Gerich, John E.

To determine whether fasting alters the ability of insulin to suppress endogenous glucose production or proteolysis, isotopic flux measurements of glucose, leucine, alpha-keto-isocaproate, and alanine were made in 13 normal volunteers after a 14-h (day 1) and an 84-h (day 4) fast. Using the “pancreatic clamp” technique, we achieved small increments in plasma insulin concentrations, as well as constant and identical plasma hormone and glucose concentrations, on both study days in seven subjects. The remaining six subjects were infused with saline and served as controls. Leucine rate of appearance (an index of proteolysis) was greater on day 4 than on day 1 (P less than 0.001), but decreased to equal values during the pancreatic clamp on each study day. During the pancreatic clamp, endogenous glucose production decreased to lesser (P less than 0.005) values on day 4 than on day 1. In conclusion, insulin suppresses proteolysis equally well before and after brief fasting, and endogenous glucose production is more completely suppressed by insulin after brief fasting than after an overnight fast.

To determine the effects of insulin on dietary and endogenous leucine metabolism, five normal subjects, seven insulin-insufficient insulin-dependent (IDDM) diabetic patients, and five diabetic patients controlled with continuous subcutaneous insulin infusion (CSII) were studied before and for 8 h after ingestion of a chemically defined elemental test meal (10 cal/kg) containing crystalline amino acids. L-[1-14C]leucine was included in the meal to trace the entry and oxidation of the dietary leucine. Total (meal + endogenous) entry of leucine into the circulation was estimated with a constant infusion of [2H3]leucine. Postabsorptive and meal-related increases in the plasma leucine concentration were greater (P < .05) in the insulin-insufficient IDDM than in the normal subjects but returned to near-normal values with CSII. Baseline leucine flux was ∼40% greater in the insulin-insufficient IDDM than in normal subjects (2.17 ± 0.17 vs. 1.55 ± 0.15 μmol · kg−1 · min−1, respectively; .05 < P < .01) but were near normal during CSII treatment (1.85 ± 0.25 μmol · kg−1 · min−1). Furthermore, total leucine entry during meal absorption was greater in the insulin-insufficient IDDM (1.41 ± 0.10 mmol · kg−1.8 h−1) than in either normal (0.96 ± 0.08 mmol · kg−1 · 8 h−1, P < .01) or IDDM subjects during CSII treatment (1.09 ± 0.11 mmol · kg−1 · 8 h−1, P < .05). Fractional oxidation (∼40–50%) and entry of dietary leucine were similar in all three groups. The calculated rate of leucine entry from endogenous proteins over the 8 h of study in insulin-insufficient IDDM (1.04 ± 0.12 mmol · kg−1 · 8 h−1) was significantly greater than in normal subjects (0.64 ± 0.07 mmol · kg−1 · 8 h−, P < .01) or in IDDM subjects during CSII treatment (0.76 ± 0.10 mmol · kg−1 · 8 h−1, P < .05). However, during meal absorption, the calculated rate of leucine entry from endogenous protein was significantly suppressed below baseline only in the normal subjects. In summary, during absorption of a mixed meal, 1) one-third of the leucine entering the peripheral plasma space is derived from the diet in normal humans; 2) the rate of absorption and oxidation of dietary leucine in IDDM is normal regardless of adequacy of insulin therapy; and 3) postprandial hyperleucinemia in poorly controlled diabetic patients is at least partly the result of inadequate suppression of the entry rate of leucine from endogenous protein, suggesting persistence of excessive rates of proteolysis, which is at least partly corrected by intensified insulin treatment. Thus, insulin-mediated suppression of endogenous proteolysis is an integral part of protein anabolism during meal absorption.

To assess the possible influence of moderate titer insulin antibodies on diabetic glycemic control, we examined insulin-antibody equilibrium binding characteristics, postprandial glucose tolerance, and plasma free-insulin profiles after subcutaneous injection of both porcine and human insulin (0.15 U/kg) in 12 patients with insulin-dependent diabetes mellitus under conditions simulating intensive insulin therapy. The patients' antibodies bound porcine and human insulin indistinguishably, and their plasma glucose and freeinsulin profiles after ingestion of a standard meal were similar with both insulins. Initial increases in plasma free-insulin levels after injection of both insulins were negatively correlated with both insulin-antibody binding (r = −.55, P < .006) and postprandial hyperglycemia (peak level r = −.56, P < .006); the latter was positively correlated with insulin-antibody binding (r = .48, P < .02). The effects of insulin antibodies on postprandial plasma free-insulin and glucose levels could be accounted for substantially by the association constant of the high-affinity insulin-antibody binding sites (K1); patients in the highest quartile for K1 had significantly slower initial increments in plasma free insulin (0.31 ± 0.04 vs. 0.46 ± 0.06 μU/min, P < .05) and greater postprandial hyperglycemia (peak value 237 ± 10 vs. 166 ± 12 mg/dl, P < .001) than patients in the lowest quartile. We conclude that moderate insulin-antibody titers commonly found in insulin-treated patients can slow the early increase in plasma free insulin after subcutaneous injection and that this impairs postprandial glucose tolerance; such an effect may Received for publication 22 April 1986 and accepted in revised form 18 September 1986. limit the effectiveness of intensive insulin therapy.

To assess the possible role of increased insulin clearance in the pathogenesis of the dawn phenomenon, we compared plasma free-insulin concentrations, free-insulin clearance rates, and plasma glucose concentrations in eight subjects with insulin-dependent diabetes mellitus (IDDM) during infusion of insulin from midnight to 0800 h (0.15 mU · kg−1 · min−1) with a Biostator and a Harvard pump. During infusion of insulin with the Biostator, plasma free insulin decreased 40% (from 14 ± 1 to 9 ± 1 μU/ml, P < .01), insulin clearance increased 54% (from 11 ± 1 to 17 ± 2 ml/min, P < .05), and plasma glucose increased from 101 ± 4 to 217 ± 27 mg/dl, P < .01. During infusion of insulin with the Harvard pump, neither plasma free insulin (14 ± vs. 13 ± 1 μU/ml) nor free-insulin clearance (12 ± 2 vs. 13 ± 2 ml/min) changed significantly, but plasma glucose increased from 100 ± 3 to 167 ± 21 mg/dl, P < .01. The increases in plasma glucose during infusion of insulin with the Biostator and the Harvard pump were not significantly different (t = 1.44, P = .19). When insulin was delivered directly into test tubes with the Biostator and the Harvard pump, insulin concentrations in the test tubes decreased 46% over 8 h (P < .05) with the Biostator, whereas no decrease was observed with the Harvard pump. We conclude that the dawn phenomenon can occur without an increase in insulin clearance and that the apparent overnight increase in insulin clearance observed in studies with the Biostator iS artifactual.

To compare glucose counter regulatory mechanisms during short-term hypoglycemia and prolonged hypoglycemia, insulin was infused either intravenously (160 mil · M−2 · min) for 10 min or subcutaneously (15 mU · M−2 · min) for 12 h in normal volunteers. With each type of insulin infusion, hypoglycemia (∼50 mg/dl) was either allowed to develop or was prevented (control experiments) by the glucose-clamp technique. During prolonged hypoglycemia, both increased glucose production (1.55 ± 0.05 versus 0.33 ± 0.14 mg · kg−1 · min in control experiments at 12 h, P < 0.01) and suppressed glucose utilization (1.55 ± 0.06 versus 3.17 ± 0.15 mg · kg−1 · min in control studies at 12 h, P < 0.01) were involved in counterregulation. During short-term hypoglycemia, only increased glucose production (3.23 ± 0.33 versus 0.06 ± 0.03 mg · kg−1 · min in control experiments at 60 min) was involved, since glucose clearance actually increased (3.99 ± 0.20 versus 2.88 ± 0.02 ml · kg−1 · min in control experiments at 60 min, P < 0.01). Estimated portal venous insulin concentrations decreased 40% (basal 24 ± 3 versus 14 ± 1 mU/ml at 60 min, P < 0.01) in the short-term hypoglycemia experiments but remained at basal levels (basal 25 ± 1 versus ∼26 μU/min between 1 and 12 h) during prolonged hypoglycemia. Despite the fact that hypoglycemia was more gradually induced in the prolonged hypoglycemia model, peak counterregulatory hormone responses were at least as great as those during short-term hypoglycemia. Plasma free fatty acids and ketone bodies increased 150–200% above basal (both P < 0.01) with counterregulation during prolonged hypoglycemia but did not increase above basal levels with counterregulation during short-term hypoglycemia. Finally, plasma alanine remained unchanged during short-term hypoglycemia but decreased nearly 40% during prolonged hypoglycemia (basal 327 ± 20 versus 208 ± 21 μM at 12 h, P < 0.01). We conclude that glucose counterregulatory mechanisms differ during short-term and prolonged hypoglycemia. In the former, only an increase in glucose production mediated by suppression of insulin secretion and increased glucagon secretion is involved, whereas during prolonged hypoglycemia, both a suppression of glucose utilization, and an increase in glucose production are important. These latter changes in glucose production and utilization may be influenced by changes in circulating nonglucose substrates (e.g., alanine, free fatty acids, and ketone bodies) as well as by hormonal factors acting on both hepatic and extrahepatic tissues.

Type A insulin resistance, associated with acanthosis nigricans and menstrual irregularity, has been ascribed to a decreased concentration of insulin receptors. We now report four affected females from one family, a mother and three daughters (including identical twins) who appear to have the type A syndrome. Two of the kindred had no apparent ovarian dysfunction, while the other two had hyperprolactinemia without other findings of polycystic ovary disease, suggesting a genetic disease with variable penetrance. All had normal erythrocyte and monocyte insulin binding. Insulin dose-response studies to assess glucose metabolism and insulinsensitivity were performed in the affected twins. The dose response to insulin was shifted to the right with a decrease in maximal response. These results are consistent with a postbinding defect in insulin action in these patients.

To assess the normality of islet A- and B-cell responses to a nonglucose secretogogue as well as the modulating effect of glucose in NIDDM, we examined plasma C-peptide and glucagonresponses to arginine in eight patients with NIDDM and in six age- and weight-matched nondiabeticvolunteers under conditions of identical hypoglycemia (∼70 mg/dl), euglycemia (94 mg/dl), and hyperglycemia (∼190 mg/dl). Plasma C-peptide responses to glucose and to arginine in the diabetic subjects were both significantly reduced at all glucose concentrations studied (P < 0.01–0.005). The modulating effect of glucose on both islet A- and B-cell responses (slope of relation between plasma Cpeptide or glucagon response versus plasma glucose concentration) was reduced 80% in the diabetic subjects (P < 0.01). We conclude that islet A- and B-cell responses to nonglucose secretogogues are abnormal in patients with NIDDM and that this may result from a functional defect in the modulating effect of glucose on insulin and glucagon secretion, which in some patients may be compensated for by hyperglycemia.

The safety, reproducibility, and reliability of an insulin infusion test for assessment of adequate glucose counterregulation were evaluated in 18 patients with type I (insulin-dependent) diabetes mellitus. When the test (a 60-min, 30-mU/m2/min insulin infusion) was administered on three separate occasions at 3–4-wk intervals, coefficients of variation for plasma glucose and counterregulatory hormone (glucagon, epinephrine, cortisol, and growth hormone) responses averaged less than 8%. No patient experienced symptoms requiring discontinuation of the test and plasma glucose concentrations increased spontaneously after stopping the insulin infusion. Using objective criteria based on plasma glucose nadirs or postnadir rates of plasma glucose recovery, no patient judged to have adequate glucose counterregulation by the test (post-nadir rates of plasma glucose recovery or plasma glucose nadir above 0.4 mg/dl/min and 45 mg/dl) developed severe hypoglycemia (plasma glucose < 40 mg/dl) during up to 7 mo of intensive insulin therapy, whereas nearly all patients with inadequate counter-regulation did. We conclude that this test, when performed in standardized conditions, is safe and reproducible and can reliably predict those patients with type I diabetes who are at risk of developing severe hypoglycemia during intensive insulin therapy.

To assess the effects of glycemie control on glucose counterregulation, rates of plasma glucose recovery from hypoglycemia and counterregulatory hormonal responses were studied in 18 C-peptide-negative patients with insulin-dependent diabetes mellitus (IDDM) before and after either improvement, no change, or deterioration in glycemic control. Hypoglycemia was induced by an i.v. insulin infusion (30 mU/m2 · min for 1 h) after maintenance of euglycemia overnight with i.v. insulin. In 13 patients with long duration of IDDM (9 ± 0.5 yr, mean ± SEM) and initially poor glycemic control (mean diurnal blood glucose, MBG 199 ± 8 mg/dl, ketoamine-HbA1 12.4 ± 0.2%; nondiabetic subjects 104 ± 4 mg/dl and 6.8 ± 0.09%, respectively), rates of plasma glucose recovery from hypoglycemia (0.30 ± 0.01 versus 0.60 ± 0.01 mg/dl · min in nondiabetic subjects, P < 0.001) and plasma glucagon (AUC 0.56 ± 0.09 versus 6.3 ± 0.50 ng/ml ·150 min in non-diabetic subjects, P < 0.01) and epinephrine (AUC 16.9 ± 0.2 versus 25.7 ± 0.2 ng/ml 150 min in nondiabetic subjects, P < 0.001) responses to hypoglycemia were impaired. Intensive therapy (three daily injections of insulin) instituted in 7 out of 13 IDDM patients for up to 9 mo improved MBG (124 ± 6 mg/dl, P < 0.01) and ketoamine-HbA1 (7.9 ± 0.02%, P < 0.01) but not rates of plasma glucose recovery (0.31 ± 0.01 mg/dl · min) and plasma glucagon (AUC 0.69 ± 0.07 ng/ml · 150 min) and epinephrine (AUC 14.9 ± 0.17 ng/ml ·150 min) responses. Similarly, no changes in glucose counterregulation were observed in the six IDDM patients in whom glycemic control was poorly maintained for 6–8 mo (MBG 201 ± 7 mg/dl, ketoamine-HbA112.3 ± 0.2%). In five patients with short duration of IDDM (11 ± 0.5 mo) and optimized glycemic control (MBG 131 ± 8 mg/dl, ketoamine-HbA1 7.9 ± 0.2%), rates of plasma glucose recovery, as well as counterregulatory responses of plasma glucagon and epinephrine, were normal. Neither deterioration of glycemic control for 2 wk (MBG 229 ± 12 mg/dl, ketoamine-HbA1 9.1 ± 0.2%) nor its improvement over the 2 subsequent wk (MBG 120 ± 8 mg/dl, ketoamine-HbA1 8.5 ± 0.2%) resulted in any significant change in glucose counterregulation. It is concluded that near-normalization of glycemic control for up to 9 mo is insufficient to reverse the impairment in glucose counterregulation found in long-term IDDM. Short-term deterioration in glycemic control, when not accompanied by alterations in counterregulatory hormone secretion, does not impair glucose counterregulation.