Paul O. Greeley

Pancreatic Diabetes in the Rabbit.

The diffuse distribution of the pancreas in the rabbit and the attending problems of surgical removal have prevented the study of pancreatic diabetes in this animal. In fact, it has been pointed out that “in rabbits the operation itself is impossible, because of the spread-out condition of the pancreas.” 1 However, a method for complete pancreatectomy is presented here together with data pertaining to insulin requirements, glycosuria, blood sugar levels, etc. The pancreas in general, is a thin sheet of tissue lying in the meso-duodenum with one large mass on the right between the portal vein and the vena cava and another mass in the mesentery of the spleen. At operation it is essential to use a Beebe binocular loupe to pick up the small fragments of pancreas which break off and to prevent injury to small intestinal blood vessels. For rabbits of about 2 kilos the anesthetic used is 1 cc. of nembutal intravenously, 0.2 cc. of 1% atropine subcutaneously and sufficient ether at the beginning to allow opening of the abdomen. Complete removal of the pancreas at one operation usually results in a very high mortality in from 24 to 60 hours from severe diarrhea, gastric detension, surgical shock, or unknown causes. A 3-stage operation with 3-4 weeks intervening between operations gives very satisfactory results. Three different abdominal incisions are used; for the first stage, about 1 inch to the left of the mid-line; for the second, a mid-line, and for the third about 1 inch to the right of the mid-line. Twenty-day chromic catgut size 00 is used for closing the abdomen. In the first stage, all pancreas in a pocket formed roughly by the transverse colon, stomach and duodenum is removed. A splenectomy may be done by ligating and sectioning the larger vessels, or the pancreas can be gently pulled off from the splenic vessels.

Sugar Utilization in Hypophysectomized Rabbits

The fact that serious hypoglycemia may develop in hypophysectomized rabbits and dogs is well known. 1 3-4 In preliminary experiments it was found that glucose must be administered to fasted hypophysectomized rabbits to prevent hypoglycemic convulsions and death. The animal requires large amounts of sugar even when the blood sugar level is low. The work reported here was concerned with the measurement of this requirement. The aim was to determine the minimum amount of glucose necessary to maintain a proper blood sugar level in fasted hypophysectomized rabbits. After a 3-day fast the pituitary was removed by an oral approach (Copes 5 ) modification of Whites method. 2 Frequent blood sugar estimations were carried out after the hypophysectomy. When the level had fallen to 80 mg. % or lower sufficient 10% glucose was given intravenously every hour thereafter to keep it from going lower. The rate of injection was adjusted according to whether the previous blood sugar had indicated the level was rising or falling. The interval between time of operation and time when the blood sugar began to drop varied in different rabbits from 11 to 32 hours. The amount of glucose required increased during the first 5 to 8 hours thereafter, by which time a maximum requirement was attained. There was little increase above this. Glucose was given in some cases by continuous intravenous injection. In a given animal, the amount required was the same whether the glucose was given at one hour intervals or by continuous injection. Urinary determinations for sugar were uniformly negative. The amounts of glucose which had to be injected during the period of maximum need is recorded in grams per kilo body weight per hour in Table I.

Measurement of Insulin Action.

The insulin required to maintain a normal blood sugar level in depancreatized dogs has been studied by Holm 1 and in the laboratories of Houssay 2 and Soskin. 3 , 4 Holm and Houssay found that 0.01 unit insulin per kilogram of body weight per hour was necessary. Soskin found values as low as 1-175th unit insulin per kg. per hour in dogs under pento-barbital sodium (Abbott). We have determined the insulin requirement in dogs of different sizes which have completely recovered from the pancreatectomy. These dogs were maintained at a constant weight on a measured balanced diet and sufficient insulin to keep the urine nearly sugar-free. They received no food or insulin for 24 hours prior to a determination. No anesthetic was used. The initial high blood sugar was lowered to about 100 mg.% by an intravenous injection of 2-6 units of insulin, depending upon the size of the animal. A continuous or hourly intravenous injection of a weak solution of insulin in physiological saline was started about 4-6 hours following the initial injection. An amount is given which will keep the blood sugar at about 120 mg. %. Table I summarizes the results on 4 different animals. Determinations of the insulin-glucose ratio were made. In one experiment the basal insulin requirement was increased from 0.21 unit insulin per hour to 0.41 unit and a continuous intravenous injection of 5% glucose was given. After 5 hours it was possible to inject 3.48 gm. of glucose per hour with the blood sugar constant at 125 mg. %. On the basis of the added insulin, the insulin-glucose ratio was therefore 1 unit to 17.4 gm. In another experiment 1 unit additional insulin per hour was added to the basal rate of 0.09 units insulin per hour, making a total of 1.09 units of insulin per hour. Eleven hours after starting the injection of glucose, 9.0 p. per hour were being given with a blood sugar of 116 mg. %. More experiments of this nature are in progress with varying amounts of insulin.

Cerebral, Head and Body Flow of Blood During Periodic Ventilation.

Periodic ventilation was produced in dogs under morphine-ure-thane anesthesia by (a) increased intracranial tension and (b) blocking of cerebral arteries. Practically complete control of head flow was obtained by ligating the vertebral arteries, and anterior spinal arteries and small arterioles of the cord, all in the region of the second cervical vertebra. All muscles at this level were severed. The vagi were left intact and one carotid was used for volume flow measurements. Blood volume flow changes were followed in the carotid and femoral arteries by the thermo-electric method (Gesell and Bronk. 1 The external jugular, vertebral, and femoral venous return was measured by the enclosed drop method; the submaxillary vein by the external drop. Blood pressure, ventilation, oxygen consumption, and time were simultaneously registered with the blood volume flow changes. Two types of respiration were obtained. Type 1 gave typical symmetrical Traube Herring blood pressure waves whose frequency was that of the respiratory waves. Apneas were either short (2 seconds) or lacking; respiration in other characteristics was quite normal. The depth of respiration decreased as the carotid flow increased, sometimes to the extent of apnea; as the flow decreased to a minimum, respiratory depth increased to a maximum. The respiratory depth again decreased as the flow increased. Type 2 was characterized by very pronounced blood pressure changes which were not typical Traube Herring waves. Apneas occurred. An apnea of 123 seconds was obtained in one animal during periodic breathing. The respiratory groups usually begin during some phase of the decreased flow or they may begin as late as the very end of decreased flow. Increasing respiratory movements may or may not carry on into the period of increasing blood flow.