Intracerebroventricular infusion but not bolus injection of vasopressin increases the cerebrospinal fluid pressure in awake rabbits.

The effect of intracerebroventricular infusion or injection of arginine vasopressin (AVP) was examined in awake rabbits with permanent ventricular cannulae. Intracerebroventricular infusion of artificial cerebrospinal fluid (CSF) 43 microliters min-1 containing AVP concentrations exceeding 0.4 ng ml-1, equivalent to an AVP infusion rate of 17.2 pg min-1, caused a dose-dependent increase in intracranial pressure (ICP) of 3 to 5 mmHg after 30-50 min of AVP infusion. Intracerebroventricular bolus injection of equivalent doses of AVP did not provoke changes in ICP. At the end of the experiments cisternal CSF concentrations of AVP were higher after infusion of AVP than after injection of the same amount of AVP. The mean arterial blood pressure increased slightly in the group of animals infused with AVP at rates above 17.2 pg min-1. It is concluded that intracerebroventricular infusion of AVP increases ICP in awake rabbits but the mechanism responsible for the elevation of ICP remains speculative.

Repetitive measurements of intracranial pressure in awake rabbits.

Previous measurements of the intracranial pressure in experimental animals suffer from acute and subacute effects of cannulation. In order to obtain reliable, repetitive or continuous values, we measured the intracranial pressures in awake rabbits with a new permanent adjustable ventricular cannula that included a separate entrance to the subarachnoid space. The mean intraventricular pressure ten days after the operation was 5.2 +/- 1.1 mmHg (SD) (70 animals). Manipulation of the cannula system and infusion of artificial cerebrospinal fluid did not damage the blood-brain barrier (indicated by extravasation of Evans Blue). The intracranial pressure was constant for as long as 6 months and as many as 22 separate measurements and infusions. The cerebrospinal fluid cells and protein content did not change in animals with permanent cannulae and in animals perfused with 2-4 ml artificial cerebrospinal fluid. In 30 animals the ventricular cannula functioned for 10-180 (median 65) days and the subarachnoid entrance for 11-23 (median 16) days.