Effects of the pyriproxyfen and fenthion on the gonadal morphology of Nile tilapia (Oreochromis niloticus: Perciformes, Cichlidae).

Commercially available insecticides present acute toxicity to the health of fish and other aquatic organisms, which may impair the local aquaculture. This study evaluated the gonadal morphology of freshwater fish exposed to pyriproxyfen and fenthion. Forty-five juvenile male Nile tilapias (Oreochromis niloticus) were divided into control, pyriproxyfen-exposed (0.01 g/L), and fenthion-exposed (0.001 g/L) groups. They were evaluated in three moments (30, 60, and 90 days). The variables analyzed were the gonadosomatic index (GSI), weight to length ratio, seminiferous tubules morphometry (diameter and height), tissue damage, and immunohistochemical analysis for caspase-3, tumor necrosis factor alpha (TNF-α), and vascular endothelial growth factor (VEGF). Pyriproxyfen and fenthion injured the seminiferous tubule tissue, and the damage progressed according to the exposure time. In addition, the GSI gradually reduced over time in all groups compared with the first moment (30 days), while caspase-3, TNF-α, and VEGF values increased only in the fenthion-exposed group. Therefore, pyriproxyfen and fenthion changed the gonadal morphology of male Oreochromis niloticus, which may affect their reproduction in the wild or captivity.

Effects of acaricides on the activities of monooxygenases in bovine liver microsomes.

Organophosphates (OPs), pyrethrins and fipronil, are acaricides commonly used in cattle, mainly as pour on formulations. Scant information is available on their potential interactions with hepatic xenobiotic metabolizing enzymes. This work aimed to evaluate in vitro the potential inhibitory effects of widely employed acaricides on catalytic activities mediated by hepatic cytochrome P450 (CYP) and flavin-monooxygenase (FMO) enzymes in cattle. Bovine (n = 4) liver microsomes were incubated in the absence (control assays) and in presence of different OPs (fenthion, chlorpyrifos, ethion, diazinon and dichlorvos), fipronil and cypermethrin at 0.1-100 µm. Five oxidative enzyme activities were assayed by spectrofluorimetric or HPLC methods: 7-ethoxyresorufin O-deethylase (for CYP1A1), methoxyresorufin O-demethylase (for CYP1A2), benzyloxyresorufin O-debenzylase (for CYP2B), testosterone 6-beta hydroxylase (for CYP3A) and benzydamine N-oxidase (for FMO). All acaricides, particularly phosphorothionate-containing OPs, inhibited to some extent more than one enzyme activity. The most frequent inhibitor was fenthion, which inhibited (p < .05) all enzyme activities tested (from 22% at 1 µm to 72% at 100 µm). However, low inhibitory potencies (IC50s higher than 7 µm) of all acaricides studied were observed against the catalytic activities assayed. Therefore, the risk of in vivo metabolic interactions due to inhibition of monooxygenases would be low under common husbandry conditions.