REN and hematocrit: Significant data from our laboratory and others have documented that angiotensin II (AII) and the renin–angiotensin system (RAS) play a critical role in maintenance of arterial BP and that this hormonal system is elevated in several experimental models of HT, as well as human essential HT (Cowley 1992; Reinhart et al. 1995; Lenkei et al. 1997; Weir and Dzau 1999; de Gasparo et al. 2000; Lifton et al. 2001; Doris 2002).