To evaluate the effects of endogenously secreted cortisol on mineral homeostasis and bone metabolism in cows, 4 ovariectomized
Holstein cows were infused for 12 h with either an adrenocorticotropic hormone (ACTH) solution (0.5 mg/2 L isotonic
NaCl solution per cow) or isotonic NaCl solution in a 2 2 crossover design. ACTH infusion stimulated cortisol secretion and
increased plasma cortisol concentrations for 18 h (P 0.001), leading to an elevated plasma glucose concentration until 36 h (P
0.001). Plasma calcium and magnesium concentrations in ACTH-infused cows fluctuated within normal ranges, whereas
hypophosphatemia was observed unequivocally. The biochemical bone resorption markers tartrate-resistant acid phosphatase 5b
and hydroxyproline decreased following ACTH infusion (P 0.001 and P 0.003, respectively). Similarly, the bone formation
marker, bone-specific alkaline phosphatase, decreased continuously until 72 h after the ACTH infusion (P 0.001). These results
demonstrate that increased secretion of cortisol via a 12-h ACTH infusion disrupted homeostasis of inorganic phosphate and
suppressed bone metabolism in ovariectomized cows without involving gonadal steroid hormones