The influence of age, sex and strain on the serum concentration of transcortin (corticosteroid-binding globulin) and vitamin D-binding protein (DBP) in mice was investigated. The effect of age was studied in two strains, C57BL/6JPfd and BALB/cmHeAPfd. The concentration of transcortin and DBP increased with age. In young animals the concentration of each protein showed a significant strain difference, which disappeared in older mice for DBP, but not for transcortin. In 7-day-old animals, no sex difference was observed for either protein, but in older animals a clear sex difference was found for transcortin. Adult males tended to have somewhat higher levels of DBP than adult females, but this difference was significant only on day 70.
The variation in transcortin and DBP levels was further investigated in a large number of mouse strains. The DBP concentration did not markedly vary among strains (5·98–9·65 μmol/l in males and 5·08–8·85 μmol/l in females). Transcortin, however, showed marked strain variations, ranging from 0·72 to 2·06 μmol/l in males and from 1·02 to 4·55 μmol/l in females and there was a significant correlation (r= 0·66, n= 26, P<0·001) between the mean transcortin levels in males and females of different strains. Interstrain variation was much higher than intrastrain variation or variation among related strains, suggesting that the transcortin concentration is largely controlled by genetically determined factors.
There was a significant correlation (r= 0·82, n = 9, P<0·01) between the mean corticosterone and transcortin concentrations (measured at 21.00 h). Consequently, differences in the free corticosterone levels in the serum of various mouse strains were smaller than the differences in the total corticosterone concentrations. The affinity of transcortin for corticosterone was similar in all but one strain; however, transcortin of the RIIIS/J strain showed a lower affinity for corticosterone.
J. Endocr. (1986) 109, 141–147