A sensitive and specific radioimmunoassay for arginine vasopressin was used to compare the relative importance of changes in plasma osmolality, angiotensin II and dopamine in the regulation of vasopressin secretion in man. One hour after water loading plasma vasopressin fell from 0.40 to 0.06 pmol/l, while 8 h and 24 h fluid restriction resulted in a rise of vasopressin from 0.29 to 0.54 and 1.37 pmol/l respectively. In contrast neither dietary sodium deprivation, when plasma angiotensin II increased 5-fold, nor dopamine infusion, at a rate which increased circulating dopamine levels up to 244-fold, had any effect on basal plasma vasopressin values. These results confirm that, under physiological conditions, osmoregulation is the major mechanism controlling vasopressin release and suggests that circulating angiotensin II and dopamine have no significant part to play.

1. Arginine vasopressin was infused at 0.5, 2, 6, 18 or 54 ng min(-1) kg(-1) for 1 hr into normal, sham-operated and DOCA-salt hypertensive rats. Complete vasopressin/blood pressure dose-response curves were constructed from circulating plasma vasopressin concentrations measured at the end of each infusion. 2. DOCA-salt hypertensive rats had a higher basal plasma vasopressin concentration (11.1 +/- SD 3.7 fmol/ml) than either the normal (3.9 +/- 2.3, P less than 0.01) or the sham-operated rats (4.5 +/- 2.4, P less than 0.01). 3. The DOCA-salt hypertensive rats did not have my detectable enhancement of pressor sensitivity, compared with either of the two normotensive groups. 4. There was no significant increase in blood pressure in either the normal rats or sham-operated rats until vasopressin was infused at 2 ng min(-1) kg(1), when the plasma concentration was between 30 and 40 fmol/ml. 5. Subpressor infusion of vasopressin in the normal and sham-operated rats, which gave plasma concentrations of 22-23 fmol/ml, completely suppressed plasma angiotensin II to levels similar to the basal values found in the DOCA- salt hypertensive rats (10.5 +/- 2.3, 14.5 +/- 4.5 and 8.0 +/- 1.6 fmol/ml respectively). 6. These findings suggest that the mechanism of vasopressin involvement in DOCA-salt hypertension is as yet unclear, that short-term changes in vasopressin concentration appear unimportant in the regulation of normal blood pressure, that small physiological changes of vasopressin in normal rats may be important in the regulation of renin secretion, and that the increase in vasopressin concentration seen in DOCA-salt hypertension may contribute to the suppression of renin and angiotensin II in this state.

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