Heart rate reduction during exerciseinduced myocardial ischaemia and stunning

Aims The respective contributions of reduction in heart rate and inotropism in the beneficial effects of beta-blockade in ischaemic heart disease remains debated. The effects of selective heart rate reduction by ivabradine (I f inhibitor) were compared to those of atenolol on exercise-induced ischaemia and stunning. Methods and results In seven instrumented dogs, coronary stenosis was calibrated to suppress increase in coronary blood flow during a 10-min treadmill exercise. When administered before exercise, atenolol and ivabradine similarly reduced heart rate versus saline at rest and during exercise (154 AE 2 and 155 AE 9 vs 217 AE 13 beats/min, respectively). During exercise, left ventricular wall thickening (LVWth) was reduced to 2 AE 1% from 23 AE 4% under saline but ivabradine limited this effect (10 AE 3%) and reduced the subsequent myocardial stunning vs saline. Atenolol also limited LVWth decrease during exercise (17 AE 4%) but had no effect during recovery. When administered after exercise, ivabradine attenuated stunning and this effect disappeared when heart rate reduction was corrected by atrial pacing. Atenolol administered after exercise severely depressed LVWth vs saline. Conclusion Selective heart rate reduction not only provides an anti-ischaemic effect but also per se improves contractility of the stunned myocardium. Additional negative inotropism is protective against ischaemia but deleterious during stunning

Impact of 20 : 4n-6 supplementation on the fatty acid composition and hemocyte parameters of the Pacific oyster Crassostrea gigas

International audienceArachidonic acid (20:4n-6, ArA) and its eicosanoid metabolites have been demonstrated to be implicated in immune functions of vertebrates, fish, and insects. Thus, the aim of this study was to assess the impact of ArA supplementation on the FA composition and hemocyte parameters of oysters Crassostrea gigas. Oyster dietary conditioning consisted of direct addition of ArA solutions at a dose of 0, 0.25, or 0.41 mu g ArA per mL of seawater into tanks in the presence or absence of T-Iso algae. Results showed significant incorporation of ArA into gill polar lipids when administered with algae (up to 19.7%) or without algae (up to 12.1%). ArA supplementation led to an increase in hemocyte numbers, phagocytosis, and production of reactive oxygen species by hemocytes from ArA-supplemented oysters. Moreover, the inhibitory effect of Vibrio aestuarianus extracellular products on the adhesive proprieties of hemocytes was lessened in oysters fed ArA-supplemented T-Iso. All changes in oyster hemocyte parameters reported in the present study suggest that ArA and/or eicosanoid metabolites affect oyster hemocyte functions