The Effects of Estradiol Treatment on the Blood Viscosity of the Bullfrog Rana catesbeiana

Increased levels of certain plasma proteins, particularly fibrinogen, immunoglobulins, and lipoproteins, result in increased blood viscosity. Upon estrogen exposure, amphibians release an additional protein into the plasma, the yolk protein vitellogenin. The purpose of this study was to investigate the effect of estrogen exposure on the blood viscosity of the bullfrog (Rana catesbeiana) as a result of increased plasma vitellogenin levels. Mean plasma total protein concentrations were nearly three times higher in estradiol treated frogs (30.52 ± 10.50 mg/ml) than in control animals (11.98 ± 3.50 mg/ml), likely because of increased vitellogenin levels. Mean plasma viscosity also was significantly greater in the estradiol treated animals (2.02 ± 0.41 cP) as compared to the control group (1.35 ± 0.06 cP). However, there was no significant difference in apparent (whole) blood viscosity at packed cell volumes of 10, 30, or 50% at any of the shear rates tested. Relative blood viscosity in the estradiol treated frogs was not significantly different from control animals. These results suggest that estradiol treatment had no effect on red blood cell deformability and that vitellogenin, unlike other lipoproteins, may not be involved in the aggregation of red blood cells. Such a lack of aggregation would be beneficial in maintaining normal blood viscosity in the face of high plasma vitellogenin concentrations, thereby maintaining ease of blood flow during the egg developing season.