title: Interaction of ageing, photoperiod and melatonin on plasma thyroid hormones and cholesterol levels in female Syrian hamsters (Mesocricetus auratus).
abstract: Plasma levels of thyroxine (T4), triiodothyronine (T3) and growth hormone (GH) as well as the free T4 and free T3 index (FT4I, FT3I) in 20-month-old female Syrian hamsters kept under long daily photoperiod [light:dark (LD) cycles of 14:10] were significantly depressed compared to the values of 2-month-old animals kept under the same photoperiodic conditions. Cholesterol levels in old females were significantly elevated compared to those in young animals. In a subsequent experiment, young (4 month) and old (15 month) female hamsters were either placed in a short photoperiod (10:14 LD) or a 14:10 LD cycle and given daily afternoon injection of either diluent or 25 micrograms melatonin. After 8 weeks, the old females, regardless of treatment or photoperiod, had significantly lower T4 levels and higher cholesterol and triglyceride levels than did young animals. In 14:10 LD, FT4I and FT3I did not differ between young and old animals, possibly because of the reduced age gap in this experiment. Although the FT4I and FT3I in young females after 8 weeks of treatment with 10:14 LD or melatonin were not significant, the old females did demonstrate a significant suppression of their FT4I and FT3I values.
mesh_terms: D000375:Aging; D000818:Animals; D002784:Cholesterol / Q000097:blood*; D006224:Cricetinae / Q000502:physiology*; D005260:Female; D008027:Light; D008550:Melatonin / Q000494:pharmacology*; D010507:Periodicity; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood
chemical_list: D013963:Thyroid Hormones; D013972:Thyrotropin; D002784:Cholesterol; D008550:Melatonin