Role of blood viscosity in the regulation of hematocrit in tail-suspended rats (Rattus norvegicus) treated with pentoxifylline.

Abstract

Previous studies have shown a significant increase in hematocrit with initial exposure to microgravity condition, with a corresponding return to normal hematocrit values with continued exposure to microgravity. Tail suspension studies have been used to mimic microgravity on earth and have shown similar changes in hematocrit. High hematocrit is correlated with increased blood viscosity. As such, increased blood viscosity during the initial exposure to microgravity may be a factor signaling the reduction ofthe hematocrit with continued exposure to microgravity. The purpose of this study was to use tail-suspension to investigate the role of blood viscosity might play in the regulation of hematocrit. Seventy Sprague-Dawley (male) rats were randomly assigned to control and tail suspended groups. All rats were given the drug pentoxifylline which should cause a reduction in blood viscosity. Suspended and control rats were monitored for hematological changes including blood viscosity over 4h, 24h, 72h, and 168h of tail suspension as well as during recovery periods from tail suspension of 24h, 72h, and 168h. Hematocrit, red blood cell count, MCV, MCH, and MCHC were not significantly different between control and experimental groups at any time. There was no significant difference in blood viscosity and plasma viscosity between control and experimental groups. Further, it appeared that pentoxifylline had little effect on blood viscosity. The lack of a significant difference in hematocrit between control and tail suspended animals makes it difficult to determine if blood viscosity acts as a regulator of hematocrit.