1. Plasma vasopressin was estimated in 20 normotensive, 46 moderate hypertensive and 14 severe hypertensive patients under normal sodium diet.
2. In moderate hypertensive patients basal values for plasma vasopressin (PVP) after overnight dehydration and 24 h urinary vasopressin (UVP) were respectively 1.82 ± 0.23 pmol/l and 44 ± 4 pmol/day, which were not different from those found in normal subjects (PVP = 1.14 ± 0.11 pmol/l and UVP = 54 ± 4 pmol/day). In contrast, basal values were significantly increased in severely hypertensive patients (PVP = 4.69 ± 1.45 pmol/l, P < 0.005; UVP = 107 ± 17 pmol/day, P < 0.01).
3. In a group of 12 moderately hypertensive patients the blood pressure reduction induced by a single 20 mg dose of nifedipine was associated with an increase in PVP from 1.48 ± 0.57 to 2.48 ± 0.74 pmol/l (P < 0.05) and in UVP from 42 ± 7 to 67 ± 17 pmol/day (P < 0.05). On the other hand, a single dose of captopril (1 mg/kg body weight) administered to the same patients did not alter PVP (1.68 ± 0.43 pmol/l) and UVP (40 ± 6 pmol/day) despite a similar blood pressure decrease.
4. In a group of 10 severely hypertensive patients, the blood pressure reduction induced by the first dose of captopril (1 mg/kg) was correlated to the pretreatment level of PVP (r = 0.89, P < 0.001) and of UVP (r = 0.70, P < 0.01). Eight days of captopril treatment reduced PVP from 5.24 ± 1.38 to 1.18 ± 0.32 pmol/l (P < 0.01) and UVP from 68 ± 17 to 25 ± 3 pmol/day (P < 0.001).
5. Increased levels of vasopressin are a marker of severe forms of hypertension. The reduction of vasopressin during captopril treatment could be an additional mechanism underlying the anti-hypertensive effect of that drug. Moreover, from the comparison between nifedipine and captopril, it appears that antihypertensive drugs have different effects on vasopressin release.
