Identification of vasopressin as a principle affecting work (105).-This study was carried out with the collaboration of Professor C. H. Li of the University of California. The rats were subjected to the work test immediately following operation. Stimulation was continued until the death of the rat or for forty-eight hours. The following operations were represented: sham, adrenalectomy, hypophysectomy, and adrenalectomy-hypophysec-tomy. Hormones were administered by continuous intravenous injection. In confirmation of earlier studies it was found that certain pituitary extracts contain a principle which has an extra-adrenal effect upon the work performance of the hypophysectomized rat. The principle was separable from corticotropin and differed from each of the known anterior lobe hormones and from oxytocin and intermedin. It was found that minute amounts of pure vasopressin added to adrenal cortex extract will normalize the work of adrenalectomized-hypophysectomized rats under the conditions of these experiments. Vasopressin was present in anterior pituitary extracts which supported work.

Effect of posterior pituitary lobectomy on work (90).-Immediately following removal of the posterior pituitary, there is a decrease in work output which can be corrected by treatment with adrenal cortex extract and vasopressin. Also in acute experiments, adrenal cortex extract can fully correct the work deficit of the anterior lobectomized rat when the posterior lobe remains present and functional. The work output of rats having one-half an anterior lobe remaining is much greater than that of completely hypophysectomized rats and is still greater, although subnormal, when the posterior lobe and one-half the anterior lobe remain in situ. This is true immediately following operation and at thirty days postoperatively.

Work Performance Of Tumor-Bearing Rats (85)

Rats bearing the transplantable Walker carcinoma 256 show a decrease in vigor, even when the tumor is small (three-day growth). The decrease in work output is related to the weight of the tumor at autopsy. Tumors implanted subcutaneously seem more toxic to the host than tumors implanted into muscle.

Growth. The Metabolic Behavior Of The Eviscerated Rat

A series of experiments concerned the factors which affect the level of plasma amino acids in the eviscerated rat. It was shown that a number of hormonal and other factors affect the level of plasma amino acids in the absence of the liver, pancreas, and gut.

Male rats were eviscerated at a weight of 250 gm. Intravenous infusions into the saphenous vein were made by a continuous injection machine.

Effect of hydrocortisone on the level of plasma amino acids (186).-Amino acid concentrations in the plasma were determined at six- and eighteen-hour intervals, at 26° and 320, respectively, in adrenalectomized, eviscerated rats given continuous intravenous infusions of glucose with and without insulin. An additional nephrectomy was done in one experiment. Cortisone acetate and hydrocortisone (non-esterified) each accelerated the rise of plasma amino acids under all the conditions tested.

Effect of epinephrine upon the level of plasma amino acids (102).-Large doses of epinephrine (5-20 µg in 20 ml/24 hr) cause a rise in plasma amino acids in the presence of insulin but not in the absence of insulin. There was no apparent relation between changes in the level of blood glucose and changes in the level of plasma amino acids.

Effect of tumors on the level ofplasma amino acids (103).-It was anticipated that a growing tumor in the eviscerated rat would suppress the rise of the plasma amino acid level which follows evisceration; the contrary was true. The rise is more rapid in rats which are hosts to a Walker carcinoma. The differences were evident at three and six hours following evisceration and in the presence and absence of insulin. The level of plasma amino acids is not elevated in tumor hosts prior to evisceration.

Level of plasma amino acids in eviscerated rats given glucose and fructose with and without insulin (104).-Insulin suppresses the rise of plasma amino acids in eviscerated rats. One hypothesis as to how the effects of insulin upon the metabolism of carbohydrate and protein are related holds that insulin stimulates the utilization of carbohydrate to meet energy requirements (thereby averting the need to catabolize protein) and also supplies the energy needed for protein synthesis.

It has been claimed that fructose is better utilized than glucose in the absence of insulin. The possibility that fructose would substitute for insulin in suppressing the rise in plasma amino acids was tested. Functionally eviscerated rats were given continuous intravenous infusions of either glucose or fructose, or fructose with and without insulin for a period of three hours. The level of plasma amino acids was suppressed by insulin but was not significandy changed when fructose was substituted for glucose.

Time-response effect of insulin upon the level of plasma amino acids in the eviscerated rat (108).- In a time-response study the levels of plasma amino acids were determined at fifteen-minute intervals following operation. It was shown that insulin causes a temporary fall below normal values and that this effect is demonstrable within fifteen minutes after the injection of insulin.

It seems probable that insulin stimulates the synthesis of proteins from plasma amino acids as well as inhibiting the peripheral breakdown of proteins, but the actual shifts in metabolism which account for these changes are not known.

Comparative effects of muscle work and insulin upon plasma amino acids and blood glucose (107, 83).-The relationship between the effects of insulin upon the utilization of carbohydrate and upon the metabolism of amino acids and proteins is not understood, although it is commonly assumed that the effects of insulin upon protein metabolism are secondary to a primary action upon the utilization of carbohydrate. Both insulin and muscle work increase the transfer of glucose and other sugars into cells (Levine, R., and Goldstein, M. S. Recent Progress in Hormone Research, 10:343, 1955). It has been suggested that the increase in the rate at which glucose enters the cell represents the primary action of insulin, and all other consequences of its action are secondary. In this study, stimulation of muscle had an insulin-like effect upon the glucose tolerance of the eviscerated rat. The effect upon glucose tolerance of a combination of muscle work (faradic stimulation of muscle of the anesthetized rat) and of optimal doses of insulin is greater than either one alone. Insulin suppresses the rise in plasma amino acids following evisceration of the rat, but muscle work does not.

Complement Titer In The Eviscerated Rat (20a)

Blood was drawn from the abdominal aorta. Complement titrations were performed by either the 100 per cent end point visual method, or by the 50 per cent hemolysis end point determined photometrically (Kabat, E. A., and Mayer, M. Experimental Immunochemistry. Springfield, 111.: Charles C Thomas, 1948).

The findings by the two methods show a depression of complement which is marked by sixteen hours, and more profound by twenty-four hours. The complement titers of sham-operated rats remain essentially unchanged. In eviscerated-rat sera no anticomplementary activity could be demonstrated. These data support the suggestions that complement is synthesized in liver. The removal of other intra-abdominal organs did not suppress complement.

The inability of the eviscerated animal to synthesize complement may be related to failure of blood-clotting in these animals. The decrease in blood complement may offer a partial explanation for failure of eviscerated animals to resist infectious diseases.

Summary Of Observations On The Eviscerated Rat

The eviscerated rat remains responsive to hormonal and other agents which affect metabolism in intact animals. The dramatic effects of insulin upon protein metabolism are not correlated with changes in the level of blood glucose or in glucose tolerance. It seems probable that the effect of insulin on the metabolism of protein is not secondary to the effect of insulin upon the utilization of carbohydrate.