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EFFECTS OF CAGING DENSITY ON PITUITARY AND TESTICLE RELATED RESPONSES
Citation:
Nyska, A., S D. Hester, D. E. House, R L. Cooper, AND D C. Wolf. EFFECTS OF CAGING DENSITY ON PITUITARY AND TESTICLE RELATED RESPONSES. Presented at Society of Toxicologic Pathologists Annual 19th Mtg, Litchfield Park, AZ, June,25-29, 2000.
Description:
Effects of caging density on pituitary and testicle related responses
A significant negative correlation between the incidence of testicular interstitial cell tumors (ICT) and of pituitary tumors (PT) in control male F344 rats is reported associated with the number of animals per cage. A striking example is an NTP 2-year study in which the incidence of ICT was 8% in singly housed animals and 90% among rats group caged. Whereas, the incidence of PT was 89% in singly and 30% in group caged rats. Single caging may cause stress and increased serum corticosteroids, which can impair estosterone synthesis by the testicular interstitial cells. Eventual atrophy of interstitial cells may result in pituitary hyerfunction md tumors. For appropriate and relevant risk assessments, it is necessary to understand the effect husbandry has on cellular processes including hormone production and cell kinetics. Twenty-four 7-week-old male F344 rats were housed individually, as )airs, or as trios and provided food and water ad libitum for 13 weeks. For the last 4 days prior to necropsy all animals received Iromodeoxyuridine (BrdU) in the drinking water. Feed consumption and body weights were collected weekly. The adrenals, Irain, epididymis, pituitary, prostate, seminal vesicles, testes, and thyroid were examined microscopically. Testicles, pituitary, and Irains were weighed at necropsy and blood was collected for complete hemogram and serum hormone analysis (LH, FSH, Irolactin, testosterone, estrogen, cortisol, and ACTH). The pituitary and testicle were stained for BrdU immunoreactivity and the nterior pituitary and testicular interstitial cells were counted for S-phase labeling index (LI). There were no differences between the groups for body weight, rate of gain, feed consumption, organ weights, or organ/body and organ/brain weight ratios. No group dependent microscopic alterations were seen. Singly housed rats had a significantly greater white blood cell count than rats housed as trios. Serum LH decreased with increasing caging density and serum prolactin was greater in pairs than singles or trios. Initial review of this study indicates that there are short-term serum hormone changes associated with caging density that could contribute to the density associated tumor response.
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