THE EFFECT OF HYPOPHYSECTOMY AND CEREBRAL MANIPULATION IN THE DOG UPON THE RESPONSE OF THE BLOOD SUGAR AND INORGANIC PHOSPHORUS TO INSULIN

Abstract

The intracranial approach for the removal of the hypophysis involves craniotomy and incision of the dura mater, retraction of the right temporal lobe, and interference in the region of the base of the brain (excision of the gland and application of cautery to the stalk). In this study the insulin sensitivity of 3 groups of dogs, in which the various stages had been performed, was compared with the normal. Craniotomy and radial incision of the dura did not alter sensitivity to insulin; but dogs in which all 3 manipulations had been performed, i.e., a complete hypophysectomy, showed a greatly increased sensitivity to the hormone. A dose of insulin (1/16 unit per kgm.), that in normal dogs led to av. max. drops of 5-8% in blood sugar and 7-10% in blood inorganic P produced in the 7 completely hypophysectomized dogs av. max. reductions of 21-52% in blood sugar and 16-41% in inorganic P. Though subsequent microscopic study of serial sections of the whole hypophyseal region of all 4 dogs that were subjected to the first 2 manipulations (craniotomy and retraction of the right temporal lobe), revealed normal hypophyses, the insulin reaction of only one of these dogs can be considered entirely normal. It is indeed striking that at 3 mos., after a cranial operation involving no apparent mechanical interference with the hypophysis, the injection of 1/16 unit of insulin per kgm. should have resulted in a drop in blood sugar to the extent of 46% and in inorganic P of 31%. The augmented sensitivity to insulin produced in dogs by craniotomy and retraction must be the result of the latter manipulation, for dogs in which craniotomy and radial incision of the dura had been performed responded to insulin in a normal manner. The mechanism whereby operative manipulation of the cerebral hemisphere is capable of producing a variable but significant increase in sensitivity to insulin is not yet known. The many structures, with as yet poorly understood functions, that are present in the small area around the pituitary gland make it difficult to avoid injury to one tissue while attempting to affect another. Hence identification of the structure or structures responsible for insulin sensitivity can be at present only a matter for speculation.