It is not clear whether blood hemoglobin concentration ([Hb]) increases with an increase in the exposure period of intermittent hypoxia (IHx) and reaches a constant level. Furthermore, it is not known whether plasma erythropoietin concentration ([EPO]) also increases with an increase in the exposure period. Using a rat model, first, we evaluated changes in [EPO] every hour after single exposure of 10% O2 for 120 min in order to determine a peak level of [EPO]. Second, we evaluated the effect of IHx of 10% O2, 120 min/day for 0 (control), 1, 2, 3, 4, 6 and 8 weeks on [Hb], arterial blood pressure (BP), heart rate (HR), arterial blood gases (ABGs) and [EPO]. [EPO] increased after cessation of the single hypoxic exposure, reached a peak at 1 h, and decreased gradually to the control levels within 18 h. IHx of 10% O2, 120 min/day, produced a time-dependent increase in [Hb], and [Hb] reached a constant level after the exposure for 6 weeks. BP increased after the exposure for 4 weeks and remained elevated. There was no significant difference in HR and ABGs. [EPO] increased significantly and remained elevated at the same level for 1–3 weeks, however, the peak level of [EPO] declined markedly after [Hb] reached a constant level.
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The skillful technical assistance of Katsuko Naito, Yoko Takahari, and Yoshiko Shinozaki is gratefully acknowledged. This study was supported, in part, by the Ministry of Education, Science, Sports and Culture, Japan, Grant-in-Aid for Exploratory Research (No. 20659133, 2008).
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