Small doses of intracarotid insulin do not lower plasma glucose in the rat

We sought to confirm the observation that 500 microU of insulin injected into the carotid artery of rats lowers plasma glucose by approximately 20 mg/dl within 2 minutes. In our hands, glucose concentrations fell gradually by approximately 20-25 mg/dl over a 45-60 minute period after insertion of a carotid artery cannula. This occurred whether 500 microU of insulin and/or anti-insulin serum or saline were injected toward the heart. There was no change in glucose concentrations following injection of 500 microU of insulin toward the head 45 minutes after insertion of the cannula. Thus, the hypoglycemic response to small amounts of insulin administered to the head via the carotid artery must be very sensitive to factors that are currently difficult to recognize.