The aim of the present study was to determine whether the intraperitoneal LD50 for
yessotoxin (YTX) in mice varies with strain or gender. Thirty-six male and 36 female
mice, of body weight 16–20 g, from each of the strains ICR (CD-1), Swiss (CFW-1) and
NMRI were employed. They were not fasted before YTX treatment. At each dose, nine
mice were injected with YTX solutions at 1.0 mL/20 g body weight, and observed for
24 h. Symptoms and time to death were recorded. Within each mouse strain and gender
arm, the study was performed as a basic four level Response Surface Pathway designed
trial with nine mice at each dose level.
YTX was isolated from a culture of Protoceratium reticulatum. The LD50 values for female
and male mice, respectively, were estimated as 380 and 462 mg/kg for the ICR, 269 and
328 mg/kg for the Swiss, and 314 and 412 mg/kg for the NMRI strains. The increases in
LD50 from female to male mice were found to be 22% for ICR, 22% for Swiss and 31% for
NMRI. The largest difference in LD50 among mouse strains was detected between the
ICR and Swiss strains, where the deviation was 41% in both females and males. The difference
between mouse strains was found significant (p ¼ 0.03).
For all three strains, females were more susceptible than males, with a difference in LD50 of
1.2–1.3-fold. The largest difference between the least- and most-susceptible strain was 1.4-
fold for both females and males. The largest difference in LD50, 1.7-fold, was observed
between female Swiss and male ICR mice. The difference between genders was not significant
(p ¼ 0.12). These results indicate that other factors, like handling of the animals, and
the source and handling of the toxin, may significantly influence the outcome of studies on
acute toxicity since the reported differences in LD50 vary by a factor of about seven