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Journal of Experimental Biology 82,345-355 (1979)
Published by Company of Biologists 1979

Acid-Base Relationships in the Blood of the Toad, Bufo Marinus: II. The Effects of Dehydration

R. G. BOUTILIER ¹, D. J. RANDALL ², G. SHELTON ¹, and D. P. TOEWS ³

¹ Department of Biology, Acadia University, Wolfville, Nova Scotia, Canada BOP 1XO; School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, England
² Department of Biology, Acadia University, Wolfville, Nova Scotia, Canada BOP 1XO; Department of Zoology, University of British Columbia, Vancouver, B.C., Canada V6T 1W5
³ Department of Biology, Acadia University, Wolfville, Nova Scotia, Canada BOP 1XO

Cutaneous CO₂ excretion is reduced as the skin dries during dehydration but an increase in breath frequency acts to regulate the arterial blood P_coco2 and thus pH. 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 P_COCO2 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.

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