca and oocyte) during the oestrous/menstrual cycle of some rodent, primate and ruminant species. Insulin signals through diverse pathways and these are discussed with specific reference to follicular cell types (granulosa, theca and oocyte). The signalling pathways for FSH in granulosa cells and LH in granulosa and theca cells are summarized. The roles of glucose and of insulin-mediated uptake of glucose in folliculogenesis are discussed. It is suggested that glucose in addition to its well-established role of providing energy for cellular function may also have insulin-mediated signalling functions in ovarian cells, involving AMPK (AMP-dependent protein kinase) and/or hexosamine. Potential interactions of insulin signalling with FSH or LH signalling at critical nodes are identified and the available evidence for such interactions in ovarian cells is discussed. Finally the action of the insulin-sensitizing drugs metformin and the thiazolidinedione rosiglitazone on follicular cells is reviewed.

Expression of adenosine 5'-monophosphate-Activated protein kinase (AMPK) in ovine testis (Ovis aries): In vivo regulation by nutritional state

In the present study, we identified AMPK and investigated its potential role in steroidogenesis in vivo in the ovine testis in response to variation in nutritional status (fed control vs. restricted). We performed immunoblotting to show that both active and non-active forms of AMPK exist in ovine testis and liver. In testis, we confirmed these results by immunohistochemistry. We found a correlation between ATP (Adenosine-Triphosphate) levels and the expression of AMPK in liver. Also, low and high caloric diets induce isoform-dependent AMPK expression, with an increase in α2, ß1ß2 and γ1 activity levels. Although the restricted group exhibited an increase in lipid balance, only the triglyceride and HC-VLDL (Cholesterol-Very low density lipoprotein) fractions showed significant differences between groups, suggesting an adaptive mechanism. Moreover, the relatively low rate of non-esterified fatty acid released into the circulation implies re-esterification to compensate for the physiological need. In the fed control group, AMPK activates the production of testosterone in Leydig cells; this is, in turn, associated with an increase in the expression of 3ß-HSD (3 beta hydroxy steroid deshydrogenase), p450scc (Cholesterol side-chain cleavage enzyme) and StAR (Steroidogenic acute regulatory protein) proteins induced by decreased MAPK ERK½ (Extracellular signal-regulated kinase -Mitogen-activated protein kinase) phosphorylation. In contrast, in the restricted group, testosterone secretion was reduced but intracellular cholesterol concentration was not. Furthermore, the combination of high levels of lipoproteins and emergence of the p38 MAP kinase pathway suggest the involvement of pro-inflammatory cytokines, as confirmed by transcriptional repression of the StAR protein. Taken together, these results suggest that AMPK expression is tissue dependent.

Short-term methionine supplementation during the early post-partum period in primiparous rabbits improves prolificacy associated with an increase in serum concentrations of IGF-I

The aim of this study was to evaluate the effects of methionine supplementation on energy metabolism and reproductive performance during the early post-partum period in primiparous does. Forty nulliparous New Zealand White does were used. Females were randomized in two groups at calving: the control group (n = 20) was fed with the basal diet, and the methionine group (n = 20) was fed the basal diet plus 1 g/animal/day of methionine from the day of calving to 4 days post-partum. Results showed that methionine supplementation increased (p = 0.032) the concentration of insulin-like growth factor-1 with respect to control group 4 days post-partum. It similarly increased the prolificacy (p = 0.03), the number of kits born alive per litter (p = 0.06) and the body gain weight of the litter during supplementation (p = 0.035). These results were observed despite the does in the methionine group having a deeper negative energy balance than the does in the control group. Finally, methionine supplementation did not affect receptivity (p = 0.23), fertility (p = 0.49), the number of kits born dead per litter (p = 0.86) insulin and metabolites as glucose, non-esterified fatty acids and triglycerides. In conclusion, our results show that methionine supplementation during the first 4 days of the post-partum period in rabbits increases total litter size and the corporal weight of kits and is associated with an increase in blood concentration of IGF-1.

Analysis of genes that influence sheep follicular development by different nutrition levels during the luteal phase using expression profiling

Nutrition is an important factor that regulates reproductive performance of sheep and affects follicle development. However, the correlation between nutrition and follicle development is poorly understood at the molecular level. To study its possible molecular mechanisms, we performed expression profiling of granulosa cells isolated from sheep that were fed different levels of nutrition levels during the luteal phase. To do this, ewes received a maintenance diet (M), and their estrus was synchronized by intravaginal progestogen sponges for 12 days. Ewes were randomly divided into the short-term dietary-restricted group (R; 0.5 × M) and the nutrient-supplemented group (S; 1.5 × M). RNA samples were extracted from granulosa cells. Transcriptome libraries from each group were constructed by Illumina sequencing. Among 18 468 detected genes, 170 genes were significantly differentially expressed, of which 140 genes were upregulated and 30 genes were downregulated in group S relative to group R. These genes could be candidates regulating follicular development in sheep. Gene Ontology, KEGG and clustering analyses were performed. Genes related to oocyte meiosis, such as ADCY7, were upregulated. We identified two important groups of related genes that were upregulated with improved nutrition: one group comprising the genes PTGS2, UCP2 and steroidogenic acute regulatory protein and the other group comprising interleukin-1A and interleukin-1B. The genes within each group showed similar expression patterns. Additionally, all five genes are involved in the reproduction process. Quantitative real-time PCR was performed to validate the results of expression profiling. These data in our study are an abundant genomic resource to expand the understanding of the molecular and cellular events underlying follicle development.

Effect of feeding greater amounts of dietary energy for a short-term with or without eCG injection on reproductive performance, serum metabolites and hormones in ewes

This study was conducted to compare the effect of transient high-energy diet in a short-term period with or without eCG injection on ovarian follicle development, twining rate, serum metabolites and hormones in ewes. A total of 45 estrous cyclic Naeini ewes were randomly assigned to three experimental groups: 1-Control (control), 2-High energy short-term feeding (HE), and 3-high energy short-term feeding + eCG injection (HEe). Ewes were housed in individual pens with free access to feed and water. The stage of the estrous cycle of all ewes was synchronized by insertion of intravaginal progesterone sponges. Focus feeding started from 4 days before until 1 day after sponge removal. Follicle development was monitored from 4 days before until 1 day after sponge removal and blood samples were taken during this time. Results showed that ewes fed high energy diets (HE and HEe) had greater (P < 0.05) large follicle numbers compared with the control group. Feeding high energy diets increased (P < 0.05) serum glucose, cholesterol and insulin, but had lesser (P < 0.05) serum urea nitrogen concentrations near the time of ovulation. After the start of experiment, ewes fed high energy diets had less (P < 0.05) serum estradiol. However, 1 day after sponge removal, serum estradiol in HE and HEe groups increased (P < 0.05). It was concluded that short-term (6-day) changes in amount of dietary energy with or without eCG injection increased twin births and had beneficial effects on the blood metabolites and hormone concentrations in Naeini ewes.

The effects of intravenous, glucose versus saline on ovarian follicles and their levels of some mediators of insulin signalling

BACKGROUND

A short-term increase in food intake and specifically dietary energy can stimulate folliculogenesis and increase ovulation rate in ewes. The mechanism appears to involve the insulin-glucose metabolic system and its interaction with FSH signalling pathways in the granulosa cells of ovarian follicles. This experiment was designed to investigate the interaction between these two systems in the granulosa cells of ovarian follicles.

METHODS

Thirty six Ile-de-France ewes were used in this controlled experiment to study the effects of intravenous glucose on folliculogenesis. Eighteen ewes were infused with glucose (10 mM/h for 72 h) from day 8 of the oestrous cycle, while the others (controls) received saline. Ovaries were collected when the infusions ended (luteal phase) or 30 h later and after a luteolytic dose of a PGF2α analogue (follicular phase). Follicles were dissected and granulosa cells and follicular fluid harvested. The blood concentrations of glucose, insulin, oestradiol and FSH were monitored over the experiment. The levels of Aromatase P450 and of the phosphorylated and non-phosphorylated forms of Akt, AMPK and ERK in granulosa cells and the concentration of oestradiol in follicular fluid, were determined.

RESULTS

Glucose increased the circulating concentration of glucose (P < 0.05) and insulin (P < 0.05). It also increased the total number of follicles >1.0 mm in diameter (P < 0.05) and small (P < 0.05) follicles (>1.0 to 2.0 mm in diameter) but not medium (>2.0 to 3.5 mm in diameter) or large (>3.5 mm in diameter) follicles. Glucose decreased circulating oestradiol (P < 0.05) but not that of FSH or progesterone. Glucose reduced aromatase P450 (P < 0.05) and decreased the phosphorylation of Akt (P < 0.05), ERK (P < 0.05) and AMPK (P < 0.05) in granulosa cells from oestrogenic follicles. The level of Aromatase P450 was greatest in large oestrogenic follicles and the phosphorylation of Akt (P < 0.05), ERK (P < 0.05) and AMPK (P < 0.05) was lower in small follicles compared to medium and large follicles.

CONCLUSIONS

These data suggest that the effect of glucose in small follicles is a direct action of glucose that increases the number of small follicles while the effect of glucose in oestrogenic follicles is an indirect insulin-mediated action.

Superovulatory response and embryo development in ewes treated with two doses of bovine somatotropin

This study evaluated whether the administration of 50 and 100mg bovine somatotropin (bST) at the start of synchronization and at the time of natural mating in ewes improves the ovulation rate, embryonic development and pregnancy rate of transferred embryos. Forty-eight donors were assigned to three treatments: the bST-100 treatment (n=15) received 100mg bST at the start of synchronization and at natural mating, the bST-50 treatment (n=15) received 50mg bST on the same schedule as the previous group, and the control (n=18) did not receive any bST. Two embryos were transferred to each recipient (n=121): 35 received embryos from bST-100; 50 received embryos from bST-50, and 36 received embryos from the control. The superovulatory rate, percentage of recovered structures, cleavage rate, percentage of transferable embryos, embryo quality and development and pregnancy rate were analyzed using the GENMOD procedure of SAS. The number of corpora lutea and the cell number were analyzed using the GLM procedure of SAS. The insulin and IGF-1 concentrations were analyzed with ANOVA for repeated measures. The bST application did not affect the superovulatory rate, number of corpora lutea and recovered structures (P>0.05). The numbers of transferable embryos and embryos reaching the blastocyst were higher (P≤0.01) in the bST-50 (96.4±3.6% and 69.0±7.8%) than the bST-100 (93.0±4.5% and 27.2±38.9%) and control (87.7±5.4% and 50.4±6.4%) groups. The insulin and IGF-1 concentrations were higher (P<0.05) in the bST-treated groups, but the insulin concentration was higher (P<0.05) in the bST-100 group than in the bST-50 group. The pregnancy rate was similar (P=0.21) in ewes receiving embryos from the two treatments [bST-50, (70.0%); bST-100, (62.5%), and control, (56.6%)]. The administration of 50mg bST at the start of synchronization and at natural mating in superovulated ewes was concluded to enhance the proportion and development of transferable embryos. However, bST did not affect the pregnancy rate of transferred embryos.

The influence of nutrition on the insulin-like growth factor system and the concentrations of growth hormone, glucose, insulin, gonadotropins and progesterone in ovarian follicular fluid and plasma from adult female horses (Equus caballus)

BACKGROUND

Feed intake affects the GH-IGF system and may be a key factor in determining the ovarian follicular growth rate. In fat mares, the plasma IGF-1 concentration is high with low GH and a quick follicular growth rate, in contrast to values observed in thin mares. Nothing is known regarding the long-term effects of differential feed intake on the IGF system. The objective of this experiment was to quantify IGFs, IGFBPs, GH, glucose, insulin, gonadotropin and progesterone (P4) in blood and in preovulatory follicular fluid (FF) in relation to feeding levels in mares.

METHODS

Three years prior to the experiment, Welsh Pony mares were assigned to a restricted diet group (R, n = 10) or a well-fed group (WF, n = 9). All mares were in good health and exhibited differences in body weight and subcutaneous fat thickness. Follicular development was scanned daily and plasma was also collected daily. Preovulatory FF was collected by ultrasound-guided follicular aspiration. Hormone levels were assayed in FF and plasma with a validated RIA.

RESULTS

According to scans, the total number of follicles in group R was 53% lower than group WF. Insulin and IGF-1 concentrations were higher in WF than in R mares. GH and IGF-2 concentrations were lower in plasma from WF mares than from R mares, but the difference was not significant in FF. The IGFBP-2/IGFBP-3 ratio in FF was not affected by feeding but was dramatically increased in R mare plasma. No difference in gonadotropin concentration was found with the exception of FSH, which was higher in the plasma of R mares. On the day of puncture, P4 concentrations were not affected by feeding but were higher in preovulatory FF than in plasma.

CONCLUSIONS

The bioavailability of IGF-1 or IGF-2, represented by the IGFBP2/IGFBP3 ratio, is modified by feed intake in plasma but not in FF. These differences partially explain the variability in follicular growth observed between well-fed mares and mares on restricted diets.

The effect of nutrition and metabolic status on the development of follicles, oocytes and embryos in ruminants

The impact of nutrition and energy reserves on the fertility of ruminants has been extensively described. However, the metabolic factors and the molecular mechanisms involved in the interactions between nutrition and ovarian function are still poorly understood. These factors could be hormonal (either reproductive and/or metabolic) and/or dietary and metabolic (glucose, amino acids and fatty acids). In this review, we briefly summarize the impact of those nutrients (fatty acids, glucose and amino acids) and metabolic hormones (insulin/IGF-I, growth hormone, T3/4, ghrelin, apelin and the adipokines (leptin, adiponectin and resistin)) implicated in the development of ovarian follicles, oocytes and embryos in ruminants. We then discuss the current hypotheses on the mechanisms of action of these factors on ovarian function. We particularly describe the role of some energy sensors including adenosine monophosphate-activated kinase and peroxisome proliferator-activated receptors in the ovarian cells.

Effect of nutrition on plasma lipid profile and mRNA levels of ovarian genes involved in steroid hormone synthesis in Hu sheep during luteal phase

Ovarian steroid hormones regulate follicular growth and atresia. This study aims to determine whether key ovarian sterol-regulatory genes are differentially expressed in Hu sheep under different short-term nutritional regimens. Estrus was synchronized using intravaginal progestagen sponges. The ewes were assigned randomly to 3 groups. On d 6 to 12 of their estrous cycle, the control (CON) group received a maintenance diet (1.0×M), the supplemented (SUP) group received 1.5×M, and the restricted (R) group received 0.5×M. On d 7 to 12, blood samples were taken. The sheep were slaughtered at the end of the treatment, and their organs and ovaries were collected. The plasma concentrations of urea (P<0.01), total cholesterol (P<0.01), low-density lipoprotein cholesterol (P<0.01), NEFA (P<0.01), FSH (P<0.05), and estradiol (P<0.05) increased with decreasing dietary intake, whereas plasma triglyceride (P<0.01) and triiodothyronine (T3) concentrations decreased (P<0.05). The ewes in the R group had higher spleen weight and percentage of spleen to BW and lower liver and small intestine weights and percentage of liver/stomach to BW than the SUP group ewes (P<0.05). Nutritional restriction decreased the cytochrome p450 (CYP17A1) and estrogen receptor 1 (ESR1) mRNA expression (P<0.05) and increased the cytochrome p450 aromatase (CYP19A1) mRNA expression (P<0.05) in follicles>2.5 mm. Follicle size affected the mRNA expression of very low density lipoprotein receptor (VLDLR), estrogen receptor 2 (ESR2), FSH receptor (FSHR), CYP17A1, and CYP19A1 (P<0.05). In conclusion, we suggest that a potential mechanism by which short-term negative energy balance inhibits follicular growth may involve responses to disrupted reproductive hormone concentrations and influenced the intrafollicular expression of CYP17A1, CYP19A1, and ESR1. This result may be due to increased plasma urea and lipid concentrations.