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M Kojima

Publications and source records attributed to M Kojima.

At least 37 records · Page 2Linked to original sources
PubMed2003

Effects of Ghrelin on growth hormone secretion from cultured adenohypophysial cells in pigs.

To clarify the direct effects of Ghrelin on growth hormone (GH) release from anterior pituitary (AP) cells in pigs, GH-releasing effects of human Ghrelin (hGhrelin) and rat Ghrelin (rGhrelin) on porcine AP cells were compared with GHRH in vitro. The AP cells were obtained from 6-month-old pigs and the cells (2 x 10(5) cells per well) were incubated for 2 h with the peptides after incubating in DMEM for 3 days. hGhrelin and rGhrelin significantly stimulated GH release from the cultured cells at doses of 10(-8) and 10(-7)M (P < 0.05). The rates of increase in GH at 10(-8) and 10(-7)M of hGhrelin were 82.7 and 131.9%, while those with rGhrelin were 43.9 and 79.5%, respectively. GHRH significantly stimulated GH release from the cells at a dose as low as 10(-11)M (P < 0.05), and the response to GHRH was greater than that induced by Ghrelins. In time-course experiments, GHRH continued to increase GH concentrations in media until 120 min after incubation; however, those in media treated with hGhrelin reached a plateau 60 min after incubation, and the maximal value was approximately one third that obtained with GHRH. When hGhrelin (10(-8)M) and GHRH (10(-8)M) were added together, additive effects of both peptides on the release of GH were observed (P < 0.05). Somatostatin (SS, 10(-7)M) significantly blunted GH release induced by hGhrelin (10(-8)M) and GHRH (10(-8)M) (P < 0.05). In the presence of SS, additive effects of hGhrelin and GHRH on the release of GH were observed (P < 0.05). These results show that Ghrelin directly stimulates GH release from anterior pituitary cells in pigs; however, the GH-releasing effect is weaker than that of GHRH in vitro. The present results also show that Ghrelin interacts with GHRH and SS to in the release of GH from porcine adenohypophysial cells.

Animals↗
PubMed2003

Biochemistry and genetics of mannan-binding lectin (MBL).

Mannose- or mannan-binding lectin (MBL) is a member of the collectin protein family, which includes lung surfactant proteins SP-A and SP-D. Each member consists of similar or identical polypeptide chains with a region of collagen-like sequence followed by a C-type lectin domain. The polypeptides associate in threes to form a subunit containing a collagen-like helix, with three clustered lectin domains. These subunits associate into larger structures, usually with 12-18 polypeptides. The collectins bind to patterns of neutral sugars on surfaces (e.g. of micro-organisms) and mediate effector functions associated with killing/phagocytosis. MBL is the only collectin which activates complement. It resembles in quaternary structure the complement protein C1q, which recognizes targets via charge clusters. Binding of MBL to a surface activates MBL-associated serine proteases (MASPs) attached to MBL, and MASP-2 activates complement proteins C4 and C2. The MASPs are homologous to the C1q-associated proteases, C1r and C1s. MBL therefore activates complement by a mechanism very similar to C1q, and engages the opsonic activity of complement to clear micro-organisms. The serum concentration of MBL is very variable in humans. The variability is largely associated with mutations leading to amino acid substitutions in the collagen-like region which decrease MBL assembly and stability. Many studies demonstrate that MBL deficiency is associated with susceptibility to a range of infectious and inflammatory diseases.

Complement Pathway, Mannose-Binding Lectin↗
PubMed2003

Effects of antioxidative agents on apoptosis induced by ischaemia-reperfusion in rat intestinal mucosa.

BACKGROUND AND AIM: We have previously demonstrated that ischaemia-reperfusion induces apoptosis in the intestinal mucosa. To evaluate that reactive oxygen species enhanced intestinal apoptosis after ischaemia-reperfusion, we examined whether antioxidants reduced apoptosis. METHODS: Rats were infused through a duodenal tube with antioxidative agents, glutathione, rebamipide and dymethylsulfoxide during 2 h before an ischaemic insult. The superior mesenteric artery was occluded for 60 min, followed by 60 min reperfusion. Apoptosis was evaluated by percentage fragmented DNA (fragmented DNA/total DNA) and immunochemical staining. RESULTS: Increase in apoptosis in the intestinal mucosa after ischaemia-reperfusion was attenuated by intraduodenal infusion of antioxidative agents, but was not completely abolished. CONCLUSION: Scavenging effects of the antioxidative agents attenuated increases in intestinal apoptosis, indicating that oxidative stress after ischaemia-reperfusion plays an important role in induction of apoptosis in the intestinal mucosa.

Alanine↗
PubMed2003

Amidated fish ghrelin: purification, cDNA cloning in the Japanese eel and its biological activity.

We purified ghrelin from stomach extracts of a teleost fish, the Japanese eel (Anguilla japonica) and found that it contained an amide structure at the C-terminal end. Two molecular forms of ghrelin with 21 amino acids were identified by cDNA and mass spectrometric analyses: eel ghrelin-21, GSS(O-n-octanoyl)FLSPSQRPQGKDKKPP RV-amide and eel ghrelin-21-C10, GSS(O-n-decanoyl) FLSPSQRPQGKDKKPPRV-amide. Northern blot and RT-PCR analyses revealed high gene expression in the stomach. Low levels of expression were found only in the brain, intestines, kidney and head kidney by RT-PCR analysis. Eel ghrelin-21 increased plasma growth hormone (GH) concentrations in rats after intravenous injection; the potency was similar to that of rat ghrelin. We also examined the effect of eel ghrelin on the secretion of GH and prolactin (PRL) from organ-cultured tilapia pituitary. Eel ghrelin-21 at a dose of 0.1 nM stimulated the release of GH and PRL, indicating that ghrelin acts directly on the pituitary. The present study revealed that ghrelin is present in fish stomach and has the ability to stimulate the secretion of GH from fish pituitary. A novel regulatory pathway of GH secretion by gastric ghrelin seems to be conserved from fish to human.

Amino Acid Sequence↗
PubMed2003

Flat and depressed lesions of the colon and rectum: Pathogenesis and clinical management.

INTRODUCTION: It is not clear whether flat lesions play a role in the pathogenesis of colorectal carcinoma. Flat lesions are being increasingly recognised with new colonoscopic techniques. MATERIALS AND METHODS: A total of 10,939 consecutive colonoscopies were performed over a 9-year period. After bowel preparation with polyethylene glycol electrolyte lavage solution, high-resolution video colonoscopy and indigocarmine spraying were performed to detect flat lesions. All lesions suggesting neoplastic change were removed by polypectomy or surgery. Cancers invading beyond the submucosal layer were excluded from this analysis. The gross appearance of flat-type lesions was classified as flat elevated type or flat depressed type based on the presence or absence of central depression. RESULTS: A total of 5408 neoplastic lesions were index lesions, including 5035 adenomas and 373 carcinomas (124 with submucosal invasion). The prevalence of flat depressed and flat elevated lesions were 2.8% and 18.1%, respectively. Submucosal invasion rates were 17.1% in the flat depressed, 0.8% in the flat elevated, 1.6% in the sessile, 4.0% in pedunculated lesions and 9.3% in creeping lesions. The submucosal invasion rate in the flat depressed lesions was significantly higher than in any others, except for creeping lesions (P = 0.06). The percentage of flat elevated and flat depressed carcinomas among all carcinomas invading the submucosa was 6.5% and 21.0%, respectively. CONCLUSION: Flat lesions were common during routine colonoscopy. One-quarter of colorectal cancers may be derived from flat lesions. Training in dye spray technique may result in a higher detection rate of flat colonic lesions.

Adenoma↗
PubMed2002

A transient ghrelin surge occurs just before feeding in a scheduled meal-fed sheep.

Ghrelin, a gastric-derived peptide, has recently been identified as an endogenous natural ligand for the growth hormone (GH) secretagogue receptor. However, secretory characteristics of ghrelin are still obscure in ruminants. To investigate the diurnal rhythm in ghrelin secretion and its relationship to GH secretion, plasma ghrelin and GH concentrations were determined in Suffolk rams fed with a roughage diet once daily (Experiment 1). Abrupt increases (P<0.05) in plasma ghrelin occurred just before a meal-feeding compared with that at 1h before feeding, then rapidly fell with a minimum during the feeding. A pulsatile surge (P<0.01) in plasma GH concentrations, which seemed to follow a single surge in plasma ghrelin, was observed during the feeding. In Experiment 2, plasma ghrelin and GH were determined in sheep subjected to a pseudo-feeding of 2h to determine whether feed ingestion itself influences ghrelin and GH secretions. Compared with those at 1h before feeding, a tendency of increases (P<0.1) in plasma ghrelin and significant increases (P<0.05) in GH occurred just before and during a pseudo-feeding, respectively. Plasma ghrelin temporally declined within 1h after the start of the pseudo-feeding, and increased again and maintained higher levels during the last period of the pseudo-feeding. These results suggest that the transient surge of ghrelin secretion just before a scheduled meal feeding would not be due to the ingestion of feed, and that a pulsatile increase in plasma GH during the actual- or pseudo-feeding could be induced by the transient ghrelin surge.

Animals↗
PubMed2002

Immunocytochemical observation of ghrelin-containing neurons in the rat arcuate nucleus.

Ghrelin is a novel peptide that stimulates the release of growth hormone from the pituitary and is involved in hypothalamic feeding regulation. A pre-embedding immunostaining technique was used to study the ultrastructure and synaptic relationships of ghrelin-containing neurons in the rat arcuate nucleus (ARC). Ghrelin-like immunoreactive (ghrelin-LI) neurons were found in the ARC, and were especially abundant in its ventral part. At the electron microscopic level, ghrelin-LI neurons received afferent synapses from many unknown axon terminals. Ghrelin-LI products in the immunoreactive cell bodies, processes, and axon terminals were detected mainly in dense granular vesicles about 110 nm in diameter. Ghrelin-LI presynaptic axon terminals often made synapses with unknown immunonegative neurons. These results suggest that ghrelin acts to regulate food intake through synaptic connections in hypothalamic neuronal networks.

Animals↗
PubMed2002

Bone growth oscillation: longitudinal metabolic process of bone growth in congenital adrenal hyperplasia and nonendocrine short stature.

To clarify the longitudinal metabolic process of bone growth in children, we observed the relationship between the level of serum osteocalcin (OC), a marker of bone metabolism, and growth velocity in 10 prepubertal patients with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency and 9 prepubertal patients with nonendocrine short stature (NESS), but no major hormonal abnormalities influencing bone metabolism. Observations were made every 6 months over a 7-year period. In patients with CAH who exhibited a wide variation in growth velocity during the course of the investigation, the levels of OC fluctuated over a wide range, suggesting metabolically variable bone growth. In contrast, in patients with NESS who exhibited a relatively stable growth velocity, the OC level remained within a narrow range, suggesting metabolically stable bone growth. The meaning of such divergent metabolic processes of bone growth observed in CAH and NESS and its relationship to actual bone structure or bone intensity should be further investigated.

Adolescent↗
PubMed2002

Ghrelin in neonatal rats: distribution in stomach and its possible role.

Ghrelin, a 28 amino acid peptide, has recently been isolated from the rat stomach as an endogenous ligand for the GH secretagogue receptor. The fact that administration of ghrelin, centrally or peripherally, stimulates both food intake and GH secretion suggests that stomach ghrelin has an important role in the growth of rats. We used immunohistochemistry and radioimmunoassay to determine the age at which ghrelin-immunostained cells begin to appear in the rat stomach. Ghrelin-immunoreactive cells were found to be expressed in the fetal stomach from pregnancy day 18. The number of ghrelin-immunoreactive cells in the fetal stomach increased as the stomach grew. The amount of ghrelin in the glandular part of the rat stomach also increased, in an age-dependent manner, from the neonatal stage to adult. Eight hours of milk restriction significantly decreased the ghrelin concentration in the stomachs of 1-week-old rats, and increased the ghrelin concentration in their plasma. Administration of ghrelin to 1- and 3-week-old rats increased plasma GH concentrations. The daily subcutaneous administration of ghrelin to pregnant rats from day 15 to day 21 of pregnancy caused an increase in body weight of newborn rats. In addition, daily subcutaneous administration of ghrelin to neonatal rats from birth advanced the day of vaginal opening from day 30.7+/-0.94 to day 27.9+/-0.05. These results suggest that ghrelin may be involved in neonatal development.

Analysis of Variance↗
PubMed2002

Role for central ghrelin in food intake and secretion profile of stomach ghrelin in rats.

Ghrelin, a 28-amino-acid peptide, has recently been isolated from the rat stomach as an endogenous ligand for the GH secretagogue receptor. We have reported previously that central or peripheral administration of ghrelin stimulates food intake, and the secretion of GH and gastric acid in rats. In the present study, we investigated how much endogenous centrally released ghrelin is involved in the control of food intake and body weight gain. We also examined the profile of ghrelin secretion from the stomach by RIA using two kinds of anti-ghrelin antiserum, one raised against the N-terminal ([Cys(12)]-ghrelin[1-11]) region and one raised against the C-terminal ([Cys(0)]-ghrelin [13-28]) region of the peptide. The former antibody recognizes specifically ghrelin with n- octanoylated Ser 3 (acyl ghrelin), and does not recognize des-acyl ghrelin. The latter also recognizes des-acyl ghrelin (i.e. total ghrelin). Intracerebroventricular treatment with the anti-ghrelin antiserum against the N-terminal region twice a day for 5 days decreased significantly both daily food intake and body weight. Des-acyl ghrelin levels were significantly higher in the gastric vein than in the trunk. Either fasting for 12 h, administration of gastrin or cholecystokinin resulted in increase of both acyl and des-acyl ghrelin levels. The ghrelin levels exhibited a diurnal pattern, with the bimodal peaks occurring before dark and light periods. These two peaks were consistent with maximum and minimum volumes of gastric content respectively. These results suggest that (1) endogenous centrally released ghrelin participates in the regulation of food intake and body weight, (2) acyl ghrelin is secreted from the stomach, (3) intestinal hormones stimulate ghrelin release from the stomach, and (4) regulation of the diurnal rhythm of ghrelin is complex, since ghrelin secretion is augmented under conditions of both gastric emptying and filling.

Animals↗
PubMed2001

Absence of exacerbation of myocardial stunning in anesthetized dogs treated with KAD-1229, a novel hypoglycemic agent.

The effect of (+)-momocalcium bis[(2S,3a,7a-cis)-alpha-benzylhexahydro-gamma-oxo-2-isoindolinebutyrate]dihydrate (KAD-1229), a novel hypoglycemic agent with a chemical structure different from that of the sulfonylureas, on myocardial stunning was assessed in anesthetized dogs by comparison with that of glibenclamide, a sulfonylurea. Even though their hypoglycemic effects were of similar magnitude, glibenclamide (1 mg/kg, i.v.), but not KAD-1229, exacerbated the myocardial stunning induced by occlusion/reperfusion of the descending coronary artery. In a receptor-binding experiment, unlabeled glibenclamide completely inhibited [(3)H]glibenclamide binding to the myocardium, but KAD-1229 did not. These results suggest that the difference in binding properties of KAD-1229 and glibenclamide toward cardiac sulfonylurea receptors is one of the causes of their different effects on myocardial stunning. It is likely that KAD-1229 is highly specific for pancreatic sulfonylurea receptors and is speculated to be a safer hypoglycemic agent than, at least, glibenclamide.

ATP-Binding Cassette Transporters↗
PubMed2001

Elevated circulating level of ghrelin in cachexia associated with chronic heart failure: relationships between ghrelin and anabolic/catabolic factors.

BACKGROUND: Ghrelin is a novel growth hormone (GH)-releasing peptide, isolated from the stomach, that may also cause a positive energy balance by stimulating food intake and inducing adiposity. We sought to investigate the pathophysiology of ghrelin in the cachexia associated with chronic heart failure (CHF). METHODS AND RESULTS: Plasma ghrelin was measured in 74 patients with CHF and 12 control subjects, together with potentially important anabolic and catabolic factors, such as GH and tumor necrosis factor (TNF-alpha). Patients with CHF were divided into two groups, those with cachexia (n=28) and those without cachexia (n=46). Plasma ghrelin did not significantly differ between all CHF patients and controls (181+/-10 versus 140+/-14 fmol/mL, P=NS). However, plasma ghrelin was significantly higher in CHF patients with cachexia than in those without cachexia (237+/-18 versus 147+/-10 fmol/mL, P<0.001). Circulating GH, TNF-alpha, norepinephrine, and angiotensin II were also significantly higher in CHF patients with cachexia than in those without cachexia. Interestingly, plasma ghrelin correlated positively with GH (r=0.28, P<0.05) and TNF-alpha (r=0.31, P<0.05) and negatively with body mass index (r=-0.35, P<0.01). CONCLUSIONS: Plasma ghrelin was elevated in cachectic patients with CHF, associated with increases in GH and TNF-alpha and a decrease in body mass index. Considering ghrelin-induced positive energy effects, increased ghrelin may represent a compensatory mechanism under catabolic-anabolic imbalance in cachectic patients with CHF.

Adolescent↗
PubMed2001

Brain-derived neurotrophic factor triggers a rapid glutamate release through increase of intracellular Ca(2+) and Na(+) in cultured cerebellar neurons.

We reported previously that BDNF induced glutamate release was dependent on intracellular Ca(2+) but not extracellular Ca(2+) in cerebellar neurons (Numakawa et al., 1999). It was revealed that the release was through a non-exocytotic pathway (Takei et al., 1998; Numakawa et al., 1999). In the present study, we monitored the dynamics of intracellular Ca(2+) and Na(+) in cerebellar neurons, and investigated the possibility of reverse transport of glutamate mediated by BDNF. As reported, BDNF increased the intracellular Ca(2+) level. We found that the Ca(2+) increase induced by BDNF was completely blocked by xestospongin C, an IP(3) receptor antagonist, and U-73122, a PLC-gamma inhibitor. Xestospongin C and U-73122 also blocked the BDNF-dependent glutamate release, suggesting that the BDNF-induced transient increase of Ca(2+) through the activation of the PLC-gamma/ IP(3) pathway was essential for the glutamate release. We found that BDNF induced a Na(+) influx. This was blocked by treatment with TTX. U-73122 and xestospongin C blocked the BDNF-induced Na(+) influx, suggesting that the Na(+)influx required the BDNF-induced Ca(2+) increase. Next, we examined the possibility that a co-transporter of Na(+) and glutamate was involved in the BDNF-induced glutamate release. BDNF-induced glutamate release was blocked by L-trans-pyrollidine-2,4-dicalboxylic acid (t-PDC), a glutamate transporter inhibitor, whereas neither the 4-aminopyridine (4AP)- nor high potassium (HK(+))-induced release was blocked by t-PDC. In addition, DL-threo-beta-benzyloxyaspartate (DL-TBOA) also blocked the BDNF-mediated glutamate release, suggesting that reverse transport of glutamate may be involved. All the results therefore suggest that Na(+)-dependent reverse transport contributes to BDNF-mediated transmitter release through the PLC-gamma/IP(3)-mediated Ca(2+) signaling.

Amino Acid Transport System X-AG↗
PubMed2001

Chronic administration of ghrelin improves left ventricular dysfunction and attenuates development of cardiac cachexia in rats with heart failure.

BACKGROUND: Ghrelin is a novel growth hormone (GH)-releasing peptide that may also induce vasodilation and stimulate feeding through GH-independent mechanisms. We investigated whether ghrelin improves left ventricular (LV) dysfunction and attenuates cardiac cachexia in rats with chronic heart failure (CHF). METHODS AND RESULTS: Ligation of the left coronary artery or sham operation was performed; 4 weeks after surgery, rat ghrelin (100 microg/kg SC BID) or saline was administered for 3 weeks. Echocardiography and cardiac catheterization were performed. Serum GH and insulin-like growth factor-1 were significantly higher in both CHF and sham rats treated with ghrelin than in those given placebo (P<0.05 for both). CHF rats given placebo showed an impaired increase in body weight compared with sham rats given placebo (P<0.05). CHF rats treated with ghrelin, however, showed a significantly greater increase in body weight than those given placebo (+10% versus +3%, P<0.05). They showed significantly higher cardiac output (315+/-49 versus 266+/-31 mL. min(-1). kg(-1), P<0.05) and LV dP/dt(max) (5738+/-908 versus 4363+/-973 mm Hg/s, P<0.05) than CHF rats given placebo. Ghrelin increased diastolic thickness of the noninfarcted posterior wall, inhibited LV enlargement, and increased LV fractional shortening in CHF rats (from 15+/-3% to 19+/-3%, P<0.05). CONCLUSIONS: Chronic subcutaneous administration of ghrelin improved LV dysfunction and attenuated the development of LV remodeling and cardiac cachexia in rats with CHF.

Animals↗
PubMed2001

Immunohistochemical studies on the distribution of nerve fibers in the human prostate with special reference to the anterior fibromuscular stroma.

BACKGROUND: Although the anterior fibromuscular stroma (AFMS) comprises up to one third of the total bulk of the prostate, its physiological function remains unknown. We recently reported the possible contribution of the AFMS to micturition. The aim of this study is to reveal the differences in the distribution of innervation between the AFMS and the other regions of the prostate. METHODS: We performed immunohistochemical stainings using antibodies such as protein gene product (PGP) 9.5, tyrosine hydroxylase(TH), neuropeptide Y (NPY), and vasoactive intestinal peptide (VIP). Morphometric analysis was made to examine the density of peripheral nerve fibers containing PGP 9.5, TH, NPY, and VIP by using a computer-assisted imaging system. RESULTS: The number of PGP 9.5-immunoreactive (IR) nerve fibers and the smooth muscle in the AFMS decreased from the base to the apex of the prostate. TH-IR nerve fibers were more abundant in the AFMS than in the transition zone. NPY- and VIP-IR nerve fibers were less numerous in the AFMS than in the peripheral zone. CONCLUSIONS: This study is the first to demonstrate that the AFMS has peculiar neuronal innervation. We observed significantly different innervation in the AFMS compared with the other regions of the prostate.

Aged↗
PubMed2001

Structure-activity relationship of ghrelin: pharmacological study of ghrelin peptides.

Ghrelin, a novel peptide purified from the stomach, is the endogenous ligand of the growth hormone secretagogue receptor. The Ser(3) residue of ghrelin is modified with a lipid n-octanoic acid, a modification necessary for hormonal activity. To clarify the role of acyl modification and to identify the active core of ghrelin, we examined the activities of partially digested ghrelin and synthetic ghrelin derivatives. The activities confirmed that the N-terminal portion is the active core. Moreover, synthetic ghrelin derivatives demonstrated that octanoic acid is not the only modification of the Ser(3) side chain to sustain the activity of ghrelin; other acyl acid modifications maintained activity. Amino acid replacement of Ser(3) indicated that an L-configuration of the third residue is critical for ghrelin activity. In addition, more stable ether or thioether bonds are capable of replacing the octanoyl ester bond in ghrelin, advantageous for the generation of pharmaceuticals with longer stability.

Amino Acid Sequence↗
PubMed2001

Bullfrog ghrelin is modified by n-octanoic acid at its third threonine residue.

We have identified the amphibian ghrelin from the stomach of the bullfrog. We also examined growth hormone (GH)-releasing activity of this novel peptide in both the rat and bullfrog. The three forms of ghrelin identified, each comprised of 27 or 28 amino acids, possessed 29% sequence identity to the mammalian ghrelins. A unique threonine at amino acid position 3 (Thr(3)) in bullfrog ghrelin differs from the serine present in the mammalian ghrelins; this Thr(3) is acylated by either n-octanoic or n-decanoic acid. The frog ghrelin-28 has a complete structure of GLT (O-n-octanoyl)FLSPADMQKIAERQSQNKLRHGNM; the structure of frog ghrelin-27 was determined to be GLT(O-n-octanoyl)FLSPADMQKIAERQSQNKLRHGN; frog ghelin-27-C10 possessed a structure of GLT(O-n-decanoyl)FLSPADMQKIAERQSQNKLRHGN. Northern blot analysis demonstrated that ghrelin mRNA is predominantly expressed in the stomach. Low levels of gene expression were observed in the heart, lung, small intestine, gall bladder, pancreas, and testes, as revealed by reverse transcription polymerase chain reaction analysis. Bullfrog ghrelin stimulated the secretion of both GH and prolactin in dispersed bullfrog pituitary cells with potency 2-3 orders of magnitude greater than that of rat ghrelin. Bullfrog ghrelin, however, was only minimally effective in elevating plasma GH levels following intravenous injection into rats. These results indicate that although the regulatory mechanism of ghrelin to induce GH secretion is evolutionary conserved, the structural changes in the different ghrelins result in species-specific receptor binding.

Amino Acid Sequence↗