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J Appl Physiol 86: 181-187, 1999;
8750-7587/99 $5.00
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Vol. 86, Issue 1, 181-187, January 1999

Splenic contraction-induced reversible increase in hemoglobin concentration in intermittent hypoxia

Ichiro Kuwahira1, Uguri Kamiya1, Tokuzen Iwamoto1, Yoshihiro Moue1, Tetsuya Urano1, Yasuyo Ohta1, and Norberto C. Gonzalez2

1 Department of Medicine, Tokai University School of Medicine, Isehara, Kanagawa 259-1193, Japan; and 2 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160-7401

The effect of intermittent hypoxia (IHx) on blood hemoglobin concentration ([Hb]) and the underlying mechanisms were studied in rats exposed to 10% O2, 1 h/day, for up to 5 wk. IHx protocols with longer daily hypoxic exposure show persistent polycythemia; however, it is unknown whether [Hb] increases transiently during hypoxia in protocols without polycythemia. Hypoxia produced a reversible [Hb] increase after 4 days of IHx but not in normoxic controls (NxC) or after shorter period of IHx. Splenectomy abolished the phenomenon. Plasma epinephrine and norepinephrine levels during hypoxia were comparable in IHx and NxC groups, but the epinephrine-induced [Hb] increase was larger in IHx. The alpha 1- and alpha 2-adrenoreceptor blockade (phentolamine) and alpha 2-blockade (yohimbine) abolished the [Hb] increase of IHx rats. Conversely, alpha 2-receptor stimulation (oxymetazoline) increased [Hb] during normoxia in IHx but not in NxC. In conclusion, this IHx protocol results in reversible [Hb] increases during hypoxia via splenic contraction mediated by increased alpha 2-adrenoreceptor response. This may protect O2 supply during hypoxia without the cardiovascular burden of polycythemia during normoxia.

alpha 2-adrenoreceptor; Sprague-Dawley rat; acclimatization; oxygen delivery


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