Nitric oxide synthase activity in brain tissues from llama fetuses submitted to hypoxemia

The fetal llama (Lama glama; a species adapted to live in chronic hypoxia i n the highlands of the Andes) did not increase cerebral blood flow and redu ce the brain oxygen uptake during hypoxemia. Although nitric oxide (NO) is a normal mediator in the regulation of vascular tone and synaptic transmiss ion, NO overproduction by hypoxemia could produce neuronal damage. We hypot hesized that nitric oxide synthase (NOS) activity is either maintained or r educed in the central nervous system of the llama fetuses submitted to chro nic hypoxemia. Approximately 85% of the Ca2+-dependent NOS activity was sol uble, at least 12% was associated with the mitochondrial fraction, and less than 5% remains associated with microsomes. To understand the role of NO i n chronic hypoxemia, we determined the effect of 24-h hypoxemia on NOS acti vity in the central nervous system. No changes in activity or the subcellul ar distribution of NOS activity in brain tissues after hypoxemia were found . We proposed that the lack of changes in NOS activity in the llama under h ypoxemia could be a cytoprotective mechanism inherent to the llama, against possible toxic effects of NO. (C) 2001 Elsevier Science Inc. All rights re served.