Cyanosis by methemoglobinemia in tadpoles of Cochranella granulosa (Anura: Centrolenidae)

Tadpoles inhabit generally well oxygenated rivers and streams, nevertheless they were found in areas with limited oxygen availability inside the rivers. To assess this feature, I examined factors that influence centrolenid tadpole behaviour using Cochranella granulosa. The tadpoles were reared in well-oxygenated and hypoxic environments and their development, survivorship and growth were compared. The tadpoles in oxygenated water acquired a pale color, while tadpoles in hypoxic water grew faster and were bright red and more active. In the oxygenated water, the ammonium, which had its origin in the tadpoles’ urine and feces, was oxidized to nitrate. In contrast, in the hypoxic treatment, the nitrogen compounds remained mainly as ammonium. Presumably, the nitrate in oxygenated water was secondarily reduced to nitrite inside the long intestine coils, because all symptoms in the tadpoles point to methemoglobinemia, which can occur when the nitrite passes through the intestine wall into the bloodstream, transforming the hemoglobin into methemoglobin. This could be checked by a blood test where the percentage of methemoglobin was 2.3% in the blood of tadpoles reared in hypoxic condition, while there was a 19.3% level of methemoglobin in the blood of tadpoles reared in oxygenated water. Together with the elevated content of methemoglobin, the growth of the tadpoles was delayed in oxygenated water, which had high nitrate content. The study about quantitative food-uptake showed that the tadpoles benefit more from the food in hypoxic water, although they spent there more energy moving around than the tadpoles living in oxygenated but nitrate-charged water. Rev. Biol. Trop. 58 (4): 1467-1478. Epub 2010 December 01.

Los renacuajos por lo general viven en ríos y arroyos bien oxigenados, sin embargo, como han sido encontrados en áreas con disponibilidad de oxígeno limitada en los ríos, se estudió como influye este factor en su comportamiento. Renacuajos de Cochranella granulosa fueron criados en ambientes bien oxigenados y de hipoxia para comparar su desarrollo, supervivencia y crecimiento. En el agua que no fue cambiada durante al menos un mes, los renacuajos mostraron diferencias en su desarrollo cuando vivían en agua hipóxica u oxigenada. Los renacuajos en el agua aireada tenían un color pálido, mientras que en la hipóxica fueron más activos y de un color rojo brillante. En el agua hipóxica, el nitrógeno que se originó de la orina y las heces de los renacuajos se mantuvo principalmente en forma de amonio; en cambio, el amonio fue oxidado a nitrato en el agua aireada. Presumiblemente, el nitrato en el agua oxigenada se redujo secundariamente a nitrito dentro del intestino, ya que todos los síntomas en los renacuajos que vivían en esta agua apuntaron a una metahemoglobinemia, que se produce cuando el nitrito pasa a través de la pared del intestino a la corriente sanguínea transformando la hemoglobina en metahemoglobina. Esto pudo comprobarse mediante un análisis sanguíneo en donde el porcentaje de metahemoglobina fue del 2.3% en la sangre de los renacuajos criados en condición hipóxica y de un 19.3% de metahemoglobina en aquellos criados en agua aireada. En la misma forma en que la metahemoglobina aumenta en la sangre de los renacuajos que viven en agua oxigenada, su crecimiento disminuye en agua con alto contenido de nitrato. El estudio cuantitativo de la ingestión de nutrientes mostró que el crecimiento de los renacuajos se beneficia más de los alimentos en agua hipóxica, a pesar de que los renacuajos son más activos en sus movimientos que los que viven en agua oxigenada pero cargada de nitratos.

Effect of fenvalerate technical grade on acetyl cholinesterase activity in Indian bullfrog Haplobatrachus tigerinus (Daudin).

Indian bullfrog Haplobatrachus tigerinus (Daudin) was exposed to sublethal dose (1/3 of LC50 I.E. 1.166 mg/kg) of fenvalerate technical grade and the effect was studied on the specific activity of acetyl cholinesterase in the different tissues of frog viz., brain, muscle, liver, kidney and testis at different time periods viz., 3,6, 12, 24, 48 and 72 hours. The inhibition of specific activity of acetyl cholinesterase was in the order of kidney > brain > muscle > liver > testis. A significant inhibition was noticed in kidney at 12 hours (-64.33%) and no effect was noticed at 3 hours in testis (+0.67%). The AChE activity was inhibited in first three hours of administration of fenvalerate in all the tissue tested. The inhibition continued upto 6 hours or 2 hours in different tissue but the recovery was started by 24 hours and almost completed by 72 hours.

Hydrogen peroxide as a tool for studying oxidative stress in the heart

Hydrogen peroxide (H2O2) was observed to depolarize the frog sartorius muscle and promote rhythmic contraction of frog cardiac ventricular rings or their contracture. This last effect was sodium-dependent. H2O2 perfused or injected into the aorta of the isolated rat heart induces a positive inotropic effect (with cardiac arrhythmias such as extrasystolic potentiations) followed by deoression of contractility or cardiac contractures, according to the dose employed. The last effects is similar to the "stone heart"observed in the reperfusion injury and may be ascribed to lipoperoxidation (LPO) of the membrane lipids, to protein damage, to reduction in the ATP level and/or to cardioactive compounds liberated by LPO. Besides its direct effect on the ATP level, H2O2 would react with iron ions to produce hydroxyl radicals that attack the cellular membranes. Deferoxamine, an iron chelator and scavenger of hydroxyl radicals, reduced the contractures induced by H2O2. Perfusion with H2O2 increased the LPO of cardiac homogenates measured by chemiluminescence, oxygen uptake and malonaldehyde formation. The fall in ATP levels and the LPO would result in calcium overload of the cardiac fibers and contracture ("stone heart"). The 45Ca uptake was increased by incubation of cardiac strips with H2O2. Previous perfusion of the isolated rat heart with nifedipine or indomethacin reduced the H2O2 cardiac contracture. Vitamin A, a quencher of singlet oxygen liberated during LPO, reduces the H2O2 cardiac contractures and also LPO. Gradual physical exercises, besides increasing the oxygen consumption, protected the heart from oxidative stress. The experimental production of hypothyroidism protected the heart against the H2O2 oxidative stress. The hearts of rats submitted to hypertension with high renin levels showed increased LPO, measured by chemiluminescence and oxygen uptake, indicating that this condition may be produced by oxygen species or causes their production. All these findings give support to the idea that the ischemia-reperfusion injury is an active oxygen species associated disorder that induces cardiac stiffness or contractures that would be produced by calcium overload. Thus, H2O2 may be useful for inducing experimental oxidative stress in the heart and for studying its oxidative status in physiological and pathological situations.