1. The effect of 25° head-up tilt on blood pressure, urinary catecholamines, and creatinine clearance has been studied in untreated essential hypertensive patients and normotensive subjects.

2. The mean rise in diastolic pressure for all subjects with hypertension was 4.9 mmHg which did not differ significantly from the mean rise of 5.4 mmHg in the normal subjects. Ten of forty-one hypertensives had a diastolic pressure response greater than the response in any of eleven normal subjects, with a rise of greater than 10 mmHg.

3. The increase in urinary noradrenaline excretion with tilt was greater in these orthostatic hypertensive patients (1.74 μg/h) than in either the remaining hypertensive (0.34 μg/h) or the normotensive subjects (0.56 μg/h). Overall there was a significant correlation between changes in diastolic blood pressure and urinary noradrenaline.

4. Creatinine clearance was reduced by tilting. The mean reduction was similar for normally reacting hypertensive and normotensive subjects (6.0% and 7.2% respectively). The ten orthostatic hypertensive patients, however, had a greater reduction in creatinine clearance (23.4%), and in the hypertensive group as a whole changes in diastolic blood pressure and creatinine clearance were negatively correlated.

5. Those patients with excessive response to tilt tended to be young, not obese, and with recent onset of hypertension when documentation of this was adequate.

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