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首页> 外文期刊>The Journal of Experimental Biology >The interplay of cutaneous water loss, gas exchange and blood flow in the toad, Bufo woodhousei: adaptations in a terrestrially adapted amphibian
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The interplay of cutaneous water loss, gas exchange and blood flow in the toad, Bufo woodhousei: adaptations in a terrestrially adapted amphibian

机译：蟾蜍的蟾蜍皮肤水分流失，气体交换和血液流动之间的相互作用：适应于陆地适应的两栖动物

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摘要

Toads experiencing dehydrating conditions exhibit complex physiological and behavioral responses, some of which can potentially impact cutaneous gas exchange, an important component of total gas exchange. We measured the effect of dehydration on cutaneous gas exchange in the xeric-adapted toad Bufo woodhousei. First, two pharmacological agents were used to stimulate cutaneous blood flow - phentolamine (an alpha-blocker) and isoproterenol, a P-stimulant and powerful cardioaccelerator - to determine a relationship between cutaneous blood flow and water loss. Both drugs increased heart rate and blood pressure, and caused visually evident extensive vasodilation of the skin. Untreated toads in a dry air stream took an average of 10.1 +/- 0.7 h to dehydrate to 80% body mass, while animals treated with isoproterenol and phentolamine requires only 7.2 +/- 0.8 h and 7.4 +/- 0.9 h, respectively. Rehydration, which was more rapid than dehydration, was similarly accelerated in pharmacologically treated toads.Cutaneous gas exchange (M-O2, M-CO2) and (CO)-O-18 diffusing capacity ((DSkinCO)-O-18) were then examined in unanesthetized toads under different states of body hydration. Blood gases and hematocrit were measured separately but under identical conditions. In fully hydrated toads at 23-25 degreesC, cutaneous gas exchange values were: M-O2 = 1.43 +/- 0.47 mumol g(-1) h(-1), M-CO2 = 1.75 +/- 0.85 mumol g(-1) h(-1), and the respiratory exchange ratio R = 1.36 +/- 0.56 (N=6, mean + 1S.D.). (DSkinCO)-O-18 was 0.48 +/- 0.03 mumol g body mass(-1) h(-1) kPa. Following an enforced 20-25% loss of body water, (DSkinCO)-O-18 fell by nearly 50% to 0.28 +/- 0.09 mumol g(-1) h(-1) kPa. However, cutaneous M-O2, M-CO2 and R were unchanged at 1.48 +/- 0.15 mumol g(-1) h(-1), 1.72 +/- 0.29 mumol g(-1) h(-1) and 1.13 +/- 0.08 mumol g(-1) h(-1), respectively. Partial pressure of arterial (sciatic) oxygen, Pa-O2, normally about 12-13 kPa, remained unchanged by dehydration, but Pa-CO2 increased about 250% from 0.93 +/- 0.27 up to 2.27 +/- 0.93 kPa. The fall in (DSkinCO)-O-18 during dehydration presumably results at least in part from decreased cutaneous blood flow, possibly in an attempt to reduce the transcutaneous water loss that would otherwise result during dehydrating conditions. Concurrently, cutaneous M-CO2 is maintained under dehyrdating conditions by a greatly increased Pa-CO2 diffusion gradient across the skin. Thus, Bufo woodhousei appears able to restrict cutaneous blood flow without compromising vital cutaneous CO2 loss.
机译：经历脱水条件的蟾蜍表现出复杂的生理和行为反应，其中一些可能潜在地影响皮肤气体交换，而皮肤气体交换是总气体交换的重要组成部分。我们在适应干旱的蟾蜍Bufo woodhousei中测量了脱水对皮肤气体交换的影响。首先，使用两种药理剂刺激皮肤血流-酚妥拉明（一种α受体阻滞剂）和异丙肾上腺素（一种P刺激剂和强大的心脏促进剂）来确定皮肤血流与水分流失之间的关系。两种药物均会增加心率和血压，并在视觉上引起皮肤明显的广泛血管舒张。未经干燥的蟾蜍在干燥的空气流中脱水平均需要10.1 +/- 0.7小时才能脱水至80％的体重，而用异丙肾上腺素和酚妥拉明处理的动物分别只需要7.2 +/- 0.8小时和7.4 +/- 0.9小时。在药物处理的蟾蜍中，补水比脱水更快，但同样加速，然后进行瞬时气体交换（M-O2，M-CO2）和（CO）-O-18扩散能力（（DSkinCO）-O-18）。在不同水分状态下在未麻醉的蟾蜍中进行了检查。分别测量血气和血细胞比容，但条件相同。在23-25摄氏度的完全水化蟾蜍中，皮肤气体交换值为：M-O2 = 1.43 +/- 0.47 mumol g（-1）h（-1），M-CO2 = 1.75 +/- 0.85 mumol g（- 1）h（-1），呼吸交换比R = 1.36 +/- 0.56（N = 6，平均值+ 1S.D.）。 （DSkinCO）-O-18为0.48 +/- 0.03摩尔g体重（-1）h（-1）kPa。在人体水分强制流失20-25％之后，（DSkinCO）-O-18下降了近50％，降至0.28 +/- 0.09摩尔g（-1）h（-1）kPa。但是，皮肤M-O2，M-CO2和R保持不变，分别为1.48 +/- 0.15摩尔g（-1）h（-1），1.72 +/- 0.29摩尔g（-1）h（-1）和1.13 +/- 0.08摩尔g（-1）h（-1）。动脉（坐骨）氧分压Pa-O2，通常约为12-13 kPa，由于脱水而保持不变，但Pa-CO2从0.93 +/- 0.27上升到2.27 +/- 0.93 kPa，增加了约250％。脱水期间（DSkinCO）-O-18的下降可能至少部分是由于皮肤血液流量减少，可能是为了尝试减少在脱水条件下可能导致的经皮水分流失。同时，通过大大增加的跨皮肤的Pa-CO2扩散梯度，皮肤M-CO2被维持在解冻条件下。因此，Bufo woodhousei似乎能够限制皮肤的血流而不会损害皮肤的重要CO2损失。

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