The perinatal llama immersed in the thin oxygen of the Andean Altiplano

The llama fetus shows specific adaptations to the challenge of low oxygen levels in the Andean Altiplano. Lowland fetal mammals like sheep respond to hypoxia with a brain-sparing effect, which increases cerebral blood flow at the expense of peripheral vasoconstriction. Fetal peripheral vasoconstriction is triggered by a carotid chemoreflex and maintained by constrictor hormones like catecholamines and neuropeptide Y, as well as local vascular responses. Highland lambs are also susceptible to exaggerated constrictor influences in the lung, rendering them susceptible to pulmonary hypertension. Unlike fetal sheep, the llama fetus shows no increase in cerebral blood flow during hypoxia. Instead, there are falls in cerebral oxygen consumption, sodium-potassium ATPase, Na channel expression and temperature, which protect against brain injury. Furthermore, the llama fetus shows intense peripheral vasoconstriction during hypoxia even following carotid chemoreceptor denervation, owing to a sensitized sympathetic drive and markedly elevated release into the fetal circulation of catecholamines and neuropeptide Y. Newborn llamas do not experience pulmonary hypertension at high altitude, as they show enhanced haem oxygenase-carbon monoxide signalling to offset pulmonary constrictor effects of hypoxia. These remarkable strategies permit fetal and newborn llamas to thrive at high altitudes despite the thin air of the Andean Altiplano.This article is part of the discussion meeting issue 'Pregnancy at high altitude: the challenge of hypoxia'.