Blood pressure variation and the risk of essential hypertension have an important genetic component. In most cases susceptibility to essential hypertension is likely determined by the action of more than one gene.

The identification of genes causing susceptibility to hypertension is important, since it would give new tools for the diagnosis and enable better etiological classification and specific treatment of the disease.

The innovation of this study is to use the response to antihypertensive therapy as an intermediate phenotype.

In the study, each subject uses one of four antihypertensive drugs, each as a monotherapy in a rotational fashion, for 28 days in a randomized order. The antihypertensive drugs to be tested include a thiazide diuretic, a beta-adrenergic antagonist, an angiotensin-II receptor antagonist and a calcium channel blocker. The drugs that are selected for the study are "typical" representatives of their groups and long-acting, and the dosages are sufficient but well tolerable.

Blood pressure variation and the risk of essential hypertension have an important genetic component. In most cases susceptibility to essential hypertension is likely determined by the action of more than one gene.

The identification of genes causing susceptibility to hypertension is important, since it would give new tools for the diagnosis and enable better etiological classification and specific treatment of the disease. Finland is an ideal place for a study like this because of the genetic homogeneity of the population, the relatively high prevalence of the disease and the established protocols for the treatment and follow-up of hypertension in public health care.

The molecular genetic studies on hypertension performed so far (by 1999) have primarily been association studies, which are based on case-control classification and may produce erroneous results. Particularly, a reliable phenotyping of cases and controls has been difficult. Consequently, more attention should be paid to the phenotyping of patients, and novel intermediate phenotypes characteristic of certain subtypes of hypertension should be used to facilitate the search for hypertension genes. The innovation of this study is to use the response to antihypertensive therapy as an intermediate phenotype.

In the study, each subject uses one of four antihypertensive drugs, each as a monotherapy in a rotational fashion, for 28 days in a randomized order. The antihypertensive drugs to be tested include a thiazide diuretic, a beta-adrenergic antagonist, an angiotensin-II receptor antagonist and a calcium channel blocker. The drugs that are selected for the study are "typical" representatives of their groups and long-acting, and the dosages are sufficient but well tolerable. The study design does not necessitate the use of equipotent doses of the various agents, since the study is not designed to compare the antihypertensive effectiveness of the study drugs or, due to the short treatment periods, their effects on clinical endpoints.

Inclusion Criteria:

• essential hypertension diagnosed on an earlier occasion or during the present study (three diastolic blood pressure readings >=95 mmHg on separate occasions are required).

Exclusion Criteria (before and during the study):

• usage of three or more antihypertensive drugs
• secondary hypertension
• left ventricular hypertrophy
• drug-treated diabetes mellitus
• coronary heart disease
• stroke and other disorders of cerebral circulation
• renal disease
• obstructive pulmonary disease
• a disease treated with corticosteroids
• a disease with drug treatment potentially influencing blood pressure levels
• significant obesity (BMI >=32 kg/m2)
• allergic reaction towards any of the study drugs
• The patient is excluded from the study if his blood pressure level rises to 200/120 mmHg or above during the study.

Based on self-representation of gender identity

The placebo tablets and drugs are packed in similar gelatin capsules.