Responsiveness of the interrenal tissue of Jundiá (Rhamdia quelen) to an in vivo ACTH test following acute exposure to sublethal concentrations of agrichemicals.

As in many aquatic environments, pollution is a widespread problem in Southern Brazil. In our previous work, we demonstrated that sublethal contamination with some agrichemicals impairs the capacity of fishes to elevate cortisol levels in response to an additional acute stressor. In earlier experiments, the experimental design did not allow us to conclude where this effect occurs. In the present work, we used the adrenocorticotropic hormone (ACTH) challenge test to help us identify if the impairment occur in the interrenal tissue. For this purpose, five experiments were conducted, each with one specific agrichemical (methyl-parathion, atrazine+simazine, atrazine, tebuconazole, and glyphosate) in sublethal concentrations of 16.6% of the LC(50-96h), as previously determined. Fish were subjected to the ACTH challenge test protocol as follows: group 1, were non-injected and maintained as the specific control group; group 2 received an injection of the vehicle alone (the saline group); and group 3 receive an injection of ACTH. One hour later, blood samples were taken from the caudal plexus, using sterile syringes. In all specific control groups, the injection of ACTH induced a strong rise in plasma cortisol, compared with the fish injected only with the vehicle and the non-injected group. Fish exposed to methyl-parathion and tebuconazole did not elevate cortisol in response to the ACTH injection, with values significantly lower than the control fish. Fish exposed to sublethal concentrations of atrazine+simazine, atrazine, and glyphosate showed a rise in plasma cortisol very similar to the control fish. We conclude that the ACTH challenge test revealed that R. quelen exposed to sublethal concentrations of tebuconazole and methyl-parathion had a reduced ability to elevate plasma cortisol in response to an intraperitoneal (i.p.) injection of exogenous ACTH, indicating that the interrenal tissue is the site of the impairment within the HPI axis. These ACTH challenge tests also revealed that the impairment of the cortisol response verified in fish exposed to atrazine+simazine and glyphosate, as shown in our previous work, seems to be related to steps of cortisol secretion in higher levels within the HPI axis.

Cortisol response to acute stress in jundiá Rhamdia quelen acutely exposed to sub-lethal concentrations of agrichemicals.

Exposure to agrichemicals can have deleterious effects on fish, such as disruption of the hypothalamus-pituitary-inter-renal axis (HPI) that could impair the ability of fish to respond to stressors. In this study, fingerlings of the teleost jundiá (Rhamdia quelen) were used to investigate the effects of the commonly used agrichemicals on the fish response to stress. Five common agrichemicals were tested: the fungicide - tebuconazole, the insecticide - methyl-parathion, and the herbicides - atrazine, atrazine+simazine, and glyphosate. Control fishes were not exposed to agrichemicals and standard stressors. In treatments 2-4, the fishes were exposed to sub-lethal concentrations (16.6%, 33.3%, and 50% of the LC(50)) of each agrichemical for 96 h, and at the end of this period, were subjected to an acute stress-handling stimulus by chasing them with a pen net. In treatments 5-7 (16.6%, 33.3%, and 50% of the LC(50)), the fishes were exposed to the same concentrations of the agrichemicals without stress stimulus. Treatment 8 consisted of jundiás not exposed to agrichemicals, but was subjected to an acute stress-handling stimulus. Jundiás exposed to methyl-parathion, atrazine+simazine, and glyphosate presented a decreased capacity in exhibiting an adequate response to cope with stress and in maintaining the homeostasis, with cortisol level lower than that in the control fish (P<0.01). In conclusion, the results of this study clearly demonstrate that the acute exposure to sub-lethal concentrations of methyl-parathion, atrazine+simazine, and glyphosate exert a deleterious effect on the cortisol response to an additional acute stressor in the jundiá fingerlings.