Oxygen transport in guinea pigs native to high altitude (Junin, Peru, 4,105 m).

Abstract

In guinea pigs native to high altitude in the Andes (Peru) the arterial and mixed-venousP O 2,P CO 2, pH, and O2 content were measured at high altitude during breathing ambient air. Identical measurements were done in Nijmegen, The Netherlands, on sea-level natives and on guinea pigs exposed for 4–5 weeks to simulated altitude in a low pressure chamber, while breathing ambient air (normoxia) or an hypoxic mixture of O2 in N2 with aP I O 2 similar to that of the ambient air at high altitude. A standard blood O2 dissociation curve (ODC) was estimated in vitro (at pH=7.4 and 37.5°C), and a standard in vivo ODC was derived from measuredP O 2,S O 2 and pH in all three groups. Both guinea pigs native to natural or simulated high altitude had a higher hematocrit and blood O2 capacity than sea-level controls. These increased altitude values were, however, almost the same as the sea-level values of man or rat. No difference in the ideal alveolararterialP O 2 difference or lung diffusing capacity for O2 was found between (natural or simulated) high altitude animals and their corresponding controls, when measured at hypoxia. Mixed-venousP O 2 was higher in guinea pigs from the natural high altitude (but not in those from the low pressure chamber) when compared with control sea-level natives studied at hypoxia. No difference among groups in cardiac output was found, while breathing the same inspiratory mixture. In the guinea pigs native to high altitude a higher P50 and a lower Hill numbern for the in vitro ODC were found when compared with the controls or with the guinea pigs exposed to simulated high altitude. This was not observed when the ODC's were estimated in vivo. The rather modest polycythemic response to high altitude in guinea pigs coincides with a low value of P50, when related to body weight. In this respect the guinea pig seems to be more closely related to the typical high altitude mammals like Andean camelids and rodents than to man or rat that respond to high altitude with a pronounced polycythemia and possess a rather high P50 with respect to body weight.