Figure 20-21 Baroreflex-induced arginine vasopressin (AVP) depletion in dogs. A, Section of the posterior pituitary gland (neurohypophysis) from a normal dog. The macrovesicles are stained with antivasopressin serum, a reaction indicative of replete stores of vasopressin. B, Section of the neurohypophysis from a dog after severe hemorrhagic hypotension (mean arterial pressure, <40 mm Hg) for 1 hour. The minimal staining with antivasopressin serum is indicative of profound baroreflex-induced depletion of AVP stores. (Reprinted, by permission, from Landry DW, Oliver JA: The pathogenesis of vasodilatory shock. N Engl J Med 345:588–595, 2001.)