The effect of alloxan diabetes on experimental cholesterol atherosclerosis in the rabbit

A comparison was made of the effects of cholesterol feeding in normal rabbits and in rabbits rendered persistently diabetic by means of alloxan. In the two groups of animals hypercholesterolemia of comparable degree was induced by the feeding procedure. Nevertheless, the severity of the atherosclerosis of the aorta produced in the diabetic rabbits was much less than in the non-diabetic control animals. Indeed, a large proportion of the diabetic animals presented no atherosclerosis whatever. There was a similar inhibition of the deposit of lipid substances in the liver, spleen, and adrenal glands of the diabetic rabbits. The inhibition of the development of experimental cholesterol atherosclerosis which was associated with the presence of alloxan diabetes was independent of the administration of alloxan per se. It was not dependent on the sex or weight of the animal, nor upon the daily dosage of cholesterol, the form in which it was administered, nor the duration of cholesterol feeding. It was also independent of changes in body weight occurring during the course of our experiments and of the actual degree of hypercholesterolemia induced by the administration of cholesterol. In addition, there was no gross or histological evidence of a morphological basis for the inhibitory effect either in the aorta or in the other organs in which it was observed. Only two factors were observed to be consistently associated with the inhibition of the expected morphological effects of cholesterol feeding, namely, the diabetic state and a degree of visible lipemia considerably greater than that observed in the control animals. The inhibitory effect observed in these experiments would appear to depend upon some as yet undetermined factor or factors implicit in the diabetic state or closely associated with it. The experimental data presented demonstrate clearly that hypercholesterolemia is not the sole factor concerned in the genesis of experimental cholesterol atherosclerosis, but that another factor, or factors, rendered inoperative in our experiments must be essential to the production of the arterial lesions. In view of the inhibitory effect on the development of experimental cholesterol atherosclerosis observed in alloxan-diabetic rabbits, the effect of alloxan diabetes on the retrogression of such arterial lesions was studied in another series of experiments. No effect on retrogression could be demonstrated within periods lasting up to a maximum of 4 months after the cessation of cholesterol feeding. The results of our two series of experiments, considered together, indicate that the process of deposition of lipids in the arterial walls is governed by factors different from those that are operative in the process of removal of lipids after they have been deposited. The inhibition of the development of experimental cholesterol atherosclerosis in alloxan-diabetic rabbits must depend on interference with the process of deposition of lipids and not on a process of removal of lipids as fast as they are deposited. Our experimental results find no direct application to the problem of arterial disease in human diabetes. Nevertheless, the experimental procedures that we have employed provide a new basis for the design of further experiments directed toward the elucidation of the nature of the unknown factors that govern the process of lipid deposition in the walls of arteries.

Activation of quiescent mucormycotic granulomata in rabbits by induction of acute alloxan diabetes

In normal rabbits subcutaneous granulomata produced by the injection of a spore suspension of Rhizopus oryzae remained confined to the site of inoculation, showed no fungus proliferation, no longer yielded the agent on culture 10 weeks after inoculation, and eventually healed. Similar well established granulomata in rabbits with acute alloxan diabetes induced 8, 10, and 15 days after injection of the fungus uniformly showed activation of the infection. This occurred only in animals showing acetonuria. In these animals the skin lesions showed proliferation of the fungus frequently associated with invasion and early necrosis of the granuloma wall. In some instances, spread of the infection to adjacent tissues with invasion of blood vessels had occurred. These experiments illustrate that changes in host metabolism can activate a preexisting quiescent infection.

The development of the acute inflammatory response to experimental cutaneous mucormycosis in normal and diabetic rabbits

The histologic changes associated with the development of the acute inflammatory response to experimental cutaneous mucormycosis were studied at various times from 5 minutes to 24 hours after inoculation into normal rabbits and in rabbits with acute alloxan diabetes and acidosis. In normal animals the response by polymorphonuclear leukocytes began within a few minutes after inoculation, increased rapidly in extent and intensity and reached its peak within 6 to 12 hours. By that time there was also early proliferation of fibroblasts and of large mononuclear cells and these cellular reactions, together with the accumulated granulocytes, began to produce a demarcation of the lesions. Beginning 4 to 6 hours after inoculation the fungus showed some growth but this remained confined to the necrotic center of the lesions. In the diabetic rabbits the onset of the response by polymorphonuclear leukocytes was delayed by several hours, reduced in intensity and was apparently less effective. There was no proliferation of fibroblasts and the lesions were spreading rather than circumscribed. Fungus growth in the tissues began shortly after inoculation, was marked, progressed rapidly, and soon extended beyond the site of inoculation. The large mononuclear cells, however, appeared at about the same time and in equal number in the lesions of both diabetic and non-diabetic animals and showed no morphologic changes. It is concluded that a significant delay and impaired effectiveness of the response by polymorphonuclear leukocytes, a lack of fibroblastic proliferation and an enhanced growth of the fungus lower host resistance to infection with it and are directly consequent on severe alterations in host metabolism.

Myocardial removal of free fatty acids under normal pathological conditions

Myocardial arteriovenous difference in free fatty acids (FFA) and coronary flow was determined in dogs under morphine-chloralose anesthesia. Fifteen minutes after the administration of insulin the A-V difference decreased. FFA uptake did not change significantly. Alloxan diabetes decreased the utilization per cent of FFA. Norepinephrine elevated myocardial uptake and arterial FFA. Hypoxia did not change FFA uptake. Hypothyroidism lowered myocardial uptake. Left ventricular O2 consumption increased after administration of atropine in both normal and hypothyroid animals, whereas hypothyroidism was associated with a decreased value. A significant correlation was found in normal dogs between arterial FFA concentration and myocardial uptake. A different relationship suggested itself in hypothyroid animals. A correlation was also shown between the per cent of myocardial O2 consumption calculated for complete oxidation of FFA and the myocardial R.Q.