Some aspects of anuran metabolism are examined, with special emphasis on possible limitations to aerobic metabolism and the effect of chronic hypoxia acclimation on maximal rates of aerobic metabolism and the metabolic fate of lactic acid accumulated after anaerobic metabolism.

Offprints of the author's articles inserted / Bibliography: leaves 130-141 / viii, 141, 25 leaves, [2] leaves of plates : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Zoology, 1986

This thesis presents two separate experiments concerning aerobic and anaerobic amphibian energetics. The first study (Part I) investigates differential alterations in the kinetics of the anaerobic enzyme lactate dehydrogenase, in nine species of anurans with varying natural histories. The second study (Part II) studies changes in different anaerobic and aerobic physiological parameters in a single species (Rana catesbeiana) after six weeks of chronic exercised, unexercised-captive and for field frogs. The common theme of these two experiments involves the potential for physiological changes due to environmental stress. Part I examines different species to infer a possible evolutionary relationship to environmental stresses at the molecular level of lactate dehydrogenase. Part II comprises the effects on captivity on aerobic and anaerobic capacities of R. catesbeiana,

The importance of hypovolemia in dehydrational death was assessed in two anuran species. Xenopus laeyis, a species which experiences a significant reduction in circulating plasma volume with dehydration, was used to evaluate the role of sympathetic reflex compensation in hypovolemia. Adrenergic blockade with propranolol or phenoxybenzamine produced no significant reduction in dehydration tolerance in this species, although β-blockade with propranolol appeared to have a minor effect. The role of hypovolemic shock in the terminal circulatory collapse that precedes death in dehydrating anurans was investigated in the toad, Bufo marinus. The activity of lysosomal proteinases (cathepsins) was used as an indicator of the shock state. An assay was developed for the determination of cathepsin activity in toad plasma and was used to demonstrate the presence of proteinases similar in pH dependence to mammalian cathepsins Bl and D. Plasma cathepsin D-type activity increased with dehydration in toads but was not significantly different from the activity in controls or in toads subjected to splanchnic artery occlusion. Toads appear to maintain plasma volume to 20% water loss at the expense of other extracellular fluids. These results do not support the hypothesis that hypovolemia is a direct cause of dehydrational death in anurans.

Two aspects of possible adaptation In cardiovascular performance caused by Increased plasma electrolytes were examined. Cells In anisotonic plasma may either act as osmometers or volume regulate. Blood flow rate Is dependent upon cell viscosity, which in turn is a consequence of cell volume and membrane deform-ability. Cell volume changes which Increase membrane deform-ability will thus potentially extend the limits of dehydration tolerance. It was found in R. catesbeiana and B. marinus that red blood cell Is maintain constant volume during dehydration. Cells in vitro Initially lose water, but then sodium, potassium and water move Into the cell. Cell viscosity within the physiologic range of hematocrits was higher In salt loaded non-regulating cell Is of B. marinus than In regulating isotonic cells.