Fluid volumes during onset of spontaneous hypertension in rats

Abstract

Body fluid volumes were examined in young spontaneously hypertensive rats (SHR) and in 2 strains of age-matched normotensive controls to ascertain whether expanded plasma volume (PV) or extracellular fluid volume (ECFV) was associated with onset of spontaneous hypertension. Mean arterial pressure (MAP) was measured in conscious male SHR, Wistar-Kyoto normotensive (WKY) and American Wistar normotensive (NR) rats 3 h after arterial cannulation. At age 10-14 days there were no differences in MAP or PV (determined with 125I-albumin) between SHR and WKY. At age 18-43 days, SHR had elevated MAP and a small but significant elevation in total body water volume (TBWV; wet weight minus dry weight) compared to WKY and NR; no differences among the 3 groups were found in PV or ECFV (estimated with inulin). Evidence that expanded PV or ECFV act in the pathogenic mechanisms of spontaneous hypertension is not provided, but the possibility of altered vascular compliance is not excluded. The slightly elevated TBWV in SHR may be related to reduced body fat in SHR.