Synthesis of vitamin K1 2,3-epoxide in rat liver mitochondria

Metabolism of vitamin K1 in rat liver mitochondria has been studied with succinate as the source of reducing equivalents. A metabolite was isolated that comigrated with vitamin K1 epoxide using four different chromatographic systems. The purified metabolite had an ultraviolet spectrum (200-330 nm) that was identical to that of synthetic vitamin K1 epoxide. The mass spectrum of the purified metabolite was identical to that of synthetic vitamin K1 epoxide. A comparison of production of vitamin K1 epoxide by mitochondrial and microsomal preparations indicates that the mitochondrial production of vitamin K1 epoxide was about 50% of that of the microsomes. Since the mitochondrial preparation was found to have only 3.4% of the glucose-6-phosphatase activity of the microsomal preparation, it can be concluded that the vitamin K1 epoxide isolated from the mitochondrial incubations was due primarily to mitochondrial synthesis. Epoxidation of vitamin K1 in mitochondria suggests that mitochondria might be sites for vitamin K-dependent carboxylation of protein(s).     

Mutagenic selectivity of carcinogenic nitroso compounds: II. N,N-Dimethylnitrosamine

The genetic properties of the hepatocarcinogen N,N-dimethylnitrosamine (DMN) were examined in Drosophila for the assessment of the role of dose, cellular metabolism and genic target in its mutagenicity. Genetic activity was assayed with respect to the induction of the non-specific X-chromosome recessives (lethals and visibles) relative to the effects on specific genic sites, especially rDNA, which yields bobbed (bb) mutations.Dose dependence followed a quadratic course for all mutational classes and germ cell types, which indicated that DMN induced at least some multiple-hit mutagenic events. The genetic activity of DMN was favoured by cellular metabolism for all mutational classes, as was indicated by the progressive increase in mutation yield during spermatogenesis — from the metabolically inert mature sperm to the actively metabolizing spermatocytes and spermatogonia.The role of DNA methylation in the mutagenicity of DMN was deduced from quantitative assays of its genetic activity relative to the methylating nitrosamide — N-methyl-N-nitrosourethane (MNUr) — over the same dose range (1–10 mM) and on identical cell types and genic targets. In the metabolically inert cells (mature sperm), the two compounds were equally active with respect to the non-specific effects (X-recessives), but MNUr was considerably more effective on rDNA (bb's). Conversely, in the metabolically active cells (spermatocytes and spermatogonia), DMN exerted a much higher non-specific mutagenicity than MNUr, but the two compounds were equally effective on rDNA. These results could not be entirely interpreted by the methylation hypothesis and indicated that a DMN aldehydic metabolite, structurally analogous to MNUr, might be responsible for the induction of the rDNA mutations.The rDNA selectivity index of DMN was significantly lower than for MNUr, which paralleled their relative carcinogenic versatilities. However, DMN was comparatively more effective on the tRNA genes, a feature which might be associated with its oncogenic specificity.     

Measuring the long-term success of small-scale marine protected areas in a Philippine reef fishery

Tropical coral reefs are subject to multiple pressures from both natural and anthropogenic sources. These pressures have caused widespread declines in reef health, resulting in the increased use of spatial management tools such as marine protected areas (MPAs). MPAs have proven generally effective if well designed and enforced, but there are limited long-term studies investigating how the presence of small-scale MPAs affects fish populations and reef communities. Using a 12-year time series, we found that small-scale (10–50 ha) community-managed MPAs along the Danajon Bank of the Philippines preserved average fish biomass within their boundaries over time relative to surrounding fished reefs. Unprotected areas are, however, showing significant long-term biomass decline. MPAs were also found to preserve more key trophic groups and larger-bodied commercially targeted reef fish families. Fish biomass of piscivore, scavenger and invertivore trophic groups inside individual MPAs is, however, still declining at a similar rate as outside. Surprisingly, long-term benthic cover and growth form composition were not significantly affected overall by MPA presence, despite the sporadic use of highly destructive dynamite fishing in this region. Coral cover has remained historically low (21–28%) throughout the study, following widespread bleaching mortality. While management tempered overall abundance declines, we found that irrespective of MPA presence, there was a generalised decline of both large- and small-bodied fish size groups across the study region, most steeply within the 20–30 cm length fish, and a shift towards proportionally higher abundances of small (5–10 cm) fish. This indicates a combination of over-exploitation, inadequate MPA size and coverage for larger fish, and the lingering effects of the 1998 bleaching event. Generalised shifts in body size and trophic structure reported here could lead to future reductions in fishery productivity and stability and will be further exacerbated unless broader fishery regulations and enforcement is instated.

     

The investigation of cytosolic phospholipase A2 using ELISA

Two studies of the behaviour of cytosolic phospholipase A(2) (cPLA(2)) in the red blood cell (RBC), as measured by ELISA, are described. In the first study we show a significant increase in cPLA(2) in patients with schizophrenia compared to controls and suggest that this measure, if corroborated, could be used as a diagnostic marker. In a second study we found that washing the RBC introduced an unknown confounding variable which led us to reject this study. A subsequent investigation of washing red cells showed that the washing effect may be due to a plasma factor likely to be more than 5kDa MW which can be removed from red cells by washing with buffers. When the cells are washed, the concentration of cPLA(2) in the red cell, as measured by ELISA, significantly increases. We advise against washing the red cell in any study that involves measuring cPLA(2) by ELISA.     

Gender differences in the attenuation of salt-induced hypertension by angiotensin (1-7)

Chronic infusion of angiotensin (1-7) [Ang-(1-7)] lowers blood pressure in spontaneously hypertensive rats (SHR). To assess the role of Ang-(1-7) in salt-induced hypertension, Ang-(1-7) (24 microg/kg/hr) or saline was administered chronically via osmotic minipump into the jugular vein of 5-6 wk-old male (M) and female (F) Dahl salt-sensitive rats placed on a high-salt (8% NaCl) diet for 2 weeks. Blood pressure (BP) and heart rate were measured prior to the start of the diet and weekly thereafter. Ang-(1-7) significantly attenuated the BP increase after 1 wk on the diet in both M and F rats, but after 2 weeks only in F rats. Enhanced release of prostacyclin, (6-keto PGF1 alpha), following Ang-(1-7) treatment was observed in both M and F rats. In addition, significant increases in aortic blood flow and plasma levels of nitric oxide were observed in the F rats following Ang-(1-7) treatment. These findings demonstrate that the reduction in BP is due to both prostacyclin and NO and that there is a gender difference in the attenuation of salt-induced hypertension by Ang-(1-7).     

Salt-loading and simulated microgravity on baroreflex responsiveness in rats

Cardiovascular adaptations observed during exposure to microgravity results in impairment of baroreflex activity partially as a result of fluid and electrolyte shifts. The head-down tilt rat model mimics some of the physiological observations that have been made in astronauts. We examined the effects of salt-loading on baroreflex activity after 7 day simulated microgravity (30 degrees tail-suspension) and the subsequent 6 hr post-suspension in Sprague-Dawley (SD) rats, using low salt (0.3% NaCl) and high salt (8% NaCl) diets. In suspended animals on a low salt diet, the baroreflex response curve was shifted to the left, while the heart rate (HR) range and MAP50 values were reduced compared to their parallel tethered, non-suspended controls. For non-suspended animals, salt-loading shifted the curve to the right with a reduced HR range. In salt-loaded, suspended animals, the curve and its parameters resemble those of non-suspended animals on a low salt diet. In summary, these data have demonstrated that a short-term (seven days) simulated weightlessness may elicit cardiovascular deconditioning in rats after release from the simulation manifested as an altered responsiveness in baroreceptor-heart rate reflex and a lowered blood pressure while the rats are tethered and horizontal. Our results also suggest the counteracting effect of salt loading on cardiovascular deconditioning.