Ana Lúcia Kalinin

The effects of selenium on oxidative stress biomarkers in the freshwater characid fish matrinxã, Brycon cephalus (Günther, 1869) exposed to organophosphate insecticide Folisuper 600 BR (methyl parathion).

Methyl parathion (MP), an organophosphate widely applied in agriculture and aquaculture, induces oxidative stress due to free radical generation and changes in the antioxidant defense system. The antioxidant roles of selenium (Se) were evaluated in Brycon cephalus exposed to 2 mg L(-1) of Folisuper 600 BR (MP commercial formulation - MPc, 600 g L(-1)) for 96 h. Catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH) and lipid peroxidation (LPO) levels in the gills, white muscle and liver were evaluated in fish fed on diets containing 0 or 1.5 mg Se kg(-1) for 8 weeks. In fish treated with a Se-free diet, the MPc exposure increased SOD and CAT activities in all tissues. However, the GPx activity decreased in white muscle and gills whereas no alterations were observed in the liver. MPc also increased GST activity in all tissues with a concurrent decrease in GSH levels. LPO values increased in white muscle and gills and did not change in liver after MPc exposure. A Se-supplemented diet reversed these findings, preventing increases in LPO levels and concurrent decreases in GPx activity in gills and white muscle. Similarly, GSH levels were maintained in all tissue after MPc exposure. These results suggest that dietary Se supplementation protects cells against MPc-induced oxidative stress.

Cardiovascular and respiratory reflexes in the tropical fish, traira (Hoplias malabaricus): CO2/pH chemoresponses

To examine the distribution and physiological role of CO2/pH-sensitive chemoreceptors in the gills of the tropical fish, traira (Hoplias malabaricus), fish were exposed to acute environmental hypercarbia (1.25, 2.5 and 5.0% CO2 in air) and subjected to injections of HCl into the ventral aorta and buccal cavity. This was done before and after selective denervation of branchial branches of the IXth and Xth cranial nerves to various gills arches. Hypercarbia produced a significant decrease in heart rate, a mild hypotension as well as increases in both ventilation rate and ventilation amplitude. The data suggest that the hypercarbic bradycardia and increase in ventilation frequency arise from receptors exclusively within the gills but present on more than the first gill arch, while extra-branchial receptors may also be involved in controlling the increase in ventilation amplitude. With the exception of a decrease in heart rate in response to HCl injected into the ventral aorta, the acid injections (internal and external) did not mimic the cardiorespiratory responses observed during hypercarbia suggesting that changes in CO2 are more important than changes in pH in producing cardiorespiratory responses. Finally, the data indicate that chemoreceptors sensitive to CO2/pH and to O2 in the gills of this species involved in producing ventilatory responses are distributed in a similar fashion, but that those involved in producing the bradycardia are not.

Cardio-respiratory function and oxidative stress biomarkers in Nile tilapia exposed to the organophosphate insecticide trichlorfon (NEGUVON).

The cardio-respiratory function, oxidative stress and fish antioxidants were analyzed in juvenile Nile tilapia exposed for 96 h to a sublethal trichlorfon (TRC-Neguvon, Bayer) concentration of 0.5 mg L(-1). The exposure to TRC induced oxidative stress in the heart, as manifested by the glutathione S-transferase depletion and hydroperoxide elevation, and was the most sensitive organ when compared to the liver and gills, in which the antioxidant mechanisms against TRC exposure were sufficient to remove reactive oxygen species (ROS), preventing the increase of lipid peroxidation. TRC exposure also reduced O(2) uptake (V O(2)) and increased the critical oxygen tension (PcO(2)), reducing the species capacity to survive prolonged hypoxic conditions. The heart rate and force contraction were significantly impaired, making the heart the most sensitive organ when exposed to the TRC.

Cardio-respiratory responses in two ecologically distinct erythrinids (Hoplias malabaricus and Hoplias lacerdae) exposed to graded environmental hypoxia

SynopsisEcologically distinct species of Hoplias were studied as to the cardio-respiratory responses to graded hypoxia. Hoplias malabaricus maintained a constant oxygen uptake down to a PiO2 of 20 mmHg. Oxygen uptake declined markedly at lower PiO2 and, concomitantly, cardiac frequency decreased. Concurrent reductions of oxygen uptake and heart rate also occurred in Hoplias lacerdae but at the considerably higher PiO2 of 35 mmHg. These species-specific differences are consistent with the respective habitats: H. malabaricus occurs in stagnant hypoxic water, whereas H. lacerdae inhabits well-oxygenated rivers.

The role of branchial and orobranchial O2 chemoreceptors in the control of aquatic surface respiration in the neotropical fish tambaqui (Colossoma macropomum): progressive responses to prolonged hypoxia.

SUMMARY The present study examined the role of branchial and orobranchial O2 chemoreceptors in the cardiorespiratory responses, aquatic surface respiration (ASR), and the development of inferior lip swelling in tambaqui during prolonged (6 h) exposure to hypoxia. Intact fish (control) and three groups of denervated fish (bilateral denervation of cranial nerves IX+X (to the gills), of cranial nerves V+VII (to the orobranchial cavity) or of cranial nerves V alone), were exposed to severe hypoxia (PwO2=10 mmHg) for 360 min. Respiratory frequency (fr) and heart rate (fh) were recorded simultaneously with ASR. Intact (control) fish increased fr, ventilation amplitude (VAMP) and developed hypoxic bradycardia in the first 60 min of hypoxia. The bradycardia, however, abated progressively and had returned to normoxic levels by the last hour of exposure to hypoxia. The changes in respiratory frequency and the hypoxic bradycardia were eliminated by denervation of cranial nerves IX and X but were not affected by denervation of cranial nerves V or V+VII. The VAMP was not abolished by the various denervation protocols. The fh in fish with denervation of cranial nerves V or V+VII, however, did not recover to control values as in intact fish. After 360 min of exposure to hypoxia only the intact and IX+X denervated fish performed ASR. Denervation of cranial nerve V abolished the ASR behavior. However, all (control and denervated (IX+X, V and V+VII) fish developed inferior lip swelling. These results indicate that ASR is triggered by O2 chemoreceptors innervated by cranial nerve V but that other mechanisms, such as a direct effect of hypoxia on the lip tissue, trigger lip swelling.

Heart performance, Ca2+ regulation and energy metabolism at high temperatures in Bathygobius soporator, a tropical marine teleost

Experiments were conducted with Bathygobius soporator (Gobbiidae), a small tropical marine teleost which lives in tide pools along the east coast of South America. In whole animals, VO2 remained constant from 25 to 30°C and then increased until it reached a maximum value at 40°C of about 160 ml·kg−1·h−1. The fH increased progressively and significantly from 25 to 35°C, at which fH reached its maximum value of about 225 beats·min−1. At 40°C, however, the fH decreased to a value similar to that recorded at 25°C. Twitch force and resting tension were determined for isolated ventricle strips. At an extracellular Ca2+ level of 1.25 mM a transition from 25 to 40°C resulted in a decrease in twitch force which was restored upon a return to 25°C. This restoration of twitch force did not occur at an extracellular Ca2+ concentration of 9.25 mM. At 25°C, increments in extracellular Ca2+ from 1.25 to 7.25 mM resulted in increases in twitch force development However, at 40°C only resting tension increased in concert with elevations in Ca2+. At 25°C, twitch force declined as frequency was increased above 30 contractions·min−1 and became irregular above 120 contractions·min−1. At 40°C, twitch force development remained constant at frequencies up to about 150 contractions·min−1 and declined thereafter. Preparations were able to maintain rhythmic response up to about 240 contractions·min−1. An increase in in vitro assay temperature from 25 to 40°C resulted in an elevation of total ATPase activity. Citrate synthase was present in high activities with hexokinase and 3-hydroxyacyl coenzyme A (CoA) being detectable but at lower activities. Heart performance is fragile at high temperature and under conditions which lead to high intracellular Ca2+. A controlled decrease in heart rate at high temperature may have a protective effect in maintaining low levels of intracellular Ca2+.

Changes in gut gross morphology of traíra, Hoplias malabaricus (Teleostei, Erythrinidae) during long-term starvation and after refeeding

Adult traíra (Hoplias malabaricus) were submitted to different periods of food deprivation (from 30 to 240 days) and refed for 30 days after 90 and 240 days of starvation. Stomach length remained constant during all the experimental period. However, the intestine length was significantly reduced after 30 days of food deprivation. Normal length was not recovered after refeeding. The number of pyloric caeca did not change significantly. Conversely, caeca thickness decreased after 150 days of starvation and their length decreased after 180 days. After refeeding, however, the pyloric caeca recovered original thickness. In fish refed after 240 days of starvation the length of these structures seemed to present compensatory growth, becoming longer than in the control group.

The influence of aquatic surface respiration (ASR) on cardio-respiratory function of the serrasalmid fish Piaractus mesopotamicus

Abstract When exposed to severely hypoxic water, many teleosts skim the better oxygenated surface layer (aquatic surface respiration, ASR). Information is scarce concerning the thresholds triggering ASR and its cardio-respiratory consequences. To assess the ambient conditions leading to ASR and to evaluate its effects on cardio-respiratory function, we exposed specimens of Piaractus mesopotamicus to gradual hypoxia (water oxygen tension ranging from 120 to 10 torr) with or, alternatively, without access to the surface. Concurrently, ASR, cardiac and respiratory frequencies, O 2 uptake and gill ventilation were monitored. With surface access, ASR developed below the critical tension for O 2 uptake (34 torr) by normal gill ventilation. Moreover, the time spent in ASR increased with prolonged hypoxic exposure to a maximum of 95% of total time. Without surface access, the species exhibited hypoxic bradycardia, that had not occurred in the group with fully developed ASR. Even without ASR, P. mesopotamicus recovered readily from hypoxic exposure, showing that this species possesses a number of mechanisms to cope with environmental hypoxia.

Dependence on body size of respiratory function in Hoplias malabaricus (Teleostei, Erythrinidae) during graded hypoxia.

Oxygen uptake and ventilatory responses to environmental hypoxia were assessed for two groups of Hoplias malabaricus of nearly tenfold different body weights (mean weights, group I = 39 g; group II = 365 g). The main purpose of the study was to evaluate the relationships between body weight and the critical O2 tension (PCO2) for maintenance of normal resting O2 uptake. The smaller specimens had a threefold larger weight-specific O2 uptake compared to that of the larger specimens. Moreover, smaller size coincided with a higher PCO2, i.e., a more limited range for maintenance of O2 uptake during hypoxia. Likewise, at any inspired PO2 the weight-specific gill ventilation was largest for group I. This was most pronounced during severe hypoxia where both tidal volume and respiratory frequency increased markedly. In addition, the oxygen cost of breathing tended to be highest in the smaller individuals. The results open questions as to correlations between development, weight-dependent O2 demands, and tolerance to hypoxia on an intraspecific level.

Gill chemoreceptors and cardio-respiratory reflexes in the neotropical teleost pacu, Piaractus mesopotamicus.

This study examined the location and distribution of O2 chemoreceptors involved in cardio-respiratory responses to hypoxia in the neotropical teleost, the pacu (Piaractus mesopotamicus). Intact fish and fish experiencing progressive gill denervation by selective transection of cranial nerves IX and X were exposed to gradual hypoxia and submitted to intrabuccal and intravenous injections of NaCN while their heart rate, ventilation rate and ventilation amplitude were measured. The chemoreceptors producing reflex bradycardia were confined to, but distributed along all gill arches, and were sensitive to O2 levels in the water and the blood. Ventilatory responses to all stimuli, though modified, continued following gill denervation, however, indicating the presence of internally and externally oriented receptors along all gill arches and either in the pseudobranch or at extra-branchial sites. Chemoreceptors located on the first pair of gill arches and innervated by the glossopharyngeal nerve appeared to attenuate the cardiac and respiratory responses to hypoxia. The data indicate that the location and distribution of cardio-respiratory O2 receptors are not identical to those in tambaqui (Colossoma macropomum) despite their similar habitats and close phylogenetic lineage, although the differences between the two species could reduce to nothing more than the presence or absence of the pseudobranch.