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Abstract
The effects and interactions of photoperiod, animal caging, aging and diet on plasma lipid levels in male FIB hamsters were examined in the current study. Sixteen young and sixteen old animals were housed on e or four per cage. Eight young animals from each housing group were placed in an animal room with either 12/12 h (PT-12) or 10/14h (PT-10) light/dark cycle while the sixteen old animals were maintained under a PT-12 light cycle. Plasma cholesterol and triglyceride concentrations were determined in all animals after a 2-week period of acclimation on chow diet and following 4-week intervention on atherogenic diet. Baseline total cholesterol (TC) levels were 131 ± 25 mg/ dl and 142 ± 39 mg/dl for young and old animals, respectively, while baseline triglyceride (Tg) levels were 202 ± 48 mg/dl and 160 ± 37 mg/dl respectively for the same animals. Following 4-weeks on an atherogenic diet, single-caged PT 12 animals had elevated but significantly lower TC levels than group-caged animals (161 ± 30mg/dl and 240 ± 58mg/dl, respectively) while single and group housed PT10 animals had TC levels of 296 ± 75mg/dl and 351 ± 124mg/dl, respectively. Similarly, plasma Tg levels rose to 330 ± 100mg/dl and 486 ± 200mg/dl in single and group housed PT12 animals (respectively) and to 668 ± 270 mg/dl and 545 ± 199 mg/dl in single and group housed PT10 animals (respectively). No significant changes related to atherogenic diet were observed in plasma TC or Tg levels in the older animals.
Although caging conditions influence the cholesterol and triglyceride response to the atherogenic diet (p <. 05), light cycle photoperiod seems to exert a greater effect (p <. 005).
In conclusion, photoperiod length dramatically affects diet-induced plasma lipid concentrations in young male FIB hamsters, and thus needs be considered in experimental designs of animal-housed lipid research.