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1. In 10 normal subjects water immersion to the neck at 35°C produced a highly significant natriuresis and diuresis. 2. Urinary prostaglandin E levels did not change significantly throughout immersion. 3. During the diuresis of water immersion a suppression of urinary antidiuretic hormone occurred.

1. We studied 12 normotensive non-ketotic diabetic patients during poor metabolic control, with sustained hyperglycaemia, and again, after an interval of 3 weeks, when metabolic control was improved. On each occasion we measured blood pressure, total exchangeable sodium, plasma volume, transcapillary escape rate of albumin, and plasma concentrations of angiotensin II and aldosterone. 2. With improved diabetic control there was a small but significant fall in arterial pressure. Total exchangeable sodium was normal when control was poor but rose significantly to above normal with improved control. 3. Plasma volume also rose significantly with improved control, and the transcapillary escape rate of albumin fell and the intravascular mass of albumin rose. 4. Plasma angiotensin II and aldosterone concentrations were significantly above normal during poor metabolic control, but fell to normal with improved control. 5. These findings indicate a resetting of the relationship between blood pressure and exchangeable sodium when diabetic control improves. The association between exchangeable sodium and concentrations of angiotensin II and aldosterone also appears altered in diabetic patients. These changes associated with varying metabolic control must be considered when studying cardiovascular disease in diabetic patients.

1. Thermoneutral water immersion produces a physiological increase of thoracic blood volume, raises central venous pressure and increases urinary sodium excretion by a hitherto ill-understood mechanism. We have investigated whether this enhanced sodium excretion could be mediated by the recently discovered natriuretic factor, atrial natriuretic peptide (ANP). 2. During water immersion there was a highly significant (P < 0.001) twofold increase of the mean plasma ANP concentration and a doubling of the mean urinary sodium excretion. Both were unchanged during the control experiments. 3. These results are consistent with the hypotheses (a) that ANP is released into plasma in response to central blood volume expansion and (b) that it functions as a natriuretic hormone in normal man under physiological conditions.