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

In guinea pigs native to high altitude in the Andes (Peru) the arterial and mixed-venousP_O2,P_CO2, 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_IO2 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_O2,S_O2 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_O2 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_O2 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.All data obtained in Peru are part of the scientific material acquired during the Italian Lake Mountain Scientific Expedition to Peru, march and April 1978, under the direction of Prof. Dr. P. G. Data from the University of Chieti, Italy.Part of the results were presented at the 12. Atmungsphysiologische Arbeitstagung, Göttingen, FRG, January 26–27, 1979