Vasovagal hypotension and vasopressin release

Mild vasovagal hypotension occurred in two normal male volunteers during insertion of indwelling venous cannulae. In spite of a rapid intravenous fluid load (3.6-4.6 litres in 90 min) both subjects passed little urine for 100 min. When the experiment was repeated without vasovagal hypotension, a rapid large diuresis followed the fluid load. The prolonged oliguria after vasovagal hypotension was the result of vasopressin release. This was demonstrated by measuring vasopressin in the blood and urine and by observing the renal response to a water load. The observation in man that a mild transient hypotensive episode may reduce urine flow for 100 min has clinical significance.