Morphine, sufentanil, and taltirelin effects on arterial blood pH (A), carbon dioxide (B), and oxygen (C) partial pressures and base excess (D) and lactate (E) levels in conscious, air-breathing rats. Data were collected using animals different than those of Figs. 1 and 2. Drug dosing and administration order and times were as in Figs. 1 and 2: 10 mg/kg i.v. morphine (M) (over 5 minutes) or 10 μg/kg i.v. sufentanil (S) by bolus (over ∼5-10 seconds) or 1 ml i.v. saline (NS) at 15 minutes followed by 1 mg/kg i.v. taltirelin (T) or 1 ml i.v. saline (NS) at 20 minutes. Data indicate change (Δ) in measured value from baseline—collected just prior to first opioid/saline administration—and 15, 30, and 45 minutes after taltirelin (or saline) administration. Data are avg. from 6–8 animals (n = 6–8). “ns” indicates no significance (P > 0.05); asterisks and diamonds (∗/⧫, ∗∗/⧫⧫, and ∗∗∗/⧫⧫⧫) indicate statistical significance (P < 0.05, P < 0.01, and P < 0.001) by one-way ANOVA test with a Sidak’s multiple comparisons post-test relative to morphine plus saline (M+NS) or sufentanil plus saline (S+NS) animals, respectively. Baseline arterial blood pH, PaCO2, PaO2, base excess, and lactate were 7.48 ± 0.01, 38.9 ± 0.8 mmHg, 90 ± 2 mmHg, +5.0 ± 0.3 mEq/L, and 0.7 ± 0.1 mmol/L, respectively; n = 21.