ROLE OF VASOPRESSIN IN ESSENTIAL-HYPERTENSION - RACIAL-DIFFERENCES

Background Arginine vasopressin (AVP), in addition to being an antidiu retic hormone, might also have presser effects relevant to the mainten ance of hypertension. Results from several experimental and clinical s tudies suggested that the presser function of AVP is more important in low-renin hypertension and in the salt-loaded state and that it might be further maximized under sympathetic suppression. Objective To asse ss whether selective vasopressin receptor inhibition lowers the blood pressure in a racially diverse group of low-renin hypertensive subject s. Methods Thirty-nine hypertensive subjects (16 Caucasian, 23 African -American) eating a 200 mmol/day sodium diet were administered a singl e intravenous dose of a selective vasopressin receptor antagonist and their blood pressure was monitored constantly for the ensuing 3 h. The protocol was repeated 3 days later after treatment with a single oral dose of 0.4 mg clonidine. Results Of these patients, 54% had their bl ood sampled for determination of hormone profiles, African-Americans w ith hypertension had higher baseline plasma AVP levels than did Caucas ians (1.13 +/- 0.05 versus 0.37 +/- 0.06 pg/ml, respectively, P< 0.05) , and lower plasma renin activity (0.34 +/- 0.07 versus 1.03 +/- 0.08 ng/ml per h, respectively, P< 0.05). Selective vasopressin receptor in hibition lowered the mean arterial pressure in African-Americans but n ot that in Caucasians (lowering by 28 +/- 4 mmHg in African-Americans versus lowering by 5 +/- 3 mmHg in Caucasians, P< 0.05). Moreover, vas opressin receptor blockade further reduced the arterial pressure in Af rican-Americans but not that in Caucasians after pretreatment with clo nidine. Conclusion AVP seems to play a more important role as a presse r hormone in maintaining the elevation of arterial pressure in African -American hypertensives than it does in Caucasian hypertensives.