Effect of D-glucosamine on glucose metabolism and insulin action in the rat intact diaphragm

Previous studies in this laboratory demonstrated that insulin, when administered simultaneously with glucosamine, significantly lowered the hyperglycemic effect of the latter. This result conflicts with reports suggesting that glucosamine competes with glucose at the site of insulin action. To explore further this apparent contradiction, the effect of insulin and glucosamine on glucose metabolism by the intact rat diaphragm preparation was studied. The distribution ratio of glucose-1-14C and glucosamine-1-14C, the glycogen content, and the 14CO2 production were measured in the presence or absence of insulin after 90 and 120 min incubation. Insulin increased glucose and glucosamine penetration 7 and 4 times respectively. Glucosamine did not interfere with glucose entry into the cell either in the presence or absence of insulin. Glycogen synthesis was not impaired by glucosamine, although glucosamine itself did not contribute to glycogen formation. 14CO2 production from glucose-1-14C was markedly depressed by glucosamine, and glucosamine-1-14C did not contribute to 14CO2 production. These results indicate that in muscle tissue, glucosamine interferes neither with the glucose transport across the cell membrane, nor with the metabolic pathway of glucose to glycogen; but glucosamine, or a metabolic intermediate, does inhibit some metabolic step in the breakdown of glucose to CO2.

Evaluation of the relative pathogenic roles of diabetes and serum cholesterol levels in the development of cardiovascular lesions in rats

Previous studies in our laboratory demonstrated that in partially pancreatectomized diabetic rats fed an atherogenic diet containing 5 per cent cholesterol, serum lipid levels rose higher and cardiovascular lesions were more frequent than in nondiabetic rats fed the same diet for three to seven months. This experiment posed the question: Didthe diabetic state per se or the higher levels of cholesterol associated with it account for the greater number of lesions in the diabetic animals?

To answer this question, the experiment was repeated, but this time some of the diabetic rats were fed diets with lower amounts of cholesterol than before in order to keep their serum cholesterol levels within the same range as those of the nondiabetic animals (intact or partially pancreatectomized but normoglyceinic) fed the basal atherogenic diet.

As before, diabetic rats fed the athero genie diet containing 5 per cent cholesterol developed higher levels of serum cholesterol and more lesions than similarly fed nondiabetics. Other serum lipids were also higher in this group, especially triglycerides and free cholesterol.

When serum cholesterol levels in the diabetic animals were not permitted to exceed those in the nondiabetics, the incidence of vascular lesions in the two groups did not differ.

The diabetic state per se in this mode, therefore, seemed to play a pathogenic role in atherogenesis by elevating serum lipid levels. Results would indicate that, under theseconditions, at any given level of serum lipid, the diabetic artery is not more susceptible than a nondiabetic artery to this type of atherogenic stimulus.

Presence of synalbumin antagonist in siblings of diabetic children

Synalbumin antagonist was investigated in a group of forty-eight siblings of diabetic children. Nine parents of these patients, ten normal controls and eleven diabetic children were included in this study. In twenty-six of the forty-eight siblings synalbumin was detected. Glucose uptake by the rat hemidiaphragm was depressed from a mean of 13.36 to 0.99 mg. per cent of glucose per 10 mg. of tissue in ninety minutes incubation in the presence of 1,000 μU. of insulin. In five of nine parents tested, synalbumin was present. In only three of fourteen families in which two or more siblings were studied was synalbumin absent. These findings suggest a familial distribution of the antagonist. Fasting blood sugar, glucose tolerance test and plasma insulin were normal in synalbumin positive siblings. Negligible amounts of immunoreactive insulin were detected in the albumin extracted from nondiabetic relatives. The synalbumin did not interfere with the immunoassay of insulin. In extracts of insulin treated diabetics, various amounts of insulin were found. Five of eleven diabetics showed antagonism, three were border line, and three did not show antagonism. The results obtained suggest that synalbumin may be used as a genetic marker and encourage further investigation to assess the role of this inhibitor in the development of diabetes and as an indicator of prediabetes.

The state of insulin in human plasma

In plasma obtained from normal fasting subjects insulin was precipitated by anti-insulin serum. Both the precipitate and the supernatant were extracted with acid-alcohol. Insulin or insulin-like activity was measured in the extracts by immunoassay, glucose uptake by the rat hemi-diaphragm and CO2 production by the rat epididymal fat pad. The amount of insulin found in plasma before extraction was quantitatively recovered from the insulin-anti-insulin precipitate extracted with acid-alcohol as measured by the immunoassay. No insulin was detected in the extracted supernatant. In close agreement were the results obtained with the diaphragm. Only the adipose tissue was able to demonstrate ILA in the extracted supernatant. This ILA was present even in control samples (buffer with known amounts of Crystalline Insulin added) in spite of the fact that all the added insulin had been recovered in the precipitate.

These results suggest that in normal human plasma all the insulin is readily available to react with insulin antibodies. Results with the epididymal fat pad method stroagly suggest the possibility that factors other than insulin stimulate the production of CO2 from glucose.

Dietary control of serum cholesterol levels in rats fed high-fat, cholate-containing diets

In a series of experiments, rats were fed semisynthetic atherogenic diets containing variable amounts of cholesterol (from 0 to 5%) with 40% of either cocoa butter, dairy butter, corn oil, or linseed oil as the source of fat, and 2% sodium cholate. It was found that serum cholesterol levels increased as the amount of dietary cholesterol increased to the 1% level, but raising the dietary cholesterol above this level did not provoke a proportional change in serum cholesterol during the first 3 months of the experiment.

Insulin secretion in glucosamine-induced hyperglycemia in rats

The hyperglycemia response produced by the injection of glucosamine in rats has been studied by comparing the effects of equal doses of glucosamine and glucose on blood glucose, circulating insulin, and pancreatic insulin content. The effect of glucosamine and glucose on insulin release from the islets has been studied in vitro by incubating slices of pancreas from normal rats and from rats injected with glucosamine. After glucosamine injection, the blood glucose rose and the circulating insulin decreased. In the glucose-injected group the hyperglycemia was lower and the circulating insulin higher. Insulin output from incubated pancreatic slices of normal rats rose when the glucose concentration in the medium was increased or when tolbutamide was added. A decrease below the base line occurred on the addition of glucosamine or when pancreas slices from glucosamine-injected rats were incubated. Insulin injection decreased the hyperglycemic effect of glucosamine whereas tolbutamide was ineffective. These results suggest that glucosamine exerts an inhibitory effect on insulin release from the pancreas.