Vasopressin, Urine Concentration, and Hypertension

Abstract

Bankir et al. (1) report that young, healthy black individuals concentrate urine significantly more than matched white individuals and excrete lower urine volumes. In addition, they found that, among men, pulse pressure was significantly higher in normotensive black individuals than in white individuals, although there was no significant difference in systolic and diastolic BP. These findings refocus attention on vasopressin as a hypertensive hormone, however with a new mechanistic twist and a novel interpretation of an ethnic difference. Bankir et al. also report a direct association between urine concentration and pulse pressure in men but not in women. Again, the correlation coefficient was stronger in black men than in white men. This early difference may be important because elevated pulse pressure is associated with an increased risk for cardiovascular events. The authors suggest that vasopressin could contribute to hypertension via its antidiuretic effects and that vasopressin V2 receptor antagonists might lower BP. Possibly, vasopressin plays a greater role in individuals with blunted renin-angiotensin system, as is the case in black individuals. Acutely, this notion has experimental support (2).In their analysis, Bankir et al.(1) relied on a data set that was generated at Indiana University Medical Center 35 yr ago. Neither urine osmolarity nor vasopressin was measured in the Indiana University protocol. Nevertheless, the studies were performed meticulously on a metabolic ward. The patients were in similar states of electrolyte intake, and the BP measurements were controlled carefully. Such broad-based metabolic studies can never be performed again, so data dredging (now termed "data mining") for the purpose of hypothesis generation is a legitimate enterprise. In this case, the data that were collected allowed the a posteriori calculation of a urine concentration index. Another data set that would be amenable for examination of this hypothesis further could be provided by the International Study of Sodium, Potassium, and Blood Pressure (INTERSALT) study (3). In INTERSALT, more than 10,000 people were studied worldwide with meticulous 24-h urine collections and random-zero BP measurements. Urine volume, electrolyte, creatinine, and urea excretion were measured in every individual, allowing a more precise calculation of urine solute excretion and concentration. With this data set, a more precise analysis of any relationships among urine concentration, sodium concentration, urine volume, and BP could be performed. Gender differences and ethnic comparisons also could be examined if only the INTERSALT investigators would accept external analyses of their data set.Support for the authors' idea is provided by another recent study by Bankir et al. (4) that reported that V2 receptor stimulation reduces sodium excretion in normal humans. In that study, infusion of a V2 receptor agonist, dDAVP, reduced sodium excretion concomitant with an increase in urine osmolality and a decrease in urine volume. The inclusion ...

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