Cucurbitane triterpenoid oviposition deterrent from Momordica charantia to the leafminer, Liriomyza trifolii

Females of Liriomyza trifolii, a polyphagous leafminer, are often deterred from ovipositing on Momordica charantia leaves. The methanol extract of M. charantia leaves showed strong oviposition deterrent activity against L. trifolii females on the host plant leaf when it was dipped in the methanol extract at a concentration of 1 g of fresh leaf equivalent/ml. Bioguided fractionation of the methanol extract of the leaves of M. charantia led to the isolation of a new cucurbitane triterpenoid, 7,23-dihydroxy-3-O-malonylcucurbita-5,24-dien-19-al, along with another known compound, momordicine I. Both 7,23-dihydroxy-3-O-malonylcucurbita-5,24-dien-19-al and momordicine I respectively had significant ovipositing deterrent effect towards the adult females of L. trifolii on host plant leaves treated at concentrations of 3.25 and 33.60 microg/cm2.     

Cucurbitane glucosides from Momordica charantia leaves as oviposition deterrents to the leafminer, Liriomyza trifolii

The American serpentine leaf mining fly, Liriomyza trifolii, whose larva feeds on more than 120 plant species is well characterized by its high degree of polyphagy. Observations on the oviposition behavior by L. trifolii demonstrated that among cucurbitaceous plants, Momordica charantia is rarely attacked by L. trifolii. The methanol extract of M. charantia leaves strongly deterred the females from ovipositing on kidney bean leaves treated at a concentration of 1 g leaf equivalent extract/ml. Analysis of the polar fraction of the methanol extract of M. charantia leaves resulted in the isolation of a novel cucurbitane glucoside, 7-O-beta-D-glucopyranosyl-3,23-dihydroxycucurbita-5,24-dien-19-al, named momordicine IV, along with another known compound, momordicine II. Momordicine II and IV deterred oviposition by L. trifolii significantly when bioassays were carried out on kidney bean leaves treated at 75.6 and 20.3 microg/cm2 leaf surface, respectively. There was no synergistic effect on oviposition deterrent when the two compounds were combined in their natural abundance.     

A new oviposition deterrent to the leafminer, Liriomyza trifolii: cucurbitane glucoside from Momordica charantia

A new cucurbitane glucoside, 23-O-beta-D-glucopyranosyl-7-hydroxy-3-O-malonylcucurbita-5,24-dien-19-al, named momordicine V, has been isolated from Momordica charantia leaves, along with the previously reported compounds, momordicines I, II, IV and 3-O-malonylmomordicine I. The structure of the new compound was established on the basis of spectral analysis, as well as by its conversion to momordicine II by alkaline catalyzed hydrolysis. Momordicine V deterred significantly the oviposition by L. trifolii on host plant leaves treated at 26.16 microg/cm2 leaf surface.     

Trinorcucurbitane and cucurbitane triterpenoids from the roots of Momordica charantia

Five cucurbitacins, kuguacins A-E (1-5), together with three known analogues, 3beta,7beta,25-trihydroxycucurbita-5,(23E)-diene-19-al (6), 3beta,25-dihydroxy-5beta,19-epoxycucurbita-6,(23E)-diene (7), and momordicine I (8), were isolated from roots of Momordica charantia. Structures of 1-5 were elucidated by NMR and MS spectroscopic analysis. Among them, compounds 3-5 possess an unprecedented 25,26,27-trinorcucurbitane backbone. Compounds 3 and 5 showed moderate anti-HIV-1 activity with EC(50) values of 8.45 and 25.62 microg/ml, and exerted minimal cytotoxicity against C8166 cells (IC(50)>200 microg/ml), with a selectivity index more than 23.68 and 7.81, respectively.     

苦瓜叶提取物对美洲斑潜蝇取食和产卵行为的抑制作用

美洲斑潜蝇是危害蔬菜、观赏植物的重大害虫之一.苦瓜叶乙醇提取物(浓度为2000～4000 μg·ml^-1)对美洲斑潜蝇成虫的取食和产卵都具有较强的抑制作用.用环己烷、乙酸乙酯、正丁醇和水依次对乙醇提取物进行萃取,并测试了4种萃取物对美洲斑潜蝇成虫取食和产卵的抑制作用.结果表明: 环己烷、乙酸乙酯、正丁醇和水萃取物在浓度为1000 μg·ml^-1时,处理后2 d对美洲斑潜蝇成虫的拒食率分别是11.08%、34.89%、22.99%和 0,产卵抑制率分别是0、30.91%、6.45%和 0.其中,乙酸乙酯萃取物的活性最强,当其浓度为4000 μg·ml^-1时,处理后2 d对美洲斑潜蝇成虫的拒食率和产卵忌避率分别为70.95％ 和69.49％.乙酸乙酯萃取物经硅胶柱层析分离得到(19S,23E)-5β,19-环氧-19-甲氧葫芦素-6,23-二烯-3β,25-二醇 (化合物1)、(19R,23E)-5β,19-环氧-19-甲氧葫芦素-6,23-二烯-3β,25-二醇(化合物2) 和3β,7β,25-三羟基葫芦素-5,23-二烯-19-醛缩-3-O-β-D-吡喃葡糖苷（化合物3）,3种化合物在供试的浓度（100～400 μg·ml^-1）条件下对美洲斑潜蝇的取食和产卵行为都有明显的抑制作用.在400μg·ml^-1浓度时,化合物1、化合物2和化合物3对美洲斑潜蝇成虫的拒食率分别是66.89%、53.53%和78.02%,产卵抑制率分别是76.32%、58.36%和78.36%.     

Cucurbitane Triterpenoid Oviposition Deterrent from Momordica charantia to the Leafminer,Liriomyza trifolii

Females of Liriomyza trifolii, a polyphagous leafminer, are often deterred from ovipositing on Momordica charantia leaves. The methanol extract of M. charantia leaves showed strong oviposition deterrent activity against L. trifolii females on the host plant leaf when it was dipped in the methanol extract at a concentration of 1 g of fresh leaf equivalent/ml. Bioguided fractionation of the methanol extract of the leaves of M. charantia led to the isolation of a new cucurbitane triterpenoid, 7,23-dihydroxy-3-O-malonylcucurbita-5,24-dien-19-al, along with another known compound, momordicine I. Both 7,23-dihydroxy-3-O-malonylcucurbita-5,24-dien-19-al and momordicine I respectively had significant ovipositing deterrent effect towards the adult females of L. trifolii on host plant leaves treated at concentrations of 3.25 and 33.60 μg/cm².     

Cucurbitane triterpenoids from the leaves of Momordica charantia, and their cancer chemopreventive effects and cytotoxicities

Seventeen cucurbitane-type triterpenoids, 1-17, including six new compounds, (23E)-3β,25-dihydroxy-7β-methoxycucurbita-5,23-dien-19-al (1), (23S*)-3β-hydroxy-7β,23-dimethoxycucurbita-5,24-dien-19-al (6), (23R*)-23-O-methylmomordicine IV (7), (25ξ)-26-hydroxymomordicoside L (8), 25-oxo-27-normomordicoside L (9), and 25-O-methylkaravilagenin D (12), were isolated from a MeOH extract of the leaves of Japanese Momordica charantia. The structures of new compounds were elucidated on the basis of extensive spectroscopic analyses and comparison with literature. Compounds 1-17 were examined for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced with 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells, a known primary screening test for inhibitors of tumor promotion. Four compounds, 1, (23E)-3β,7β-dihydroxy-25-methoxycucurbita-5,23-dien-19-al (2), karavilagenin D (11), and 12, showed potent inhibitory effects on EBV-EA induction with IC(50) values in the range of 242-264 mol ratio/32 pmol TPA. In addition, compounds 1 and 11 exhibited inhibitory effects on skin-tumor promotion in an in vivo two-stage mouse skin carcinogenesis test based on 7,12-dimethylbenz[a]anthracene (DMBA) as initiator, and with TPA as a promoter. Furthermore, upon evaluation of the cytotoxic activities of compounds 1-17 against human cancer cell lines, compounds 2, 5-7, 9, and 14 showed potent activities against HL60 cell line, and compound 2 against SK-BR-3 cell line.     

Momordica charantia fruit juice stimulates glucose and amino acid uptakes in L6 myotubes

The fruit of Momordica charantia (family: Cucurbitacea) is used widely as a hypoglycaemic agent to treat diabetes mellitus (DM). The mechanism of the hypoglycaemic action of M. charantia in vitro is not fully understood. This study investigated the effect of M. charantia juice on either 3H-2-deoxyglucose or N-methyl-amino-a-isobutyric acid (14C-Me-AIB) uptake in L6 rat muscle cells cultured to the myotube stage. The fresh juice was centrifuged at 5000 rpm and the supernatant lyophilised. L6 myotubes were incubated with either insulin (100 nM), different concentrations (1-10 microg ml(-1)) of the juice or its chloroform extract or wortmannin (100 nM) over a period of 1- 6 h. The results were expressed as pmol min(-1) (mg cell protein)(-1), n = 6-8 for each value. Basal 3H-deoxyglucose and 14C-Me-AIB uptakes by L6 myotubes after 1 h of incubation were (means +/- S.E.M.) 32.14 +/- 1.34 and 13.48 +/- 1.86 pmol min(-1) (mg cell protein)(-1), respectively. Incubation of L6 myotubes with 100 nM insulin for 1 h resulted in significant (ANOVA, p < 0.05) increases in 3H-deoxyglucose and 14C-Me-AIB uptakes. Typically, 3H-deoxyglucose and 14C-Me-AIB uptakes in the presence of insulin were 58.57 +/- 4.49 and 29.52 +/- 3.41 pmol min(-1) (mg cell protein(-1)), respectively. Incubation of L6 myotubes with three different concentrations (1, 5 and 10 microg ml(-1)) of either the lyophilised juice or its chloroform extract resulted in time-dependent increases in 3H-deoxy-D-glucose and 14C-Me-AIB uptakes, with maximal uptakes occurring at a concentration of 5 microg ml(-1). Incubation of either insulin or the juice in the presence of wortmannin (a phosphatidylinositol 3-kinase inhibitor) resulted in a marked inhibition of 3H-deoxyglucose by L6 myotubes compared to the uptake obtained with either insulin or the juice alone. The results indicate that M. charantia fruit juice acts like insulin to exert its hypoglycaemic effect and moreover, it can stimulate amino acid uptake into skeletal muscle cells just like insulin.     

Further saponins from Taverniera aegyptiaca

From the saponin fraction of the total methanolic extract of the dried root and stem barks of Taverniera aegyptiaca Boiss, six new triterpenoidal saponins of oleanane type were isolated and identified as 28-methyl serratagenate-3-beta-O-beta-xylopyranosyl (1-->2)-beta-glucopyranoside (2), 28-methyl serratagenate 3-beta-O-alpha-rhamnopyranosyl (1-->2)-beta-glucopyranoside (3), 3beta-O-alpha-rhamnopyranosyl (1-->2) beta-glucopyranosyl-olean-11,13(18)-dien-1beta, 3beta, 22beta-triol (4), 3beta-O-beta-glucopyranosyl (1-->2)-beta-glucuronopyranosylolean-11,13(18)-dien-1beta,3beta,22beta-triol (5), 3beta-O-beta-xylopyranosyl(1-->2)-beta-glucuronopyranosylolean-11,13(18)-dien-1beta,3beta,22beta-triol (6), 3beta-O-alpha-rhamnopyranosyl (1-->2)-beta-glucuronopyranosylolean-11,13(18)-dien-1beta, 3beta, 22beta-triol (7) together with the known oleanolic acid 3-beta-O-beta-glucoside (1). The identification of the isolated compounds was done on the basis of chemical and spectral evidences.     

Glycosidic inhibitors of melanogenesis from leaves of Momordica charantia

Eight glycosidic compounds, 1-8, including two new compounds, (4ξ)-α-terpineol 8-O-[α-L-arabinopyranosyl-(1→6)-β-D-glucopyranoside] (5) and myrtenol 10-O-[β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside] (7), were isolated from the BuOH-soluble fraction of a MeOH extract of Momordica charantia leaves. The structures of the new compounds were elucidated on the basis of extensive spectroscopic analyses and comparison with literature. Upon evaluation of compounds 1-8 on the melanogenesis in B16 melanoma cells induced with α-melanocyte-stimulating hormone (α-MSH), these compounds were found to exhibit inhibitory activities with 7.1-27.0% and 23.6-46.4% reduction of melanin content at 30 μM and 100 μM, respectively, with no or almost no toxicity to the cells (80.0-103.5% of cell viability at 100 μM). Western blot analysis showed that compound 7 reduced the protein levels of MITF, tyrosinase, TRP-1, and TRP-2 mostly in a concentration-dependent manner, suggesting that this compound inhibits melanogenesis on the α-MSH-stimulated B16 melanoma cells by, at least in part, inhibiting the expression of MITF, followed by decreasing the expression of tyrosinase, TRP-1, and TRP-2.     

Cucurbitane-type triterpenoids from the aerial parts of Momordica charantia L.

Six new cucurbitane-type triterpenoids (1–6), together with two known analogues (7 and 8) were isolated from the aerial parts of Momordica charantia L. The structures of new compounds were identified as cucurbita-6,24-dien-3β,23-diol-19,5β-olide (1), (19R)-5β,19-epoxy-19-methoxycucurbita-6,24-dien-3β,23-diol (2), (19S)-5β,19-epoxy-19-methoxycucurbita-6,24-dien-3β,23-diol (3), (19R)-5β,19-epoxy-19-isopropoxycucurbita-6,24-dien-3β,23-diol (4), 3β,23-dihydroxy-5-methoxycucurbita-6,24-dien-19-al (5) and (19R)-7β,19-epoxy-19-methoxycucurbita-5,24-dien-3β,23-diol (6), by extensive MS, 1D and 2D NMR spectroscopic technologies. This is the first report of the isolation of tetracyclic triterpenoids possessing a 7β,19-epoxy system, viz., 6, from M. charantia L.     

Role and differential expression of calpastatin mRNA and protein in cultured cardiomyocytes exposed to hypoxic stress

This study investigated the beneficial effects and mechanism of action of the juice of Momordica charantia in streptozotocin (STZ)-induced diabetes mellitus in rats. Diabetes mellitus was associated with significant (p < 0.01) time course reductions in body weight, plasma insulin and the number of insulin positive cells per islet and significant (p < 0.01) time course elevation in blood glucose and osmolarity and systolic blood pressure compared to age-matched healthy controls. Oral intake of M. charantia juice by STZ-induced diabetic rats partially reversed all the diabetes-induced effects measured. Daily oral administration of M. charantia juice to STZ-induced diabetic rates significantly (p < 0.01) reduced the Na+- and K+-dependent absorptions of glucose by the brush border membrane vesicles of the jejunum compared to the responses obtained in STZ-induced diabetic rat. Either insulin (100 MM) or the fruit juice lyophilised extract (5 microg x ml(-1)) can stimulate 14C-D-glucose uptake in L6 myotubes. These effects were completely blocked by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. High concentrations (10-200 microg x ml(-1)) of M. charantia juice extract inhibited 14C-D-glucose uptake in L6 myotubes compared to the control response. The effect of M. charantia treatment was also investigated on myelinated fibre abnormalities in the tibial nerve of STZ-induced diabetic and control rats. The results show that diabetes was associated with significant (p < 0.05) reduction in the mean cross-sectional myelinated nerve fibres, axonal area, myelin area and maximal fibre area compared to end controls. Treatment of STZ-induced diabetic rats with M. charantia juice normalised the structural abnormalities of peripheral nerves. The results indicate that M. charantia can exert marked beneficial effects in diabetic rats, and moreover, it can regulate glucose uptake into jejunum membrane brush border vesicles and stimulate glucose uptake into skeletal muscle cells similar to the response obtained with insulin.     

Cytotoxic steroids from Monascus purpureus-fermented rice

Bioassay-guided fractionation of an EtOH extract of Monascus purpureus-fermented rice led to the isolation of two new steroids (22S, 23R, 24S)-20β,23α,25α-trihydroxy-16,22-epoxy-4,6,8(14)-trienergosta-3-one (1), the first example of a steroid possessing both a conjugated triene ketone system and a fused 4H-furan ring side chain within one molecule, and (22E, 24R)-3β,5α-dihydroxyergosta-23-methyl-7,22-dien-6-one (2), as well as two known compounds (22E, 24R)-3β,5α-dihydroxyergosta-7,22-dien-6-one (3) and (22E, 24R)-6β-methoxy-ergosta-7,22-diene-3β,5α-diol (4). Their structures were assigned by detailed interpretation of HRESIMS, 1D and 2D NMR spectroscopic data. The absolute stereochemistry of 1 was determined by single-crystal X-ray crystallography while the absolute stereochemistry of 2 was established by CD. Compounds 1-4 showed cytotoxic activity against the lung adenocarcinoma (A549) with IC(50) values of 0.08, 0.94, 12.6 and 13.5 μM, respectively. In addition, compounds 1 and 2 exhibited moderate activities against human ovarian cancer (A2780), with IC(50) values of 2.8 and 5.1 μM.     

Oleanane-type triterpene saponins from the bark of Aralia elata and their NF-κB inhibition and PPAR activation signal pathway

Two new oleanane-type triterpene saponins, tarasaponin IV (1) and elatoside L (2), and four known; stipuleanoside R(2) (3), kalopanax-saponin F (4), kalopanax-saponin F methylester (5), and elatoside D (6) were isolated from the bark of Aralia elata. Kalopanax-saponin F methyl ester was isolated from nature for the first time. Their chemical structures were elucidated using the chemical and physical methods as well as good agreement with those of reported in the literature. Oleanane-type triterpene saponins are the main component of A. elata. All compounds were investigated the anti-inflammatory activity. We measured their inhibition of NF-κB and activation of PPARs activities in HepG2 cells using luciferase reporter system. As results, compounds 2 and 4 were found to inhibit NF-κB activation stimulated by TNFα in a dose-dependent manner with IC(50) values of 4.1 and 9.5 μM, respectively, when compared with that of positive control, sulfasalazine (0.9 μM). Compounds 2 and 4 also inhibited TNFα-induced expression of iNOS and COX-2 mRNA. Furthermore, compounds 1-6 were evaluated PPAR activity using PPAR subtype transactivation assays. Among of them, compounds 4-6 significantly increased PPARγ transactivation. However, compounds 4-6 did not activate in any other PPAR subtypes.     

Antiinflammatory triterpenoids and steroids from Ganoderma lucidum and G. tsugae

The antiinflammatory properties of triterpenoids and steroids from both Ganoderma lucidum and Ganoderma tsugae were studied. Twelve compounds, including ergosta-7,22-dien-3beta-ol (1), ergosta-7,22-dien-3beta-yl palmitate (2), ergosta-7,22-dien-3-one (3), ergosta-7,22-dien-2beta,3alpha,9alpha-triol (4), 5alpha,8alpha-epidioxyergosta-6,22-dien-3beta-ol (5), ganoderal A (6), ganoderal B (7), ganoderic aldehyde A (8), tsugaric acid A (9), 3-oxo-5alpha-lanosta-8,24-dien-21-oic acid (10), 3alpha-acetoxy-5alpha-lanosta-8,24-dien-21-oic acid ester beta-d-glucoside (11), and tsugaric acid B (12), were assessed in vitro by determining their inhibitory effects on the chemical mediators released from mast cells, neutrophils, and macrophages. Compound 10 showed a significant inhibitory effect on the release of beta-glucuronidase from rat neutrophils stimulated with formyl-Met-Leu-Phe (fMLP)/cytochalasin B (CB) whereas compound 9 significantly inhibited superoxide anion formation in fMLP/CB-stimulated rat neutrophils. Compound 10 also exhibited a potent inhibitory effect on NO production in lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma)-stimulated N9 microglial cells. Moreover, compound 9 was also able to protect human keratinocytes against damage induced by ultraviolet B (UV B) light, which indicated 9 could protect keratinocytes from photodamage.     

Galanin and pancreastatin inhibit stimulated insulin secretion in the mouse: comparison of effects

The effects of the two intrapancreatic peptides galanin and pancreastatin on basal and stimulated insulin and glucagon secretion in the mouse were compared. It was found that at 2 min after intravenous injection of galanin or pancreastatin (4.0 nmol/kg), basal plasma glucagon and glucose levels were slightly elevated. Galanin was more potent than pancreastatin to elevate basal plasma glucagon levels: they increased from 60 +/- 15 to 145 +/- 19 pg/ml (p less than 0.01) after galanin compared to from 35 +/- 5 to 55 +/- 8 pg/ml (p less than 0.05) after pancreastatin. Plasma insulin levels were lowered by galanin (p less than 0.05), but not by pancreastatin. CCK-8 (6.3 nmol/kg) or terbutaline (3.6 mumol/kg) markedly increased the plasma insulin levels. Galanin (4.0 nmol/kg) completely abolished the insulin response to CCK-8 (p less than 0.001), but pancreastatin (4.0 nmol/kg) was without effect. Galanin inhibited the insulin response to terbutaline by approximately 60% (p less than 0.01), but pancreastatin inhibited the insulin response to terbutaline by approximately 35% only (p less than 0.05). CCK-8 and terbutaline did both elevate plasma glucagon levels by moderate potencies: neither pancreastatin nor galanin could affect these responses. Thus, in the mouse, galanin and pancreastatin both inhibit basal and stimulated insulin secretion, and stimulate basal glucagon secretion. Galanin is thereby more potent than pancreastatin. The study also showed that galanin potently inhibits insulin secretion stimulated by the octapeptide of cholecystokin and by the beta 2-adrenoceptor agonist terbutaline, and that pancreastatin inhibits terbutaline-induced insulin secretion.     

Opiate-prostaglandin interactions in the regulation of insulin secretion from rat islets of Langerhans in vitro

The inadequate insulin secretory response to glucose stimulation in non-insulin dependent diabetes has been attributed to many factors including high PGE2 levels blunting the secretory response, and to the existence of inhibitory opiate activity in vivo. The purpose of the present work was to see if there was a connection between these two independent theories. Radioimmunoassayable PGE2 in islets of Langerhans was found to be proportional to islet number and protein content and was typically 4 to 5pg/micrograms islet protein. Indomethacin (2.8 X 10(-5) M), sodium salicylate (1.25 X 10(-3) M) and chlorpropamide (7.2 X 10(-5) M) all lowered islet PGE2 levels and stimulated insulin release in vitro. Dynorphin (1-13), stimulated insulin release at a concentration of 6 X 10(-9) M, while lowering islet PGE2. Conversely, at a higher concentration, (6 X 10(-7) M), dynorphin had no stimulatory effect on insulin secretion and did not lower PGE2 levels in islets or in the incubation media. The stimulatory effects of dynorphin and sodium salicylate on insulin secretion were blocked by exogenous PGE2 (10(-5) M). PGE2 at a lower concentration (10(-9) M) did not exert any inhibitory effect on dynorphin- or sodium salicylate-induced insulin release. This concentration of exogenous PGE2 stimulated insulin release in the presence of 6mM glucose. Results from these experiments suggest that since an opioid peptide can lower endogenous PGE2 production in islets and since the stimulatory effects of the opioid peptide are reversed by exogenous PGE2 there may be interactions between these two modulators of insulin secretion.     

The effect of calcium on somatostatin inhibition of insulin release and cyclic AMP production in mouse pancreatic islets

The effect of somatostatin on glucose-induced insulin secretion and cyclic AMP accumation in isolated islets from obese, hyperglycemic ob/ob mice was studied in a microperifusion system. The normal biphasic pattern of insulin release as well as the inhibitory pattern of insulin release produced by somatostatin (0.5–1 μg/ml) was matched by similar changes in the intracellular concentration of cyclic AMP. When islets were stimulated by glucose (3 mg/ml) plus 3-isobutyl-1-methylxanthine (0.1 mM), somatostatin (0.5 μg/ml) failed to inhibit insulin secretion or cyclic AMP formation in the second phase whereas in the first phase both parameters were significantly reduced by somatostatin (0.5 μg/ml). In batch-type incubations it was shown that addition of excess calcium (to 6 mM) reversed this inhibition. In the second phase calcium potentiated the (glucose + 3-isobutyl-1-methylxanthine)-stimulated insulin secretion without affecting the cyclic AMP production. This potentiation was inhibited by somatostatin (0.1 μg/ml). Somatostatin (1 μg/ml) inhibited adenylate cyclase activity in islet homogenates. No effect of somatostatin on islet glucose utilization could be demonstrated.The results indicate a dual action of somatostatin in the inhibition of insulin release, one involving the islet adenylate cyclase and one affecting the islet uptake of calcium.     

Potent Lipolytic Activity of Lactoferrin in Mature Adipocytes

Momilactone A, a major rice diterpene phytoalexin, could be synthesized by dehydrogenation at the 3-position of 3β-hydroxy-9β-pimara-7,15-dien-19,6β-olide in rice leaves. The presence of 3β-hydroxy-9β-pimara-7,15-dien-19,6β-olide in UV-irradiated rice leaves was confirmed by comparing the mass spectra and retention times after a GC/MS analysis of the natural and synthetic compounds. The soluble protein fraction from UV-irradiated rice leaves showed dehydrogenase activity to convert 3β-hydroxy-9β-pimara-7,15-dien-19,6β-olide into momilactone A. The enzyme required NAD⁺ or NADP⁺ as a hydrogen acceptor. The optimum pH for the reaction was 8. The K _m value to 3β-hydroxy-9β-pimara-7,15-dien-19,6β-olide was 36 μM when NAD⁺ was supplied as a cofactor at a concentration of 1 mM. 3β-Hydroxy-9β-pimara-7,15-dien-19,6β-olide and its dehydrogenase activity were induced in a time-dependent manner by UV irradiation.     

Mechanism of action of growth-hormone-releasing hormone in stimulating insulin secretion in vitro from isolated rat islets and dispersed islet cells

Human growth-hormone-releasing hormone [(1-44)NH2] (hGHRH) was a potent stimulus for insulin release from rat islets of Langerhans in vitro; the optimum concentration used was 10(-11) M. The dose response curves for hGHRH effects on insulin secretion were notably different in intact islets of Langerhans compared to cultured dispersed islet cells. Pancreatic islets responded to a very low hGHRH concentration (10(-12) M), but at a higher hGHRH concentration (10(-9) M) no stimulation of insulin release was observed. When somatostatin antiserum was included in the incubation medium, hGHRH (10(-9) M) stimulated insulin release from intact islets. In cultured dispersed islet cells, which are principally insulin-secreting B cells, hGHRH directly and potently stimulated insulin release even at a concentration of 10(-9) M. Addition of somatostatin (10(-7), 10(-8) M) significantly reduced the hGHRH-induced insulin-secretory responses of dispersed islet cells. hGHRH (10(-11)-10(-9) M) raised islet cAMP levels; individually, hGHRH and theophylline exerted positive effects on insulin release, their combined effect was greater than that caused by either one. We conclude that hGHRH directly affects insulin secretion in vitro by a cAMP-dependent mechanism, and that the difference in responses of intact islets versus islet cells to increasing concentrations of hGHRH may be related to hGHRH-induced release of somatostatin in intact rat islets.