Central blood volume in spontaneously hypertensive rats and Wistar-Kyoto normotensive rats

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Abstract
Central blood volume and total blood volume were determined in spontaneously hypertensive rats and Wistar Kyoto rats at 6 and 12 wk, representing borderline hypertension and early established hypertension, respectively. A technique was used where plasma and erythrocyte indicators were injected into conscious rats. Blood volume in the cardiopulmonary compartment, present in the resting awake steady-state, could then be estimated by sudden freezing of the entire rat; 12 wk old spontaneously hypertensive rats showed a decreased total blood volume, while the blood fraction contained in the cardiopulmonary area was significantly increased compared with that of normotensive Wistar Kyoto rats. In 6 wk old spontaneously hypertensive rats, total blood volume was only marginally decreased but a tendency towards centralization of the blood was seen. Along with the development of hypertension in the spontaneously hypertensive rat their decreasing blood volume tends to become increasingly centralized to the cardiopulmonary area. Both neurohormonal influences and structural wall changes in the low-pressure capacitance side may contribute to this.