Changes in plasma corticosterone and catecholamine contents induced by low doses of deltamethrin in rats

The effects of low doses of (S)-alpha-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (Roussel UCLAF, Paris, France), (deltamethrin) upon sympathetic-adrenomedullary and pituitary-adrenocortical activity were investigated in rats by measuring plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations. Blood was sampled from freely-moving animals provided with heart catheters at short intervals up to 60 min after intravenous administration of deltamethrin (0.05, 0.15 and 0.45 mg/kg) or vehicle. Behavioral activity was recorded shortly after the sampling times. Time course and magnitude of the biochemical changes were compared with the effects of exposure to uncontrollable white noise in a similar sampling and recording procedure. Dose-dependent increases were observed for NA and A as well as for CS contents. The dose-response relations however, were different among the neuro-edocrine respondents. Discrete step-wise increases were observed for plasma CS only, indicating greater sensitivity for neurotoxical actions. Already at a dose of 0.15 mg/kg of deltamethrin, CS contents rose to values that were considerably higher than those found during noise exposure. In contrast, plasma CA concentrations increased to noise stress values only after the 0.45 mg/kg dose. The behavioral activity pattern appeared to resemble both CA patterns. The results suggest that rather low doses of deltamethrin elicit vigorous autonomic and neuro-endocrine responses that indicate high levels of stress, presumably caused by the neurotoxic effect of the insecticide.