Letrozole Exposure Effects on Rat Offspring

Pregnant rats were housed in standard plastic cages individually. They were randomly divided into 4 experimental groups (n = 3/each) to orally receive letrozole at 4 doses (0.25, 0.75, 1.00, and 1.25 mg/kg BW) and a control group. Considering the reports on the embryotoxic effects of letrozole on pregnant rats and rabbits (16), a pilot study was performed to identify the doses above the physiological levels that were not lethal to the mother or the offspring. Accordingly, letrozole administration between 1.5 and 3.0 mg/kg BW caused fetal mortality, adsorption or death in early life, and uterine infection.
Letrozole (L6545, Sigma-Aldrich, St. Louis, USA) was dissolved in 1% carboxymethylcellulose (C5013, Sigma-Aldrich, St. Louis, USA) and was orally administered on days 16-18 of gestation (13). Testicular testosterone surge on 16-18 GDs is necessary for the brain masculinization and normal development of male rats (9, 10). The control rats were administrated with 1% carboxymethylcellulose on same days. The offspring's number, birth weight, and sex were recorded. The offspring remained with their mothers until weaning. At postnatal day (PND) 21, they were weaned, sexed, and weighed, and their AGD was measured. The anogenital distance index (AGDI) was calculated as AGD/BW $\times$ 100 (17). Male offspring (n = 4 per group) were kept in separate standard cages and were weighed weekly until the end of the study.