Biomedical subjects

Kenji Kangawa

Publications and source records attributed to Kenji Kangawa.

At least 181 records · Page 10Linked to original sources

PubMed2003

Enhanced plasma ghrelin levels in rats with streptozotocin-induced diabetes.

Ghrelin is a novel gastrointestinal peptide that stimulates growth hormone secretion, food intake, and body weight gain. Increased ghrelin secretion has been reported in such negative energy states as starvation and low body weight. We investigated the dynamics of ghrelin in rats with streptozotocin-induced diabetes, because they present reduced body weight and hyperphagia. The plasma ghrelin levels and gastric preproghrelin mRNA expression levels of the diabetic rats increased significantly and their gastric ghrelin levels decreased significantly. Negative energy balance may enhance preproghrelin mRNA expression and ghrelin secretion into the bloodstream.

Animals↗

PubMed2003

The role of circulating ghrelin in growth hormone (GH) secretion in freely moving male rats.

To examine the physiological significance of plasma ghrelin in generating pulsatile growth hormone (GH) secretion in rats, plasma GH and ghrelin levels were determined in freely moving male rats. Plasma GH was pulsatilely secreted as reported previously. Plasma ghrelin levels were measured by both N-RIA recognizing the active form of ghrelin and C-RIA determining total amount of ghrelin. Mean +/- SE plasma ghrelin levels determined by N-RIA and C-RIA were 21.6 +/- 8.5 and 315.5 +/- 67.5 pM, respectively, during peak periods when plasma GH levels were greater than 100 ng / ml. During trough periods when plasma GH levels were less than 10 ng / ml, they were 16.5 +/- 4.5 and 342.1 +/- 29.8 pM, respectively. There were no significant differences in plasma ghrelin levels between two periods. Next, effect of a GH secretagogue antagonist, [D-Lys-3]-GHRP-6, on plasma GH profiles was examined. There were no significant differences in both peak GH levels and area under the curves of GH (AUCs) between [D-Lys-3]-GHRP-6-treated and control rats. These findings suggest circulating ghrelin in peripheral blood does not play a role in generating pulsatile GH secretion in freely moving male rats.

Animals↗

PubMed2003

Effect of chronic treatments with ghrelin on milk secretion in lactating rats.

Ghrelin, a novel acylated peptide and endogenous ligand for growth hormone (GH) secretagogue receptor, was originally isolated from rat and human stomachs. In addition to its GH-releasing activity, ghrelin plays an important role in many physiological functions, including food intake, gastric acid secretion, neonatal development, and so on. In this study, the effect of daily treatment with ghrelin on milk production was investigated in lactating rats and the development of the pups was monitored. Daily subcutaneous injection of ghrelin into nursing dams for 8 days from parturition caused a significant increase in milk yield and litter weight gain. When litters nursed by ghrelin-treated and saline-treated dams were interchanged on day 4 of lactation, the growth curves were reversed. Daily injections of ghrelin also increased plasma GH levels. Northern blot analysis revealed that daily injection of ghrelin significantly increased mammary casein mRNA expression. In addition, RT-PCR analysis showed that a ghrelin receptor was present in the mammary glands of lactating rats. These results suggest that ghrelin may play an important role in milk production in lactating dams.

Animals↗

PubMed2003

Potentiation of C-type natriuretic peptide with ultrasound and microbubbles to prevent neointimal formation after vascular injury in rats.

OBJECTIVES: Long-term intravenous infusion of high-dose C-type natriuretic peptide (CNP) is known to prevent neointimal formation after vascular injury. Ultrasound (US) irradiation during microbubbles (MBs) infusion (US/MBs) has been used for local delivery of bioactive agents. We examined whether short-term infusion of CNP could also inhibit neointimal development and whether combined US/MBs treatment at the beginning of the CNP infusion could enhance its effect. METHODS: In the rat carotid artery-balloon injury model, the intima/media area (I/M) ratio 14 days after injury was compared among various short-term post-injury treatments. For combined US/MBs, a commercial echocardiograph (1.8 MHz, mechanical index 1.0) and albumin-coated octafluoropropane gas MBs were used. RESULTS: Infusion of high-dose CNP (1.0 microg/kg/min) immediately after injury for only 24 h successfully reduced the I/M ratio (0.18+/-0.05) to 18% of the ratio in control rats (1.00+/-0.13) that underwent only balloon injury. Although low-dose CNP (0.1 microg/kg/min for 24 h) alone was not effective in reducing the I/M ratio (0.83+/-0.18), combined US/MBs treatment for the first 80 min of the infusion markedly reduced the I/M ratio (0.17+/-0.07), which persisted until 28 days after injury (0.16+/-0.04). CONCLUSIONS: The effects of CNP on the events occurring early after arterial injury may be important in preventing subsequent neointimal development. Thus, intravenous infusion of CNP with US/MBs at its initiation may provide a clinically feasible anti-restenosis therapy applicable immediately after vascular interventions.

Analysis of Variance↗

PubMed2003

Existence of ghrelin-immunopositive and -expressing cells in the proventriculus of the hatching and adult chicken.

Ghrelin was isolated from the rat stomach as an endogenous ligand for the growth hormone secretagogue receptor (GHS-R) and has been found in the gastrointestinal tract of many vertebrates. Although the sequence and structure of chicken ghrelin has recently been determined, morphological characteristics of ghrelin cells in the chicken gastrointestinal tract are still obscure. In this study, we investigated ghrelin expression and distribution of ghrelin-producing cells in the hatching and adult chicken gastrointestinal tract by RT-PCR, immunohistochemistry and in situ hybridization. Ghrelin mRNA expression was observed mainly in the proventriculus in the hatching chicken and in the proventriculus, pylorus and duodenum of the adult chicken by RT-PCR. Ghrelin-immunopositive (ghrelin-ip) cells in the proventriculus were located at the mucosal layer but not in the myenteric plexus or smooth muscle layer. The number of ghrelin-ip cells in the adult chicken was greater than that in the hatching chicken. Interestingly, in the adult chicken, the number of ghrelin-ip cells were almost the same as that of ghrelin mRNA-expressing (ghrelin-ex) cells; however, in the hatching chicken, the number of ghrelin-ex cells was greater than that of ghrelin-ip cells. These results clearly demonstrate that ghrelin-producing cells exist in the chicken gastrointestinal tract, especially in the proventriculus, from hatching to adult stages of development, as well as in mammals.

Animals↗

PubMed2003

Somatostatin suppresses ghrelin secretion from the rat stomach.

Ghrelin is an acylated peptide that stimulates food intake and the secretion of growth hormone. While ghrelin is predominantly synthesized in a subset of endocrine cells in the oxyntic gland of the human and rat stomach, the mechanism regulating ghrelin secretion remains unknown. Somatostatin, a peptide produced in the gastric oxyntic mucosa, is known to suppress secretion of several gastrointestinal peptides in a paracrine fashion. By double immunohistochemistry, we demonstrated that somatostatin-immunoreactive cells contact ghrelin-immunoreactive cells. A single intravenous injection of somatostatin reduced the systemic plasma concentration of ghrelin in rats. Continuous infusion of somatostatin into the gastric artery of the vascularly perfused rat stomach suppressed ghrelin secretion in both dose- and time-dependent manner. These findings indicate that ghrelin secretion from the stomach is regulated by gastric somatostatin.

Animals↗

PubMed2003

Neuromedin U acts in the central nervous system to inhibit gastric acid secretion via CRH system.

Neuromedin U (NMU) is a hypothalamic peptide involved in energy homeostasis and stress responses. NMU, when administered intracerebroventricularly, decreases food intake and body weight while increasing body temperature and heat production. In addition, NMU, acting via the corticotropin-releasing hormone (CRH) system, induces gross locomotor activity and stress responses. We studied the effect of intracerebroventricularly administered NMU (0.5-4 nmol) in the regulation of gastric functions in conscious rats. Intracerebroventricular administration of NMU significantly decreased gastric acid output to 30-60% and gastric emptying to 35-70% in a dose-dependent manner. Vagotomy did not abolish the inhibitory effect of NMU on pentagastrin-induced gastric acid secretion. Pretreatment with indomethacin (10 mg/kg), an inhibitor of prostaglandin synthesis, also did not affect NMU-induced acid inhibition. Pretreatment with anti-CRH IgG (1 microg/rat), however, completely blocked NMU-induced acid inhibition (P < 0.01). Administration of yohimbine (4 mg/kg), an alpha(2)-adrenergic receptor antagonist, also abolished NMU-induced acid inhibition (P < 0.01). These findings suggest that NMU is critical in the central regulation of gastric acid secretion via CRH.

Animals↗

PubMed2003

Anti-cachectic effect of ghrelin in nude mice bearing human melanoma cells.

Ghrelin is a novel brain-gut peptide that stimulates food intake and body weight gain. We studied the anabolic effect of ghrelin in a cancer cachexia mouse model. SEKI, a human melanoma cell line, was inoculated into nude mice to examine the effects of ghrelin on food intake and body weight. The intraperitoneal administration of ghrelin twice a day (6 nmol/mice/day) for 6 days suppressed weight loss in SEKI-inoculated mice and increased the rate of weight gain in vehicle-treated nude mice. Ghrelin administration also increased food intake in both SEKI- and vehicle-treated mice. Both the weight of white adipose tissue and the plasma leptin concentration were reduced in tumor-inoculated mice compared with vehicle-treated mice; these factors increased following ghrelin administration. The levels of both ghrelin peptide and mRNA in the stomach were upregulated in tumor-inoculated mice. The anabolic effect of ghrelin efficiently reverses the cachexia in mice bearing SEKI human melanoma. Ghrelin therefore may have a therapeutic ability to ameliorate cancer cachexia.

Animals↗

PubMed2003

Decreased mature adrenomedullin levels in feto-maternal tissues of pregnant women with histologic chorioamnionitis.

Adrenomedullin (AM) gains its bioactivity by amidation at its C-terminal, forming "mature AM." The mature AM and the expression of AM receptor component mRNAs, receptor activity-modifying protein 2 and calcitonin receptor-like receptor, from feto-maternal tissues of normal pregnant women and women with histologic chorioamnionitis were examined to clarify the pathophysiological features of this intrauterine infection. Samples of the placenta and fetal membranes were obtained from 10 normal pregnant women and eight women with histologic chorioamnionitis under informed consent. Mature AM in the fetal membranes was significantly lower in patients with chorioamnionitis than in normal pregnant women. On the other hand, there were no differences in mature AM levels in the placenta between the two groups. The total AM levels as a sum of mature and immature AM were not significantly different between the two groups in either area. The ratio of mature AM/total AM was significantly decreased in the fetal membranes of the patients with chorioamnionitis compared with normal pregnancies, but not in the placenta. Also, levels of mature AM were negatively correlated with C-reactive protein concentrations. The present results thus suggested that mature AM may have some role in chorioamnionitis.

Adrenomedullin↗

PubMed2003

Ventricular adrenomedullin system in the transition from LVH to heart failure in rats.

We investigated whether adrenomedullin (AM) participates in the pathophysiology during the transition from left ventricular hypertrophy (LVH) to heart failure (HF). We used the Dahl salt-sensitive (DS) rat model, in which systemic hypertension causes LVH at the age of 11 weeks, followed by HF at the age of 18 weeks. Two molecular forms of AM levels in the plasma and myocardium at the LVH stage were significantly elevated compared with those in controls, and they were further increased at the HF stage. Interestingly, the LV tissue AM-mature/AM-total ratio was higher only in the HF group than in controls and LVH. The LV tissue AM-mature/AM-total ratio, AM-mature, and AM-total concentrations had close relations with the LV weight/body weight (r=0.72, r=0.79, and r=0.70, respectively; all P<0.001). AM gene expression was significantly increased at the LVH stage and was further increased at the HF stage. Furthermore, gene expression of AM receptor system components such as calcitonin receptor-like receptor (CRLR), receptor activity-modified protein 2 (RAMP2), and RAMP3 were significantly increased at the stage of LVH and HF. Regarding other neurohumoral factors, plasma renin and aldosterone levels were not increased at the LVH stage but were increased at the HF stage, whereas atrial natriuretic peptide was increased in both the plasma and myocardium at the LVH stage and was further increased at the HF stage. These results suggest that induction of the cardiac AM system, including the ligand, receptor, and amidating activity, may modulate pathophysiology during the transition from LVH to HF in this model.

Adrenomedullin↗

PubMed2003

Calcitonin receptor-stimulating peptide, a new member of the calcitonin gene-related peptide family. Its isolation from porcine brain, structure, tissue distribution, and biological activity.

We isolated a novel biologically active peptide, designated calcitonin receptor-stimulating peptide (CRSP), from the acid extract of the porcine brain by monitoring cAMP production in the porcine kidney cell line LLC-PK(1). Determination of the amino acid sequence and cDNA analysis encoding a CRSP precursor showed that this peptide has approximately 60% identity in the amino acid sequence with human calcitonin gene-related peptide type-alpha (alphaCGRP), type-beta (betaCGRP), and porcine CGRP. Northern blot analysis and radioimmunoassay demonstrated that CRSP is expressed mainly in the thyroid gland and the central nervous system, in which the calcitonin receptor was abundantly expressed. Synthetic CRSP elicited a potent stimulatory effect on the cAMP production in LLC-PK(1) cells. Although it shows significant sequence similarity with CGRPs, this peptide did not elicit cAMP elevation in cells that endogenously expressed a CGRP receptor or an adrenomedullin receptor or were transfected with either of these recombinant receptors. Administration of CRSP into anesthetized rats did not alter the blood pressure but induced a transient decrease in the plasma calcium concentration. In fact, this peptide potently increased the intracellular cAMP concentration in COS-7 cells that expressed the recombinant calcitonin receptor. These unique properties indicate that CRSP is not a porcine counterpart of betaCGRP and probably elicits its biological effects via the calcitonin receptor.

3T3 Cells↗

PubMed2003

Identification of tilapia ghrelin and its effects on growth hormone and prolactin release in the tilapia, Oreochromis mossambicus.

We have identified ghrelin and cDNA encoding precursor protein from the stomach of a euryhaline tilapia, Oreochromis mossambicus. The sequence of 20-amino acid tilapia ghrelin is GSSFLSPSQKPQNKVKSSRI. The third serine residue was modified by n-decanoic acid. The carboxyl-terminal end of the peptide possessed an amide structure. RT-PCR analysis revealed high levels of gene expression in the stomach and low levels in the brain, kidney and gill. Tilapia ghrelin stimulated growth hormone (GH) and prolactin (PRL) release from the organ-cultured tilapia pituitary at a dose of 10 nM. Thus, a novel regulatory mechanism of GH secretion by gastric ghrelin seems to be conserved in the tilapia. Stimulation of PRL release by homologous ghrelin has been reported in human, bullfrog and eel, and suggests the presence of growth hormone secretagogue receptor not only on somatotrophs but also on PRL cells of the tilapia pituitary.

Amino Acid Sequence↗

PubMed2003

Ghrelin improves left ventricular dysfunction and cardiac cachexia in heart failure.

Ghrelin is a novel growth-hormone-releasing peptide isolated from the stomach that has been identified as an endogenous ligand for the growth-hormone secretagogue receptor. This peptide results in a positive energy balance by stimulating food intake and inducing adiposity through growth-hormone-independent mechanisms. In addition, ghrelin has several cardiovascular effects, as indicated by the presence of its receptor in blood vessels and ventricles of the heart. Infusion of ghrelin decreases systemic vascular resistance and increases cardiac output in patients with heart failure. Furthermore, repeated administration of ghrelin improves cardiac structure and function, and attenuates the development of cardiac cachexia in rats with heart failure. These results suggest that ghrelin has therapeutic potential in the treatment of severe chronic heart failure.

Animals↗

PubMed2003

Cardiovascular and hormonal effects of subcutaneous administration of ghrelin, a novel growth hormone-releasing peptide, in healthy humans.

Ghrelin is a novel GH (growth hormone)-releasing peptide isolated from the stomach. The cardiovascular and hormonal effects of the subcutaneous administration of ghrelin in humans remain unknown. Six healthy volunteers each received subcutaneous administration of three doses of ghrelin (1, 5 or 10 microg/kg) and placebo; the order of administration was randomized, and separate doses were given at least 24 h apart. The serum GH level dose-dependently increased from 0.5 +/- 0.4 to 3.6 +/- 2.1 ng/ml (1 microg/kg ghrelin; P=0.99 compared with baseline), 27.1 +/- 12.0 ng/ml (5 microg/kg; P<0.01 compared with baseline) and 45.4 +/- 12.8 ng/ml (10 microg/kg; P<0.01 compared with baseline) 30 min after ghrelin administration. Subcutaneous administration of ghrelin did not significantly alter circulating levels of corticotropin, cortisol, insulin-like growth factor-1, noradrenaline or adrenaline, although 10 microg/kg ghrelin slightly increased the prolactin level. No significant changes in heart rate or mean arterial pressure were observed. In contrast, the left ventricular ejection fraction, as assessed by echocardiography, increased dose-dependently from 63.5 +/- 0.6% to 65.1 +/- 0.9% (1 microg/kg ghrelin; P=0.97 compared with baseline), 69.6 +/- 1.3% (5 microg/kg; P<0.01 compared with baseline) and 71.5 +/- 0.9% (10 microg/kg; P<0.01 compared with baseline) 30 min after ghrelin administration. These haemodynamic and hormonal changes were still apparent 60 min after ghrelin injection. In conclusion, subcutaneous administration of ghrelin dose-dependently induced relatively specific GH release and enhanced cardiac performance in humans.

Adrenocorticotropic Hormone↗

PubMed2003

Microsatellite DNA polymorphism of human adrenomedullin gene in type 2 diabetic patients with renal failure.

BACKGROUND: Adrenomedullin (AM) is a hypotensive peptide widely produced in the cardiovascular organs and tissues such as the heart, kidney, and the vascular cells. We have previously cloned and sequenced the genomic DNA encoding human AM gene, and determined that the gene is located in the short arm of chromosome 11. The 3'-end of the gene is flanked by the microsatellite marker of cytosine adenine (CA) repeats. In this study, we investigated the association between DNA variations in AM gene and the predisposition to develop nephropathy in type 2 diabetes mellitus. METHODS: Genomic DNA was obtained from the peripheral leukocytes of 233 normal healthy subjects (NH), 139 type 2 diabetic patients on hemodialysis (DM-HD), 106 control patients with type 2 diabetes without nephropathy (DM-C) and 318 hemodialysis patients due to chronic glomerulonephritis (CGN-HD). The genomic DNA was subject to polymerase chain reaction (PCR) using a fluorescence-labeled primer, and the number of CA repeats were determined by polyacrylamide gel electrophoresis (PAGE). RESULTS: In our Japanese subjects, there existed four types of alleles with different CA-repeat number; 11, 13, 14, and 19. The frequencies of these alleles were 11: 27.7%, 13: 32.8%, 14: 35.6%, and 19: 3.9% in NH. These allele frequencies were not significantly different in DM-C and CGN-HD. However, DM-HD showed significantly different distribution of allele frequency from other groups (chi 2 = 18.9, P = 0.026). Namely, the frequency of 19-repeat allele in DM-HD was higher (9.0%) than NH, DM-C, and CGN-HD (P = 0.005, 0.041, and 0.004, respectively). CONCLUSION: The microsatellite DNA polymorphism of AM gene may be associated with the genetic predisposition to develop nephropathy in Japanese patients with type 2 diabetes mellitus.

Adrenomedullin↗

PubMed2003

Endothelin a receptor blockade and endothelin B receptor blockade improve hypokalemic nephropathy by different mechanisms.

Hypokalemia causes renal tubulointerstitial injury with an elevation in renal endothelin-1 (ET-1). It was hypothesized that hypokalemic tubulointerstitial injury is ameliorated by the blockade of ET-A receptors (ETA), whereas ET-B receptor (ETB) antagonism may exacerbate the injury, because ETB is thought to mediate vasodilation. Rats were fed a K(+)-deficient diet alone (LC) or with an ETA-selective antagonist ABT-627 (LA) or an ETB-selective antagonist A-192621 (LB) for 8 wk. Control rats were on a normal K(+) diet alone or with the ETA-selective or ETB-selective antagonists. The severity of hypokalemia was not significantly different among LA, LB, and LC. LC developed tubulointerstitial injury with an elevation of renal preproET-1 mRNA level. There was an increase in tubular osteopontin expression, macrophage infiltration, collagen accumulation, and tubular cell hyperplasia. ETA blockade significantly ameliorated all parameters for renal injury in the cortex without suppressing local ET-1 and ETA expression. By contrast, ETB blockade significantly reduced local ET-1 and ETA expression and improved the injury to a similar extent in the cortex. In the medulla, ETA or ETB blockade only partially blocked renal injury. ETA blockade did not affect BP in normokalemic or hypokalemic rats. ETB blockade induced a BP elevation with a decrease in urinary Na(+) excretion in normokalemic but not in hypokalemic rats. These results indicate that ET-1 can mediate hypokalemic renal injury in two different ways: by directly stimulating ETA and by locally promoting endogenous ET-1 production via ETB. Thus, ETA as well as ETB blockade may be renoprotective in hypokalemic nephropathy.

Albuminuria↗

PubMed2003

Repeated inhalation of adrenomedullin ameliorates pulmonary hypertension and survival in monocrotaline rats.

Adrenomedullin (AM) is a potent vasodilator peptide. We investigated whether inhalation of aerosolized AM ameliorates monocrotaline (MCT)-induced pulmonary hypertension in rats. Male Wistar rats given MCT (MCT rats) were assigned to receive repeated inhalation of AM (n = 8) or 0.9% saline (n = 8). AM (5 mug/kg) or saline was inhaled as an aerosol using an ultrasonic nebulizer for 30 min four times a day. After 3 wk of inhalation therapy, mean pulmonary arterial pressure and total pulmonary resistance were markedly lower in rats treated with AM than in those given saline [mean pulmonary arterial pressure: 22 +/- 2 vs. 35 +/- 1 mmHg (-37%); total pulmonary resistance: 0.048 +/- 0.004 vs. 0.104 +/- 0.006 mmHg.ml(-1).min(-1).kg(-1) (-54%), both P < 0.01]. Neither systemic arterial pressure nor heart rate was altered. Inhalation of AM significantly attenuated the increase in medial wall thickness of peripheral pulmonary arteries in MCT rats. Kaplan-Meier survival curves demonstrated that MCT rats treated with aerosolized AM had a significantly higher survival rate than those given saline (70% vs. 10% 6-wk survival, log-rank test, P < 0.01). In conclusion, repeated inhalation of AM inhibited MCT-induced pulmonary hypertension without systemic hypotension and thereby improved survival in MCT rats.

Administration, Inhalation↗

PubMed2003

The role of ghrelin and growth hormone secretagogues receptor on rat adipogenesis.

Recent research progress indicates a close link between ghrelin, a natural ligand of GH secretagogues receptor (GHS-R), and both the metabolic balance and body composition. To clarify the involvement of ghrelin and GHS-R in the process of adipogenesis, we measured the expression of GHS-R and peroxisome proliferator-activated receptor gamma 2 (PPAR-gamma 2) mRNA in rat adipocytes using semiquantitative RT-PCR methods. The levels of GHS-R mRNA increased by up to 4-fold in adipose tissue from epididymal and parametrial regions as the rat aged from 4-20 wk and were significantly elevated during the differentiation of preadipocytes in vitro. Ghrelin (10(-8) M for 10 d) stimulated the activity of glycerol-3-phosphate dehydrogenase and the differentiation of rat preadipocytes in vitro. Ghrelin treatment also significantly increased the levels of PPAR-gamma 2 mRNA in primary cultured rat differentiated adipocytes. In addition, isoproterenol (10(-8) M, 40 min)-stimulated lipolysis was significantly reduced by simultaneous ghrelin treatment in a dose-dependent manner in vitro. In conclusion, the expression of GHS-R in rat adipocytes increases with the age and during adipogenesis. Ghrelin in vitro stimulates the differentiation of preadipocytes and antagonizes lipolysis. Ghrelin may therefore play an important role in the process of adipogenesis in rats.

Adipocytes↗