Platelet vasopressin levels in childhood idiopathic nephrotic syndrome
H. Trachtman and B. Gauthier
Department of Pediatrics, State University of New York, Stony Brook.
Despite the importance of disturbances in plasma volume in nephrotic
patients, the only clinically accepted measurement of this value in common
use is plasma renin activity. We assessed the usefulness of plasma
vasopressin levels as an index of plasma volume in patients with idiopathic
nephrotic syndrome. However, since 80% to 90% of arginine vasopressin
circulates bound to platelets, we measured vasopressin levels in
platelet-rich and platelet-poor plasma. The nephrotic patients (n = 19) had
significantly higher vasopressin levels in platelet-poor and platelet-rich
plasma compared with controls (3.2 +/- 0.6 vs 1.0 +/- 0.3 pg/mL, and 10.4
+/- 3.6 vs 3.3 +/- 0.6 pg/mL. respectively). The percent binding of
vasopressin to platelets was reduced in nephrotic patients compared with
controls (50.2% +/- 6% vs 70.4% +/- 2.9%). The values for platelet-poor
vasopressin, but not platelet-rich vasopressin, correlated significantly
with the plasma renin activity (r = .83). We conclude that in nephrotic
patients, platelet-poor vasopressin levels correlate with plasma renin
activity and may provide a useful measure of minute-to-minute vasopressin
release in response to changes in plasma volume.
