T3 deficiency prolongs convulsions induced by acute pentylenetetrazole.

The effects of 3,5,3'-triiodothyronine (T3) levels on threshold, latency and duration of pentylenetetrazole-induced seizures were tested in rats treated with thyroxine (300 micrograms/kg.day, N = 9) or methimazole (60 mg/kg.day, N = 5) dissolved in drinking water. Compared to controls (N = 7), methimazole treatment reduced T3 levels (45.4 +/- 2.0 vs. 33.0 +/- 4.8 ng/dl) and increased seizure duration (36.2 +/- 22.4 vs. 289.6 +/- 24.4 s) and threshold (29.0 +/- vs. 45.5 mg/kg). Thyroxine treatment increased T3 levels (45.4 +/- 2.0 vs. 67.7 +/- 4.8 ng/dl), but had no significant effect on seizures.