Impactos do organofosforado triclorfon sobre a frequência cardíaca de Nauphoeta cinérea Oliver 1974

Abstract

In Brazil the use of organophosphate insecticides is provoking serious environmental problems because of the large dosages used. The toxic effects of these compounds are not completely understood in the different physiological systems of insects. In this work we sought to investigate the activity of the organophosphate Trichlorfon in the cardiac rhythm of Nauphoeta cinerea cockroaches. The cockroach N. cinerea of both sex were kept in insectary under controlled temperature (24-25 ° C) with water and food ad libitum. Cockroach semi-isolated heart preparation (CSIB) was mounted by anesthetizing the animals by cooling at 4 °C for 10 min. The animals were then fixed in a platform with entomological needles and the sides of the abdomen edges were cut along each side. The abdominal cuticle was removed with the aid of surgical scissors and with tweezers to expose the viscera which have been carefully removed to improve the heart observation. The heart was bathed in insect saline 0.15 mM at room temperature in a final volume of 200 µl. The heart rate was monitored by means of a stereomicroscope (Olympus, Damstat, Germany) for 30 minutes. The recordings were made in a total time of 120 min. Statistical analysis was applied using Two way ANOVA test. The analysis of control heart rate (CSIB) incubated only with saline was 90 ± 1% beats per minute (bpm). When trichlorfon was incubated at concentrations of 20, 100, 500μg / mL, there was a time dependent effect on heart rate, causing a maximal decrease of 50 ± 2% (100μg / ml) in the frequency of the heart beats in 30min (n = 9, p <0.05). When octopamine 0,5-5μg / ml was tested, there was a decrease in maximum heart rate of 25 ± 3% with the highest concentration at 30 min (n = 9, p<0.05). Acetylcholine and neostigmine, 5μg / ml, were also assayed and induced a decrease of 20 ± 3% and 19 ± 1% of cardiac frequency in 30 minutes, respectively (n = 9, p <0.05). When dexamethasone 20 / ml was tested, there was a decrease in heart rate of 35 ± 4% at 30 min (n = 9, p <0.05). These results demonstrate that the organophosphate pesticides exert a toxic effect on the cardiovascular system of insects. Inhibition of phospholipase A2 by dexamethasone demonstrated that this pathway is important for modulating the cardiac frequency in insects and will be subject of further studies. Also reinforce the role of cholinergic agents acting directly on the cardiac rhythm of insects. These data demonstrate the toxic potential of organophosphates that in nature can directly influence non-target insects, causing serious damage to the environment.