Tissue wet weight as well as total protein content, 5’-nucleotidase activity, alkaline phosphatase activity and Ca2+ accumulation associated with a plasma membrane fraction isolated from spontaneous hypertensive rats (SHR) and rats with deoxycorticosterone (DOC) induced hypertension were investigated. Enhanced alkaline phosphatase activity and reduced ATP-dependent Ca2+ accumulation preceded the development of hypertension in SHR and these effects were reversed by DOC withdrawal followed by lowering of blood pressure in DOC hypertension. Increased arterial tissue wet weight and 5’-nucleotidase occurred only at the later stage of hypertension in SHR and the increased tissue wet weight was not reversed by DOC withdrawal in DOC hypertension. These observations suggest that enhanced alkaline phosphatase and reduced ATP-dependent Ca2+ uptake may play a significant role in initiating hypertension, while increased arterial wet weight and 5’-nucleotidase activities may participate in the maintenance of hyperte