Abstract:
Many amphibians experience low temperature conditions associated with hibernation. Decreasing temperature results in increased viscosity, thereby potentially affecting blood flow. Therefore, amphibians might have difficulty maintaining blood flow at low temperatures. As bullfrogs hibernate underwater, the hibernation microenvironment may have low oxygen levels making it hard for them to oxygenate tissues. The purpose ofthis study was to evaluate hematological properties and blood viscosity in hibernating bullfrogs (Rana catesbeiana), a species better able to extract oxygen from its aquatic environment than some other hibernating ectothermic species. Blood was collected from bullfrogs submerged in aerated water for 20 or 50 days at 5°C, as well as 0 day bullfrogs exposed to 5°C but not submerged. A group of bullfrogs kept at 25°C served as a room temperature, nonhibernating group for comparison. No significant differences were found in hematocrit, hemoglobin, red blood cell count (RBCC), or mean cell volume (MCV) among the four groups of bullfrogs. Mean cell hemoglobin (MCH) showed a significant decrease (P=0.001) in the 0 and 20 day submerged bullfrogs compared to 50 day submerged bullfrogs. The values for mean cell hemoglobin concentration (MCHC) were significantly lower (P=0.001) in 20 day submerged bullfrogs relative to 0 and 50 day submerged bullfrogs. Apparent viscosity,
plasma viscosity, and relative viscosity (apparent viscosity/plasma viscosity) measurements were obtained and showed no significant differences among the four groups. Plasma osmolality significantly decreased (P<O.OO 1) in SoC groups relative to the 2SoC group. The results of this study suggest bullfrogs are able to extract sufficient amounts of oxygen from well-aerated water, negating the need of any hematological increases. However, because of the initial increase in hematocrit and decrease in plasma osmolality of 0 day bullfrogs, it is possible that bullfrogs in this study are trying to maintain an optimal hematocrit during hibernation.
