Effect of endogenous vasopressin on blood flow to choroid plexus during hypoxia and intracranial hypertension.

Exogenous vasopressin decreases blood flow to the choroid plexus and production of cerebrospinal fluid. Some studies indicate that hypoxia and increases in intracranial pressure (ICP) produce increases in circulating vasopressin. We examined the hypothesis that endogenous release of vasopressin decreases blood flow to the choroid plexus during hypoxia and increased ICP. Blood flow to the choroid plexus was measured in anesthetized rabbits using microspheres. Hypoxia increased cerebral blood flow more than twofold but had little effect on blood flow to the choroid plexus. In contrast, hypoxia produced a marked increase in blood flow to the choroid plexus in the presence of a vasopressin V1-antagonist, [d(CH2)5Tyr(Me)]AVP. During intracranial hypertension, blood flow to the choroid plexus decreased from 409 +/- 42 to 295 +/- 25 ml.min-1 x 100 g-1 (means +/- SE; P < 0.05 vs. control) when ICP was increased from 1 to 40 mmHg. The vasopressin antagonist inhibited the decrease in blood flow to the choroid plexus in response to increased ICP. Thus release of vasopressin during hypoxia and increased ICP have a constrictor effect on blood vessels of the choroid plexus. Plasma levels of vasopressin increased minimally during hypoxia and increased ICP, which suggests that sources of vasopressin other than plasma affect blood vessels of the choroid plexus. We propose that endogenous vasopressin may play a protective role during hypoxia and intracranial hypertension by a negative feedback mechanism to reduce blood flow to the choroid plexus.