Reduced Na+, K+ -ATPase activity in intact red cells and isolated membranes from obese man.

Na+, K+ -ATPase activity was measured in red blood cells from 20 nondiabetic euthyroid male Pima Indians with varying degrees of obesity; their body mass indices ranged from 22-60 kg/m2. The na+, K+ -ATPase, measured both by 86Rb uptake in intact cells and ATP hydrolysis by purified membranes, was inversely correlated with body mass index (r = -0.62; P less than 0.005 and r = -0.75; P less than 0.0001, respectively). These results confirm that obesity is associated with decreased Na+, K+ -ATPase in intact red blood cells, and provide the first demonstration of a reduced sodium pump in isolated red cell membrane preparations from obese men.

Improvement of insulin secretion but not insulin resistance after short term control of plasma glucose in obese type II diabetics.

Insulin secretion and insulin resistance were examined in seven obese type II diabetics before and after control of plasma glucose levels without weight loss. Control was achieved by regular insulin injection (60-205 U/day in four doses). After 10 days of therapy, plasma insulin and C-peptide responses to oral glucose were significantly improved. Insulin-induced glucose rates, estimated by the glucose clamp technique, averaged 1.08 +/- 0.30 mg/kg. min (mean +/- SEM; n = 7) before treatment and were unchanged (1.08 +/- 0.25) after treatment. These indicate that short term control of plasma glucose improved insulin secretion but not insulin sensitivity. The impaired insulin secretion and insulin sensitivity in type II diabetics appears to be, in part, secondary to metabolic abnormalities associated with hyperglycemia.

Insulin and glucagon secretion from rat islets maintained in a tissue culture-perifusion system.

A tissue culture-perifusion system is described that allows for long-term culture of pancreatic islets and study of the dynamics of islet hormone secretion. Islets cultured in this system demonstrate brisk, reproducible biphasic insulin and glucagon release. Glucose-stimulated insulin release is similar after 1 or 14 days in culture. Freshly isolated islets are relatively insensitive to somatostatin, requiring 100 ng/ml to suppress partially the glucose-induced insulin secretion. After 24 h of culture, the same islets demonstrate a marked increase in sensitivity to this hormone. Glucagon secretion from islets maintained in this system occurred in a predictable fashion to arginine stimulation and glucose inhibition.

Unexplained hyperinsulinemia in normal and "prediabetic" Pima Indians compared with normal Caucasians. An example of racial differences in insulin secretion.

The pattern of insulin response to oral and/or intravenous glucose has been claimed to be characteristic of diabetes and even prediabetes. To determine if differences in insluin secretion might explain the exceptionally high prevalence of diabetes in the Pima Indians, 26 genetically normal Pimas (nondiabetic offspring of nondiabetic parents), 32 genetically prediabetic Pimas (nondiabetic offspring of diabetic parents), 10 diabetic Pimas, and 29 normal Caucasians were studied. All subjects received an intravenous glucose tolerance test (IVGTT) to examine the acute-phase insulin response, and all nondiabetic subjects received an oral glucose tolerance test (OGTT) and arginine infusion (AI). The prediabetics also received a cortisone-primed oral glucose tolerance test (CGTT) and were classified by the result of this test. While acute-phase insulin release during the IVGTT was absent in the diabetics, there was a rapid response in all nondiabetics. Prediabetic Pimas with normal or abnormal CGTT had insulin levels similar to normal Indians during the IVGTT, OGTT, and AI. Thus, no evidence of impairment of acute- or late-phase insulin release was found. The normal and prediabetic Indians had fasting and stimulated insulin levels during all the tests two-to-threefold greater than the Caucasians. Differences in insulin levels between the two races could not be explained by differences in glucose level, age, or obesity.

Immunoreactive glucagon (IRG) responses to intravenous glucose in prediabetes and diabetes among Pima Indians and normal Caucasians.

Immunoreactive glucagon (IRG) response to a 3 min iv infusion of 25 g glucose was examined in 7 nondiabetic Caucasians, 8 nondiabetic, 8 prediabetic and 16 diabetic Pima Indians to define the normal IRG response and to determine if abnormalities of IRG suppression occur in diabetic and prediabetic Pima Indians. Fasting IRG levels were similar in the 3 nondiabetic groups. In response to the glucose infusion the maximum percentage fall in plasma IRG concentration was similar in the normal Caucasians (37+/-4%) and the normal (42+/-2%) and prediabetic Indians (43+/-3%). In the diabetic Indians the relative fall was less at all sampling times than among the prediabetic or normal Indians. No evidence of any differences in IRG suppression in prediabetic and normal Indians or normal Caucasians was found. Without detectable change in insulin levels during the first 10 min following the glucose infusion, IRG levels in the diabetics fell but to a lesser degree than that in the other groups.

Normal glucagon response to arginine infusion in "prediabetic" Pima Indians.

To determine whether abnormalities in glucagon secretion might precede the onset of hyperglycemia in diabetes mellitus, 32 prediabetic Pima (American) Indians, 27 normal Pima Indians and 34 normal Caucasians received an infusion of arginine monochloride (5 mg/kg/min for 40 minutes) with measurement of glucose, insulin, and glucagon. [Prediabetes is the period between conception and the development of diabetes. In most studies the term is used to characterize patients who on genetic grounds are believed to be at high risk of developing the disease, including the normoglycemic monozygotic co-twin of a diabetic or the normoglycemic offspring of two diabetic parents. The latter definition is used in the present study recognizing that in the final analysis the true prediabetic can be identified only in retrospect after the development of diabetes.] The three groups had similar mean fasting glucagon levels. During arginine infusion, the prediabetic Indians reached a mean maximum glucagon level of 315 +/- 14 pg/ml (mean +/- 1 SEM) compared with 294 +/- 20 pg/ml in the normal Indians and 292 +/- 25 pg/ml in the normal Caucasians. The calculated mean areas above baseline under the glucagon curves were 5704 +/- 324 pg-min/ml in the prediabetics, 5189 +/- 446 pg-min/ml in the normal Indians, and 4239 +/- 613 pg/min/ml in the normal Caucasians. The differences among the groups in these variables were not statistically significant. Thus, arginine induced hyperglucagonemia could not be identified as a characteristic of the prediabetic state in Pima Indians.

Arginine-stimulated hyperglucagonemia in diabetic Pima Indians.

Groups of 27 nondiabetic Pima Indians, 34 nondiabetic Caucasians, and 12 diabetic Pima Indians with recent onset of their disease received an arginine infusion to determine if (1) nondiabetic Pima Indians and Caucasians had a similar glucagon response to arginine and (2) diabetic Pimas had excessive glucagon response to arginine as reported in other racial groups. The fasting glucagon levels in the three groups were not significantly different. During arginine monochloride infusion (5 mg./kg./minute for 40 minutes) the diabetic Pimas had glucagon levels significantly higher at 10 minutes and at all sampling points thereafter than the normo-glycemic Pimas. Plasma insulin levels also increased during the infusion but, notably, never differed significantly between these two groups. There was no significant difference in the glucagon levels at any sampling point between the nondiabetic Pimas and Caucasians. The differences in glucagon levels between the nondiabetic and diabetic Indians are similar to those differences reported between diabetic and nondiabetic subjects of other racial origins.