Effects of immobilization restraint on Syrian golden hamsters

Rodent nose-only inhalation toxicology systems comprise whole-body immobilization in plastic restraint tubes. This method of restraint is known to have a variety of effects on animals. In the studies reported here, two independent toxicology laboratories examined the effects of inhalation tube restraint in Syrian golden hamsters, a species that has recently gained importance in inhalation studies of fibrous particulates. Body weight, food and water consumption, core body temperature, and plasma cortisol and corticosterone concentrations were assessed in animals immobilized in nose-only inhalation tubes, and the results were compared with those from unrestrained cage-control animals. Animals were immobilized for either 6 h/ day, 5 days/week for 13 weeks (subchronic), or 4 h/day for 14 consecutive days (subacute), mimicking exposure conditions commonly used in nose-only inhalation studies. Tube restraint was found to induce a marked decrease in body weight, which increased in response to cessation of restraint. The body weight decrement was associated with significant differences in food and water consumption between the restrained and control groups in the subacute study and only food consumption in the subchronic study. During the restraint period, core body temperature in the immobilized animals increased slightly but not above the normal range for this species. Plasma cortisol and corticosterone concentrations were not significantly increased with use of restraint, compared with values in controls. Immobilization-associated body weight depression in Syrian golden hamsters is important for the evaluation of nose-only inhalation study results because many normal physiologic parameters, as well as toxicant-induced effects, are associated with body weight status.