Changes in plasma cortisol and glucose concentrations
are presented in Fig. 1. Plasma cortisol concentrations
after ACTH infusion peaked at 12 h (74.5
17.8 ng/mL) and returned to the baseline concentration
within 9 h of the end of infusion (P 0.001). Cows
infused with ACTH solution had higher plasma cortisol
concentrations than those infused with isotonic NaCl
solution (P 0.05 or P 0.01) until 18 h. Plasma
glucose concentrations were higher in ACTH-infused
cows than in control cows from 6 to 36 h after the start
of infusion (P 0.05 or P 0.01).
Plasma mineral concentrations fluctuated following
ACTH infusion (Fig. 2). Although within the normal
range (2.0 to 2.7 mmol/L), plasma Ca concentrations at
21 h following ACTH infusion increased compared
with the baseline concentration (P 0.05). The plasma
Pi concentration decreased immediately after the start
of ACTH infusion, reaching a minimum of 0.95 0.30
mmol/L (below the dairy cattle plasma Pi concentration
reference range of 1.2 to 2.3 mmol/L) at 15 h. The Pi
concentration returned to baseline by 36 h. Plasma Mg
concentrations at 60 h were higher in ACTH-infused
cows compared with control cows (P 0.05), but were
within the normal range (0.74 to 1.32 mmol/L).
The levels of all bone metabolic markers decreased
after ACTH infusion (Fig. 3). Plasma TRAP5b activity
decreased immediately after the start of ACTH infusion
Fig.