Adult male Syrian hamsters were subjected to 1, 3, 5, 7 or 11 weeks of either natural winter conditions or rigorously controlled laboratory conditions (LD 10:14; 22 ± 2‡C). Although both groups of hamsters gained weight over the course of the experiment, hamsters housed indoors were significantly heavier after 5 weeks of treatment compared to their outdoors counterparts. Animals housed under natural conditions exhibited a significant decrease in circulating levels of thyroxine (T4) and a rapid rise in triiodothyronine (T3) levels; the free T4 and free T3 index (FT4I and FT3I) mirrored the changes in circulating levels of the respective hormones. Laboratory-housed animals had a slight rise in T4 and FT4I at 3 weeks followed by a slow steady decline in these values; T3 and FT3I values did not change remarkably in these animals. Plasma cholesterol declined steadily over the course of the experiment in laboratory-maintained animals but increased slightly during the first 5 weeks in animals under natural conditions. Since the photoperiodic conditions were approximately of the same duration in these 2 groups, it is concluded that the major differences in body weight, thyroid hormone values and plasma cholesterol are due to some component (possibly temperature) in the natural environment.
ASJC Scopus subject areas
- Atmospheric Science
- Health, Toxicology and Mutagenesis