The relationship between antidiuretic hormone and plasma or urine osmolalities during water restriction test and hypertonic saline loading test in normal children--a change in the apparent tubular response to AVP during these two tests.

We present here the results of water restriction test (WRT) and hypertonic saline loading test (HSLT) in normal children. Maximal urine osmolality during WRT (W-Umax; 1040 +/- 154 mOsm/kg) may be age-dependent (W-Umax = 812 + 23*age, r = 0.52, p < 0.05), although maximal arginine vasopressin (AVP) levels during WRT did not show any correlation with age. The relationship between plasma osmolality (Posm) and AVP during HSLT in children (AVP = 0.31* (Posm-277)) was similar to that in normal adults. A plateau urine osmolality during HSLT (H-Umax) was 713 +/- 109 mOsm/kg. It did not increase with age. AVP levels 3 h after the infusion did not correlate with age. Minimal AVP and Posm values (about 6 pg/ml, 295 mOsm/kg, respectively) for creating H-Umax apparently existed during HSLT. The minimal AVP value (about 6 pg/ml) for H-Umax (during HSLT) was higher than the AVP levels (2.41 +/- 1.37 pg/ml) at W-Umax (during WRT). W-Umax (1040 +/- 154 mOsm/kg) was significantly higher than H-Umax (713 +/- 109 mOsm/kg). Judging from the above comparison of AVP and Uosm (W, H-Umax) at the plateau state of WRT and HSLT in normal children, a change in the apparent tubular response to AVP may be one of the important factors to maintain circulatory volume (CV).