Plasma ghrelin levels in patients with end-stage renal disease

Ghrelin is an acylated peptide stimulating secretion of the growth hormone (GH). It was originally isolated from the rat stomach as an endogenous ligand for the growth hormone secretagogue receptor. Although being predominantly produced by endocrine cells of the gastric fundus, its secretion has been found in various tissues including the kidney. To study the influence of renal failure on plasma ghrelin levels we examined 16 patients with end-stage renal disease (ESRD) receiving hemodialysis (8 men and 8 women) and 19 controls (10 men and 9 women). Both groups were comparable in age and BMI. In all subjects we assessed plasma levels of ghrelin, leptin, soluble leptin receptor, insulin, IGF-I, IGFBP-1, IGFBP-3 and IGFBP-6. Ghrelin levels were significantly higher in the group of dialyzed patients (4.49+/-0.74 vs. 1.79+/-0.15 ng/ml; p<0.001). These patients had significantly higher levels of GH, IGFBP-1, IGFBP-6, leptin and percentage of body fat (p<0.05). In the group of patients with ESRD plasma ghrelin levels positively correlated with IGFBP-1 (p<0.01). In the control group, ghrelin positively correlated with GH concentrations (p<0.01) and negatively correlated with the levels of insulin and creatinine (p<0.05). In conclusion, patients with ESRD have higher ghrelin concentrations, which might be caused by a decreased excretion/metabolism of ghrelin in the kidney during renal failure.     

Plasma adiponectin concentrations in patients with chronic renal failure: relationship with metabolic risk factors and ischemic heart disease.

AIMS: To compare plasma adiponectin levels between healthy controls and patients with chronic renal failure and to examine for a relationship between plasma adiponectin levels and ischemic heart disease as well as aortic distensibility which is an early marker of atherosclerosis. METHODS: We included 89 patients with CRF (45 on and 44 not on hemodialysis) and 70 controls in a cross-sectional study. Plasma adiponectin levels were measured by radioimmunoassay. Aortic distensibility was assessed by high-resolution ultrasonography. RESULTS: Plasma adiponectin levels were significantly almost twice as high in patients with renal failure compared to controls (9.7 +/- 1.1 vs. 5.4 +/- 0.6 microg/ml, p < 0.0001). No significant differences were found between renal patients on hemodialysis and not on hemodialysis (p = 0.71). Multivariate linear regression analysis in the renal patient group demonstrated a significant negative relationship between plasma adiponectin levels and ischemic heart disease (p = 0.02). The same analysis in the control subjects group showed a significant, negative relationship between plasma adiponectin levels and body mass index (p = 0.02) and a highly significant positive relationship with the high density lipoprotein cholesterol (p < 0.0001). In the total study population, glomerular filtration rate was the only independent predictor of plasma adiponectin concentrations. Aortic distensibility was lower in renal patients than in controls at a high level of significance (p < 0.0001). However, no significant relationship could be found between plasma adiponectin and aortic distensibility in either the controls or the renal patients. CONCLUSIONS: Plasma adiponectin levels are almost twice as high in patients with chronic renal failure in comparison with healthy controls, but not different between renal patients on and those not on hemodialysis. In addition, low plasma adiponectin levels are strongly associated with ischemic heart disease, but not with aortic distensibility in chronic renal failure.     

Ghrelin suppresses cardiac sympathetic activity and prevents early left ventricular remodeling in rats with myocardial infarction

A recent study suggests that exogenous ghrelin administration might decrease renal sympathetic nerve activity in conscious rabbits. In the present study, we investigated whether ghrelin administration would attenuate left ventricular (LV) remodeling following myocardial infarction (MI) via the suppression of cardiac sympathetic activity. Ghrelin (100 microg/kg sc, twice daily, n = 15) or saline (n = 15) were administered for 2 wk from the day after MI operation in Sprague-Dawley rats. The effects of ghrelin on cardiac remodeling were evaluated by echocardiographic, hemodynamic, histopathological, and gene analysis. In addition, before and after ghrelin (100 microg/kg sc, n = 6) was administered in conscious rats with MI, the autonomic nervous function was investigated by power spectral analysis obtained by a telemetry system. In ghrelin-treated rats, LV enlargement induced by MI was significantly attenuated compared with saline-treated rats. In addition, there was a substantial decrease in LV end-diastolic pressure and increases in the peak rate of the rise and fall of LV pressure in ghrelin-treated MI rats compared with saline-treated MI rats. Furthermore, ghrelin attenuated an increase in morphometrical collagen volume fraction in the noninfarct region, which was accompanied by the suppression of collagen I and III mRNA levels. Importantly, a 2-wk administration of ghrelin dramatically suppressed the MI-induced increase in heart rate and plasma norepinephrine concentration to the similar levels as in sham-operated controls. Moreover, acute administration of ghrelin to MI rats decreased the ratio of the low-to-high frequency spectra of heart rate variability (P < 0.01). In conclusion, these data suggest the potential usefulness of ghrelin as a new cardioprotective hormone early after MI.     

Acylated ghrelin secretion is acutely suppressed by oral glucose load or insulin-induced hypoglycemia independently of basal growth hormone secretion in humans

BACKGROUND: Ghrelin has been reported to be the natural ligand of growth hormone (GH) secretagogue receptor, and it is known that exogenous ghrelin administration strongly stimulates GH release in humans. However, the effects of endogenous ghrelin on GH secretion and changes in ghrelin levels during dynamic changes in GH levels are not well understood. METHODS: Therefore, we measured circulating acylated ghrelin concentrations during oral glucose tolerance tests (OGTTs) in patients with active acromegaly (AA, n = 9) and in age/sex/BMI-matched group A controls (n = 12), and during insulin tolerance testing (ITT) in patients with GH deficiency (GHD, n = 10) and in group B controls (n = 10). Plasma acylated ghrelin, serum GH, insulin and glucose levels were measured during each test. RESULTS: Fasting plasma ghrelin levels correlated negatively with serum insulin levels in both group A and B controls (r = -0.665; p < 0.05) but not in patients with AA or GHD. During OGTTs, circulating ghrelin levels decreased significantly with a nadir at 30 min in both patients with AA (p < 0.05) and group A controls (p < 0.01). Also, ITTs were followed by a significant decrease in circulating ghrelin levels with a nadir at 30 min in patients with GHD (p < 0.05) and in group B controls (p < 0.05). CONCLUSION: The results of the study show that at baseline acylated ghrelin levels do not differ with respect to the GH status (GH excess or GH deficiency) and, furthermore, the suppression of acylated ghrelin levels during OGTT or ITT is independent of the GH response to the tests.     

Absence of effects of short-term fasting on plasma ghrelin and brain expression of ghrelin receptors in the tilapia, Oreochromis mossambicus

Ghrelin is an important endocrine peptide that links the gastrointestinal system and brain in the regulation of food intake and energy expenditure. In human, rat, and goldfish plasma levels of ghrelin and GH are elevated in fasted animals, suggesting that ghrelin is an orexigenic signal and a driving force behind the elevated plasma levels of GH during fasting. Ghrelin's orexigenic action is mediated by the ghrelin receptor (GHS-R1a and GHS-R1b) which is localized on neuropeptide Y (NPY) neurons in the brain. Studies were undertaken to investigate the effect of short-term fasting on plasma ghrelin and brain expression of GHS-R1a, GHS-R1b, and NPY in the tilapia. Fasting for 7 days had no effect on plasma ghrelin concentrations, whereas significant increases in plasma levels of GH were observed on day 3. Fasting significantly reduced plasma levels of IGF-I on days 3 and 7, and of glucose on days 3, 5, and 7. Brain expression of ghrelin and GHS-R1b were significantly elevated in fasted fish on day 3, but were significantly reduced on day 5. This reduction was likely due to a significant increase in the expression in the fed controls on day 5 compared to day 0. No change was detected in the expression of GHS-R1a or NPY in the brain. These results indicate that ghrelin is not acting as a hunger signal in short-term fasted tilapia and is not responsible for the elevated levels of plasma GH.     

Elevated ghrelin plasma levels in patients with polycystic ovary syndrome.

Polycystic ovary syndrome is a common endocrine disorder in women. It is associated with hirsuitism, obesity, insulin resistance, abnormality in the growth hormone/insulin-like growth factor I (IGF-1) axis and polycystic ovaries. The etiology of PCOS has not been clarified. Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor. It is mainly secreted by stomach cells but has also been shown to be present in hypothalamus, pituitary, pancreas and gonads. Ghrelin is a regulator of energy homeostasis and GH secretion. The influence of ghrelin on insulin secretion and gonadal function is known. Since ghrelin may play an important role in pathophysiology of PCOS, we studied ghrelin levels in a group of 52 women with PCOS and in 16 women in a control group. Plasma levels of insulin, total testosterone, SHBG, LH, and FSH were also measured. In conclusion, PCOS women have higher ghrelin levels than controls. Ghrelin negatively correlates with BMI and insulin levels in PCOS group. A relation between ghrelin and SHBG was observed. Our data suggest that ghrelin could be the possible link in PCOS etiology.     

Ghrelin对改善心衰大鼠左室功能紊乱的作用研究

目的:慢性心力衰竭(CHF)患者终末期阶段常发生左室(LV)重塑和心脏性恶病质,有研究称Ghrelin可能对CHFLV功能和能量代谢产生保护作用。本文旨在探讨Ghrelin对CHF大鼠LV功能紊乱和心源性恶病质的作用。方法:建立左冠状动脉结扎术和假手术组,手术后4周,给予大鼠Ghrelin或生理盐水3周。用超声心动图和心脏导管术监测结果。结果:与给予安慰剂组相比,用Ghrelin治疗的CHF和假手术组,血浆GH和胰岛素样生长因子1明显升高(t=1.49,t=0.71,P0.05)。与Sham-Placebo组相比,CHF-Placebo组大鼠体重明显减轻(t=2.18,P0.05)。然而与CHF-Placebo组相比,CHF-Ghrelin组大鼠,体重(t=3.89,P0.05),心输出量(t=3.28,P0.05),LV dP/dtmax(t=3.90,P0.05)明显增加。Ghrelin增加了CHF大鼠心脏舒张压,抑制LV扩大,增加LV缩短分数。结论:长期注射Ghrelin可改善CHF大鼠LV功能紊乱,减缓LV重构和心脏性恶病质的发展,有望为CHF的治疗提供新的途径和方法。     

Relationship Between Serum Parathyroid Hormone and Trace Elements (Serum Zinc and Magnesium) in Hemodialyzed Chronic Renal Failure Children

Secondary hyperparathyroidism and trace elements’ metabolism disturbances are common, important, and treatable complications of chronic renal failure (CRF).The relation between parathyroid hormone (PTH) and some trace elements in CRF patients on hemodialysis is still not completely elucidated. The aim of this work is to determine the serum levels of PTH and the trace elements zinc (Zn) and magnesium (Mg) in children with CRF under hemodialysis. The relation between PTH and those trace elements will be investigated. The study included 24 children (15 males and nine females) with CRF on regular hemodialysis. Also, 15 healthy age-matched children were included as control group. Serum levels of PTH, zinc, and magnesium were determined in all cases and controls. PTH and magnesium levels in patients were significantly higher than controls. Serum zinc levels were significantly lower than controls. There was a significant negative correlation between serum levels of PTH and zinc as well as an insignificant negative correlation between PTH and serum magnesium in CRF patients. Elevated PTH may play a role in the pathogenesis of hypozincemia. However, this is another negative report on the relation between PTH and serum Mg in children with CRF.     

Ghrelin对心肌梗死大鼠恶性心律失常和早期左室重构的影响(英文)

目的:本文主要研究ghrelin对心肌梗死大鼠恶性心律失常和早期左室重构的影响。方法:心肌梗死大鼠模型每天两次注射ghrelin(100μg/kg)或生理盐水。通过超声心动图评估大鼠的心脏重量并且观察大鼠的血流动力学。使用酶免疫分析法测定血清胰岛素生长因子I(IGF-1)、血浆肾上腺素、去甲肾上腺素和多巴胺的浓度。注射药物前后分析大鼠的神经功能。结果:与对照组相比,ghrelin治疗的心肌梗死模型大鼠生存率显著增加(P0.05),心脏功能增强,但心肌梗死面积差异不大(P0.05)。结论:Ghrelin能够提高心肌梗死模型大鼠的生存率、缓解心肌梗死大鼠心率失常、改善心肌梗死大鼠左心室重构。     

Effects of high-fat feeding and fasting on ghrelin expression in the mouse stomach

Ghrelin is a peptide identified as an endogenous ligand for the growth hormone secretagogue receptor. Studies have shown that ghrelin stimulates growth hormone, promotes food intake and decreases energy expenditure. Furthermore, feeding status seems to influence plasma ghrelin levels, as these are increased during fasting, whereas feeding and oral glucose intake reduce plasma ghrelin. This study examined whether standardized obesity and fasting affect cellular expression of ghrelin. Specimens from the gastrointestinal tract of fed or 18-h fasted, low-fat or high-fat fed (10 weeks on diet) C57BL/6J mice were studied by immunocytochemistry (ICC) for ghrelin and in situ hybridization (ISH) for ghrelin mRNA. Ghrelin was expressed in especially the corpus but also the antrum of the stomach of all groups studied. Cells positive for ghrelin and ghrelin mRNA in the stomach were reduced in high-fat fed mice. In contrast, ghrelin expression was not affected by fasting. The reduction in ghrelin expression in the high-fat fed mice was associated with a reduction in plasma levels of ghrelin, whereas after fasting, when expression rate was not altered, there was an increase in plasma ghrelin. In conclusion, ghrelin is highly expressed in the corpus and antrum of the stomach of C57BL/6J mice. This expression is reduced in obesity, whereas fasting has no effect.     

Atrial natriuretic hormone secretion in patients with renal failure

To study the effects of volume overload and renal failure on plasma levels of immunoreactive atrial natriuretic hormone (IR-ANH), we measured levels of this hormone in normal subjects, in patients with advanced chronic renal failure (CRF) with and without clinically evident volume overload, and in patients with end-stage renal disease (ESRD) treated with chronic hemodialysis. The levels were 13 +/- 2 pmol/l in normal volunteers, 77 +/- 24 pmol/l in patients with CRF without volume overload, and 219 +/- 50 pmol/l in patients with CRF and clinically evident volume overload (analysis of variance, p less than 0.001, alpha = 0.05 compared to normals). In patients with ESRD, the levels of IR-ANH were 145 +/- 46 pmol/l before dialysis and decreased to 87 +/- 31 after dialysis (p less than 0.025). No correlation was found between the decrease in IR-ANH levels and the decrease in weight during dialysis. A significant positive correlation was found between the IR-ANH levels and blood urea nitrogen in patients with CRF (r = 0.658, p less than 0.01). Volume overload appears to be the most important stimulatory factor for ANH secretion in renal failure patients but other mechanisms, especially a decrease in metabolic clearance, may also contribute to elevated plasma levels. The increased secretion of ANH in patients with renal failure may be an important adaptive response to volume overload and hypertension.     

Correlation between pentosidine and endothelin-1 in subjects undergoing chronic hemodialysis.

Advanced glycation end-products (AGEs), which accumulate in the blood and tissues of patients with chronic renal failure (CRF) undergoing chronic hemodialysis, play an important role in the pathogenesis of uremic complications. Endothelin 1 (ET1), a 21-amino acid peptide with vasoconstricting and mitogenic properties, is an important factor in the endothelial dysfunction occurring in uremia. The circulating levels of both AGEs and ET1 have been reported to be increased in chronic renal failure. In the present study we evaluated the possible relationship between pentosidine and ET1 plasma levels in CRF patients undergoing chronic hemodialysis treatment. The plasma concentrations of "free" and bound pentosidine (HPLC methods) and endothelin-1 (RIA method) were measured before the hemodialysis session in 40 nondiabetic CRF patients (22 males and 18 females; 54+/-3 years) on chronic hemodialysis for at least 1 year. Forty age- and sex-matched normal subjects served as a control group. In hemodialyzed patients, the overall pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein levels (24.9+/-2.04 pmol/mg protein and 110.5+/-5.9 pmol/ml, respectively) were significantly higher than those recorded in normal subjects (2.0+/-0.2 pmol/mg protein and 0.7+/-0.2 pmol/ml, respectively ). Endothelin-1 was also significantly (p<0.01) increased in CRF patients (10.6+/-0.4 pmol/ml in CRF patients and 2.7+/-0.3 pmol/ml in normal subjects). A significant positive correlation (p<0.01) was seen between "total" pentosidine (pentosidine residues and pentosidine-free adduct plus pentosidine-free adduct bound reversibly to protein) levels and endothelin-1 plasma values. The correlation between pentosidine and endothelin-1 provides further evidence that some AGEs exert a detrimental effect on the vascular endothelium, thereby contributing to the hypertension and other cardiovascular damage seen in CRF patients.     

Effects of ghrelin injection on plasma concentrations of glucose, pancreatic hormones and cortisol in Holstein dairy cattle

Ghrelin affects not only growth hormone secretion but also nutrient utilization and metabolic hormone secretion in humans and experimental animals. The effects of ghrelin on plasma metabolic hormone and metabolite levels in domestic herbivores remain unclear despite the fact that the physiological characteristics of nutrient digestion and absorption imply specific responses to ghrelin. Therefore, the effects of ghrelin on plasma glucose, pancreatic hormones and cortisol concentrations were investigated in Holstein dairy cattle in various physiological states. Ghrelin (0.3 nmol/kg) or placebo (2% bovine serum albumin in saline) was intravenously injected in pre-ruminant calves (pre-rumen function), adult non-lactating (functional rumen) and lactating cows (functional rumen and lactation), and plasma glucose, insulin, glucagon and cortisol concentrations were then determined. Ghrelin injection increased plasma glucose concentrations in adult cows, especially in lactating cows. No hyperglycemic response was observed in pre-ruminant calves. A transient rise of insulin and glucagon levels was distinctively found in lactating cows in response to the ghrelin administration. Ghrelin injection decreased the insulin level in pre-ruminant calves. Ghrelin increased cortisol secretion independently of the physiological state. The results of the present study suggest that the effects of ghrelin on plasma glucose and pancreatic hormone levels may reflect differences in the physiological states of dairy cattle.     

Dopamine control of aldosterone secretion in end-stage renal failure

The role of the tonic inhibitory effect of dopamine on aldosterone secretion has been investigated in 10 patients with chronic renal failure (CRF) on hemodialysis, in 8 normotensive renal transplant recipients (Tx) with normal renal function and in 8 normotensive volunteers (NV). The following tests were performed: the response of plasma aldosterone (PA) to metoclopramide administration; the response of plasma prolactin (PRL) to TRH administration, and the changes induced by Lisuride (a dopaminergic agonist, on the values of PA and PRL). The basal values of PA and PRL were higher in CRF than in NV and Tx. The inverse was true for plasma renin activity (PRA) values. The response of PA and PRL to metoclopramide showed blunted increases in CRF when compared to NV, in the absence of changes of PRA, cortisol and potassium. After TRH administration, PRL increase in CRF was also inferior. Lisuride induced a decrease of both PA and PRL both in CRF and NV. In Tx, basal values of PA and PRL were similar to NV. Nevertheless, the response to metoclopramide and TRH were partially blunted when compared to that of NV. These results point to the existence of a deranged dopaminergic regulation of aldosterone secretion in end-stage renal failure patients. The alterations are partially corrected by a well-functioning kidney graft.     

Enriched protein diet-modified ghrelin expression and secretion in rats

Gastrointestinal (GI) integrity and function are regulated by nutrition and growth factors. The discovery of ghrelin, a natural growth hormone (GH) secretagogue produced by the gastrointestinal (GI) tract, is a potential link between diet and growth signals. The aim of this study was to evaluate macronutrient effect on ghrelin expression and secretion in addition to some possible function in intestinal trophic status. Wistar rats were fed a high-carbohydrate, high-protein (HP), high-fat or standard (St) diet. Animals received the same daily food volume and caloric intake. After 7 days, animals were fasted for 24 h and blood and tissue samples were obtained just before feeding or at 2 or 6 h after feeding. Fasting high-protein-fed rats had higher ghrelin plasma levels than with rats fed the high-carbohydrate, high-fat or standard diets. Two-hours after refeeding, ghrelin plasma levels had decreased in all groups with a slight recovery at 6 h after refeeding, except in the high-protein group. Ghrelin plasma levels in rats fed with the high-protein diet correlated negatively with their GH and insulin-like growth factor 1 (IGF-1) plasma concentrations which were also the lowest among the study groups. In conclusion, ghrelin secretion was nutritionally manipulated because a protein-enriched diet increased its levels.     

Oxidative stress, phosphate and creatinine levels are independently associated with vascular endothelial growth factor levels in patients with chronic renal failure

Elevated VEGF levels has been reported in patients with chronic renal failure (CRF), but the reasons for its higher level in renal insufficiency remain unknown. We assessed VEGF, SOX markers: total peroxide, Cu/Zn superoxide dismutase (Cu/Zn SOD), the levels of autoantibodies against oxidized LDL (OxLDL-Ab), and inflammation markers: high sensitivity C-reactive protein (hs CRP), interleukine-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) in 55 CRF patients and 18 controls. The patients with CRF showed a significant increase in plasma levels of VEGF, markers of inflammation, total peroxide and Cu/Zn SOD levels compared with controls. The strong positive associations were between VEGF and creatinine, urea, phosphate and CaxP product (all p<0.0001), Cu/Zn SOD (p<0.001) and hs CRP levels (p<0.01). VEGF showed a strong inverse relationship with eGFR (p<0.0001). In multiple regression analysis increased Cu/Zn SOD, phosphate and creatinine levels were found to be independent factors affecting VEGF. This study documented significant elevation in plasma values of VEGF in patients with CRF, which appears early during the progression of renal insufficiency. Increased oxidative stress, phosphate levels and impaired elimination by kidney were the main factors affecting the plasma levels of this growth factor in CRF patients.     

Ghrelin对心肌梗死后心肌重塑及心脏功能的影响及其机制研究

目的:观察ghrelin对心肌梗死(MI)大鼠心肌重塑和心脏功能的影响,并探讨其可能的机制。方法:应用冠状动脉结扎术创建大鼠MI模型,并设立假手术组作为对照;造模成功后每天2次注射ghrelin(100μg/kg),持续4周,以此作为MI-ghrelin组,并以每天注射生理盐水的MI大鼠作为MI-生理盐水组。检测和比较各组大鼠左心室重塑和血流动力学的改变情况;非梗死心肌中白介素(IL)-1β、肿瘤坏死因子-α(TNF-α)、基质金属蛋白酶(MMP)-2、MMP-9 mRNA和蛋白的表达;梗死边界心肌细胞的凋亡情况。结果:Ghrelin可使心肌梗死后的MI大鼠降低的缩短分数(FS)、左室内压最大变化率均显著下降(dP/dtmax)、疤痕厚度明显升高,增加左室舒张末压(LVEDP)、左室收缩末内径(LVESD)、左室舒张末期内径(LVEDD)、梗死边界心肌细胞的凋亡指数显著降低。此外,ghrelin可抑制心肌梗死后的MI大鼠非梗死心肌中白介素(IL)-1β、肿瘤坏死因子-α(TNF-α)、质金属蛋白酶(MMP)-2和MMP-9的mRNA和蛋白的表达。结论:Ghrelin可缓解MI后大鼠LV功能紊乱及心室重塑,这可能与其抑制炎症反应及基质金属蛋白酶的表达有关。     

Regulation of ghrelin secretion during pregnancy and lactation in the rat: possible involvement of hypothalamus

We investigated the plasma concentration of ghrelin peptide during pregnancy and lactation in rats. Plasma ghrelin levels on days 10 and 15 of pregnancy were significantly lower than those of the non-pregnant rats. Thereafter, the plasma ghrelin levels on day 20 of pregnancy sharply increased to levels comparable with those in non-pregnant rats. Ghrelin peptide concentrations in the stomach did not change significantly during pregnancy. In the hypothalamus, ghrelin mRNA levels were significantly lower on day 15 of pregnancy than in the non-pregnant rats. Also, plasma ghrelin levels were significantly lower in lactating dams than non-lactating controls on days 3 and 8 of lactation. We examined the possible involvement of prolactin and oxytocin in the regulation of plasma ghrelin concentrations during lactation. Although plasma prolactin levels were decreased by the administration of bromocriptine, plasma ghrelin levels did not differ significantly between vehicle- and drug-treated lactating rats. Administration of haloperidol produced a marked increase in plasma prolactin levels as compared with the non-lactating controls. However, plasma ghrelin levels were not significantly different between vehicle- and drug-treated rats. Administration of an oxytocin antagonist into the lateral ventricle significantly inhibited the increase in the plasma oxytocin level induced by acute suckling. However, plasma ghrelin levels did not significantly between the groups. These observations indicated that the decrease in serum ghrelin is caused by a loss of the contribution of hypothalamic ghrelin. Furthermore, the present results suggested that the suckling stimulus itself, but the release of prolactin or oxytocin, is the factor most likely to be responsible for the suppression of ghrelin secretion during lactation.     

Ghrelin Acts as an Antioxidant Agent in the Rat Kidney

Ghrelin has recently been shown to improve renal function in rat with acute renal failure. In this setting, the protective effects have been suggested to be due to its antioxidant properties. Thus, the aim of this study was to measure the antioxidant abilities of this hormone via enzymatic and lipid peroxidation analyses. Wistar rats were divided into two control and two treatment groups, the treated animals receiving 3 nmol of ghrelin as subcutaneous administrations on each of 10 consecutive days and physiological saline injected to controls. Catalase (CAT) activity was significantly higher in the treated animals when compared to controls, while in contrast, lipid peroxidation measured by thiobarbituric acid reactive substances (TBARS), was significantly reduced in the ghrelin treated animals. Furthermore, superoxide dismutase (SOD) activity and glutathione (GSH) content were both much higher in treated female rats than in controls and although there was a slight increase in glutathione peroxidase (GPx) activity in kidneys of ghrelin treated rats, the difference was insignificant. These findings suggest that ghrelin has beneficial antioxidant properties in the rat kidney by increasing antioxidant enzyme activities. These effects were more noticeable in treated female rats, possibly due to higher levels of estrogen.