Relationship between administered dose, target tissue levels and thermoregulatory response alterations after acute oral exposure to the potent tremor inducing pyrethroid bifenthrin in rats.

MOSQUERA ORTEGA, M.E., PATO, A., SOSA-HOLT, C., RIDOLFI, A., WOLANSKY, M.J., VILLAAMIL LEPORI, E.

San Antonio, Texas

Congreso; Annual Meeting - Society of Toxicology; 2013

Society of Toxicology (USA)

In toxicological studies, potency estimates for pyrethroid insecticides (PYRs) in rats may depend on the exposure and testing conditions. This experimental factor may challenge present efforts to reconsider the health risks posed to humans by exposure to PYRs. We are using exposure-dose-effect studies to explore the influence of the testing conditions on the qualitative toxicological classification of, and relative potencies for, these insecticides. Four PYRs (tefluthrin, bifenthrin [BIF], deltamethrin, alpha-cypermethrin) are evaluated in Wistar adult rats. Body temperature is measured using microchip-like transponders implanted in rat backs 5-7 days before testing. Subcutaneous temperature (T-SC) is then monitored by radiotelemetry at 30 min intervals for 5 h after oral dosing of PYRs in corn oil. Basal T-SC is recorded before the test day, and 30 min before dosing (i.e., physiological T-SC). The maximal difference in T-SC compared to the pre-dosing baseline (i.e., ΔT-max) is here used as a measure of peak response. Soon after the thermoregulation assay, target tissues are dissected out. Blood, liver and brain (striatum, cortex, cerebellum) are collected at 6 h post-dosing for posterior determination of PYR residues using a SPE-GC-ECD protocol. Results for BIF are shown in this first presentation. 0, 0.5, 3, 9 and 12 mg BIF/Kg (N=4-8) produced dosage-related increases in temperature and ΔT. Dose-related increases in both BIF levels in target tissues and ΔT-max were observed. R-squared values were +0.6 in all pairwise relationships. These results are mostly consistent with previous BIF studies carried out using motor activity and rectal temperature as endpoints (Wolansky et al., 2006, 2007), and a toxicokinetic study (Scollon et al., 2011).