慢性低酸素状態における心臓形態学的特性について

Cardiac morphological features under chronic hypoxia

　慢性低酸素状態は先天性心疾患や慢性肺疾患および血液疾患等において臨床的にしばしば経験され，また虚血性心疾患も心灌流量の低下による単一臓器の慢性低酸素状態とも考えられる。このような低酸素状態に対して生体はあらゆるシステムにおいて適応反応を示すが，とりわけ心臓の適応は生存に関わる重要な問題と考えられる。しかしながら実際には著しい心室腔狭小を伴う心肥大や良好な血液灌流を妨げるような高ヘマトクリット血症等の過剰適応と考えられる場合も少なからず経験され，また一方で適応不全をきたす例もあって，適応過程は必ずしも合目的に達成されるとはかぎらないように思われる。これまでも慢性低酸素状態における一般的な適応現象については詳しく研究されているものの，これら異なる適応反応を示す条件に関する知見はまだ乏しく，今回我々は慢性低酸素状態における適応像を規定する条件に関して，その心形態学的特性を解析すべく実験を試みたので報告する。

An experiment was carried out to analyse the cardiac morphological features under chronic hy-poxia. Three groups of male Wistar strain rats such as newborn, 3 weeks-aged and 8 weeks-ages were employed to postulate the adaptative ability of age-dependent variability.

These rats were raised to 2,400m altitude and had been kept for 7 to 9 weeks. Control groups had been maintained to the respective experimental groups at 600 m altitude during same period. Each group was consisted of 5 to 8 rats respectively.

At the end of the experiment, body weight, heart weight, heart weight/body weight, hematocrit, ven-tricular wall thickness, myocardial fiber diameter, capillary supply and mitochondria were measured. Mitochondria were examined in their size, cristal density and % area of proportion to myocardial fibers.

Mean value and standard deviation were calculated and statistical analysis (t-test) was performed in each experimental group's value in proportion to the respective control group.

We evaluated good body weight gain as one of important adaptative indices because all rats were in growing period. At this point of view, we tried to analyse the characteristic features of 3 weeks-aged group as well grown one in comparison with the other groups.

This group showed following cardiac morphologi-cal features in contrast to those of other experimentalgroups. Heart weight and heart weight/body weight were low. Hematocrit level was intermediate. Ven-tricular wall thickness were rather thin in right ventricle but thick in interventricular septum and left ventricle. Myocardial fiber diameters were small in right ventricle, intermediate in interventricular septum and large in left ventricle. Capillary supplies were intermediate in left ventricle but sparse in right ventricle and interventricular septum. Mito-chondrial analysis revealed larger in size, denser in crista but low in % area.

To summarize these data, in well grown rats under chronic mild hypoxia, cardiac hypertrophy should be restricted and hematocrit being moderately elevated. Concerning ventricular wall, right-sided should not react excessively but left-sides should achieve good growth. Mitochondria should attain some develop-ment.