We studied the effects of nifedipine, a calcium-channel blocker, in 2 acutely instrumented groups of newborn lambs during normoxic and hypoxic conditions. Nifedipine at 10 or more μg/kg reduced systemic, but not pulmonary artery pressure and resistance in normoxic lambs. When acute hypoxia was produced in these animals, 50 or more μg/kg reduced, but did not prevent, the expected rise in pulmonary pressure and resistance. When infused into already hypoxic lambs, nifedipine in doses of 50 μg/kg or more reduced both systemic and pulmonary pressures and resistances equally. Thus, nifedipine is a nonspecific vasodilator in newborn lambs.
