John H. Karam

A polymorphic locus near the human insulin gene is associated with insulin-dependent diabetes mellitus.

A polymorphic region flanking the human insulin gene on the short arm of chromosome 11, the insulin-gene-linked DNA polymorphism, can be described as a locus with at least three classes of alleles: a common small “class 1” allele averaging 570 base pairs, a rare intermediate “class 2” allele of about 1320 base pairs, and a large “class 3” allele averaging 2470 base pairs in size. We have determined the genotype at this locus of 393 unrelated diabetic and nondiabetic individuals. Differences were observed in the genotypie and allelic frequencies between groups of different races. Asians [17 nondiabetic, 2 with insulin-dependent diabetes mellitus (IDDM), and 8 with non-insulin-dependent diabetes mellitus (NIDDM)] exhibited the least variation in the size of this locus and 98% of the alleles in this group were class 1. A group of American blacks (32 nondiabetic, 5 with IDDM, and 40 with NIDDM) exhibited considerable variation in the size of this locus, and about 22% of the individuals examined had a genotype that included a rare class 2 allele. In neither of these two racial groups were the genotypie or allelic frequencies different between the nondiabetic and diabetic segments of these groups. However, in a group of Caucasians (83 nondiabetic, 113 with IDDM, and 76 with NIDDM), there was a significantly higher frequency of class 1 alleles and genotypes containing two class 1 alleles in the diabetic patients compared with nondiabetic controls. A strikingly higher frequency of class 1 alleles (P < 0.0001) and genotypes containing two class 1 alleles (P < 0.0001) was observed in the IDDM group compared with nondiabetic Caucasians, whereas the difference between NIDDM and controls was only near the level of statistical significance (P = 0.025). Analysis of the combined data of our Caucasian population and those reported from studies of Caucasians from Denmark and St. Louis, Missouri, continued to show an increased frequency of class 1 alleles and genotypes containing two class 1 alleles in the IDDM group (P = 0.0001) compared with the nondiabetic group; however, there were no longer differences in genotypic or allelic frequencies between NIDDM and nondiabetic groups.

Lack of glucagon response to hypoglycemia in diabetes: evidence for an intrinsic pancreatic alpha cell defect

Despite excessive glucagon responses to infusion of arginine, plasma glucagon did not rise in six juvenile-type diabetics during severe insulin-induced hypoglycemia, whereas glucagon in the controls rose significantly. Thus in diabetics pancreatic alpha cells are insensitive to glucose even in the presence of large amounts of circulating insulin. An intrinsic defect common to both alpha and beta pancreatic cells—failure to recognize (or respond to) plasma glucose fluctuations—may be operative in juvenile diabetes.

Prevention of human diabetic ketoacidosis by somatostatin. Evidence for an essential role of glucagon.

To evaluate the role of glucagon in the pathogenesis of diabetic ketoacidosis in man, we studied the effect of suppression of glucagon secretion by somatostatin on changes in plasma beta-hydroxybutyrate and glucose concentrations (as well as changes in their precursors) after acute withdrawal of insulin from seven patients with juvenile-type diabetes. Suppression of glucagon secretion prevented the development of ketoacidosis for 18 hours after acute insulin withdrawal, whereas in control studies mild ketoacidosis occurred 10 hours after insulin was stopped. Plasma beta-hydroxybutyrate, glucose, free fatty acid, and glycerol levels were all markedly lower during suppression of glucagon secretion (p smaller than 0.001), whereas plasma alanine levels were higher (p smaller than 0.001). These studies indicate that insulin lack per se does not lead to fulminant diabetic ketoacidosis in man and that glucagon, by means of its gluconeogenic, ketogenic, and lipolytic actions, is a prerequisite to the development of this condition.

Effects of Somatostatin on Plasma Glucose and Glucagon Levels in Human Diabetes Mellitus: Pathophysiologic and Therapeutic Implications

Abstract To evaluate the role of pancreatic alpha-cell dysfunction in human diabetes mellitus, somatostatin, an inhibitor of glucagon secretion, was infused (1 mg over two hours) in 10 insulin-dependent diabetic subjects. Fasting plasma glucagon fell from 150 ± 15 (mean ± S.E.M.) to 77 ± 10 pg per milliliter (p<0.001), and plasma glucose from 260 ± 20 to 191 ± 21 mg per 100 ml (p<0.001). Similar responses occurred in a hypophysectomized diabetic patient, indicating that these effects of somatostatin were independent of suppression of growth hormone secretion. Somatostatin (4 mg subcutaneously) was active transiently. In additional studies, somatostatin infusion combined with insulin completely abolished post-meal hyperglycemia in four diabetic patients and was more effective than insulin alone. These results indicate that excessive glucagon secretion accounts for about 25 per cent of the fasting plasmaglucose levels in such patients. Furthermore, somatostatin may be a useful adjunct to insulin in treating...

Effects of physiologic levels of glucagon and growth hormone on human carbohydrate and lipid metabolism. Studies involving administration of exogenous hormone during suppression of endogenous hormone secretion with somatostatin.

To study the individual effects of glucagon and growth hormone on human carbohydrate and lipid metabolism, endogenous secretion of both hormones was simultaneously suppressed with somatostatin and physiologic circulating levels of one or the other hormone were reproduced by exogenous infusion. The interaction of these hormones with insulin was evaluated by performing these studies in juvenile-onset, insulin-deficient diabetic subjects both during infusion of insulin and after its withdrawal. Infusion of glucagon (1 ng/kg-min) during suppression of its endogenous secretion with somatostatin produced circulating hormone levels of approximately 200 pg/ml. When glucagon was infused along with insulin, plasma glucose levels rose from 94 +/- 8 to 126 +/- 12 mg/100 ml over 1 h (P less than 0.01); growth hormone, beta-hydroxy-butyrate, alanine, FFA, and glycerol levels did not change. When insulin was withdrawn, plasma glucose, beta-hydroxybutyrate, FFA, and glycerol all rose to higher levels (P less than 0.01) than those observed under similar conditions when somatostatin alone had been infused to suppress glucagon secretion. Thus, under appropriate conditions, physiologic levels of glucagon can stimulate lipolysis and cause hyperketonemia and hyperglycemia in man; insulin antagonizes the lipolytic and ketogenic effects of glucagon more effectively than the hyperglycemic effect. Infusion of growth hormone (1 mug/kg-h) during suppression of its endogenous secretion with somastostatin produced circulating hormone levels of approximately 6 ng/ml. When growth hormone was administered along with insulin, no effects were observed. After insulin was withdrawn, plasma beta-hydroxybutyrate, glycerol, and FFA all rose to higher levels (P less than 0.01) than those observed during infusion of somatostatin alone when growth hormone secretion was suppressed; no difference in plasma glucose, alanine, and glucagon levels was evident. Thus, under appropriate conditions, physiologic levels of growth hormone can augment lipolysis and ketonemia in man, but these actions are ordinarily not apparent in the presence of physiologic levels of insulin.

Pharmacokinetics of tolbutamide: prediction by concentration in saliva.

The excretion of tolbutamide in saliva of diabetic patients receiving single intravenous doses of 1 gm tolbutamide is described. Gas chromatography with electron capture was used for analysis. Pharmacokinetic parameters could be obtained from either salivary or plasma tolbutamide levels. There was a good linear relationship between tolbutamide concentration in saliva and in plasma; salivary levels were 1.2% of plasma levels. Equations are presented that account for the excretion in saliva based on extent of protein binding and degree of ionization of tolbutamide in plasma and saliva. Correlation of the saliva to plasma concentration ratio was extended to data in the literature on two other drugs.

Pharmacokinetics and Pharmacodynamics of Metformin in Healthy Subjects and Patients with Noninsulin‐Dependent Diabetes Mellitus

This study was conducted to assess the effect of noninsulin‐dependent diabetes mellitus (NIDDM) and gender on the pharmacokinetics of metformin and to investigate whether or not metformin exhibits dose‐dependent pharmacokinetics. The pharmacodynamic effects (on plasma glucose and insulin) of metformin in patients with NIDDM and in healthy subjects also were assessed. Nine patients with NIDDM and 9 healthy subjects received 4 single‐blind single‐dose treatments of metformin HCl (850 mg, 1,700 mg, 2,550 mg, and placebo) and a multiple‐dose treatment of 850 mg metformin HCl (3 times daily for 19 doses). After each single‐dose treatment and the final dose of the multiple‐dose phase, multiple plasma and urine samples were collected for 48 hours and assayed for metformin levels. Plasma samples were also assayed for glucose and insulin levels. There were no significant differences in metformin kinetics in patients with NIDDM compared with healthy subjects, in men compared with women, or during multiple‐dose treatment versus single‐dose treatment. Plasma concentrations of metformin increase less than proportionally to dose, most likely due to a decrease in percent absorbed. In patients with NIDDM, single doses of 1,700‐mg or higher of metformin significantly decrease postprandial, but not preprandial, glucose concentrations and do not influence insulin concentrations. With multiple doses, both preprandial and postprandial glucose concentrations and preprandial insulin concentrations were significantly lower than with placebo. The effect of metformin on glucose level is correlated with the average fasting plasma glucose level without drug. In healthy subjects, single and multiple doses of metformin showed no effect on plasma glucose, but significantly attenuated the rise in immediate postprandial insulin levels.

Early Phase of Insulin Release

The early phase of insulin release in the first five minutes after intravenous administration of glucose, glucagon, and glucose-plus-glucagon was investigated systematically in various clinical conditions. In normal subjects there is an immediate release of insulin after glucose, glucagon, and glucose-plus-glucagon infusions. The latter combination produced the highest insulin levels. Of a group of nonobese subjects with diabetic heritage, some had impaired early release of insulin, but0 their mean response did not differ significantly from the normal group. Investigation of nonobese potential diabetics (offspring of two diabetic parents) revealed that as a group average they had decreased insulin levels during the early phase of insulin release, even though intravenous glucose tolerance was normal. Four of ten subjects had a normal response. Nonobese, noninsulin-dependent diabetics had no insulin response to infused glucose, but when glucagon was added to glucose a significant and rapid insulin discharge was observed. However, the magnitude of this response was about half that seen in normal subjects after glucose-plusglucagon. Finally, the early phase of insulin release was studied in obese nondiabetic subjects who demonstrated an exaggerated insulin release to each stimulus. Again, glucose-plusglucagon was the most potent stimulator of insulin release. It is postulated that impairment in the early phase of insulin release may be the first detectable abnormality of insulin secretion in diabetes mellitus and that glucagon has the capability of restoring this toward normal.

Studies on the Mechanism of Epinephrine-induced Hyperglycemia in Man: Evidence for Participation of Pancreatic Glucagon Secretion

In man, epinephrine induces increases in plasma levels of glucagon, a lipolytic and hyperglycemic hormone. To determine glucagons contribution to this hyperglycemia and lipolysis, the effects of inhibition of pancreatic alpha-cell responses to epinephrine were investigated with somatostatin and adrenergic receptor blockade. To avoid ambiguities that might result from concomitant changes in endogenous insulin secretion, these studies were performed in juvenile-type, insulin-deficient diabetic subjects. Compared with normal subjects, the diabetics had excessive glucagon responses to epinephrine, which had been infused to attain circulating levels within the range found in man in severe stress. Both somatostatin and propranolol completely prevented glucagon responses and diminished the glycemic response to epinephrine by 40 to 50 per cent. Free fatty acid responses to epinephrine were completely prevented by propranolol but unaffected with somatostatin. Phentolamine had no effect on glucose, free fatty acid, or glucagon responses to epinephrine. These studies demonstrate that epinephrine, via a betaadrenergic receptor mechanism, causes excessive plasma glucagon elevation in human diabetes mellitus and indicate that this hyperglucagonemia participates in the hyperglycemic, but not the lipolytic, response to epinephrine. Catecholamine-induced hyperglucagonemia may thus provide an additional explanation for the deterioration in carbohydrate tolerance associated with stress.

Inhibition of Pancreatic Glucagon Responses to Arginine by Somatostatin in Normal Man and in Insulin-Dependent Diabetics

Somatostatin, a recently synthesized hypothalamic peptide thought to represent growth hormone-release-inhibiting factor, has been previously shown to inhibit pancreatic glucagon secretion in species other than man. To determine whether somatostatin also inhibits human glucagon secretion, plasma glucagon responses during intravenous infusion of arginine alone (250 mg. per kilogram over twenty-five minutes) and in combination with synthetic cyclic somatostatin (20,μg. per minute) were compared in six normal and six insulin-dependent diabetic subjects. Somatostatin abolished glucagon responses to arginine in both groups, with plasma glucagon declining transiently below basal levels; this occurred despite the fact that the diabetic subjects had fasting hyperglucagonemia and exaggerated glucagon responses during control arginine infusions. In both groups plasma glucose rises seen after arginine were diminished during somatostatin infusions, and, in the normal subjects, insulin responses were also inhibited. These results demonstrate that somatostatin is a potent inhibitor of glucagon secretion in man. Accordingly, it may prove useful as an adjunct to insulin therapy in treatment of insulin-requiring diabetes mellitus.