Cutaneous blood flow and water absorption by dehydrated toads

Blood cell flux (BCF) in ventral pelvic skin capillaries was measured in toads, Bufo woodhouseii and Bufo punctatus, using a chamber that allowed hydration behavior and water absorption to be observed concurrently in unrestrained animals. Dehydrated B. woodhouseii and B. punctatus placed on a rehydration solution significantly increased BCF relative to that on a dry surface in less than 2 min. Skin contact with a rehydration solution rather than dehydration alone is the primary stimulus for increased seat patch blood flow. In B. woodhouseii, the water absorption response was initiated after the increase in BCF had started but before maximum BCF was reached. BCF and water uptake across the ventral skin of both species placed on deionized water were not different from those of toads placed on 50 mM NaCl. Similarly, no significant correlation between BCF and rate of water uptake could be observed in dehydrated toads of either species. Angiotensin II (AII) injection in hydrated B. punctatus had no effect on BCF, suggesting that factors other than AII are responsible for the increase in blood flow upon water contact in dehydrated toads.