Figure 1.

Protocol 1 description. Lambs were instrumented 3 days before the experiment. The day of the experiment, lambs were exposed to four sequential 30 min intervals of: normoxia (Nx, breathing room air), normoxia₁ (Nx₁) after an i.v., bolus of 0.17 mg kg⁻¹ melatonin (M) or vehicle (V), hypoxia (Hx, PaO₂₌ 30 ± 2 mmHg) followed by recovery (R) under room air. – –Lambs returned to their mothers until next day (protocol 2). *Time of cardiac output measurements and blood sample collection. Heart rate and pulmonary and systemic arterial blood pressure were measured from 0 to 120 min.