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Abstrait
Dynamics of Erythropoietic Markers in Response to Hypoxia in Rats
Ying Zhang, Indrajeet Singh and Wojciech Krzyzanski
Purpose: Erythropoietin (EPO) regulates production of red blood cells in response to hypoxia. Decreased arterial oxygen saturation results in an increased production of EPO in various tissues including kidney as a major stimulation site leading to an increase in EPO plasma levels. This study aims to investigate the relationship between hypoxia and resultant erythropoietic response in rats.
Methods: The in house hypoxia chamber was designed to regulate the fraction of inspired oxygen (FiO2) = 10% supplied to Wistar male rats (N=4) for 6 hours by mixing room air with N2 to maintain air pressure at 1 atm. Plasma and kidney samples were collected at various times during and after exposure to hypoxia. Kidney EPO mRNA, HIF-2α, plasma EPO concentration, reticulocyte counts and hemoglobin were measured. The time course of above markers and fold changes from pre-hypoxia values were used to quantify responses to hypoxia under the normoxic condition.
Results: The arterial oxygen saturation of rats decreased from 95% to 60% during the hypoxia. Hypoxia resulted in 6-fold increase in kidney EPO mRNA expression, 10-fold increase in plasma EPO concentrations and 1.5-fold increase in reticulocytes count. The increase of HIF-2α expression is 2.4 fold after one hour hypoxia and returns below the baseline value after 1.5 hours. The result of DNA binding activity of HIF-2α is quite similar, which increased 1.5 fold at 0.5 hour and then went below baseline.
Conclusion: After 6 hours hypoxia, the observed increase in the levels of kidney EPO mRNA, plasma EPO concentrations and reticulocytes count, and delays in peak response are consistent with times necessary for the stimulation for EPO mRNA transcription, synthesis of plasma EPO, and enhanced release of reticulocytes. The tolerance effect observed in HIF-2α time course implies existence of a counter-regulatory mechanism in a HIF-2α mediated signal for mRNA production.