Metoprolol in diabetes mellitus: effect on glucose homeostasis

1. In eight hypertensive diabetic subjects receiving hydrochlorothiazide, glucose homeostasis as measured by the changes in plasma glucose, insulin and glucagon after an oral glucose load was not significantly affected by 8 weeks of therapy with metoprolol. 2. The combination of metoprolol plus hydrochlorothiazide significantly lowered blood pressure in all subjects. 3. Plasma renin activity was suppressed by therapy with metoprolol.

A simple and reliable method for calcium balance using combined period and continuous fecal markers

Calcium balances were determined in 13 patients during 2--4 3-day periods following both period marking (with carmine) and continuous marking (with polyethylene glycol or chromium). The reliability coefficient for the uncorrected fecal calcium (obtained from period marking) from one period to another was 0.82, whereas it was 0.97 for corrected fecal calcium (determined from recovery of continuous marker in 3-day fecal pools). Thus, the addition of continuous marking yielded a significantly more reliable measure of fecal calcium than obtainable by the use of period marking alone (p < 0.05); the error variance for corrected fecal calcium from one period to another was 3%, whereas it was 18% for uncorrected fecal calcium. It is concluded that a reliable measure of fecal calcium, and hence calcium balance, could be obtained by combined use of continuous and period markers, involving fecal collection over only one 3-day study period (marked by period marker), and correction of fecal calcium for the completeness of fecal collection (determined from continuous fecal marker).

Changes in nerve conduction velocity after six weeks of glucoregulation with portable insulin infusion pumps

Near normal glucoregulation was maintained in 10 patients with insulin-dependent (type I) diabetes mellitus for 6 wk with preprogrammed continuous subcutaneous insulin infusion using a portable battery-powered infusion pump (CSII). This form of therapy resulted in a statistically significant increase in motor nerve conduction velocity in the median and peroneal nerves compared with baseline values. There was no significant change in the motor nerve conduction velocity in the ulnar nerve or in the sensory nerve conduction studies. No changes occurred in five additional patients studied in similar fashion while on a conventional insulin regimen. These results suggest that the prevention of sustained hyperglycemia with CSII could theoretically result in the prevention of diabetic neuropathy. However, only long-term studies of CSII will provide the information necessary to determine the clinical relevance of the findings.

The T lymphocyte insulin receptor in diabetes and obesity: an intrinsic binding defect

Based on in vitro studies of insulin receptors in a variety of tissues, it was postulated that circulating insulin levels govern receptor number in vivo ahd that the insulin resistance characteristic of adult-onset diabetics is the consequence of reduced receptor numbers secondary to hyperinsulinemia. The quiescent T lymphocyte in vivo uniquely does not bear a receptor for insulin. The receptor appears after activation by a mitogen or antigen. Thus, free from the influence of endogenous insulin levels, this cell is an excellent model to study the intrinsic relations between diabetes and the insulin receptor. Specific binding to T cells activated by lectin in culture from 20 juvenile-onset diabetics (26 yr, 109 ± 5% fat) was 1.52 ± 0.08 × 10−21 mol/cell, no different from the 1.55 ± 0.08 in 20 normal subjects (20 yr, 100 ± 3% fat) or than in an aged non-obese group. In contrast, binding was reduced to 1.23 ± 0.05 × 10−21 mol/cell in 11 obese subjects (38 yr, 143 ± 5% fat) and even further to 1.0 ± 0.06 × 10−21 mol/cell in 21 adult-onset diabetics (53 yr, 160 ± 10% fat). The appearance of the insulin receptor on cultured stimulated T cells was analyzed by Scatchard plots, which demonstrated that receptor affinity was normal (Kd = 3−5 nM) but the receptor number was distinctly fewer (6131 ± 465 vs 2904 ± 172 sites/cell). In summary, these data show that (1) T lymphocyte insulin receptor characteristics are normal in juvenile-onset diabetics and in elderly nonobese subjects, (2) obesity itself reduces insulin receptor numbers, (3) insulin receptor binding in adult-onset diabetics is significantly less than in. obese controls and represents a defect in receptor number unrelated to in vivo insulin concentrations. We conclude that, in both obesity and adult-onset diabetes, a reduction in T cell insulin receptors is produced by a novel mechanism not attributable to classic ligand-receptor interactions.

Effect of streptozotocin-induced diabetes on renal ornithine decarboxylase activity

The effects of streptozotocin(SZ)-induced diabetes on renal ornithine decarboxylase (ODC) activity, the rate-limiting enzyme in polyamine biosynthesis, were studied. Sixteen hours after the injection of SZ, renal ODC activity increased 50% above that of the vehicle-injected controls. The maximum increase in activity--600%--was observed from 24 to 72 h after SZ. Within a week, ODC activity fell below control levels and remained suppressed during a 3 wk follow-up period. Insulin treatment within 10 h of the SZ injection prevented the increase of ODC activity; however, insulin given after enzyme activity had increased did not restore ODC activity to control levels. The early increase of ODC activity occurred in the presence of mild hyperglycemia without ketosis or hyperglucagonemia, but the levels were much higher in severely diabetic animals. Adrenalectomy, performed before the initial increase in enzyme activity, prevented the subsequent increase in diabetic animals; however, when adrenalectomy was performed after the enzyme had increased, enzyme activity did not normalize.

Effect of somatostatin infusion on jejunal water and electrolyte transport in a patient with secretory diarrhea due to malignant carcinoid syndrome

The effect of intravenous somatostatin infusion was investigated in a patient with severe secretory diarrhea due to malignant carcinoid syndrome. Continuous somatostatin infusion for 48 hr (4 microgram/kg/hr) reduced stool volume from 2.2 to 0.7 liters/day. Intestinal perfusion studies before intravenous somatostatin infusion revealed decreased water and sodium absorption and jejunal chloride secretion. Somatostatin infusion for 2 hr (8 microgram/kg/hr) reversed chloride secretion to absorption and markedly enhanced water and sodium absorption. These results suggest that somatostatin inhibited a secretory component of water and ion movement in the small bowel of the patient with malignant carcinoid syndrome.

Changes in glucagon levels after four to five weeks of glucoregulation by portable insulin infusion pumps

Near-normal glucoregulation was maintained in five patients with juvenile-onset diabetes mellitus for 4--5 wk with a preprogrammed, continuous, subcutaneous insulin infusion using a portable battery-powered infusion pump. This form of therapy significantly lowered immunoreactive glucagon (IRG) levels below those observed while on conventional insulin treatment at several times during the 24-h profile. The maximum IRG levels were also reduced in all five subjects. Thus, a flexible system of insulin delivery, as is provided by certain open-loop pump systems, can overcome inappropriate glucagon secretion that occurs with conventional insulin therapy.

Somatostatinoma syndrome. Biochemical, morphologic and clinical features

Diabetes mellitus, steatorrhea, cholelithiasis and a tumor distorting the duodenum prompted a work-up for somatostatinoma in a 52-year-old man. The responses of pancreatic B-cells but not of A-cells to nutrient stimuli were inhibited, and growth-hormone release was suppressed, suggesting somatostatin resistance in some target tissues. Plasma somatostatin-like immunoreactivity ranged from 9000 to 13,000 pg per milliliter (normal: 88+/-8, mean +/- S.E.M.) and was distributed in four molecular forms, including free somatostatin. The primary tumor contained 5 microgram of somatostatin-like immunoreactivity per milligram of wet tissue, distributed in three of the molecular forms noted in plasma. Plasma calcitonin was also elevated (4650 pg per milliliter; normal: less than 120). Immunocytochemical studies showed that cells of the primary tumor contained somatostatin and calcitonin but no other peptide hormones. Only somatostatin was present in the metastases. Somatostatin was localized electron microscopically in all secretory granules, irrespective of size and shape, whereas calcitonin was present only within a single subpopulation of small granules in the same cells.

Treatment of diabetes mellitus: the future

For more than half a century the management of hyperglycemia in diabetes mellitus has included rigid diets and intermittent subcutaneous insulin administration. These methods have been totally unsuccessful in restoring glucose homeostasis to normal in most diabetic patients. This review focuses on techniques that offer promise as alternatives or adjuncts to the current modalities of treatment. Specific areas discussed include pancreatic transplantation, islet cell transplantation, artificial beta cell devices, and the glucagon-suppressing agent somatostatin. Although many of these show promise for the future, a cure for the metabolic abnormalities of diabetes is not imminent.

Effects of insulin on the response of immunoreactive glucagon to an intravenous glucose load in human diabetes

The effects of exogenous insulin upon the response of immunoreactive glucagon (IRG) to i.v. glucose were studied in diabetic and nondiabetic subjects. In nondiabetics, a rapid injection of 25 g of glucose lowered plasma IRG levels. In adult-onset diabetics, the glucose-induced decline in IRG was normal despite a subnormal glucose-induced insulin rise, in contrast to impaired IRG suppressibility previously reported when such patients received an oral glucose load. The magnitude of their glucose-induced IRG decline was not augmented by exogenous insulin, even when insulin levels were acutely raised above 300 micro units/ml. In juvenile-type diabetics, basal IRG levels were normal following overnight insulin infusion, but the glucose-induced IRG decline was only half that of the nondiabetics. However, it became normal when hyperinsulinemia was acutely produced by supplementary insulin. Thus, whenever insulin levels rise in response to an increase in hyperglycemia, as they do spontaneously in nondiabetics and in adult-type diabetics and as they do when juvenile diabetics are given supplementary insulin together with the glucose bolus, the decline in IRG in response to an i.v. glucose load is as great as in nondiabetics. The findings are compatible with the view that glucose-induced suppression of IRG may require a concomitant rise in insulin.

Effect of streptozotocin-induced diabetes on hepatic ornithine decarboxylase activity in the rat

The effect of diabetes on rat hepatic ornithine decarboxylase (ODC) activity was studied in male rats 4 h to 8 days after the ip or iv administration of streptozotocin. Hepatic ODC activity increased 4-fold above control on the fourth day of diabetes. Increased ODC activity was observed with a dose of streptozotocin (70 mg/kg iv) which increased plasma ketones and glucagon and reduced plasma insulin. No change was seen with doses causing only mild hyperglycemia without change in plasma ketones, glucagon, or insulin. Insulin therapy prevented the increase in hepatic ODC activity in diabetic rats. Adrenalectomy or hypophysectomy also prevented the diabetes-associated increase of ODC activity. The studies suggest that insulin deficiency may result in increased hepatic polyamine synthesis.

The hypercalciuria of diabetes mellitus: its amelioration with insulin

Calcium and phosphous metabolism was investigated in 20 patients with diabetes mellitus when their diabetes was under poor metabolic control and again once optimal glycaemic control was achieved with aggressive insulin therapy. Ten of the twenty uncontrolled diabetics had hypercalciuria; insulin therapy returned calcium excretion to normal in five. Twenty-four hour calcium excretion fell in all but two patients when optimal diabetic control was achieved and calcium excretion was positively correlated with glucose excretion. Urinary cyclic AMP excretion, which was in the high normal range during poor control, decreased significantly during optimal insulin therapy. These data suggest that the hypercalciuria of uncontrolled diabetes may be a form of renal hypercalciuria which could result in parathyroid stimulation which might contribute to the development of osteopenia in patients with diabetes mellitus.

Hyperglucagonemia and its suppression. Importance in the metabolic control of diabetes

The role of glucagon in diabetes was studied in four patients with juvenile-type diabetes during continuous insulin infusion and a diet containing 150 g per day of carbohydrate. During insulin alone, plasma glucagon, measured at two-hour intervals, averaged 182 +/- 34 pg per milliliter, glucose 269 +/- 11 mg per deciliter, glucose excretion 52 +/- 8 g per 24 hours, ketone excretion 1.3 +/- 0.3 mmol per 24 hours, and urea nitrogen 12 +/- 2 g per 24 hours (mean +/- S.E.M.). Somatostatin (2 mg per day) lowered glucagon to 60 +/- 13 pg per milliliter, glucose to 111 +/- 17 mg per deciliter, glucose excretion to 1 +/- 0.7 g per 24 hours, ketone excretion to 0.5 +/- 0.2 mmol per 24 hours and urea nitrogen excretion to 8 +/- 2 g per 24 hours. Replacement of glucagon raised glucagon to 272 +/- 30 pg per milliliter, glucose to 202 +/- 20 mg per deciliter, glucose excretion to 14 +/- 7 g per 24 hours, ketone excretion to 0.8 mmol per 24 hours and urea nitrogen excretion to 11 +/- 2 g per 24 hours. In a subsequent study, similar improvement occurred on a diet of 30 g of carbohydrate daily, when absorption of dietary glucose was negligible. Hyperglucagonemia has an important role in diabetes; its correction reduces diabetic abnormalities to or toward normal.

Glucagon and diabetes

We have considered the evidence, first, that the presence of glucagon is essential in the pathogenesis of the full syndrome that results from complete insulin deficiency; second, that in the diabetic in whom insulin levels are relatively fixed, a rise in glucagon concentration contributes to endogenous hyperglycemia; and, third, that conventional methods of treatment of diabetes do not fully correct either the abnormal glucagon levels or the hyperglycemia, but when insulin therapy is supplemented with somatostatin, an agent which suppresses both glucagon and growth hormone, both hyperglycemia and hyperglucagonemia are corrected. These facts may one day provide a rationale for therapeutic efforts to suppress excess glucagon secretion in the management of diabetes in man.

Effect of insulin therapy on the profiles of plasma immunoreactive glucagon in juvenile-type and adult-type diabetics

To determine if the abnormal A-cell function of human diabetes can be corrected by insulin therapy, 10 patients with juvenile-type and 10 with adult-onset types of diabetes were aggressively treated with insulin for up to 10 days. Glucose, immunoreactive glucagon (IRG), and, where possible, insulin were measured in plasma specimens obtained at two-hour intervals for periods of up to 10 days. These patients were compared with nine nondiabetics who were studied similarly.

During a two-day “uncontrolled” period, marked hyperglycemie, glycosurie, and elevated IRG concentrations were present in both groups of diabetic patients. “Improved control” was achieved in the juvenile-type diabetic group with an average insulin dose of 115 ± 24 U. per day. Such therapy significantly reduced the mean plasma glucose (p &lt; 0.001) and IRG (p &lt; 0.05) concentrations when compared with the “uncontrolled” period, but both remained above (p &lt; 0.05) the values seen in the nondiabetk subjects.

“Improved control” was achieved in the maturity-onset group of patients with an average insulin dose of 160 ± 24 U. per day. This dose was associated with a mean plasma-insulin value of 106 ± 26 μU. per milliliter, significantly greater (p &lt; 0.05) than that of the nondiabetk: group. Mean plasma glucose (p &lt; 0.001) and IRG (p &lt; 0.02) concentrations were reduced significantly as compared with the “uncontrolled” period; the mean IRG level was the same as that of the nondiabetics, but the mean plasma glucose levels remained significantly greater (p &lt; 0.001) than in the nondiabetics.

The results indicate that aggressive administration of insulin by conventional means does significantly reduce the average IRG level in juvenile-type and adult-type diabetics. However, despite the large doses of insulin and unphysiologically high concentrations of circulating insulin in the juvenile-diabetic group, IRG remained significantly above that of the nondiabetics. In the adult-onset group, although it was reduced to normal, the IRG level can be viewed as above normal relative to the persistent hyperglycemie and hyperinsulinemia.

Diabetic regulation and its relationship to microangiopathy

This review addresses the question of the effectiveness of rigid regulation of the blood glucose in delaying or preventing the vascular complications of diabetes mellitus. Morphometric, pathologic, biochemical, and clinical evidence on both sides of this question are presented. It is concluded that because of present inadequate methods of completely returning glucose homeostasis to normal in diabetics, the question remains moot.

Effects of exogenous hyperglucagonemia in insulin-treated diabetics

This study was designed to determine if hyperglucagonemia approximating that believed to be present in the portal vein of poorly controlled diabetics can exert metabollcally deleterious effects in insulin-treated diabetics. Three juvenile-type diabetics and one maturity-onset-type patient were given glucagon intravenously at a dose of 6 ng./kg./min. for 24 hours while receiving a continuous infusion of Insulin. This raised their plasma IRG levels from an average of 122 ± 15 pg./ml. on the control day to 594 ± 60 pg./ml. Mean plasma glucose concentration, measured at two-hour intervals around the clock, averaged 200 ± 20 mg./dl. on the control day and increased significantly in all four patients to 293 ± 18 mg./dl. (p &lt; 0.05) during glucagon administration; fasting glucose rose from 138 ± 10 mg./dl. to 201 ± 17 (p &lt; 0.05). Glucose excretion rose significantly from the control value of 36 ± 14 gm. per 24 hours to 152 ± 19 gm. per 24 hours (p &lt; 0.05). The excretion of both urea nitrogen and ketones also increased significantly (p &lt; 0.05) during glucagon administration. The three juvenile-diabetic patients also received a glucagon infusion at a rate of only 3 ng./kg./min., and in each evidence of deterioration in metabolic control was observed. In every experiment, termination of the glucagon infusion was followed by a recession in the metabolic abnormalities.

These data indicate that exogenous hyperglucagonemia of the magnitude believed to be present in the portai vein of uncontrolled diabetics can cause metabolic deterioration in diabetics receiving continuous insulin treatment.