Increase of plasma adrenocorticotrophin and cortisol in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated dogs.

Neuroendocrine abnormality of the hypothalamic-pituitary-adrenal axis was investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated dogs as a model of Parkinson's disease. Blood samples were collected every 4 h for 3-4 days before MPTP treatment, around 2 and 4 weeks after the treatment of MPTP (2.5 mg/kg). Adrenocorticotrophin (ACTH) and cortisol concentrations in plasma were determined by radioimmunoassay. The concentrations of plasma ACTH and cortisol increased by 40% and 60% after MPTP treatment, respectively. Circadian rhythms of neither plasma ACTH nor cortisol concentrations were observed in both MPTP-treated and control dogs. This high hypothalamic-pituitary-adrenal function in MPTP-treated dogs suggests that MPTP may influence the activity of the hypothalamic neurons of the dog.