Stanley S. Hillman

Dehydrational Effects on Cardiovascular and Metabolic Capacity in Two Amphibians

Blood flow rate and metabolic rate during activity were measured at various degrees of dehydration in Bufo marinus and Rana catesbeiana to evaluate to what degree cardiac output and aerobic metabolism were compromised with dehydration. Both aerobic and cardiovascular capacity were compromised in a similar way with dehydration. Both aerobic capacity and flow were less compromised under equivalent dehydrational stress in the more dehydration-tolerant species, B. marinus. The principal reason for the decline in flow was a decrease in pulse volume. A reduction in the maximal heart rate was a secondary effector in both species. Associated with the decline in cardiac output was a decline in the arteriovenous pressure difference. Peripheral resistance increased in both species during dehydration. The increase in peripheral resistance could be accounted for by hemoconcentration influences on blood viscosity in B. marinus but were greater than predicted in R. catesbeiana, which indicates vasoconstriction in this species. The results in both species indicate that loss of plasma volume is the principal stress on maintaining cardiac output with a secondary effect of vasoconstriction contributing to the more rapid decline of blood flow in R. catesbeiana.

Physiological Correlates of Differential Dehydration Tolerance in Anuran Amphibians

oocyte maturation in vivo and in vitro. Developmental Biology 62:354-369. WIEBE, J. 0. 1968. The reproductive cycle of the viviparous sea perch, Cymatogaster aggregata Gibbions. Canad. J. Zool. 46:1221-1235. WOOTON, R. J. 1974. The inter-spawning interval of the female three spined stickleback, Gasterosteus aculeatus. J. Zool. Lond. 172:331-342. SCHOOL OF LIFE AND HEALTH SCIENCES AND COLLEGE OF MARINE STUDIES, UNIVERSITY OF DELAWARE, NEWARK, DELAWARE 19711. Accepted 16 Nov. 1978.

The effects of erythrocythemia on blood viscosity, maximal systemic oxygen transport capacity and maximal rates of oxygen consumption in an amphibian.

Summary1.Graded erythrocythemia was induced by isovolemic loading of packed red blood cells in the toad,Bufo marinus. Blood viscosity, hematocrit, hemoglobin concentration, maximal aortic blood flow rate and maximal rates of oxygen consumption were determined after each load.2.Blood viscosity was related to hematocrit in the expected exponential manner; ln η=0.43+0.035 Hct (Fig. 2).3.Maximal blood flow rates in the dorsal aorta were inversely proportional to blood viscosity and fit predictions of the Poiseuille-Hagen flow formula (Fig. 3). The effect of increased blood viscosity was to reduce aortic pulse volume, but not maximal heart rate (Figs. 4, 5).4.Maximal systemic oxygen transport capacity (aortic blood flow rate x hemoglobin concentration x O2 binding capacity of hemoglobin) was linearly correlated with the maximal rate of oxygen consumption (Fig. 6).5.These data indicate that optimal hematocrit theory is applicable for maximal blood flow rates in vivo, and that systemic oxygen transport is the primary limitation to aerial

Thermoregulatory Response to Heat in the Waterproof Frogs Phyllomedusa and Chiromantis

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The hemodynamic consequences of hemorrhage and hypernatremia in two amphibians

max in amphibians.

An analysis of respiratory surface area as a limit to activity metabolism in anurans

Bufo marinus is more tolerant of dehydration than Rana catesbeiana. Dehydration led to increases in plasma sodium, protein, and hematocrit. The increases in plasma protein concentration were greater in both species than predicted from passive concentration during dehydration, indicating protein redistribution to the vascular space. Increases in hematocrit with dehydration were delayed in Bufo, indicating that plasma volume was maintained. The colloid osmotic pressure of plasma increased with protein concentration during dehydration, as predicted by data for mammals. Venous blood pressures did not vary with dehydration in either species. Interstitial fluid pressure became more negative with dehydration. The balance of transcapillary fluid forces predict ultrafiltration during all stages of dehydration in Rana and during dehydration below 24% in Bufo. The transcapillary forces do not predict the fluid redistribution to the plasma space, which is consequently attributed to lymphatic return. The changes in plasma protein concentration during dehydration are consistent with lymphatic return. Greater interstitial fluid volumes may be an important corollary of enhanced tolerance to dehydration.

EFFECTS OF TEMPERATURE AND PHYSICAL ACTIVITY ON BLOOD FLOW SHUNTS AND INTRACARDIAC MIXING IN THE TOAD BUFO MARINUS

The thermal relations of waterproof frogs of two genera (Phyllomedusa and Chiromantis) were studied in an outdoor enclosure and, in the laboratory, in a thermal gradient, in a heated wind tunnel, and under an imposed radiant heat load. When allowed to move freely in a thermal gradient, no frogs showed a distinct preferred temperature, although Chiromantis spp. consistently avoided the cool end of the gradient. Both Chiromantis spp. and Phyllomedusa sauvagei voluntarily tolerated high body temperatures of 38 and 40 C, respectively. When subjected to a convective heat load, either outdoors or in the laboratory wind tunnel, both C. xerampelina and P. sauvagei allowed body temperature (Tb) to track air temperature (Ta) until Tb reached 38-39 C. Further increases in Ta resulted in little or no increase in Tb, whereas evaporative water loss (EWL) increased in direct proportion to the temperature difference (Ta − Tb) and with wind speed to the power of about 0.4. Phyllomedusa azurae increased water loss at a lower Tb (ca. 35-36 C) and did not regulate as precisely. A similar pattern was seen when frogs were subjected to rapid radiant heating. A sudden increase in EWL was observed when Chiromantis spp. reached a body temperature of 39 C and when P. azurae reached 35 C. Glands in the skin begin secretory activity when EWL increases, and the mechanism for thermoregulation in these frogs is apparently analogous to sweating.

Lymph Pools in the Basement, Sump Pumps in the Attic: The Anuran Dilemma for Lymph Movement

Maximal aerobic metabolic rates (MMR) in vertebrates are supported by increased conductive and diffusive fluxes of O2 from the environment to the mitochondria necessitating concomitant increases in CO2 efflux. A question that has received much attention has been which step, respiratory or cardiovascular, provides the principal rate limitation to gas flux at MMR? Limitation analyses have principally focused on O2 fluxes, though the excess capacity of the lung for O2 ventilation and diffusion remains unexplained except as a safety factor. Analyses of MMR normally rely upon allometry and temperature to define these factors, but cannot account for much of the variation and often have narrow phylogenetic breadth. The unique aspect of our comparative approach was to use an interclass meta-analysis to examine cardio-respiratory variables during the increase from resting metabolic rate to MMR among vertebrates from fish to mammals, independent of allometry and phylogeny. Common patterns at MMR indicate universal principles governing O2 and CO2 transport in vertebrate cardiovascular and respiratory systems, despite the varied modes of activities (swimming, running, flying), different cardio-respiratory architecture, and vastly different rates of metabolism (endothermy vs. ectothermy). Our meta-analysis supports previous studies indicating a cardiovascular limit to maximal O2 transport and also implicates a respiratory system limit to maximal CO2 efflux, especially in ectotherms. Thus, natural selection would operate on the respiratory system to enhance maximal CO2 excretion and the cardiovascular system to enhance maximal O2 uptake. This provides a possible evolutionary explanation for the conundrum of why the respiratory system appears functionally over-designed from an O2 perspective, a unique insight from previous work focused solely on O2 fluxes. The results suggest a common gas transport blueprint, or Bauplan, in the vertebrate clade.