RESUMO
Hypoxia and mercury contamination often co-occur in tropical freshwater ecosystems, but the interactive effects of these two stressors on fish populations are poorly known. The effects of mercury (Hg) on recorded changes in the detailed form of the electrocardiogram (ECG) during exposure to progressive hypoxia were investigated in two Neotropical freshwater fish species, matrinxã, Brycon amazonicus and traíra, Hoplias malabaricus. Matrinxã were exposed to a sublethal concentration of 0.1 mg L-1 of HgCl2 in water for 96 h. Traíra were exposed to dietary doses of Hg by being fed over a period of 30 days with juvenile matrinxãs previously exposed to HgCl2, resulting in a dose of 0.45 mg of total Hg per fish, each 96 h. Both species showed a bradycardia in progressive hypoxia. Hg exposure impaired cardiac electrical excitability, leading to first-degree atrioventricular block, plus profound extension of the ventricular action potential (AP) plateau. Moreover, there was the development of cardiac arrhythmias and anomalies such as occasional absence of QRS complexes, extra systoles, negative Q-, R- and S-waves (QRS complex), and T wave inversion, especially in hypoxia below O2 partial pressures (PO2) of 5.3 kPa. Sub-chronic dietary Hg exposure induced intense bradycardia in normoxia in traira, plus lengthening of ventricular AP duration coupled with prolonged QRS intervals. This indicates slower ventricular AP conduction during ventricular depolarization. Overall, the data indicate that both acute waterborne and sub-chronic dietary exposure (trophic level transfer), at sublethal concentrations of mercury, cause damage in electrical stability and rhythm of the heartbeat, leading to myocardial dysfunction, which is further intensified during hypoxia. These changes could lead to impaired cardiac output, with consequences for swimming ability, foraging capacity, and hence growth and/or reproductive performance.
Assuntos
Peixes/fisiologia , Mercúrio/toxicidade , Poluentes Químicos da Água/toxicidade , Animais , Caraciformes , Ecossistema , Eletrocardiografia , Eutrofização , Água Doce , HipóxiaRESUMO
The present study has revealed that the lungfish has both structural and functional features of its system for physiological control of heart rate, previously considered solely mammalian, that together generate variability (HRV). Ultrastructural and electrophysiological investigation revealed that the nerves connecting the brain to the heart are myelinated, conferring rapid conduction velocities, comparable to mammalian fibers that generate instantaneous changes in heart rate at the onset of each air breath. These respiration-related changes in beat-to-beat cardiac intervals were detected by complex analysis of HRV and shown to maximize oxygen uptake per breath, a causal relationship never conclusively demonstrated in mammals. Cardiac vagal preganglionic neurons, responsible for controlling heart rate via the parasympathetic vagus nerve, were shown to have multiple locations, chiefly within the dorsal vagal motor nucleus that may enable interactive control of the circulatory and respiratory systems, similar to that described for tetrapods. The present illustration of an apparently highly evolved control system for HRV in a fish with a proven ancient lineage, based on paleontological, morphological, and recent genetic evidence, questions much of the anthropocentric thinking implied by some mammalian physiologists and encouraged by many psychobiologists. It is possible that some characteristics of mammalian respiratory sinus arrhythmia, for which functional roles have been sought, are evolutionary relics that had their physiological role defined in ancient representatives of the vertebrates with undivided circulatory systems.
Assuntos
Peixes/fisiologia , Coração/fisiologia , Mamíferos/fisiologia , Respiração , Animais , Fibras Autônomas Pré-Ganglionares/fisiologia , Sistema Nervoso Autônomo/fisiologia , Tronco Encefálico/anatomia & histologia , Peixes/metabolismo , Gases/metabolismo , Coração/inervação , Frequência Cardíaca/fisiologia , Hipóxia/fisiopatologia , Condução Nervosa/fisiologia , Nervo Vago/fisiologia , Nervo Vago/ultraestruturaRESUMO
The localization, distribution and orientation of O(2) chemoreceptors associated with the control of cardio-respiratory responses were investigated in the neotropical, Hoplias lacerdae. Selective denervation of the cranial nerves (IX and X) was combined with chemical stimulation (NaCN) to characterize the gill O(2) chemoreceptors, and the fish were then exposed to gradual hypoxia to examine the extent of each cardio-respiratory response. Changes in heart rate (f(H)) and ventilation amplitude (V(amp)) were allied with chemoreceptors distributed on both internal and external surfaces of all gill arches, while ventilation rate (f) was allied to the O(2) chemoreceptors located only in the internal surface of the first gill arch. H. lacerdae exposed to gradual hypoxia produced a marked bradycardia (45%) and 50% increase in V(amp), but only a relatively small change in f (32%). Thus, the low f(R) response yet high V(amp) were in accord with the characterization of the O(2) chemoreceptors. Comparing these results from H. lacerdae with hypoxia-tolerant species revealed a relationship existent between general oxygenation of the individual species environment, its cardio-respiratory response to hypoxia and the characterization of O(2) chemoreceptors.
Assuntos
Adaptação Fisiológica/genética , Fenômenos Fisiológicos Cardiovasculares , Células Quimiorreceptoras/fisiologia , Peixes/fisiologia , Oxigênio/fisiologia , Fenômenos Fisiológicos Respiratórios , Animais , Pressão Sanguínea/fisiologia , Nervos Cranianos/cirurgia , Denervação , Brânquias/irrigação sanguínea , Brânquias/efeitos dos fármacos , Brânquias/inervação , Frequência Cardíaca/fisiologia , Especificidade de Órgãos , Cianeto de Sódio/farmacologia , Especificidade da Espécie , Estresse Fisiológico/fisiologiaRESUMO
Oxidative stress biomarkers, in vivo heart rate (f (H)), and contraction dynamics of ventricle strips of bullfrog (Lithobates catesbeiana) tadpoles were evaluated after 48 h of exposure to a sub-lethal concentration (1 ppm) of the herbicide Roundup Original (glyphosate 41%). The activities of the antioxidant enzymes superoxide dismutase and catalase were increased in the liver and decreased in muscle, while oxidative damage to lipids increased above control values in both tissues, showing that the generation of reactive oxygen species and oxidative stress are involved in the toxicity induced by Roundup. Additionally, tadpoles' hyperactivity was associated with tachycardia in vivo, probably due to a stress-induced adrenergic stimulation. Ventricle strips of Roundup-exposed tadpoles (R-group) presented a faster relaxation and also a higher cardiac pumping capacity at the in vivo contraction frequency, indicating that bullfrog tadpoles were able to perform cardiac mechanistic adjustments to face Roundup-exposure. However, the lower maximal in vitro contraction frequency of the R-group could limit its in vivo cardiac performance, when the adrenergic-stimulation is present. The association between the high energetic cost to counteract the harmful effects of this herbicide and the induction of oxidative stress suggest that low and realistic concentrations of Roundup can have an impact on tadpoles' performance and success, jeopardizing their survival and/or population establishment.
Assuntos
Glicina/análogos & derivados , Herbicidas/toxicidade , Estresse Oxidativo/efeitos dos fármacos , Animais , Catalase/efeitos dos fármacos , Catalase/metabolismo , Glicina/toxicidade , Hipercinese/induzido quimicamente , Larva/efeitos dos fármacos , Larva/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Contração Miocárdica/efeitos dos fármacos , Rana catesbeiana/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Superóxido Dismutase/efeitos dos fármacos , Superóxido Dismutase/metabolismo , Taquicardia/induzido quimicamente , GlifosatoRESUMO
Experiments were carried out to investigate the heart rate of Synbranchus marmoratus after changing the temperature of the water contained in the experimental chamber of the acclimated fish (from 25 to 35 degrees C and from 25 to 15 degrees C). Then, an isometric cardiac muscle preparation was used to test the relative importance of Ca(2+) released from the sarcoplasmic reticulum and Ca(2+) influx across the sarcolemma for the cardiac performance under different thermal conditions: 25 degrees C (acclimation temperature), 15 and 35 degrees C. Adrenaline and ryanodine were used to modulate the Ca(2+) flux through the sarcolemma and the sarcoplasmic reticulum, respectively. Ryanodine reduced the peak tension by approximately 47% at 25 degrees C, and by 53% at 35 degrees C; however, it had no effect at 15 degrees C. A high adrenaline concentration was able to ameliorate the negative effects of ryanodine. Despite increasing the peak tension, adrenaline increased the times necessary for contraction and relaxation. We conclude that the sarcoplasmic reticulum is active in contributing Ca(2+) to the development of tension at physiological contraction frequencies. The adrenaline-stimulated Ca(2+) influx is able to increase the peak tension, even after addition of ryanodine, at physiologically relevant temperatures and pacing frequencies.
Assuntos
Epinefrina/farmacologia , Contração Miocárdica/efeitos dos fármacos , Retículo Sarcoplasmático/fisiologia , Smegmamorpha/fisiologia , Clima Tropical , Aclimatação , Animais , Relação Dose-Resposta a Droga , Feminino , Frequência Cardíaca , Ventrículos do Coração/anatomia & histologia , Contração Isométrica , Cinética , Masculino , Rianodina/farmacologia , Temperatura , Função VentricularRESUMO
The first analysis of water pollutants using biomarkers at the Guarapiranga Reservoir, which supplies water for one-third of the population of the São Paulo megalopolis (Brazil), is reported. Studies were performed before and after the start of water pumping to the Guarapiranga from the highly polluted Billings reservoir. Billings's water was purified by passing through the natural wetland located near Guarapiranga. Liver enzymes of Oreochromis niloticus (tilopias) obtained from both reservoirs served as biomarkers of pollution in a comparison with animals obtained from a reference site. Enhanced levels of total cytochromes P450 (3.4 times) and b5 (2.7 times) and activity of cytochrome c (P450) reductase (2.2 times) were observed in specimens collected near the water influx from the Billings before the pumping started. However, these parameters were significantly decreased 3 months later. This effect is probably due to dilution of pollutants because of the increased level of water in the Guarapiranga.
Assuntos
Ciclídeos/metabolismo , Sistema Enzimático do Citocromo P-450/metabolismo , Monitoramento Ambiental , Microssomos Hepáticos/enzimologia , Poluentes Químicos da Água/análise , Animais , Benzo(a)pireno/análise , Brasil , Cidades , Sistema Enzimático do Citocromo P-450/análise , Citocromos b5/análise , Citocromos b5/metabolismo , Indução Enzimática , Resíduos Industriais , Fenantrenos/análise , Bifenilos Policlorados/análise , Esgotos , Gerenciamento de Resíduos , Abastecimento de ÁguaRESUMO
We performed a comparative analysis of cytochrome P450, cytochrome b5, MFO associated enzymes and cytosolic antioxidant enzymes in hepatic microsomes and cytosolic fractions prepared from five animal species representing three vertebrate classes living in tropical conditions (Brazil). The data obtained show that rats have higher hepato-somatic index, specific cytochrome b5 concentration, and NADPH-dependent cytochrome c (P450) activity compared to ectothermic species, SOD activity similar to those in amphibians, and specific concentration of cytochrome P450 and catalase activity lower than in a toad, but higher than in fishes and a frog. Our data indicate that tropical fishes may have reduced xenobiotic-metabolizing ability compared to the rat and amphibians. In contrast to fish and rat, amphibians have a low ratio (< 0.5) of cytochrome b5 concentration to that of P450. Most species showed cytochrome b5 sensitivity to oxygen. Thus, the use of sodium dithionate as a reducer, rather than NADPH, may be preferential in b5 determinations.
Assuntos
Antioxidantes/metabolismo , Fígado/enzimologia , Oxigenases de Função Mista/metabolismo , Animais , Anuros , Feminino , Peixes , Masculino , Ratos , Ratos Wistar , Fatores Sexuais , Especificidade da EspécieRESUMO
We examined the cardiorespiratory responses to 6 h of acute hypercarbia (1, 2.5, and 5% CO(2)) in intact and gill-denervated (bilateral denervation of branchial branches of cranial nerves IX and X) tambaqui, Colossoma macropomum. Intact fish exposed to 1 and 2.5% CO(2) increased respiratory frequency ( f(R)) and ventilation amplitude ( V(AMP)) slowly over a 1- to 3-h period. Denervated fish did not show this response, suggesting that tambaqui possess receptors in the gills that will produce excitatory responses to low levels of hypercarbia (1 and 2.5% CO(2)) if the exposure is prolonged. The cardiac response to stimulation of these receptors with this level of CO(2) was a tachycardia and not a bradycardia. During exposure to 5% CO(2), intact fish increased f(R) and V(AMP), and showed a pronounced bradycardia after 1 h. After 2 h, the heart rate ( f(H)) started to increase, but returned to control values after 6 h. In denervated fish, the increase in f(R) was abolished. The slow increase in V(AMP) and the bradycardia were not abolished, suggesting that these changes arose from extra-branchial receptors. Neither intact nor denervated fish developed the swelling of the lower lip or performed aquatic surface respiration, even after 6 h, suggesting that these are unique responses to hypoxia and not hypercarbia.