Cerebral Blood Flow Changes During Insulin and Metrazol (Pentamethylenetetrazol) Shock

The use of insulin and metrazol in shock therapy for schizophrenia is now well known.

Using a greatly modified, flexible thermoströmuhr simultaneous records of blood flows in carotid artery and meningeal branch of the jugular vein were made in rabbits throughout the course of 128 shock experiments.

Normal venous and arterial blood flows were recorded for one hour. Blood was taken for initial glucose determination.∗ Insulin was injected subcutaneously (2 units per kilo). Blood sugars were estimated at half-hour intervals for 1 1/2 hours, after which 15-minute samples were taken. Blood flow readings were taken at intervals of 2 minutes or less.

The animals usually developed convulsions within 1 1/2-2 hours (Fig. 1). At the onset of the convulsions the blood sugar was always 6 mg % or less. During the convulsions the blood sugar was always undetectable. In the coma stage, following the initial convulsion, the blood sugar fluctuated from 6 mg % to 8 mg %. Spontaneous secondary convulsions frequently occurred, during which time the blood sugar was again undetectable.

At the onset of the primary convulsion the blood flow (Fig. 1) in the cerebral branch of the jugular vein increased very markedly, even up to 50%, while at the same time the arterial blood flow remained constant. This initial phase was followed by a simultaneous decrease in both arterial and venous flow to as low as 25% of the normal level.

In cases where the animals did not go into convulsions there were no significant changes in blood flow, even though the blood sugar had decreased from 95 mg % to 6 mg %.

Shock was induced by metrazol injections in another series of animals prepared in a manner similar to that already described. It has been found that typical convulsions are produced in rabbits (2-3 kilo) by the intravenous injection of 0.75 cc of a 4% solution of metrazol in distilled water.