Phytoplankton, zooplankton, benthic invertebrates, and pond smelt were collected in a eutrophic lake (Lake Suwa, Japan) from spring to autumn in 1986 and 1987. Their stable carbon and nitrogen isotope ratios were analyzed together with conventional examination of the gut contents of pond smelt. Temporal variations in isotope rations were similar among the organisms other than benthic animals. The @d15N values of diet for several animals in the pelagic food web were estimated, assuming a stepwise enrichment in 15N with increasing trophic level. A calanoid copepod, Eodiaptomus japonicus, seemed to feed on the predominant phytoplankton, including Microcystis spp., while Microcystis did not seem to be important as an organic source for other zooplankton and pond smelt. The temporal variation of the isotope ratios of pond smelt was well explained by visual gut content analysis. It is suggested that intensive measurements of carbon and nitrogen isotope ratios of each species serve to effectively assess the yearly dynamics of the food web structure in eutrophic lakes when productivity and species composition of plankton change seasonally.

Temporal variability in the concentration of toxic heptapeptide microcystin was studied ( ) ( ) during the warm season of four years 1991 -1994 in a hypertrophic lake Lake Suwa in central ( ) ( Honshu, Japan. Lake water samples ca. 5 L were filtered to separate intracellular microcystin cell ) ( ) fraction from extracellular microcystin filtered lake water fraction . These fractions were analyzed to measure the total quantity of microcystin in lake water. Total amounts of extra-and intracellular microcystin were measured with high performance liquid chromatography. Concentrations of intracellu-( ) lar microcystin usually exceeded concentrations of extracellular microcystin 24 out of 26 times . High concentrations of intracellular microcystin were found during the exponential growth phase of the blooms, whereas concentrations of extracellular microcystin were highest at the end of the blooms.( ) However, concentrations of extracellular microcystin remained very small -4 g / L compared to the levels of intracellular microcystin. The relatively higher percentages of microcystin in filtered lake water ( ) )20% at the end of blooms suggests that release of microcystin from cells occurs during senescence and the decomposition period of Microcystis cells.

DipeptiDyl peptiDase-4 (DPP-4) inhibitor is a new class of anti-diabetic drug which enhances circulating levels of a gut incretin hormone, glucagon-like peptide-1 (GLP-1), by inhibiting the degradation of GLP-1 [1]. GLP-1 stimulates insulin secretion from pancreatic β-cells in a blood glucose-dependent manner and suppresses glucagon release from pancreatic abstract. Dipeptidyl peptidase-4 (DPP-4) inhibitor is a new class of anti-diabetic drug which exerts its glucose-lowering action by suppressing the degradation of a gut incretin hormone glucagon-like peptide-1 (GLP-1). To elucidate whether treatment with stronger DPP-4 inhibitor on top of angiotensin II type 1 receptor blocker (ARB) provides greater renal protective effects, we performed a crossover study with two DPP-4 inhibitors, sitagliptin and alogliptin, in twelve type 2 diabetic patients with incipient nephropathy taking ARBs. This study consisted of three treatment periods: sitagliptin 50 mg/day for 4 weeks (first period), alogliptin 25 mg/day for 4 weeks (second period), and sitagliptin 50 mg/day for 4 weeks (third period). Significant changes in body mass index, blood pressure, serum lipids, serum creatinine, estimated glomerular filtration rate, and HbA1c were not observed among the three treatment periods. Reduced urinary levels of albumin and an oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG), increased urinary cAMP levels, and elevated plasma levels of stromal cell-derived factor-1α (SDF-1α) which is a physiological substrate of DPP-4 were observed after the switch from sitagliptin to a stronger DPP-4 inhibitor alogliptin. Given a large body of evidence indicating anti-oxidative action of cAMP and up-regulation of cellular cAMP production by SDF-1α, the present results suggest that more powerful DPP-4 inhibition on top of angiotensin II type 1 receptor blockade would offer additional protection against early-stage diabetic nephropathy beyond that attributed to glycemic control, via reduction of renal oxidative stress by SDF-1α-cAMP pathway activation.

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Amounts of hepatotoxic microcystin and neurotoxic anatoxin-a were estimated in natural blooms and strains of cyanobacteria from freshwaters in Japan. A simultaneous analysis method of anatoxin-a and microcystin was applied to natural bloom samples, which has been dominated by several species and the strains of cyanobacteria which produced simultaneously both toxins. The natural blooms examined in the present study were mainly composed of Anabaena and Oscillatoria, but most also contained Microcystis and other cyanobacteria. Only one sample was almost unialgal, Anabaena spiroides, collected from Lake Sagami. The toxins in 14 samples collected from nine different natural blooms during 1988-1992 were identified as microcystins-RR, -YR, and -LR; desmethyl-7-microcystin-LR (7-DMLR); and anatoxin-a. Microcystins were the main toxins contained in these natural blooms, with anatoxin-a not being detected or of very little quantity. 7-DMLR was detected in samples only from Lake Kasumigaura. Five strains of Anabaena isolated from waters in Japan produced a small amount of anatoxin-a, but no microcystins. One half of the strains of Microcystis produced microcystins and/or anatoxin-a. This is the first study showing Microcystis producing both anatoxin-a and microcystins.