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Incidences of Selected Lesions in Control Female Harlan Sprague–Dawley Rats from Two-Year Studies Performed by the National Toxicology Program

¹ Experimental Pathology Laboratories, Research Triangle Park, North Carolina 27709, USA
² Laboratory of Experimental Pathology, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina 27709, USA
³ Biostatistics Branch, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina 27709, USA
⁴ Battelle Columbus Laboratories, Columbus, Ohio 43201, USA
⁵ Pathology Associates—A Charles River Company, Durham, North Carolina 27713, USA
⁶ Laboratory of Computational Biology and Risk Analysis, National Institute of Environmental Health Sciences (NIEHS), Research Triangle Park, North Carolina 27709, USA

Correspondence: Address correspondence to: Amy E. Brix, Experimental Pathology Laboratories, Inc., P.O. Box 12766, Research Triangle Park, North Carolina 27709, USA; e-mail:brix{at}niehs.nih.gov

The NTP has a long history of using Fischer rats and has compiled a large database of incidences of lesions seen in control animals. Such a database is lacking for Harlan Sprague–Dawley (SD) rats. The intention of this paper is to report spontaneous lesions observed in female vehicle control Harlan SD rats, and to compare the incidence in 2 strains of rats (Fischer and Harlan SD) used in NTP studies. Female Harlan SD rats served as the test animals for a special series of 2-year studies. Male rats were not used in these studies. Complete histopathology was performed on all animals, and the pathology results underwent comprehensive NTP pathology peer review. The most commonly observed neoplasms in these female control Harlan SD rats were mammary gland fibroadenoma (71%), tumors of the pars distalis of the pituitary (41%) and thyroid gland C-cell tumors (30%). Female Fischer rats had incidences of 44% for mammary gland fibroadenomas, 34% for tumors of the pars distalis, and 16% for thyroid gland C-cell tumors. Fischer rats had a 15% incidence of clitoral gland tumors, while the Harlan SD rats had an incidence of < 1%. In contrast to Fischer F344 rats, the Harlan SD rats had a high incidence of squamous metaplasia of the uterus (44.2%). Squamous metaplasia is not a lesion commonly observed in NTP control Fischer rats. The Harlan SD rats had a very low incidence of mononuclear cell leukemia (0.5%), compared with an incidence of 24% in female Fischer rats.

Key Words: Spontaneous Lesions • Harlan SD rats • 2-year study

Abbreviations: DLCs, dioxin-like compounds • NBF, neutral buffered formalin • NTP, National Toxicology Program • SD, Sprague–Dawley

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