3. Results
All OPs produced a rapid onset and recovery from the behavioral
effects. This was especially true with mevinphos, for which effects
started almost immediately and completely recovered by 45 min.
Unexpected lethality occurred only with the high dose of mevinphos
in PND17 rats. ChE inhibition data are presented in Figs. 1–4, and
motor activity in Fig. 5; point estimates from fitted curves are listed in
Table 1. In adult rats, there were little or no differential effects on
horizontal counts compared to vertical activity for any of the
chemicals tested (data not shown).
3.1. Mevinphos
Due to the quick onset of mevinphos effects, rats were placed in
the motor activity chambers almost immediately (3 min) after dosing,
and were sacrificed about 25 min after dosing. The high dose (1.5 mg/
kg) was unexpectedly and severely toxic in the PND17 pups, such that
while little toxicity was observed in the adults, 6 out of the 10 pups
died while in the activity chambers. A comparison of ChE inhibition
(Fig. 1) in adults and pups reveals a marked shift to the left in the
PND17 brain dose–response data, with a smaller shift in the RBC data.
The dose-by-age interactions were significant for both tissues. In
pups, doses from 0.25 to 1.5 mg/kg produced significant brain
inhibition compared to control, whereas only 0.75 and 1.5 mg/kg
were effective in adults. For RBC ChE, 0.25–1.5 mg/kg dose groups
were significantly different from control, and although the inhibition
data at 0.1 mg/kg was very similar in both age groups, only the adult
data achieved statistical significance. For motor activity counts