Acides gras omega-3 et prévention cardiovasculaire

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Dietary fish oil is antihypertrophic but does not enhance postischemic myocardial function in female mice.

Clinically and experimentally, a case for omega-3 polyunsaturated fatty acid (PUFA) cardioprotection in females has not been clearly established. The goal of this study was to investigate whether dietary omega-3 PUFA supplementation could provide ischemic protection in female mice with an underlying genetic predisposition to cardiac hypertrophy. Mature female transgenic mice (TG) with cardiac-specific overexpression of angiotensinogen that develop normotensive cardiac hypertrophy and littermate wild-type (WT) mice were fed a fish oil-derived diet (FO) or PUFA-matched control diet (CTR) for 4 wk. Myocardial membrane lipids, ex vivo cardiac performance (intraventricular balloon) after global no-flow ischemia and reperfusion (15/30 min), and reperfusion arrhythmia incidence were assessed. FO diet suppressed cardiac growth by 5% and 10% in WT and TG, respectively (P < 0.001). The extent of mechanical recovery [rate-pressure product (RPP) = beats/min x mmHg] of FO-fed WT and TG hearts was similar (50 +/- 7% vs. 45 +/- 12%, 30 min reperfusion), and this was not significantly different from CTR-fed WT or TG. To evaluate whether systemic estrogen was masking a protective effect of the FO diet, the responses of ovariectomized (OVX) WT and TG mice to FO dietary intervention were assessed. The extent of mechanical recovery of FO-fed OVX WT and TG (RPP, 50 +/- 4% vs. 64 +/- 8%) was not enhanced compared with CTR-fed mice (RPP, 60 +/- 11% vs. 80 +/- 8%, P = 0.335). Dietary FO did not suppress the incidence of reperfusion arrhythmias in WT or TG hearts (ovary-intact mice or OVX). Our findings indicate a lack of cardioprotective effect of dietary FO in females, determined by assessment of mechanical and arrhythmic activity postischemia in a murine ex vivo heart model

The Paleoproterozoic Waterberg Group, South Africa: Provenance and its relation to the timing of the Limpopo orogeny

Four Paleoproterozoic formations of the Waterberg Group in South Africa are composed of coarse clastic detritus derived from erosion of the Limpopo Belt. Timing of the Limpopo orogeny, an event involving the collision of the Kaapvaal and Zimbabwe cratons, has long been a contentious issue. The results of point counting, major and trace element geochemistry, and U–Pb detrital zircon geochronology indicate that the Waterberg sedimentary formations in the study area were primarily sourced by siliceous (rifted margin) sedimentary and minor mafic volcanic rocks of the Archean Beit Bridge Complex, Limpopo Central Zone. The volumetrically predominant beige/brown sandstones in the four studied formations are quartzrich with average QFR ratios of 80:7:13 (Blouberg), 70:19:11 (Setlaole), 88:5:7 (Makgabeng), and 89:3:8 (Mogalakwena). Chert and arenite account for >90% of lithic fragments in all formations, with minor siliceous gneiss fragments. Although all formations are silica enriched, the Makgabeng dune samples produce extremely high SiO2 abundances (92–99 wt%), which are attributed to the presence of silica cement and quartz within rock fragments. Geochemically, the stratigraphically highest Mogalakwena Formation is unique with elevated Ti and Zr values, and intra-formational differences in REE patterns; the latter feature is consistent with a mixed provenance. Volumetrically minor green and purple sandstones in the Waterberg formations contain the greatest Cr, Ni, Ti, and V abundances, which supports localized derivation from a mafic or ultramafic source. Chemical index of alteration (CIA) values range from 57 to 89, which could indicate significant chemical weathering of the source rocks, but a plot of Th/Sc versus Zr/Sc illustrates that the sandstones have undergone recycling, which was probably responsible for enrichments in Al2O3 relative to Na2O3, CaO and K2O. Combinations of well rounded and subangular quartz grains support a recycled origin. Detrital zircons in the lowermost Blouberg Formation produced a wide array of ages ranging from ca. 3379 to 2043 Ma. The youngest peak at 2046 Ma is also the largest, and represents the maximum age of deposition for the formation. Additional peaks at 3281 Ma, 3330 Ma, and 3379 Ma are consistent with ages previously determined from the Beit Bridge Complex, whereas peaks at 2578 Ma and 2649 Ma coincide with ages determined from gneisses of the Limpopo Central Zone. Derivation of detritus from the Beit Bridge Complex is directly indicated by sedimentary and siliceous gneiss fragments in the sandstones, subrounded quartz grains suggestive of relatively short transport distances, green and purple sandstone drapes derived from mafic volcanic units, and paleocurrent patterns consistent with south to southwest flow directions. Therefore the timing of deposition of the Blouberg Formation (2046 Ma) equates to the end stages of the Limpopo orogeny. This negates previous suggestions that the Limpopo orogeny occurred only during the Neoarchean.http://www.elsevier.com/locate/precamreshb201