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.