Adipsic diabetes insipidus (ADI) occurs in association with a heterogenous group of conditions. We report vasopressin (AVP) responses to hypotension in nine patients with ADI and nine controls. Hypertonic saline infusion produced absent thirst (1.7 ± 1.7 to 1.5 ± 1.7 cm, P = 0.99) and AVP responses (0.3 ± 0.1 to 0.4 ± 0.1 pmol/liter, P = 0.99) in the ADI group, who also drank less than the control group (258 ± 200 ml vs. 1544 ± 306 ml, P < 0.001). Intravenous infusion of trimetaphan camsylate produced a fall in mean arterial pressure of 31.6% ± 8.9% in patients and 29.4% ± 6.1% in controls. Plasma AVP concentrations rose from 1.4 ± 0.8 to 340.3 ± 497.4 pmol/liter (P < 0.001) in the control group. In three patients with craniopharyngioma, there was no rise in plasma AVP concentrations (0.3 ± 0.1 to 0.3 ± 0.1 pmol/liter, P = 0.96), but plasma AVP rose significantly in response to hypotension in the other six patients (0.4 ± 0.2 to 204.5 ± 223.2 pmol/liter, P < 0.001). We concluded that the AVP responses to hypotension in ADI are heterogenous and reflect the site of the lesion causing the diabetes insipidus.

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