Effects of dehydration on plasma osmolality, thirst-related behavior, and plasma and brain angiotensin concentrations in Couch's spadefoot toad,Scaphiopus couchii

Abstract

Under dehydrating conditions, many terrestrial vertebrates species exhibit increases in plasma osmolality and their drinking behavior. Under some circumstances, this behavioral change is accompanied by changes in plasma and central angiotensin concentrations, and it has been proposed that these changes in angiotensin levels induce the thirst‐related behaviors. In response to dehydration, the spadefoot toad, Scaphiopus couchii, exhibits thirst‐related behavior in the form of cutaneous drinking. This behavior has been termed water absorption response (WR) behavior. Spadefoot toads live in harsh desert environments and are subject annually to dehydrating conditions that may induce thirst‐related behavior. We tested the hypothesis that an increase in WR behavior is associated with both an increase in plasma osmolality and an increase in plasma and brain angiotensin concentrations. First, we determined the degree of dehydration that was necessary to initiate WR behavior. Animals dehydrated to 85% of their standard bladder‐empty weight via deprivation of water exhibited WR behavior more frequently than control toads left in home containers with water available. Next, using the same dehydration methods, we determined the plasma osmolality and sodium concentrations of dehydrated toads. Toads dehydrated to 85% standard weight also had a significant increase in plasma osmolality, but exhibited no overall change in plasma sodium concentrations, indicating that while an overall increase in plasma osmolality appears to be associated with WR behavior in S. couchii, changes in sodium concentrations alone are not sufficient to induce the behavior. Finally, plasma and brain angiotensin concentrations were measured in control toads and toads dehydrated to 85% standard weight. Plasma and brain angiotensin concentrations did not increase in dehydrated toads, indicating that dehydration‐induced WR behavior that is associated with changes in plasma osmolality may not be induced by changes in endogenous angiotensin concentrations in S. couchii. J. Exp. Zool. 286:572–584, 2000. © 2000 Wiley‐Liss, Inc.

When less means more: dehydration improves innate immunity in rattlesnakes

“…Therefore, many animals maintain plasma osmolality within a small osmotic range (300 mOsm kg −1 ±5%), even during periods during which they do not drink (Ramsay and Thrasher, 1984). Juxtaposed to this, some animals adapted to living in xeric environments can tolerate extreme variation in osmolality [toads: 250-370 mOsm kg −1 (Johnson and Propper, 2000); tortoises: 290-400 mOsm kg −1 (Nagy and Medica, 1986); lizards: 280-350 mOsm kg −1 (Davis and DeNardo, 2009); and birds: 325-425 mOsm kg −1 (Williams et al, 1991)] and appear to function normally. However, impacts on immune function may be inconspicuous yet still significant to the survival of the organism.…”

Pericardium of the frog, Rana esculenta, is morphologically designed as a lymphatic space

“…In amphibians, lymphatic-regulated salt and water balance is controlled by several substances such as the antidiuretic hormone and arginine vasotocin (Wentzell et al, 1993). Recently, ANG II was shown to exert an influence on amphibian osmotic equilibrium through the control of several physiological mechanisms (i.e., thirst-related behavior, cutaneous water gain, and renal handling of ions and water), all directly and/or indirectly modulating lymphatic system function (Hillyard, 1999;Johnson and Propper, 2000). The changed morphological profile observed in the frog PP after ANG II treatment is consistent with an ANG II-dependent stimulation of the pericardial mesothelial transport of fluids.…”

Effect of changes in water-salt balance on ion- and osmoregulatory renal functions in the lake frog

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