Glucocorticoid receptor down-regulation in neutrophils of periparturient cows

Objective-To determine effects of parturition on glucocorticoid receptor (G R) expression in neutrophils, serum cortisol concentration, and total blood leukocyte and neutrophil counts in periparturient dairy cows. Animals-23 Holstein cows. Procedure-Blood samples were collected from 8 multiparous and 5 primiparous periparturient cows at various times from 28 days before parturition until 14 days after parturition. Glucocorticoid receptor expression in neutrophi ls, serum cortisol concentration, and total blood leukocyte and neutrophil counts were determined. Results were compared with results from control sam ples obtained from 5 multiparous and 5 primiparous Holstein cows in midpreg nancy. Results-Neutrophils from periparturient cows had 49% reduction in GR expres sion at calving, compared with GR expression 2 to 4 weeks before carving, a nd 39% reduction, compared with neutrophils from cows in midpregnancy. Redu ction in neutrophil GR expression began 1 week before carving and was most severe at calving and 24 hours after calving; a significant difference in G R expression was detected between primiparous and multiparous cows. Serum c ortisol concentrations and total leukocyte and neutrophil counts were signi ficantly increased at calving and returned to baseline values by 24 hours a fter calving. Significant negative correlations were detected between neutr ophil GR expression and serum cortisol concentration, total leukocyte count , and neutrophil count. Conclusions and Clinical Relevance-Reduced GR expression in blood neutrophi ls of periparturient dairy cows was associated with increased serum cortiso l concentrations, leukocytosis, and neutrophilia. Thus, GR down-regulation in neutrophils may be involved in periparturient neutrophil dysregulation a nd may cause increased susceptibility to mastitis.