Up-regulated expression of peroxisome proliferator-activated receptor γ in the hypothalamic–pituitary–adrenal axis of weaned pigs after Escherichia coli lipopolysaccharide challenge

The expression of peroxisome proliferator-activated receptor γ (PPARγ) was investigated in the hypothalamic–pituitary–adrenal (HPA) axis of weaned pigs after injection with 100 μg/kg bodyweight Escherichia coli lipopolysaccharide (LPS) (n = 6) and control pigs injected with sterile saline (n = 6). LPS increased PPARγ mRNA and protein expression in the hypothalamus (23.8 and 3.1-fold relative to controls, respectively), pituitary gland (9.2 and 2.0-fold, respectively) and adrenal gland (3.5 and 2.3-fold, respectively) (P < 0.05). LPS also induced an increase in PPARγ immunohistochemical staining in the hypothalamus (1.3-fold), adenohypophysis (1.3-fold), adrenal cortex (1.4-fold) and adrenal medulla (1.6-fold) (P < 0.05). Concurrent with up-regulated expression of PPARγ, LPS increased the concentrations of plasma corticotrophin-releasing hormone (2.1-fold) and adrenocorticotrophin (1.4-fold) (P < 0.05). LPS also induced elevations of interleukin 6 and tumour necrosis factor α mRNA levels in the hypothalamus (4.0 and 3.2-fold, respectively), pituitary gland (20.7 and 5.1-fold, respectively) and adrenal gland (3.9 and 3.3-fold, respectively) (P < 0.05). PPARγ may play a role in the regulation of neuroendocrine responses associated with immunological stress in pigs.