The effects of aging on leukocyte glucocorticoid receptor concentration and response to dexamethasone in dogs

Glucocorticoid receptor concentration (GR) was determined in mononuclear (MNS) and polymorphonuclear (PMNS) cells isolated from 8 aged and 9 young male dogs. In addition, leukocyte responses to dexamethasone (0.1 mg kg(-1) i.v.) and plasma glucose concentration were also measured. The GR in MNS and PMNS was higher (p<0.05) in young dogs (6.64 +/- 0.57 and 7.04 +/- 0.29 fmolesx10(6) cells, respectively, versus 4.40 +/- 0.24 and 5.06 +/- 0.33 fmolesx10(6) cells, respectively, in aged dogs). The maximum increase in neutrophils (DeltaNEU) was lower (p<0.05) in aged dogs 6003.38 +/- 1398.5x10(6) versus 11168.67 +/- 1863.16x10(6) cells l(-1) in young dogs. The maximum decrease in lymphocytes (DeltaLYM) was lower (p<0.05) in aged dogs 550 +/- 56.75x10(6) cells l(-1) versus 1825.89 +/- 313.1x10(6) cells l(-1) in young dogs. In young dogs, significant (p<0.05) correlations between GR in PMNS and DeltaNEU (r=0.80) and between GR in MNS and DeltaLYM (r=0.76) were observed. In aged dogs, these correlations were not significant. The lower GR value and the lack of correlation between this parameter and its respective Delta in aged dogs suggest that changes in leukocytes responsiveness to glucocorticoids is occurring during the aging process.