The investigators are proposing that individuals with elevated levels of NT-proBNP are resistant to natriuretic peptides and are unable to handle sodium loads and maintain optimal blood pressure values.The investigators will test this hypothesis by comparing the blood pressure response to low and high salt diets in individuals with pre- or hypertension and who have normal or elevated levels of NT-proBNP. The investigators expect that blood pressure values in those with normal levels of NT-proBNP will not change with high salt diets, whereas, in those with elevated levels of NT-proBNP, blood pressure values will increase significantly when exposed to high salt diets.