On the Nature of Insulin Convulsions

Abstract

With the injection of doses of insulin just adequate to induce convulsions, the animal will usually exhibit only clonic convulsions, but if twice that dosage be given to this same animal, tetanic convulsions usually result. If the low sugar level be the sole cause of the convulsions, then why would their character change with the increased dose? With doses of insulin adequate to render an animal convulsive, or even sub-convulsive, animals, as well as man, exhibit evidence of a functionally modified nervous system long before the true blood sugar level has fallen to zero and before any convulsions appear. Some of the evidences of this functional modification are marked salivation, profuse sweating, pupillary changes (dilation just before the onset of the convulsions and hippus often accompanied by nystagmus during the seizure), marked restlessness and increased sensitivity to stimuli such as light or noise.

The barbiturates are being employed both clinically as well as experimentally for the prevention of insulin convulsions. In a search for the mechanism for this action of the barbiturates, the question arose as to whether the drug modified the effect of a convulsive dose of insulin upon the blood sugar. Table I summarizes some of the results.

The resulting values approximate the true sugar level of zero as found by Dotti. 1 In no case, however, were there any signs either of convulsions, or even of the prodromal signs. Although no glucose was administered, none of these animals died despite the fact that the true blood sugar levels remained at or near the zero level for at least the 3-hour observation period. Apparently, the protective mechanism of the barbiturate is independent of the blood sugar concentration. This would seem to indicate either that the drug so affects the central nervous system that it does not respond to the low sugar concentration in the usual manner, or that insulin has some effect on the central nervous system which is unrelated or, at most, related only indirectly to the low sugar level.