Insulin binding to monocytes and total mononuclear leukocytes from normal and diabetic patients

Isolated circulating mononuclear leukocyte preparations were obtained from 19 normal and 11 adult diabetic patients. No differences in monocyte, T cell, or B cell content were found when preparations from the two study groups were compared. The amount of insulin bound to cells from the diabetic patients was found to be decreased regardless of the cell type to which the data were normalized. This indicates that the previously reported decrease in the ability of mononuclear cells of diabetic patients to bind insulin was not a result of differences in mononuclear cell subpopulation.

Postprandial plasma triglyceride and cholesterol responses to a low-fat meal

Postprandial plasma cholesterol and triglyceride (TG) levels were measured after the consumption of a relatively low-fat (35% of calories) diet in 41 subjects. Plasma cholesterol levels did not change appreciably during the postprandial state. In 34 subjects a biphasic plasma TG response curve was noted, with an initial peak occurring 1 to 3 hr after feeding and a secondary TG peak 4 to 7 hr after the meal. The primary peak was greater than 90%, accounted for by chylomicrons, whereas the secondary peak represented very low-density lipoproteins (greater than 82%). Furthermore, the heights of the primary and secondary peaks were closely correlated to the fasting TG level (r = 0.61 and 0.72, respectively) indicating that the fasting TG concentration is an important determinant of the postprandial TG response. Because low-fat (high-carbohydrate) diets are known to raise fasting TG levels in patients who do not have fasting hyperchylomicronemia, and because relatively few patients have chylomicrons in the fasting state, these data suggest that such diets may lead to day long increases in plasma TG levels in the majority of subjects.

Induction of hypertriglyceridemia by a low-fat diet

We have studied the effects of moderate dietary fat restriction on plasma triglyceride, cholesterol, glucose, and insulin response in 27 subjects. Compared with a control diet (45% fat, 40% carbohydrate [CHO], 15% protein) the low fat (higher CHO) diet (30% fat, 55% CHO, 15% protein) produced a 41% increase in fasting triglyceride level (155 +/- 17 to 219 +/- 23 mg%) with no change in fasting plasma cholesterol level. Furthermore, this increase in triglyceride levels; induced by the higher CHO content of the low fat diet, was seen in 26 out of 27 subjects. Postprandial triglyceride, glucose, and insulin levels were also higher on the low fat (higher CHO) diet. Since hypertriglyceridemia is a significant risk factor for the development of coronary heart disease, and since our data indicate that the moderate increase in dietary CHO associated with a low fat diet will elevate plasma triglyceride levels, we believe that more caution is necessary before recommending the wide-spread use of low fat diets for heart disease prevention.

Effect of food deprivation and hypophysectomy on in vitro protein synthesis by membrain-bound and free hepatic ribosomes

The protein synthetic activities of membrane-bound and free hepatic ribosomes isolated from intact rats fed ad libitum, and normal rats subjected to food restriction to match that of hypophysectomised (Hx) rats were compared to the in vitro protein synthetic capacity of hepatic ribosomes isolated from Hx rats. Hypophysectomy resulted in decreased protein synthetic ability of bound ribosomes, whether protein synthesis was directed by endogenous messenger RNA (mRNA) (p less than 0.05) or by polyuridylic acid (polyU) (p less than 0.01). In contrast, the protein synthetic activity of free hepatic ribosomes from Hx rats was reduced when protein synthesis was directed by endogenous mRNA (p less than 0.05) but, when polyU was substituted as the messenger, the protein synthetic activity of these free ribosomes was equal to that of control rats. On the other hand the effects of food restriction on hepatic ribosomal function could be clearly differentiated from the effects observed following hypophysectomy. Thus, the reduced protein synthetic activity of hepatic bound ribosomes isolated from food restricted normal rats was not demonstrable, when polyU was used to direct protein synthesis. Further, food restriction had no effect on the protein synthetic activity of free hepatic ribosomes, and this was true when protein synthesis was directed by either endogenous or artificial messenger. It is concluded that hypophysectomy reduces the protein synthetic ability of both bound and free hepatic ribosomes, and this change of ribosomal function of Hx rats cannot be attributed to their decreased food intake.

Hypercalcemia in acute uremia and following citric acid administration: differential effect on parathyroid gland microtubule content

Hypercalcemia, which occurs 4 hr after bilateral nephrectomy in normal rats, is not seen 4 hr after either bilateral ureterotomy or sham surgery. These results indicate that it is loss of renal mass per se, not the uremic syndrome, which is responsible for the hypercalcemia. Citric acid levels also increase 4 hr after nephrectomy, and a degree of hypercalcemia and hypercitricemia comparable to that which follows nephrectomy can be produced by administration of citric acid to normal rats. In an attempt to evaluate the role of the parathyroid gland in the development of hypercalcemia in these two situations, the microtubule content of parathyroid gland chief cells was determined by ultrastructural sterologic techniques 4 hr after either bilateral nephrectomy or citric acid administration. The results of these measurements indicate that parathyroid gland chief cell microtubule content increases after citric acid administration but not following bilateral nephrectomy. The significance of these results is not clear. However, since a previous study has suggested a correlation between increased microtubule content and increased secretory status in the chief cell, one may speculate that increased microtubule content resulting from citric acid administration may also be associated with increased parathyroid hormone secretion. By this formulation, citric acid-induced hypercalcemia would be secondary to increased parathyroid hormone secretion, but the transient hypercalcemia that occurs after nephrectomy would take place in the absence of an increase in parathyroid hormone secretion. In this latter instance, it is possible that loss of the kidney, a major site of parathyroid hormone removal from plasma, leads to an increase in circulating parathyroid hormone level, and hypercalcemia, in the absence of an increase in hormone secretion rate.

Effects of sulfonylurea therapy on insulin binding to mononuclear leukocytes of diabetic patients

We have studied insulin binding to circulating mononuclear cells obtained from 31 untreated, adult, nonobese, nonketotic diabetic subjects with fasting hyperglycemia, 40 normal subjects and four patients with fasting hyperglycemia secondary to chronic pancreatitis. Our results show that the mononuclear cells of untreated adult diabetic patients have a decreased ability to bind insulin when they are compared to cells obtained from normal subjects. The binding affinity for insulin was the same for both groups of cells, and the decreased binding could be accounted for by a 45 per cent decrease in the number of available insulin receptor sites per cell. Treatment with chlorpropamide (one to three months, average dose equals 375 mg/day) was associated with a marked reduction in hyperglycemia and an increase toward normal in insulin binding to mononuclear cells. In conclusion, (1) mononuclear cells from nonobese, nonketotic, untreated adult diabetic patients with fasting hyperglycemia demonstrate a decreased ability to bind insulin due to decreased numbers of insulin receptors per cell; (2) treatment with an oral hypoglycemic agent is associated with a diminution in hyperglycemia and a return toward normal of insulin binding.

Nonketotic diabetes mellitus: insulin deficiency or insulin resistance?

Ninety-five nonobese, nonketotic subjects were divided into five groups (one normal and four with varying degrees of glucose intolerance) according to their plasma glucose responses during an oral glucose tolerance test. These five groups were then compared on the basis of their insulin response during the oral glucose tolerance test and on the ability of exogenously infused insulin to limit hyperglycemia during a continuous infusion of glucose and insulin, while endogenous insulin was inhibited by the infusion of epinephrine and propranolol. The mean plasma insulin response of patients with either borderline abnormalities of glucose tolerance or chemical diabetes was equal to or greater than that of normal subjects at all points during the glucose tolerance test. Thus, the glucose tolerance of these two patient groups cannot be attributed to lack of insulin. On the other hand, the mean insulin response of patients with moderate fasting hyperglycemia (plasma glucose of 110 to 150 mg/100 ml) was somewhat attenuated, and patients with severe fasting hyperglycemia (plasma glucose greater than 150 mg/100 ml) had unequivocal insulin deficiency. In contrast, all four patient groups with abnormal carbohydrate metabolism were more resistant than normal subjects to the action of insulin. These results indicate that there is a very complex relationship between insulin deficiency and insulin resistance in patients currently classified as having nonketotic diabetes. Patients with either borderline abnormal glucose tolerance or chemical diabetes are more resistant to insulin than normal subjects, and are not insulin deficient. In these patients it seems reasonable to assume that their glucose intolerance is a direct function of their insulin resistance. Patients with severe fasting hyperglycemia are suffering from both insulin deficiency and insulin resistance, and the relationship between these two variables in the genesis of hyperglycemia in these subjects remains obscure. It seems apparent from these studies that nonketotic diabetes mellitus can no longer be considered to be a simple function of insulin lack, and that in order to understand this syndrome we will need to increase our knowledge of the relationship between insulin deficiency and insulin resistance in these patients.

A quantitative ultrastructural study of microtubule content and secretory granule accumulation in parathyroid glands of phosphate- and colchicine-treated rats

Microtubule involvement in secretory events of the parathyroid gland was investigated in rats treated with colchicine and/or phosphorus, agents which have been shown to modify parathyroid secretion. Quantitative ultrastructural techniques were used in an effort to assess the cytoplasmic microtubule and secretory granule content of chief cells 3 h after treatment, when hypocalcemia was well established. After cochicine administration, the chief cells appeared to have lost all assembled microtubules and accumulated greater than normal amounts of cytoplasmic secretory granules. On the other hand, phosphorus treatment was associated with increased microtubule content although the cytoplasmic content of secretory granules remained unchanged. When colchicine and phosphorus were given concomitantly, microtubules were again absent, but the secretory granule content of the cells was markedly increased. These data provide direct evidence that colchicine disrupts assembled microtubules in chief cells of rat parathyroids; the consequence of this effect appears to be a blockage of hormone release which is reflected in the accumulation of secretory granules in the cell. The fact that microtubules also show a significant increase in content when hormone release from chief cells is presumed to increase, suggests that microtubules may participate in the physiological control of parathyroid hormone secretion.

Effect of hypophysectomy on protein synthetic-activity of free and bound hepatic ribosomes from insulin-deficient rats

Acute insulin deficiency in rats results in a decrease in the in vitro protein synthetic activity of isolated hepatic membrane-bound ribosomes and an increase in activity of free ribosomes. These changes are prevented by concomitant insulin treatment and are reversed by the administration of insulin. The current study evaluated the role of the pituitary in the genesis of these changes. The severity of diabetes produced by streptozotocin was less in hypophysectomized (Hx) rats, and in Hx rats receiving hormone replacement, as compared with similarly streptozotocin-treated intact rats. Although acute insulin deficiency in intact rats produced the previously described increase in protein synthetic activity of free hepatic ribosomes and decrease in activity of hepatic bound ribosomes, these changes did not occur in Hx rats, even when Hx rats received replacement doses of thyroxine, ACTH, and growth hormone. Thus, the changes in hepatic protein synthetic activity that occur in rats with acute experimental diabetes mellitus are secondary to the metabolic sequalae of insulin lack and the response of the pituitary gland to insulin deficiency.

Effects of age and obesity on insulin binding to isolated adipocytes

We have measured insulin binding to isolated adipocytes prepared from rats of varying ages and body weights. The ability of adipocytes to bind insulin progressively decreases as animals get older and fatter until about 70 days of age and 300 g body weight are reached. From this point on further decreases in insulin binding to adipocytes were not seen as rats got older and fatter. Analysis of the data indicated that this decrease in insulin binding could be accounted for by decreased numbers of insulin receptor sites per cell. Further studies were conducted in which animals were allowed to age, but obesity was prevented or reversed by hypocaloric diets. In these experiments decreased insulin binding was either prevented or restored to normal by the negative caloric state, indicating that age had no appreciable effect on the ability of adipocytes to bind insulin. The influence of the obesity associated variables-hyperinsulinemia and increased fat cell size-on insulin binding was also examined. These latter studies are consistent with the concept that elevated in vivo plasma insulin levels lead to decreased insulin receptors, and further suggest a role for additonal factors in regulating the adipocyte insulin receptor.

IN CONCLUSION

1. Decreased insulin binding to adipocytes is closely related to the obese state. 2. This decrease in insulin binding can be accounted for by decreased numbers of receptor sites per cell, and 3. The mecahnism(s) underlying this decreased insulin binding are complex and probably represents an effect of more than one variable.

Effect of duration of insulin deficiency on membrane-bound and free ribosomes from livers of diabetic rats

In order to define the effect of duration of diabetes on hepatic protein sysntesis, membrane-bound and free ribosomes were isolated from livers of rats, 3, 7 and 28 days after administration of intravenous streptozotocin (75 mg/kg). Hepatocytes from the same rats were subjected to ultrastructural quantitative analysis. By day 3 there was a significant loss in the amount of rough endoplasmic reticulum (RER) per volume cytoplasm; however, the normal ratio of membrane-bound ribosomes per unit length of membrane was maintained. These hepatocyte ultrastructural changes continued over the ensuing four weeks. In spite of this decrease in amount of RER, in vitro protein synthetic activity of hepatic membrane-bound polyribosomes was unchanged from controls at three days, and by 28 days protein synthetic activity of bound hepatic ribosomes from diabetic rats was almost twice that of normal controls (p less than .01). In contrast to the effect of diabetes on bound ribosomes, there was no change in protein synthetic activity of free polyribosomes isolated from livers of rats, 3, 7 or 28 days after induction of diabetes. Thus, the effect of any given degree of diabetes on hepatic protein synthesis appears to vary with the population of hepatic ribosomes being studied, and with duration of insulin deficiency.

Protein synthetic activity of membrane-bound and free ribosomes from parathyroid glands of dogs

1. Membrane-bound and free polyribosomes were isolated from parathyroid glands of normal dogs by a discontinuous density-gradient technique. 2. The conditions necessary for optimum incorporation by bound and free ribosomes of [3-H]-phenylalanine into protein were determined for assays in vitro directed by both endogenous messenger ribonucleic acid (mRNA) and polyuridylic acid [poly(U)]. 3. When the specific cofactors were available in optimum amounts, the rate of incorporation of amino acids into protein was directly proportional to the number of ribosomes present. This applied to assays directed by endogenous mRNA and poly-(U). 4. The results indicate that it is possible to isolate and directly study the protein synthetic activity of membrane-bound and free parathyroid ribosomes.

Diabetic hypertriglyceridemia

The conference opened with the clinical presentation of a 50-year-old male with fasting hyperglycemia (296 mg per cent) and hypertriglyceridemia (2736 mg per cent). The discussion began with a summary of current concepts regarding the manner in which chylomicra (intestine) and very low density lipoproteins (intestine and liver) are formed, transported into the plasma, and removed from the circulation. This was followed by a consideration of diabetic hypertriglyceridemia in which this syndrome was subdivided into two categories. The first form is seen in patients with severe fasting hyperglycemia, and is characterized by marked insulin deficiency, decreased very low density lipoprotein production, a fall in the activity of lipoprotein lipase, and hypertriglyceridemia secondary to a defect in removal of lipoproteins from the plasma. In contrast the other form of diabetic hypertriglyceridemia is seen in patients with minimal abnormalities of carbohydrate tolerance, and in this instance insulin resistance, not insulin lack, seems to play the pivotal role. In these patients, the rise in plasma triglyceride levels seems to be secondary to increased production of very low density lipoproteins, presumably as a result of the hyperinsulinemia associated with the insulin resistance. The conference ended with an attempt to relate the patient presented to the models of diabetic hypertriglyceridemia that had been defined.

Metabolic effects of increased caloric intake in man

In order to determine if increased caloric intake could be responsible for the insulin resistance and elevated plasma glucose, insulin, and triglyceride levels commonly associated with obesity, hypercaloric diets were fed for 3 wk to eight normal subjects, and the metabolic consequences of this diet were assessed before significant weight gain had occurred. One wk of increased caloric intake led to statistically significant increases in fasting plasma insulin (22 per cent), glucose (5 per cent), and triglyceride (30 per cent) levels, as well as an increased insulin response (20 per cent) to oral glucose. Since the average weight gain during this period was only 1.6 kg, the observed changes appear to be secondary to increased caloric consumption, not obesity. Most of these changes returned toward baseline values during the succeeding 2 wk of increased caloric intake, but statistically significant elevations of fasting plasma glucose (10 per cent), insulin (8 per cent) and cholesterol (15 per cent) levels were still seen at the end of the hypercaloric dietary period. On the other hand, insulin resistance, as estimated by direct measurement of insulin responsiveness, did not change as a result of 3 wk of increased caloric intake. These results indicate that acute increases in caloric intake can lead to elevated plasma glucose, insulin, cholesterol, and triglyceride levels. These changes occurred before significant weight gain had taken place, and raised the possibility that at least some of the abnormalities of carbohydrate and lipid metabolism attributed to obesity may be due to increased caloric intake. However, this conclusion would not seem to apply to the insulin resistance associated with obesity, as 3 wk of increased caloric intake did not produce any change in the responsiveness of these subjects to insulin's action.

The effects of acute and chronic dexamethasone administration on insulin binding to isolated rat hepatocytes and adipocytes

In an effort to determine the possible relationship between changes in insulin-receptor binding and the glucocorticoid-induced insulin-resistant state, we studied insulin binding to specific receptors located on isolated adipocytes and hepatocytes obtained from dexamethasone (D)-treated rats. Three groups of D-treated rats were studied: (1) acute high-dose treatment (1.5 mg/kg/6 days), (2) acute low-dose treatment (0.125 mg/kg/6 days), and (3) chronic low-dose treatment (0.125 mg/kg/21 days). When insulin binding to isolated hepatocytes was studied, we found that binding to isolated hepatocytes was studied, we found that binding was only 30%-50% of control values when cells from the D-treated animals were used. This decrease in binding was greatest for cells from the acute high-dose group, indicating a dose-response effect, and least for cells from the chronic group, suggesting a tendency toward return of insulin-receptor binding during chronic treatment. When insulin binding to isolated adipocytes was studied, binding was 50%-60% of control values when cells from both acute D-treated groups were used. While the magnitude of the decrease in insulin binding was not as great as that seen with hepatocytes, the decrease was still greatest using cells from the acute high-dose group as compared to the acute low-dose group. Thus, a dose-response effect was suggested in both tissues. On the other hand, the effects of chronic D treatment on insulin binding were strikingly different in the two cell systems. After chronic D treatment, insulin binding to adipocytes returned to near-normal levels, while a 55% decrease in binding to hepatocytes persisted. Thus, the tendency toward return of insulin binding after chronic D treatment seen with hepatocytes was almost fully expressed by adipocytes. This might be related to the amelioration of the corticosteroid-induced insulin-resistant state which has been reported after chronic corticosteroid administration to humans. In conclusion, (1) a decrease in insulin binding is associated with corticosteroid excess, and it is possible that this decreased binding is related to the insulin resistance which results from corticosteroid administration; (2) the return of insulin binding toward normal after chronic D treatment could well be related to the improvement in insulin resistance seen during chronic corticosteroid administration to humans; and (3) the difference in effects of chronic D treatment on insulin binding to hepatocytes versus adipocytes indicates that changes in insulin binding can be tissue specific.

Demonstration of insulin resistance in untreated adult onset diabetic subjects with fasting hyperglycemia

We have used a continuous intravenous infusion of glucose (6 mg/kg/min), insulin (80 mU/min), epinephrine (6 mug/min), and propranolol (0.08 mg/min) to directly assess insulin resistance in 14 untreated adult onset diabetics with a mean (plus or minus SE) fasting plasma glucose level of 217 plus or minus 17 mg/100 ml. During the infusion endogenous insulin secretion is inhibited and steady-state plasma glucose and insulin levels are achieved after 90 min. Since similar steady-state levels of plasma insulin are achieved in all subjects, the plasma glucose concentration observed during the steady-state period is a measure of an individual's insulin resistance. Under these conditions, the mean (plus or minus SE) steady-state plasma glucose level of the 14 diabetic patients was 350 plus or minus 16 mg/100 ml, while that of 12 normal subjects was 121 plus or minus 4 mg/100 ml. Additional studies were performed in which control subjects and patients with diabetes had their fasting plasma glucose levels acutely raised or lowered to comparable levels before receiving the basic infusion mixture of glucose, insulin, epinephrine, and propranolol. The results of these studies indicated that differences in initial plasma glucose levels could not account for the different glucose responses of the two groups to the basic infusion. Finally, the mean (plus or minus SE) steady-state plasma glucose level of 104 plus or minus 17 mg/100 ml observed during the same basic infusion in five patients with fasting hyperglycemia (mean plus or minus SE, 142 plus or minus 12 mg/100 ml) secondary to chronic pancreatitis suggested that neither chronic hyperglycemia nor hypoinsulinemia per se necessarily lead to insulin resistance. These results demonstrate that marked insulin resistance exists in adult onset diabetics with fasting hyperglycemia. Since previous studies have documented the presence of insulin resistance in patients with chemical diabetes, the possibility exists that insulin resistance may be characteristic of adult onset diabetes mellitus.

Evidence that parathyroid hormone is not required for phosphate homeostasis in renal failure

Varying degrees of renal failure were produced by surgical reduction of renal mass in normal dogs and in thyroparathyroidectomized dogs (TPTX) in whom serum calcium levels were maintained in the normal range by the administration of vitamin D. Both groups of dogs maintained normal serum phosphate levels in spite of progressive decreases in glomerular filtration rates (GFR). Furthermore, both groups of dogs were able to increase the fractional excretion of phosphate as GFR decreased. Thus the same renal response to loss of GFR was maintained in the complete absence of parathyroid tissue. Finally, stable serum phosphate levels and increased fractional excretion of phosphate in response to a decrease in GFR were also demonstrated in acutely TPTX dogs who were not receiving vitamin D. These results indicate that phosphate homeostasis can be maintained in renal failure in the total absence of parathyroid hormone secretion.

Insulin sensitivity of isolated perfused rat liver

The responsiveness of the isolated perfused rat liver to different metabolic effects of insulin was investigated during recycling perfusion. Infusion of porcine insulin at rates of 6, 9, 16 and 33 mU/hr. resulted in stable perfusate insulin levels averaging 41, 72, 120 and 229 muU/ml., respectively. Since the portal vein insulin concentration in the intact rat averaged 48 muU/ml. after a twenty-six-hour fast and 125 muU/ml. two hours after removal of food, the studies were conducted at insulin levels within the physiological range. The effect of each insulin concentration on the net accumulation of K+, AMINO ACID NITROGEN, UREA NITROGEN AND GLUCOSE IN The perfusing medium was assessed against the net accumulation of perfusate constituents during perfusion of control livers and livers perfused with perfusate insulin levels greater than 500 muU/ml. The results indicate that essentially maximal suppression of amino acid nitrogen outflow and retention of K+ OCCURRED AT INSULIN CONCENTRAtions of 72 muU/ml., with lesser effects being noted at 41 muU/ml. Inhibition of ureogenesis was demonstrated at insulin levels above 120 muU/ml. However, significant effects of insulin on suppressing net glucose outflow was not observed until insulin levels had reached 500 muU/ml. due presumably to the absence of a sustained rate of glycogenolysis by control livers. The observation that perfused livers from normal rats are extremely sensitive to several metabolic effects of insulin at physiological concentrations suggests that this experimental approach can provide useful information as to the role of the liver in the pathogenesis of various insulin resistant states.

Removal of insulin by perfused rat liver: effect of concentration

The kinetics of insulin removal by isolated rat liver were investigated by measuring the rate of disappearance of insulin from the perfusate during recycling perfusion and by comparing the extraction of insulin over a wide range of constant arterial hormone levels during nonrecycling perfusion. In the recycling studies, insulin was removed from the perfusing medium at a uniform rate between 5 and 45 min. The reaction velocity constant, or hepatic clearance, during this period of uniform disappearance averaged 1.8 ml/min and represented 34% of the volume flow through the liver. In the nonrecycling flow-through studies at constant arterial insulin concentration, an initial period of accelerated hepatic uptake of insulin was seen. This period lasted for 3 to 7 min, was seen at every level of arterial insulin concentration, and was followed by a period of constant hepatic insulin removal. The hepatic removal rate during the period of constant uptake increased in a linear fashion until arterial insulin concentration reached 500 muU/ml and attained a maximal value at concentrations over 800 muU/ml. These findings indicate that the time course of hepatic insulin uptake by the perfused rat liver consists of two phases-an initial rapid phase, possibly associated with insulin binding, followed by a sustained rate of insulin removal, which probably represents insulin utilization and degradation. The rate of hepatic insulin removal was found to be proportional to arterial insulin concentration overa range of 20 to 500 muU/ML. Above this concentration, hepatic removal processes became saturated, reaching a maximal value of 183 muU of insulin per gram of liver per minute.

Decreased insulin binding to lymphocytes from diabetic subjects

We have studied insulin binding to circulating lymphocytes isolated from 20 untreated adult, nonobese, nonketotic, diabetic subjects with fasting hyperglycemia, 20 normal subjects, and four patients with fasting hyperglycemia secondary to chronic pancreatitis. The results of these studies show that lymphocytes from diabetic patients have decreased ability to specificity bind insulin when compared to lymphocytes from normal subjects. For example, when lymphocytes from diabetic patients and a trace amount of [(125)I]insulin (3.3 x 10(-11) M) were incubated, binding was less than 50% of the value obtained with lymphocytes from normal subjects (2+/-0.2% vs. 4.2+/-0.4%). Furthermore, the data show that lymphocytes from diabetic patients have only 1,200 insulin receptor sites per cell compared to 2,200 sites per cell for lymphocytes from normal subjects. Competitive inhibition studies using unlabeled insulin indicate that the affinity for insulin of lymphocytes from both groups is comparable. Consequently the decreased insulin binding of diabetics' lymphocytes is primarily due to a decreased number of available receptors rather than decreased binding affinity. This decreased insulin binding is not due to chronic hyperglycemia since insulin binding to lymphocytes, obtained from four patients with fasting hyperglycemia secondary to chronic pancreatitis, was completely normal. The possibility that some factor present in the plasma of diabetic patients could cause decreased insulin binding also seems unlikely since we could demonstrate no in vitro effects of diabetics' plasma on insulin binding. Lastly, the proportion of lymphocytes which were thymus derived and bone marrow derived were the same in each of the study groups indicating that differences in lymphocyte subpopulations do not account for our results.

IN CONCLUSION

(a) lymphocytes from nonobese, untreated, adult diabetic patients with fasting hyperglycemia demonstrate a decreased ability to bind insulin; (b) this decreased insulin binding to lymphocytes obtained from diabetic patients can be accounted for primarily by an absolute decrease in the number of available receptor sites per cell; and (c) these data suggest that this defect in insulin binding is a primary phenomenon.

Mechanisms for development of diabetic hypertriglyceridemia in streptozotocin-treated rats. Effect of diet and duration of insulin deficiency

A combined ultrastructural and functional approach was employed to define the effects of duration of diabetes and of diet on various aspects of lipid metabolism in rats with severe streptozotocin (SZ)-induced insulin deficiency. Plasma triglyceride (TG) levels rose to a mean of 479 mg/100 ml 24 h after SZ administration in rats eating a fat-free, high carbohydrate diet as compared to a mean of 324 mg/100 ml in rats eating a high fat diet. These changes were associated with a commensurate increase in hepatocyte Golgi very low density lipoprotein (VLDL) content, but only a small increase in estimates of VLDL-TG secretion rate (post-Triton WR 1339 increment in plasma TG level). Although these findings are consistent with the thesis that VLDL-TG synthesis and secretion are increased 24 h after administration of SZ, it seemed unlikely that the observed increase in VLDL-TG secretion could entirely account for the severity of the hypertriglyceridemia. Thus, although lipoprotein removal rate was not measured directly, it was necessary to postulate that a defect in VLDL-TG removal was also present at this stage. Hypertriglyceridemia was still present 7 days later, only in this instance plasma TG levels were higher in rats eating the high fat diet (a mean of 589 mg/100 ml, as compared to 263 mg/100 ml). Rats with diabetes of 7-day duration had a 50% decrease in both TG entry rate and hepatocyte Golgi complex VLDL content, irrespective of diet. Thus, there was no evidence of increased VLDL-TG secretion in chronic insulin deficiency. In this instance, although not assessed directly, it was necessary to postulate that the hypertriglyceridemia in chronically insulin-deficient rats is due entirely to a defect in lipoprotein removal, involving both dietary and endogenous fat.