Deciphering the Role of Vasopressin in Primary Aldosteronism.

CONTEXT: The role of vasopressin (AVP) in the pathophysiology of primary aldosteronism (PA) remains unclear.

OBJECTIVES

The primary aim of this study was to investigate AVP secretion in PA by measuring the plasma concentration of copeptin (PCop), the C-terminal portion of provasopressin. The secondary aim was to assess renal sensitivity to AVP.

DESIGN AND

SETTING

This was a cross-sectional study in a tertiary-care hospital.

PROTOCOL: We recruited 115 patients with PA, 48 patients with essential hypertension (EH), and 108 normotensive healthy subjects (HS). Blood was sampled for biochemical and hormonal evaluations in fasting condition after 1-h rest in supine position. Osmolality was determined in 24-h urine. PCop was determined by immunoassay.

MAIN OUTCOME MEASURE: The main outcome measure was adjusted difference in PCop between groups.

RESULTS

After adjustment for sex, body mass index, systolic blood pressure, natremia, and kalemia, PCop was significantly higher in patients with PA than in HS (geometric mean ratio, 1.61; 95% confidence interval [CI], 1.26-2.06; P < .0001) and patients with EH (1.40; 95% CI, 1.08-1.82; P = .0070) PCop was positively correlated with natremia (P = .0094). Urine osmolality was significantly lower in patients with PA than in HS (0.82; 95% CI, 0.74-0.92; P = .0002) and 24-h urinary output was significantly higher in patients with PA than in HS (1.32; 95% CI, 1.11-1.56; P = .0005). The relationship between urine osmolality and PCop was shifted downward in patients with PA but was similar in patients with EH and HS, indicating peripheral resistance to AVP.

CONCLUSION

PCop increases in patients with PA in response to an increase in natremia and a renal resistance phenomenon, indicating that AVP release is chronically stimulated in PA.