Söderström V, Renshaw G M, Nilsson G E
Division of General Physiology, Department of Biology, University of Oslo, N-0316 Oslo, Norway.
J Exp Biol. 1999 Apr;202(Pt 7):829-35. doi: 10.1242/jeb.202.7.829.
The key to surviving hypoxia is to protect the brain from energy depletion. The epaulette shark (Hemiscyllium ocellatum) is an elasmobranch able to resist energy depletion and to survive hypoxia. Using epi-illumination microscopy in vivo to observe cerebral blood flow velocity on the brain surface, we show that cerebral blood flow in the epaulette shark is unaffected by 2 h of severe hypoxia (0.35 mg O2 l-1 in the respiratory water, 24 C). Thus, the epaulette shark differs from other hypoxia- and anoxia-tolerant species studied: there is no adenosine-mediated increase in cerebral blood flow such as that occurring in freshwater turtles and cyprinid fish. However, blood pressure showed a 50 % decrease in the epaulette shark during hypoxia, indicating that a compensatory cerebral vasodilatation occurs to maintain cerebral blood flow. We observed an increase in cerebral blood flow velocity when superfusing the normoxic brain with adenosine (making sharks the oldest vertebrate group in which this mechanism has been found). The adenosine-induced increase in cerebral blood flow velocity was reduced by the adenosine receptor antagonist aminophylline. Aminophylline had no effect upon the maintenance of cerebral blood flow during hypoxia, however, indicating that adenosine is not involved in maintaining cerebral blood flow in the epaulette shark during hypoxic hypotension.
在缺氧环境中生存的关键在于保护大脑免受能量耗竭的影响。肩章鲨（Hemiscyllium ocellatum）是一种能够抵抗能量耗竭并在缺氧环境中存活的软骨鱼。我们通过体内落射荧光显微镜观察大脑表面的脑血流速度，发现肩章鲨的脑血流在严重缺氧2小时（呼吸水中氧气含量为0.35毫克/升，水温24摄氏度）的情况下不受影响。因此，肩章鲨与其他已研究的耐缺氧和耐无氧物种不同：不存在像淡水龟和鲤科鱼类那样由腺苷介导的脑血流增加。然而，在缺氧期间，肩章鲨的血压下降了50%，这表明发生了代偿性脑血管舒张以维持脑血流。当用腺苷灌注常氧状态下的大脑时，我们观察到脑血流速度增加（这使鲨鱼成为发现这种机制的最古老脊椎动物类群）。腺苷受体拮抗剂氨茶碱可降低腺苷诱导的脑血流速度增加。然而，氨茶碱对缺氧期间脑血流的维持没有影响，这表明在缺氧性低血压期间，腺苷不参与维持肩章鲨的脑血流。
