Osmoregulation of thirst and vasopressin release in severe chronic renal failure

Subjects with severe chronic renal failure (CRF) have higher plasma concentrations of arginine vasopressin (AVP) than normal subjects, and some develop severe thirst. Eight patients with CRF and seven matched controls underwent hypertonic saline infusion to explore the relationship of thirst and plasma AVP with plasma osmolality. Differences in urea concentration between the two groups were controlled for by correcting measured osmolality to a urea of zero. Linear regression analysis of the relationships between plasma AVP and thirst with plasma osmolality (corrected for urea) was performed. Mean results were: control, pAVP = 0.26 (pOsmc - 283.7) versus CRF, pAVP = 0.72 (pOsmc - 282.0); and control, thirst = 4.0 (pOsmc - 279.4) versus CRF, thirst = 3.5 (pOsmc - 281.8). The apparent sensitivity (slope) of AVP release was greater in severe CRF than in normal controls (P = 0.04). There was no significant difference between the groups in thirst sensitivity, threshold for thirst onset and threshold for AVP release. Osmoregulated thirst was normal in severe CRF, but increasing osmolality leads to higher concentrations of AVP than would be expected.