Depletion of neurohypophyseal content of vasopressin in septic shock

OBJECTIVES To assess the mechanisms underlying the inappropriately low plasma vasopressin levels reported in septic shock. DESIGN Prospective case series. SETTING A 26-bed general medical intensive care unit at a university hospital. PATIENTS Septic shock patients. MEASUREMENTS AND MAIN RESULTS In three consecutive patients with septic shock, plasma vasopressin levels, circulating vasopressinase activity, baroreflex sensitivity, and neurohypophyseal vasopressin content were assessed. Plasma vasopressin concentration was unexpectedly within normal range in two patients (1.6 pg/mL and 1.8 pg/mL) and increased in one (16 pg/mL). In all cases, vasopressinase activity was undetectable, baroreflex sensitivity was decreased, and the high signal intensity of the posterior lobe of the pituitary gland on T1-weighted magnetic resonance images was absent. Magnetic resonance imaging and plasma vasopressin levels normalized after recovery from shock in the patient who survived. CONCLUSION These data suggest that in septic shock, inappropriately low plasma levels of vasopressin are at least partly related to a depletion of vasopressin stores in the neurohypophysis.