Biomedical subjects

D Blache

Publications and source records attributed to D Blache.

At least 19 recordsLinked to original sources

PubMed2003

Clarification of emu serum for peptide hormone assay using polyethylene glycol precipitation.

Interference in radioimmunoassays (RIAs) was frequently encountered during endocrinological studies of the emu (Dromaius novaehollandiae). Interference was greatest when serum was cloudy or opaque. Such samples appeared seasonally, in spring and summer during the phase of fat deposition, and in the winter when females were laying. These poor quality samples did not allow accurate measurement by RIAs of several peptide hormones for a full year. To prepare them for assay, these sera were clarified using a polyethylene glycol (PEG) solution at a final concentration of 7.5%. This treatment was effective in most cases. After treatment with the PEG, recoveries of LH, glucagon, and prolactin were greater than 75% and that for insulin was 40%. Regardless of the level of recovery, there was a high correlation of assay results between non-opaque native and PEG-treated sera. Serum samples containing large amounts of interfering high molecular weight components, such as lipoproteins, can be clarified with PEG, enabling their accurate measurement by RIA.

Animals↗

PubMed2003

Relationships between plasma concentrations of leptin and other metabolic hormones in GH-transgenic sheep infused with glucose.

To study the regulation of leptin secretion in sheep, we infused glucose (0.32 g/h/kg for 12 h) into GH-transgenic animals (n = 8) that have chronically high plasma concentrations of ovine GH and insulin, but low body condition and low plasma leptin concentrations, and compared the responses with those in controls (n = 8). In both groups, the infusion increased plasma concentrations of glucose and insulin within 1 h and maintained high levels throughout the infusion period (P < 0.0001). Compared with controls, GH-transgenics had higher concentrations of insulin, IGF-1, GH (all P < 0.0001) and cortisol (P < 0.05), but lower GH pulse frequency (P < 0.0001). Overall, leptin concentrations were lower in GH-transgenics than in controls (P < 0.01). A postprandial increase in leptin concentrations was observed in both groups, independently of glucose treatment, after which the values remained elevated in animals infused with glucose, but returned to basal levels in those infused with saline, independently of transgene status. In both GH-transgenics and controls, glucose infusion did not affect the concentrations of GH, IGF-1, or cortisol. In conclusion, GH-transgenic and control sheep show similar responses to glucose infusion for leptin and other metabolic hormones, despite differences between them in body condition and basal levels of these hormones. Glucose, insulin, GH, IGF-1 and cortisol are probably not major factors in the acute control of leptin secretion in sheep, although sustained high concentrations of GH and IGF-1 might reduce adipose tissue mass or inhibit leptin gene expression.

Animals↗

PubMed2003

Effects of short-term high carbohydrate or fat intakes on leptin, growth hormone and luteinizing hormone secretions in prepubertal fat-tailed Tuj lambs.

The aim of the current study was to evaluate the effects of high carbohydrate or fat diets, fed for 15 days at the end of breeding season, on leptin, GH and LH secretions in prepubertal fat-tailed Tuj lambs. For that purpose, 9-month-old ram-lambs were divided into three groups as control group (fed with basal ration, n = 4), high carbohydrate (HC) group, basal ration plus barley, n = 4), or high fat (HF) group (basal ration plus by-pass fat, n = 4). For the measurement of leptin and GH, blood plasma samples were collected on days 1, 4, 9 and 14 of the experiment. For the measurement of LH pulse frequency, serial blood samples were collected every 15 min for 6 h on day 14. Lambs were weighed and body condition scored (BCS) on days 1 and 15. Body weight and BCS increased towards the end of the study (p < 0.05). The BCS was higher in high energy groups at the end of the experiment (p < 0.05). Diet affected plasma leptin concentrations (p = 0.002) but time did not. The GH concentrations were not affected by diet or time. The LH pulse frequency appeared to be higher in HC and HF groups but there were no statistical difference between the groups. There was a significant positive relationship between overall BCS and corresponding leptin concentrations (R2 = 0.263; p = 0.010) and between LH pulse frequency and leptin concentrations (R2 = 0.594; p = 0.003). In conclusion, the present study suggests that rather than type of energy, amount of energy intake and body energy reserves are much important regulators of plasma leptin concentrations and LH pulse frequency in fat-tailed Tuj lambs.

Animal Nutritional Physiological Phenomena↗

PubMed2003

Reproduction and plasma concentrations of leptin, insulin and insulin-like growth factor 1 in growth-hormone-transgenic female sheep before and after artificial insemination.

The transgenic sheep used in this study expressed an additional copy of the gene for ovine growth hormone (GH), so they had continuously high plasma concentrations of GH. They were used to test whether the GH transgene affected plasma concentrations of the metabolic hormones leptin, insulin-like growth factor 1 (IGF-1) and insulin, and whether these effects were associated with changes in conception, pregnancy or parturition following artificial insemination. Compared with control animals, the GH-transgenic sheep had higher bodyweight, lower body condition score and less subcutaneous fat (P < 0.05). These sheep also had lower plasma concentrations of leptin, higher plasma concentrations of insulin, and higher plasma concentrations of IGF-1 (P < 0.001). A similar proportion of GH-transgenic and control ewes came into oestrus, but the conception rate to artificial insemination was lower in GH-transgenic ewes than in the controls. Only four live lambs were recovered from 12 GH-transgenic ewes (33%) compared with 38 lambs from 43 controls (88%). This outcome was not associated with any difference in plasma progesterone profile in the period leading up to artificial insemination (Day 0). The GH-transgenic ewes had lower concentrations of FSH at all times measured (Day -19, Day -2 and Day 19). These results indicate that appropriate regulation of GH secretion from pituitary or peripheral tissues is necessary for normal reproduction and normal levels of metabolic hormones. Chronically high concentrations of GH were associated with increased levels of IGF-1 and insulin, and decreased levels of leptin.

Animals↗

PubMed2002

Folliculogenesis and ovarian expression of mRNA encoding aromatase in anoestrous sheep after 5 days of glucose or glucosamine infusion or supplementary lupin feeding.

Improved nutrition increases ovulation rate in sheep and there is evidence that intra-ovarian pathways mediate responses to nutrition. An experiment was conducted to examine the effect of dietary energy on folliculogenesis. Anoestrous Merino ewes were fed a diet of wheat straw alone (control, n = 5), or wheat straw supplemented with lupins (500 g day(-1), n = 5). Other ewes were fed wheat straw and infused with glucose (50 mmol h(-1), n = 5) or with glucosamine (3.5 mmol h(-1), n = 5). Intravaginal progestagen sponges were inserted for 12 days, and nutritional treatments were started 5 days before sponge removal. At sponge removal, the ewes were injected with a regimen of GnRH pulses (500 ng every 4 h from 0 to 12 h; 250 ng every 2 h from 14 to 24 h; and 200 ng every 1 h from 25 to 36 h) to simulate normal follicular development. Thirty-six hours after sponge removal, the animals were killed and the ovaries were collected and stored at -80 degrees C. The ovaries were sectioned serially every 10 microm. Every 20th section was stained (to estimate number and diameter of follicles) and every 17-19th section was probed by in situ hybridization for P(450) aromatase. Data were analysed using ANOVA and chi-squared tests. There was an effect of treatment (P < 0.05) on the number of follicles 2-3, 3-4 and 6-7 mm in diameter. Aromatase-positive follicles (1.6-7.9 mm) were detected in 31 follicles from 15 ewes across all four groups. In ten animals, the largest follicle was aromatase-positive. The diameters of aromatase-positive follicles were larger (P = 0.004) in lupin fed compared with glucose-infused ewes (4.9 +/- 0.5, 3.6 +/- 0.7, 5.3 +/- 0.5 and 4.2 +/- 0.5 mm for control, glucose-infused, lupin-fed and glucosamine-infused groups, respectively). Treatment did not affect the plasma concentration of FSH when compared with controls, indicating that the energy supplements were modifying recruited (2-3 mm and 3-4 mm) and selected follicles (> 6 mm) directly. In conclusion, dietary energy can directly stimulate folliculogenesis in recruited and selected follicles, and this effect may be mediated by changes in systemic leptin concentrations and the hexosamine energy-sensing pathway in the follicle.

Analysis of Variance↗

PubMed2002

The mature male sheep: a model to study the effects of nutrition on the reproductive axis.

We have been using mature male sheep to study the ways in which nutrition affects reproduction, with a focus on the brain-pituitary axis and, in particular, GnRH activity. The sheep model has four major advantages for such studies. Firstly, sheep are large enough to support long periods of frequent serial sampling of peripheral blood, hypophyseal portal blood and cerebrospinal fluid from the cerebral ventricles. Importantly, this can be done with freely moving animals and, thus, avoids many of the potential complications associated with restraint. The second advantage, particularly relevant to nutrition-reproduction interactions, is the vast history of nutritional research for this species, providing us with techniques (for example, gut cannulation) and an extensive database on the requirements of sheep for energy, protein and specific dietary components such as amino acids, fatty acids and trace elements. Thirdly, subtle manipulations of diet can be used that cover the range seen in the real world, where animals (including humans) rarely encounter the uninterrupted, ad libitum food supplies that are normal for laboratory animals. Within this normal range of conditions, clear reproductive outcomes can be measured without resorting to starvation and both short- and long-term responses can be studied. Finally, the sheep model has an intrinsic economic relevance and findings from sheep can be transposed readily to other agricultural mammals. The sheep model is also relevant to human biology, often directly, but also indirectly because it often leads us to question the significance of findings from studies with rodents. Using mature male sheep to study the reproductive endocrine responses to acute and chronic changes in diet, we have shown that glucose does not appear to be involved directly, but that fatty acids can stimulate GnRH-dependent pathways that initiate changes in testicular function. Our work also indicates that GnRH-independent (perhaps also neuroendocrine) mechanisms may be involved. In the brain, it seems likely that intracerebral insulin and orexin are important mediators of the GnRH response to nutritional changes, but it is unlikely that leptin plays a role, at least in mature animals.

Animal Nutritional Physiological Phenomena↗

PubMed2001

Impaired homocysteine metabolism and atherothrombotic disease.

Based on recent retrospective, prospective, and experimental studies, mild to moderate elevation of fasting or postmethionine-load plasma homocysteine is accepted as an independent risk factor for cardiovascular disease and thrombosis in both men and women. Hyperhomocysteinemia results from an inhibition of the remethylation pathway or from an inhibition or a saturation of the transsulfuration pathway of homocysteine metabolism. The involvement of a high dietary intake of methionine-rich animal proteins has not yet been investigated and cannot be ruled out. However, folate deficiency, either associated or not associated with the thermolabile mutation of the N(5,10)-methylenetetrahydrofolate reductase, and vitamin B(6) deficiency, perhaps associated with cystathionine beta-synthase defects or with methionine excess, are believed to be major determinants of the increased risk of cardiovascular disease related to hyperhomocysteinemia. Recent experimental studies have suggested that moderately elevated homocysteine levels are a causal risk factor for atherothrombotic disease because they affect both the vascular wall structure and the blood coagulation system. The oxidant stress that results from impaired homocysteine metabolism, which modifies the intracellular redox status, might play a central role in the molecular mechanisms underlying moderate hyperhomocysteinemia-mediated vascular disorders. Because folate supplementation can efficiently reduce plasma homocysteine levels, both in the fasting state and after methionine loading, results from further prospective cohort studies and from on-going interventional trials will determine whether homocysteine-lowering therapies can contribute to the prevention and reduction of cardiovascular risk. Additionally, these studies will provide unequivocal arguments for the independent and causal relationship between hyperhomocysteinemia and atherothrombotic disease.

Age Factors↗

PubMed2001

Photoperiodic control of the concentration of luteinizing hormone, prolactin and testosterone in the male emu (Dromaius novaehollandiae), a bird that breeds on short days.

The objective of this study was to establish, for a short-day breeding bird, the male emu, whether the breeding season is principally controlled by changes in photoperiod, and to investigate the endocrine mechanisms involved. Two groups of adult males were subjected to three alternating periods of 150-185 days of 14 h light/day (LD) and 10 h light/day (SD) terminating in a 360-day period of LD or SD. Transfer from LD to SD led to increases in plasma concentrations of luteinizing hormone (LH) and testosterone, after 82 +/- 8 and 73 +/- 3 (SEM) days, and an increase in prolactin concentrations after 115 +/- 12 days. Concentrations of LH and testosterone began to decrease before transfer back to LD, at a time when prolactin concentrations were approaching peak values. Transfer from LD to 360 days of SD resulted in increases in LH and testosterone concentrations, and these terminated after an increase in prolactin concentrations. After transfer from SD to 360 days of LD, plasma concentrations of LH and testosterone began to increase, after delays of 222 +/- 24 and 225 +/- 13 days, and were high at the end of the study, while prolactin values remained depressed throughout. These observations clearly show that seasonal breeding in the emu is directly controlled by changes in photoperiod. The dynamics of the hormonal responses to change of photoperiod suggest that, despite being short-day breeders, the photoregulation of breeding in emus involves mechanisms that are currently accepted for birds, rather than mechanisms that have been proposed for short-day breeding mammals. The initiation of breeding in emus is due to dissipation of photorefractoriness by short days which leads to an increase in the secretion of gonadotrophins to levels that are sufficient to support full reproductive condition. The termination of breeding, while days are still short, is due to the antigonadotrophic action of prolactin which, unusually for birds, increases while the days are still short. In conclusion, breeding activity in male emus is strongly controlled by photoperiod. Emus are short-day breeders, but the central mechanisms that regulate the secretion of reproductive hormones seem to be similar to those previously proposed for long-day breeding birds. The pattern of prolactin secretion in emus suggests an important role for this hormone in the termination of the breeding cycle.

Animals↗

PubMed2001

Plasma thyroid hormones and growth hormone in embryonic and growing emus (Dromaius novaehollandiae).

Growth hormone (GH), thyroxine (T4) and tri-iodothyronine (T3) are known to be involved in the regulation of growth and development in a variety of avian species. It has been suggested that an absence of GH and thyroid hormones in ostriches is the cause of their neoteny, a phenomenon in which juvenile characteristics are retained into adulthood. Neoteny is typical of all ratites, the single group of flightless birds that includes the ostrich, but similar endocrine studies have not been performed for other members of the group, such as the emu. To test the neoteny hypothesis further, in the present study we measured the plasma concentrations of T4, T3 and GH in emus during embryonic development and from hatching to 1 year of age. Concentrations of T4 and GH increased during the last weeks of incubation, whereas concentrations of T3 were highly variable. After hatching, the concentrations of both thyroid hormones were high during the first 3 days of life and then fell to a constant low level. Plasma concentrations of GH were high at the time of hatching and decreased gradually over the first 22 weeks of age; thereafter, the concentrations of GH were highly variable. No correlation was observed between hormone concentrations and live weight at any time. These results support the hypothesis that thyroid function is abnormally low in ratites, whereas patterns of GH secretion are similar to those observed in other birds. Dysfunction of the thyroid axis could explain, in part, the neotenous physical aspect of adult emus.

Animals↗

PubMed2001

The importance of proteins in defense against oxidation.

Free radicals are a normal feature of cellular oxygen metabolism. However, free radical-associated damage is an important factor in many pathological and toxicological processes. For a long time, lipid peroxidation, mediated by oxygen-derived free radicals, was probably the most extensively investigated process. From more recent studies, it has become evident that proteins are also the targets of free radicals, and this has important implication for their activity, unfolding, and degradation, as well as in cell functioning. After giving a brief overview of the key role of proteins in the overall antioxidant defense, this review examines their role as targets of oxidation reactions, taking into account the reactivity of amino acid residues and some of their oxidation products. In light of recent data, we then consider the specific role of sulfur-containing amino acids in protein degradation and their possible interplay with the reversal of limited oxidative lesions. The participation of proteins in the overall antioxidant defense is also discussed, specifically the role of metallothionein as an intracellular antioxidant and that of albumin as a circulating antioxidant.

Animals↗

PubMed2001

Moderate intake of n-3 fatty acids is associated with stable erythrocyte resistance to oxidative stress in hypertriglyceridemic subjects.

BACKGROUND: The important triacylglycerol-lowering capacity of n-3 fatty acids is counterbalanced by their inherent sensitivity to oxidation. Inconsistent results about the latter have been reported in hypertriglyceridemic individuals. After incorporation into cell membranes, n-3 fatty acids may alter membrane-related functions. In view of the distinct composition of hypertriglyceridemic membranes and the prooxidant status in this condition, it can be surmised that cell enrichment with the oxidizable n-3 fatty acids will be associated with an increased hemolytic process. OBJECTIVE: We sought to evaluate the effect of fish oil consumption on n-3 fatty acid incorporation into erythrocyte membranes and subsequent ex vivo oxidative-stress-induced hemolysis in normotriglyceridemic and hypertriglyceridemic subjects. DESIGN: Sixteen normotriglyceridemic and 12 hypertriglyceridemic subjects were given 6 g fish oil/d for 8 wk. Blood samples were collected before and 4 and 8 wk after treatment. Resistance to 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced hemolysis was assayed in fresh erythrocyte suspensions, and erythrocyte samples were stored at -70 degrees C for later analysis of cholesterol, hemoglobin, fatty acids, vitamin E, and glutathione peroxidase activity. RESULTS: Fish oil supplementation induced n-3 fatty acid incorporation in normotriglyceridemic and hypertriglyceridemic erythrocyte membranes without decreasing their resistance to AAPH. n-3 Fatty acids significantly protected normotriglyceridemic but not hypertriglyceridemic erythrocytes against hemolysis. In normotriglyceridemic subjects only, the higher resistance to hemolysis correlated with changes in cell vitamin E. CONCLUSION: Although they exhibit a high susceptibility to oxidation, n-3 fatty acids may preserve membrane integrity and represent an added benefit in the treatment of hypertriglyceridemic patients.

Adult↗

PubMed2001

Effect of nutritional supplementation on quantities of glucose transporters 1 and 4 in sheep granulosa and theca cells.

The stimulatory effect of nutritional supplementation on ovarian activity in sheep has been linked to an increase in glucose availability that, with insulin, directly decreases follicular steroidogenesis. Glucose uptake occurs by glucose transporters, but it is not known which glucose transporters are present in the sheep ovary or whether they are affected by nutritional stimulation. The aim of this study was to determine whether widely distributed glucose transporter 1 (GLUT1) or insulin-responsive GLUT4 are present in the granulosa or theca cells of sheep ovarian follicles, and whether their concentrations are affected by nutritional stimulation. Merino ewes (n = 49-51 per group) were stimulated nutritionally for 5 days before luteolysis with lupin grain or with one of two regimens of a glucogenic mixture, administered orally, which increases blood glucose concentrations towards the upper end of the normal range. Water was used as a control. Ovaries (n = 3 per group) were dissected and the granulosa cells and thecal shell from individual follicles were examined for glucose transporters using western blotting. GLUT1 concentration was 7-18 times higher in the granulosa than in the theca cells. GLUT4 was detected at a similar concentration in both types of cell. Nutritional treatment had no effect on the concentration of GLUT1 or GLUT4 in either tissue, and did not increase ovulation rate, despite increased concentrations of glucose and insulin. Concentrations of glucose transporters were not correlated with follicular concentrations of oestradiol or androstenedione. The presence of GLUT1 and GLUT4 in the granulosa and theca of sheep follicles indicates that the transporters have a role within the ovary in the modulation of follicular function.

Animal Feed↗

PubMed2000

Role of the cyclic AMP-dependent pathway in free radical-induced cholesterol accumulation in vascular smooth muscle cells.

We have previously reported that free radical-treated vascular smooth muscle cells (SMC) lead to cholesterol accumulation in vitro. In the current study, we investigated the effects of oxidative stress on cyclic AMP concentration and cAMP-dependent enzymes involved in cholesterol homeostasis in A7r5 cells. Under our conditions of a mild oxidative stress, namely with no change in cell viability, we found that free radicals, initiated using azobis-amidinopropane dihydrochloride (AAPH), resulted in a dose-dependent decrease in cellular cAMP which was opposed by vitamin E preincubation. Although the addition of adenylate cyclase activators (carbacyclin and forskolin) increased cAMP levels it did not succeed in restoring the AAPH-induced decrease. The oxidative stress-induced increase in activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and of acyl coenzyme A: cholesterol acyltransferase and the decrease in neutral cholesteryl ester hydrolase activity were suppressed by addition of dibutyryl cAMP. Taken together, these results strongly suggest that free radicals reduce cAMP concentrations by altering cell membrane adenylate cyclase activity. The changes of cAMP-dependent enzymes induced by oxidative stress resulting in cholesterol accumulation might be one of the processes leading to SMC-derived foam cells depicted in atheroma plaque. Moreover, if extrapolated to in vivo, these data may explain in part the beneficial effects of antioxidants in the reduction of cardiovascular diseases.

Adenylyl Cyclases↗

PubMed2000

Decrease in voluntary feed intake and pulsatile luteinizing hormone secretion after intracerebroventricular infusion of recombinant bovine leptin in mature male sheep.

The aim of the present study was to determine whether leptin might play a role in the gonadotrophic response of mature merino rams to changes in the level of nutrition in rams fed ad libitum. Recombinant bovine leptin was infused intracerebroventricularly and voluntary food intake (VFI) and luteinizing hormone (LH) pulse frequency were measured. In Experiment 1, rams (n = 5) were infused for 24 h per day for 5 days with vehicle or with leptin (0.04, 0.4 and 4.0 microg h(-1)). All doses decreased both VFI and LH pulse frequency. In Experiment 2, rams were infused for 24 h per day for 5 days with vehicle (n = 10) or leptin (4 pg h(-1); n = 5); a sub-group of 5 controls was pair-fed to the leptin-infused group to control for effects of changes in feed intake. LH pulse frequency was reduced equally in both the leptin-infused and pair-fed groups. Leptin did not affect other systems controlled by the hypothalamic-pituitary axis. Thus, rather than stimulate LH secretion, intracerebral leptin specifically inhibits it by reducing food intake, so it is unlikely that effects of nutrition on the reproductive axis in mature rams involves leptin as a single blood-borne signal. A range of nutritional or metabolic inputs may be needed, and perhaps interconnections between neural centres that control appetite and reproduction.

Animals↗

PubMed2000

Relationships between changes in plasma concentrations of leptin before and after parturition and the timing of first post-partum ovulation in high-producing Holstein dairy cows.

During early lactation, dairy cattle are in negative energy balance and the delay to first post-partum ovulation depends on the time taken to recover from this situation. Lactating cows rely heavily on body fat to meet their requirements, leading to the suggestion that leptin, a hormone secreted mainly by adipocytes, is acting as a metabolic signal to sites that control the reproductive axis. The relationship between plasma leptin concentrations and the timing of the first ovulation post partum in 20 high-producing Holstein dairy cows, using a radioimmunoassay based on recombinant bovine leptin was studied. Plasma leptin concentrations declined after parturition, reached a nadir of 0.74 +/- 0.17 ng mL(-1) on 10.1 +/- 2.2 days after parturition (all values are mean +/- SEM). They then increased and became stable near the time of ovulation. Leptin concentrations averaged 1.81 +/- 0.31 ng mL(-1) in the 14 days prepartum, 1.32 +/- 0.21 ng mL(-1) in the post-partum preovulatory period and 1.61 +/- 0.24 ng mL(-1) in the post-ovulatory period. The differences between periods were significant (P<0.01). The interval from parturition to first ovulation averaged 25.9 +/- 2.0 days and was not correlated with the prepartum, preovulatory or post-ovulatory leptin values. However, the interval to first ovulation correlated significantly (r = 0.83 P < 0.0001) with the interval from parturition to the leptin nadir. These results show that plasma concentrations of leptin decrease in dairy cows in the early post-partum period and suggest that a delay in the recovery of leptin secretion increases the delay to the first ovulation.

Adipose Tissue↗

PubMed2000

Involvement of oxysterols and lysophosphatidylcholine in the oxidized LDL-induced impairment of serum albumin synthesis by HEPG2 cells.

Oxidized low density lipoproteins (Ox-LDLs) are increasingly thought to be a key element in atherogenesis. We have previously reported that serum albumin has important antioxidant properties and that a reduced synthesis of albumin may represent a crucial point in the overall antioxidant defense. In the present work, we aimed at determining whether Ox-LDL could modulate albumin synthesis in cultured human hepatocytes (HepG2 cells). With the use of enzyme immunoassay and radiolabeled leucine incorporation followed by specific immunoprecipitation, Ox-LDL was found to lead to a dose-dependent decrease in albumin secretion. Moreover, the protein synthesis and mRNA levels were decreased in the presence of Ox-LDL, as assessed by Northern blot analysis. Because oxysterols and lysophospholipids are key components of Ox-LDL, we tested the effects of oxysterols (7-ketocholesterol and 25-hydroxycholesterol) and lysophosphatidylcholine on albumin secretion and expression. In our experimental conditions, we found that incubations with oxysterols or lysophosphatidylcholine at pathophysiological concentrations similar to those measured in Ox-LDLs reproduced the above-mentioned inhibitory effects on albumin synthesis. On the basis of our in vitro data, we propose that this newly described biological effect of Ox-LDL might partly explain the findings of epidemiological studies indicating that reduced levels of serum albumin are associated with increased mortality.

Antioxidants↗

PubMed2000

Long-term alterations in adiposity affect the expression of melanin-concentrating hormone and enkephalin but not proopiomelanocortin in the hypothalamus of ovariectomized ewes.

We have developed a ruminant model to study long-term alterations in adiposity on the expression of appetite-regulating peptides in the hypothalamus. In this model endocrine and metabolic status are fully defined as well as body composition. The current study sought to define the effects of altered adiposity on the expression of genes for neuropeptide Y (NPY), POMC, enkephalin (ENK), and melanin-concentrating hormone (MCH). Ovariectomized ewes with high (60 +/- 1 kg) (FAT) or low (37 +/- 3 kg) body weights (THIN) were blood sampled every 10 min for 8 h to determine metabolic and endocrine status. The animals were then killed and the brains perfused for in situ hybridization. Body composition analysis was performed on the carcass using dual energy x-ray absorptiometry; this indicated that the FAT animals were 36 +/- 1% fat, whereas the THIN animals were 15 +/- 2% fat. The LH interpulse interval was lower and mean GH concentrations were higher in the THIN animals; cortisol and TSH levels were not different between the two groups but free T4 and free T3 levels were lower; the FT3:FT4 ratio was higher in THIN ewes. Levels of insulin, lactate, and nonesterified fatty acids were lower in the THIN group, and plasma glucose and urea concentrations were similar in THIN and FAT animals. Levels of gene expression of NPY and MCH were higher in THIN ewes. POMC expression was similar in the two groups. In the THIN animals, ENK expression was lower in the paraventricular and ventromedial nuclei but higher in the periventricular region. In conclusion, we have shown that alterations in adiposity influence the expression of appetite-regulating peptides in the absence of ovarian steroids. The appetite stimulators, NPY and MCH, appear to be involved in the metabolic response to altered adiposity, whereas ENK in the periventricular region may be linked to the secretion of GH and possibly LH. Our results suggest that altered expression of appetite- regulating peptides can be linked with the endocrine and metabolic adaptations that occur with long-term changes in adiposity.

Adipose Tissue↗

PubMed2000

Level of nutrition affects leptin concentrations in plasma and cerebrospinal fluid in sheep.

In mature male sheep, the level of nutrition acutely influences the secretion of reproductive hormones. The mechanism involved is not fully understood but findings in humans and laboratory rodents would suggest a major role for leptin that is secreted from adipose tissue and then travels via the circulation to the central nervous system. Before we can begin to test this hypothesis, we need to be able to measure leptin concentrations in blood plasma and cerebrospinal fluid. We have therefore developed a radioimmunoassay using antibodies raised against biologically active recombinant bovine-ovine leptin. Using this assay, we found that plasma concentrations of leptin were highly correlated to back-fat thickness and to the ratio of back-fat thickness to liveweight, in female and castrated male sheep. Plasma concentrations of leptin were higher in female sheep than in castrated or intact male sheep. Serial samples (every 5 min) suggested that the secretion of leptin in male sheep is episodic but it does not appear to show clear pulsatility, increases post-prandially, or a diurnal rhythm. Leptin concentrations in both plasma and cerebrospinal fluid increased within 5 days in male sheep fed a diet with a high content of energy and protein that also stimulates the secretion of LH pulses. These data suggest that in sheep, as in other species, leptin production is correlated with the mass of adipose tissue and that the hormone passes from the circulation to the cerebrospinal fluid and then to hypothalamic sites. There, it may affect appetite and perhaps GnRH secretion. The role of leptin in the link between nutrition and reproduction needs further investigation.

Adipose Tissue↗