Retrospective Study of the Incidence of Spontaneous Nonneoplastic Lesions in Wistar Rats (Mlac:WR) from 90-Day Oral Gavage Studies
Keywords:
Wistar rat, Spontaneous lesions, Nonneoplastic, 90-day oral toxicity studiesAbstract
Historical control data (HCD) of background lesions provide useful information on the range and incidence of spontaneous lesions in a specific animal model. The microscopic examination data were collected from 84 male and 86 female Wistar rats (Mlac:WR) used in 90-day oral gavage studies conducted at the National Laboratory Animal Center, Mahidol University (NLAC-MU), from 2023 to 2025. We retrospectively evaluated spontaneous nonneoplastic findings in the vital organs for toxicity assessment. This study reported the organ weights, numbers, incidence, and severity of the spontaneous nonneoplastic findings in the Wistar rat, aiming to establish a contemporaneous three-year database on the incidence of background lesions, as part of microscopic alterations, and to aid in the future evaluation of 90-day oral toxicity studies. The most common spontaneous findings observed in both sexes were minimal to moderate multifocal hemorrhage in the thymus (32.14% males, 22.09% females), minimal to moderate hemorrhage in bronchus-associated lymphoid tissue (BALT) (23.81% males, 17.44% females), ectopic adrenocortical tissue in the adrenal cortex (21.43% males, 19.77% females), and minimal to moderate dilation of gastric glands in the stomach (23.81% males, 12.79% females). We also reported sex-related spontaneous lesions, including hyaline casts in the renal cortex (23.81% males, 1.16% females), tubular basophilia in the renal cortex (9.52% males, 1.16% females), and ectopic thymus tissue in the thyroid gland (9.52% males, 0% females). In summary, HCD of background lesions in Wistar rats from 90-day oral gavage studies is essential for accurate histopathological interpretation in 90-day oral toxicity studies.
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