Age-associated changes and sex differences in urinary 6-sulphatoxymelatonin circadian rhythm in the rat.
The circadian rhythm of 6-sulphatoxymelatonin (aMT6s) excretion has been determined in male and female rats at 3 weeks and at 2, 8, 14 and 20 months of age. All animals have a pronounced circadian pattern of aMT6s excretion under a 12 hour dark: 12 hour light cycle. A significant increase in aMT6s excretion is observed from 3 weeks to 14 months followed by a decrease at 20 months. There is a highly significant correlation between aMT6s excretion and body weight (r = 0.73 for female rats and r = 0.74 for male rats; p values are all less than 0.001). Thus, a decrease in aMT6s excretion associated with increasing age occurs when body weight is taken into consideration. aMT6s excretion is higher in males at 3 weeks and at 2 and 8 months of ages. Urinary testosterone in male rats and estradiol in female rats increase from 3 weeks to 8 months and decrease at older ages. These data suggest that increase of body weight from 3 weeks to 14 months is an important factor responsible for the age-related alteration. The sex differences in aMT6s excretion in younger rats may be associated with their sex hormonal milieu.
Yie
S M
SM
Department of Biomedical Sciences, McMaster University Hamilton, Ontario, Canada.
Liu
G Y
GY
Johansson
E
E
Brown
C
C
Brown
G M
GM
D000367:Age Factors; D000818:Animals; D001835:Body Weight; D002940:Circadian Rhythm; D004958:Estradiol / Q000652:urine; D005260:Female; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D012727:Sex Characteristics; D013739:Testosterone / Q000652:urine
C054513:6-sulfatoxymelatonin; D013739:Testosterone; D004958:Estradiol; D008550:Melatonin