NHP referred to our outpatient clinic will be enrolled (150 newly recruited) in acute saline test for phenotype characterisation of PNat relationship(7). For each patient we will collect urine and blood samples for standard clinical biochemistry, including electrolytes, creatinine, EO, aldosterone, plasma renin activity, urinary uromodulin (ELISA), urinary and serum uric acid and blood samples for genetic test.

Acute salt load test: after the equilibration period and achievement of a steady state, a constant-rate i.v. infusion of 2 L of 0.9% NaCl was carried out in 2 hours. BP (mean of 3 measurements taken 3 minutes apart) was measured every 30 minutes during the 2 hours of loading and 3 times at 3-min intervals at the end of the infusion. These last 3 BP values were averaged and used in the analysis.

The results of these tests will be added to an already collected database of salt load test collected in the previous studies (already published)

Inclusion Criteria:

• age 18 to 65years;
• body mass index (BMI) <30 kg/m2;
• Na intake, evaluated as urinary Na excretion of <300 mEq/24 hours; .office systolic BP (SBP) >140 mm Hg and diastolic BP (DBP) >90 mm Hg in 3 consecutive visits to their family doctors.

Exclusion criteria:

• Female patients
• history of myocardial infarction,
• stroke,
• congestive heart failure,
• liver disease, secondary cause of hypertension,
• diabetes,
• severe hypertension (>160/110 mm Hg),
• abuse of drugs or alcohol, .creatinine clearance < 80 mL/m.

Secondary forms of hypertension (e.g. primary aldosteronism) were ruled out with specific investigations when deemed appropriate

We enrolled newly discovered, never treated, mild hypertensive male patients in the 'Outpatient Clinic for Hypertension' of San Raffaele Hospital, Milan (Italy)