Microsphere studies of amphibian systemic blood flow redistribution during dehydration, hypovolemia, and salt load

Abstract

Systemic blood flow distribution was monitored in a variety of anuran amphibians using trapping of 54-pm mean radionuclidelabeled micre spheres during control, dehydration, hypovolemia, and salt load treatments. The head was the only region which showed significant increases in its proportion of systemic blood distribution in both dehydration and hypovolemia relative to controls. Proportionate declines in blood flow were observed to skeletal muscle regions during dehydration and hypovolemia. Salt loading had no effect on blood flow distribution. The redistribution results are consistent with sympathetic reflex control during hypovolemia and dehydration. The magnitude of the cerebral redistribution did not correlate with a species' tolerance to dehydration.

The significance of hypovolemia in dehydrational death in anurans

“…Xenopus is particularly suited to this type of study because of its relatively low dehydration tolerance, insignificant bladder volume, and lack of any hydroosmotic response (Hillman, 1978a). Also, much is known about the physiological consequences of dehydration in this species (Hillman, 1978a;1978b;1980;Hillman and Sommerfeldt, 1981).…”

Regulation of glutathione-based antioxidant defenses in response to dehydration stress in the African clawed frog, Xenopus laevis

“…The progress of whole-animal dehydration is highly controlled in X. laevis during aestivation. Up to about 18% whole-body dehydration, the frog can maintain systemic circulation to visceral organs but appears to favour redirection of oxygen and nutrient supply to the brain over circulation to skeletal muscle and the gastrointestinal tract (Hillman and Sommerfeldt, 1981). As dehydration persists, the transcutaneous loss of water leads to hypovolemia and increased hematocrit levels which reduces oxygen delivery within the frog resulting in dehydration-induced hypoxia (DIH) and ischemia (Hillman, 1978).…”

“…Dehydration-induced hypoxia (DIH) is a consequence of wholebody dehydration due to increased hematocrit levels and hypovolemia which limits adequate oxygen delivery to vital organs and peripheral tissues (Hillman, 1978). Since circulation is preferentially redirected to the heart and brain during dehydration stress, this hypoxic condition would be notable in other vital organs including the liver (Hillman and Sommerfeldt, 1981). DIH causes the frog to rely increasingly on anaerobic metabolism for ATP production by dysregulating the TCA cycle and compromising the ETC, in part as a result of HIF-1-mediated trans-activation of pyruvate dehydrogenase kinase-1 (Kim et al, 2006).…”

The significance of hypovolemia in dehydrational death in anurans

“…Sympathetic reflexes have been implicated in the maintenance of blood pressure (Sham~ .al,., 1984), the redistribution of blood flow (Hillman and Sommerfeldt, 1981), and the hydroosmotic (water uptake) response (Yokota and Hillman, 1984) in a number of anuran species. It should be possible to reduce dehydration tolerance using adrenergic blocking agents if adrenergically-mediated adjustments to hypovolemia are important to survival in dehydration.…”

“…Xenopus is particularly suited to this type of study because of its relatively low dehydration tolerance, insignificant bladder volume, and lack of any hydroosmotic response (Hillman, 1978a). Also, much is known about the physiological consequences of dehydration in this species (Hillman, 1978a;1978b;1980;Hillman and Sommerfeldt, 1981).…”