Ohtsuka T, Browne V A, Gilbert R D
Department of Physiology and Obstetrics and Gynecology, Loma Linda University, School of Medicine, CA 92350, USA.
J Soc Gynecol Investig. 1997 Jul-Aug;4(4):197-202.
We tested the hypothesis that hearts of fetal and nonpregnant adult sheep exposed to long-term hypoxemia would be able to sustain higher contractile function during exposure to acute hypoxia than hearts from normoxic animals.
Pregnant and nonpregnant sheep were exposed to high altitude (3820 m) for 100 days. Right and left ventricular papillary muscle strips were obtained from fetuses and nonpregnant adults, mounted in an isolated bath system, stimulated electrically and subjected to acute hypoxia in a dose response manner. Measurements were made of maximum tension production (Tmax), maximum rate of tension development (+dT/dtmax), maximum rate of relaxation (-dT/dtmax), time to peak tension, and duration of contraction. Results were compared to papillary muscle from a normoxic group of animals.
Baseline values (95% O2 + 5% CO2 bubbled in the bath) of Tmax and +/- dt/dtmax for each ventricle were greater in adults than fetuses in both normoxic and long-term hypoxemic groups. During hypoxia (at 40 and 20% O2) Tmax and +/- dT/dtmax, were all maintained at significantly higher values in papillary muscle from long-term hypoxemic fetuses than in papillary muscle from normoxic fetuses. Duration of contraction and time to peak tension did not differ between the normoxic and hypoxemic groups. In both ventricles of the long-term hypoxemic adult, Tmax and +/- dT/dtmax, as well as duration and time to peak tension, were significantly higher than in normoxic adults, but only at the lowest level of hypoxia (20% O2).
Contrary to the original hypothesis, heart muscle from both fetal and adult sheep that had been exposed to long-term hypoxemia could maintain contractile function better during acute hypoxia. The responsible mechanisms are not clearly understood.
我们检验了这样一个假设，即长期处于低氧血症环境下的胎儿和未怀孕成年绵羊的心脏，在急性缺氧期间比常氧动物的心脏能够维持更高的收缩功能。
将怀孕和未怀孕的绵羊置于高海拔（3820米）环境中100天。从胎儿和未怀孕的成年绵羊获取左右心室乳头肌条，安装在离体浴槽系统中，进行电刺激，并以剂量反应方式使其遭受急性缺氧。测量最大张力产生（Tmax）、最大张力发展速率（+dT/dtmax）、最大舒张速率（-dT/dtmax）、达到峰值张力的时间以及收缩持续时间。将结果与常氧动物组的乳头肌进行比较。
在常氧组和长期低氧血症组中，各心室的Tmax以及+/- dt/dtmax的基线值（浴槽中通入95% O₂ + 5% CO₂）在成年绵羊中均高于胎儿。在缺氧期间（40%和20% O₂时），长期低氧血症胎儿的乳头肌中的Tmax以及+/- dT/dtmax均显著高于常氧胎儿的乳头肌。常氧组和低氧血症组之间的收缩持续时间和达到峰值张力的时间没有差异。在长期低氧血症成年绵羊的两个心室中，Tmax以及+/- dT/dtmax，还有收缩持续时间和达到峰值张力的时间，均显著高于常氧成年绵羊，但仅在最低水平的缺氧（20% O₂）时如此。
与最初的假设相反，长期处于低氧血症环境下的胎儿和成年绵羊的心肌在急性缺氧期间能够更好地维持收缩功能。其相关机制尚不清楚。
