Effects of cortisol secreted via a 12-h infusion of adrenocorticotropic hormone on mineral homeostasis and bone metabolism in ovariectomized cows

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.