Boutilier R G, Randall D J, Shelton G, Toews D P
Department of Biology, Acadia University, Wolfville, Nova Scotia, Canada BOP IXO.
J Exp Biol. 1979 Oct;82:345-55. doi: 10.1242/jeb.82.1.345.
Cutaneous CO2 excretion is reduced as the skin dries during dehydration but an increase in breath frequency acts to regulate the arterial blood PCO2 and thus pHa. Moreover, the toad does not urinate and water is reabsorbed from the bladder to replace that lost by evaporation at the skin and lung surfaces. The animal does, however, produce a very acid bladder urine to conserve circulating levels of plasma [HCO3-] and this together with an increased ventilation effectively maintains the blood acid-base status for up to 48 h of dehydration in air. Water loss and acid production are presumably also reduced by the animal's behaviour; animals remain still, in a crouched position or in a pile if left in groups. Dehydrated toads are less able than hydrated toads to regulate blood pH during hypercapnia: they hyperventilate and mobilize body bicarbonate stores in much the same fashion as hydrated animals but due to the restrictions on cutaneous CO2 excretion and renal output, there is comparatively little reduction in the PCO2 difference between arterial blood and inspired gas thereby resulting in a more severe respiratory acidosis. These factors further contribute to the persistent acidosis which continues even when the animals are returned to air.
脱水过程中皮肤变干时，皮肤二氧化碳排泄减少，但呼吸频率增加可调节动脉血PCO2，进而调节动脉血pH值。此外，蟾蜍不排尿，膀胱会重吸收水分，以补充皮肤和肺表面蒸发所损失的水分。然而，动物会产生酸性很强的膀胱尿液，以维持血浆[HCO3-]的循环水平，这与增加的通气量一起，在空气中脱水长达48小时的情况下有效地维持了血液酸碱状态。动物的行为可能也减少了水分流失和酸的产生；如果成群放置，动物会保持静止，呈蹲伏姿势或聚成一堆。脱水蟾蜍在高碳酸血症期间调节血液pH值的能力不如水化蟾蜍：它们过度通气并以与水化动物大致相同的方式动用体内碳酸氢盐储备，但由于皮肤二氧化碳排泄和肾脏排出受限，动脉血与吸入气体之间的PCO2差异相对减少较少，从而导致更严重的呼吸性酸中毒。这些因素进一步导致了持续性酸中毒，即使动物回到空气中，酸中毒仍会持续。
