Effects of infused administration volume on clinicochemical parameters and histopathology in vehicle control rats

Infusion studies run during the last 10 years in three rat strains with different flow rates of saline as vehicle were compared as to a potential impact of infused volume on clinicochemical values and histopathology. There were no effects on white and red blood counts, except for a possible slight decrease of red blood cells with concomitant increase of reticulocytes after infusion of higher volumes over several weeks. There was also no volume-related effect on enzyme activities, metabolites/substrates, thyroid hormones and electrolytes in peripheral blood. As anticipated urinalyses proved an increase of excreted urine volume with increased infusion volume, while excreted protein, urine density and pH were not changed. Histopathological changes specific for intravenous infusion via indwelling catheter were seen in lungs, spleen and along the course of the catheter. Neither frequency nor severity of these findings was changed in relation to volume in the three rat strains examined. However, animal numbers are small for each rat strain examined and studies were run over almost 10 years. The impact of potential genetic drift, methodical changes and/or a change of infusion accessories (especially catheter) is unknown. An exchange of data and experience between laboratories should help differentiate between incidental and true effects.