VENTILATORY RESPONSES TO BRIEF HYPOXIC STIMULI AFTER SIMULATED ALTITUDE EXPOSURE IN RAT

A blunted ventilatory response to acute hypoxia is described in altitu de acclimatized small mammals. The peripheral or central origin of thi s blunting remains controversial. As the O2 sensitivity is always test ed by steady-stale steps of progressive hypoxia, an enhanced central i nhibiting mechanism similar to those created by sustained hypoxia is s uspected to be involved in the blunting. To avoid such central effect, we analyzed the ventilatory responses to very short glomic stimuli su ch as N-2 tests and administration of NaCN by intravenous bolus in chr onically hypoxic rats. The blunted ventilatory response was present on ly for hypoxemic hypoxia. A D-2-receptor blockade failed to restore th is response to those of littermate controls. We concluded that in rats , after altitude acclimatization, the central transduction of glomic a fferences was intact because of the unchanged ventilatory response to cyanide. Reduced glomic sensitivity to low P-O2 appeared specifically responsible for the blunted response to N-2 tests with a very limited contribution from inhibitory dopaminergic mechanisms.