 Randomized, placebo-controlled double-blind, crossover design study; 116 subjects randomized on Day 1 to obtain 98 completed subjects. Study will be composed of a 7-day period of therapy with randomized active or placebo treatment with a subsequent 6-8 day washout period, followed by a second 7-day period of double-blind therapy with the other agent. Ambulatory blood pressure measurement will be performed beginning on Day 7 of each treatment period following administration of the study drug. 