Effect of vasopressin on intracranial pressure of rabbit

Effect of vasopressin on intracranial pressure (ICP) was examined by an intraventricular administration of the hormone to a rabbit. ICP was determined at the cisterna magna with a manometer and recorded automatically with a recorder. An injection of over 150 micro U of vasopressin lowered ICP, but there was no clear dose-response relationship of the effect of vasopressin on ICP. When vasopressin was injected intraventricularly after lowering ICP by an intravenous injection of acetazolamide which inhibits the production of cerebrospinal fluid (CSF), an additive effect of the hormone on ICP was observed. The effect of vasopressin on excretion of water in CSF was examined by the determination of drainage of tritiated water injected into the lateral ventricle of a rabbit. Drainage of radioactive water into vein was measured by collection of blood at the internal jugular vein and radioactivity of the plasma was counted. Vasopressin accelerated excretion of tritiated water into vein. These results indicate that vasopressin facilitated drainage of CSF into vein to lower ICP.