Mechanisms of PVP-functionalized silver nanoparticle toxicity in fish: Intravascular exposure disrupts cardiac pacemaker function and inhibits Na+/K+-ATPase activity in heart, but not gill.

Polyvinylpyrrolidone-functionalized silver nanoparticles (nAgPVP) are popular in consumer products for their colloidal stability and antimicrobial activity. Whole lake additions of nAgPVP cause long term, ecosystem-scale changes in fish populations but the mechanisms underlying this effect are unclear. We have previously shown that in fish, nAgPVP impairs cardiac contractility and Na+/K+-ATPase (NKA) activity in vitro, raising the possibility that heart dysfunction could underlie population-level exposure effects. The goal of this study was to determine if nAgPVP influences the control of heart rate (fh), blood pressure, or cardiac NKA activity in vivo. First, a dose-response curve for the effects of 5 nm nAgPVP on contractility was completed on isometrically contracting ventricular muscle preparations from Arctic char (Salvelinus alpinus) and showed that force production was lowest at 500 µg L-1 and maximum pacing frequency increased with nAgPVP concentration. Stroke volume, cardiac output, and power output were maintained in isolated working heart preparations from brook char (Salvelinus fontinalis) exposed to 700 µg L-1 nAgPVP. Both fh and blood pressure were elevated after 24 h in brook char injected with 700 µg kg body mass-1 nAgPVP and fh was insensitive to modulation with blockers of ß-adrenergic and muscarinic cholinergic receptors. Na+/K+-ATPase activity was significantly lower in heart, but not gill of nAgPVP injected fish. The results indicate that nAgPVP influences cardiac function in vivo by disrupting regulation of the pacemaker and cardiomyocyte ionoregulation. Impaired fh regulation may prevent fish from appropriately responding to environmental or social stressors and affect their ability to survive.

Epidemiological study of the claimed zinc phosphide intoxication in Kom Ombo district April 1996.

INTRODUCTION: In April 1996, in Aswan Governorate, Egypt, an outbreak of vomiting without diarrhea, abdominal and leg pain was reported. METHODS: A case-control study was conducted to determine the cause of the outbreak. 25 cases who had vomiting without diarrhea, abdominal and leg pain. Controls were randomly chosen from adjacent houses to cases and another village. RESULTS: No occupational exposure was associated with the disease, 84% of cases lived in households where chemical rodenticide had been used for rat infestations compared to 22% of controls. Laboratory analysis and field investigation identified zinc phosphide intoxication as the probable cause of this outbreak.

Effect of bromazepam on stress-induced gastric ulcer in rats and its relation to brain neurotransmitters.

The possible antiulcer potential of bromazepam was investigated in relation to its effect on the levels of central neurotransmitters in rats. Peptic ulcer was induced by cold-restraint stress, by immobilizing the animals in open wire restraint cages placed for 2 h at 4 degrees C. Bromazepam (1 and 2 mg x kg(-1), i.p.) was given as prophylactic regimens, either as a single (2 h before ulcer induction) or repeated (twice daily for 15 days) administration. Results revealed that single (1 mg x kg(-1)) and repeated (1 and 2 mg x kg(-1)) dose regimens of bromazepam succeeded in preventing gastric ulceration, without significant effects on the protein-bound hexose content of gastric mucus. Increases in gamma-aminobutyric acid (GABA) concentrations in almost all tested brain regions were observed in bromazepam-treated groups, as compared to the control stressed group. Cortical dopamine (D) concentrations were reduced following single (2 mg x kg(-1)) as well as repeated administration of bromazepam. Similarly, norepinephrine (NE) concentrations were decreased in the cerebral cortex and thalamus/hypothalamus by repeated doses of bromazepam. Cortical 5-hydroxytryptamine (5-HT) was elevated by single (1 mg x kg(-1)) and repeated (1 mg x kg(-1)) doses of the drug. It could be concluded that bromazepam affords a good gastroprotective potential against cold-restraint stress-induced gastric ulceration and the possible mechanisms might involve an increase in the inhibitory GABA and a suppression of the stimulatory NE and D in central regions, especially the cerebral cortex and/or thalamus/hypothalamus.