Biomedical subjects

D M Mott

Publications and source records attributed to D M Mott.

At least 19 recordsLinked to original sources

PubMed1992

Defective insulin response of phosphorylase phosphatase in insulin-resistant humans.

Insulin-stimulated glycogen synthase activity in human muscle is reduced in insulin-resistant subjects. Insulin regulation of human muscle glycogen synthase may require activation of a type-1 protein phosphatase (PP-1). We investigated the change of phosphorylase phosphatase and glycogen synthase activities in muscle biopsies obtained during a 2-h hyperinsulinemic euglycemic clamp in 12 insulin-sensitive (group S) and 8 insulin-resistant (group R) subjects. Fasting phosphorylase phosphatase activity was lower in group R than in group S, and did not increase significantly with insulin infusion in group R until 20 min. In group S, phosphorylase phosphatase was significantly stimulated by 10 min, remaining significantly higher than in group R at all time points. The insulin-mediated changes in phosphatase activities were not decreased by 3 nM okadaic acid but were completely inhibited by 1 microM okadaic acid, thereby verifying that insulin-stimulated phosphorylase phosphatase is accounted for by a PP-1. Subcellular fractionation demonstrated reduced fasting PP-1 activities in both the glycogen and cytosolic fractions of muscle obtained from subjects in group R compared to those in group S. These results suggest that insulin activation of PP-1 could contribute to the stimulation of glycogen synthase by this hormone in human muscle. Lower fasting PP-1 activity in cytosol and glycogen fractions plus lower insulin-stimulated PP-1 activity could explain, in part, reduced insulin-stimulated glycogen synthase in skeletal muscle of insulin-resistant subjects.

Adult↗

PubMed1992

Tyrosine kinase activity of skeletal muscle during insulin infusion in humans.

Insulin receptor tyrosine kinase is stimulated by insulin in vivo, and this provides a mechanism by which the signal from insulin is transmitted into target cells. This study examined the time course of the in vivo activation of the kinase. Five nondiabetic Pima Indians had a euglycemic clamp at an insulin dose of 600 mU/min.m2, resulting in plasma insulin concentrations of about 15 nM by 30 min. Percutaneous muscle biopsies were taken from the vastus lateralis before and at regular intervals during insulin infusion, and the in vivo and in vitro tyrosine kinase activities were measured. There was a rapid in vivo activation of the kinase, detectable at less than 10 min and reaching a maximum within 30 min of insulin infusion. The time course of in vivo kinase activity, plasma insulin concentrations, and insulin-mediated glucose disposal rates displayed parallel patterns, indicating close interrelationships among these variables. The insulin concentration at which the kinase activity was maximal was about 10 nM both in vivo and in vitro. In vitro, however, this maximum increased with the degree of the kinase activation in vivo, indicating that the kinase potential in vitro is dependent on previous insulin exposure in vivo. We conclude that in vivo activation of the insulin receptor tyrosine kinase in human skeletal muscle is a rapid process, related to insulin action on glucose disposal, and that circulating insulin primes inactive insulin receptor molecules for subsequent tyrosine kinase activation by a mechanism that remains to be elucidated.

Adult↗

PubMed1991

Amylin activates glycogen phosphorylase in the isolated soleus muscle of the rat.

The pancreatic beta-cell hormone amylin acts in isolated rat skeletal muscle to decrease insulin-stimulated incorporation of glucose into glycogen. It also increases blood levels of lactate and glucose in fasted rats in vivo. However, it remained uncertain whether amylin exerts direct effects to stimulate muscle glycogenolysis. We now report that amylin caused a dose-dependent increase in activity of muscle glycogen phosphorylase in isolated rat soleus muscle by stimulating phosphorylase a. Insulin inhibited amylin-stimulated activation of phosphorylase. Effects of amylin to stimulate muscle glycogenolysis are consistent with observed effects of amylin in vivo and could be a major mechanism whereby amylin modulates carbohydrate metabolism.

Amyloid↗

PubMed1991

Studies of the etiology of obesity in Pima Indians.

Studies have been conducted on various metabolic characteristics of lean and obese Pima Indians, including studies of fat-cell morphology, glucose transport, and lipolysis; lipoprotein lipase activities; sodium-potassium ATPase in red cells, adipocytes, and fibroblasts; lipids and lipoprotein metabolism; fatty acid metabolism; and sterol balance. Insulin concentrations, insulin binding, insulin action on glucose disposal, fatty acid metabolism, and islet function were compared in lean and obese individuals, and the relationship between insulin resistance and muscle morphology was explored. To explore potential abnormalities in energy balance, calorie intake and gastric emptying were compared in lean and obese Pimas and measurements of energy expenditure were performed. The data suggest that there are multiple metabolic differences that accompany obesity in Native Americans. A lower metabolic rate was a determinant of future weight gain, and abnormalities in use of free fatty acids and cell insulin action were suggested, which emphasize the need for further studies in these areas.

Adenosine Triphosphatases↗

PubMed1991

Basal and insulin-mediated carbohydrate metabolism in human muscle deficient in phosphofructokinase 1.

Biopsies were obtained from the quadriceps femoris muscle of two male patients deficient in phosphofructokinase (PFK) 1. In the basal state the patients had markedly higher contents of UDP-glucose (approximately 5-fold), hexose monophosphates (approximately 7- to 13-fold), inosine monophosphate (IMP) (approximately 15-fold), and fructose 2,6-bisphosphate (F-2,6-P2; approximately 6-fold) than controls. Fructose 1,6-bisphosphate was not detectable, and phosphocreatine was lower (33 and 54 mmol/kg dry wt) than in controls [72 +/- 4 (SD)]. Patients had normal fasting plasma glucose and insulin levels and basal glucose turnover rates and responded normally to a 75-g oral glucose challenge. Patients were also studied during euglycemic hyperinsulinemia (approximately 95 mg/dl; 40 and 400 mU.m-2.min-1). Whole body glucose disposal rates were normal during both insulin infusion rates. Biopsies taken after the 400 mU insulin infusion showed decreases in acetylcarnitine and citrate and increases in the fractional activity of glycogen synthase. It is suggested that the high basal levels of F-2,6-P2 are, at least partly, a consequence of the high levels of fructose 6-phosphate, which will stimulate flux through PFK-2 and inhibit fructose-2,6-bisphosphatase. The low phosphocreatine and high IMP contents indicate that carbohydrate availability is important for control of high-energy phosphate metabolism, even in the basal state. The insulin-mediated decreases in acetylcarnitine and citrate suggest an activation of the tricarboxylic acid cycle in skeletal muscle but an absence of the normal response to replenish these intermediates.

Carbohydrate Metabolism↗

PubMed1991

Hyperglycemia induces accumulation of glucose in human skeletal muscle.

The effect of hyperglycemia on whole body substrate utilization and the metabolic profile of skeletal muscle has been investigated. Eight glucose-tolerant men were infused with somatostatin (S) for 190 min. During the last 120 min of S infusion, glucose was infused to achieve a steady-state plasma level of 26 mmol/l. Biopsies were obtained from the quadriceps femoris muscle immediately before and 35 and 120 min after induction of hyperglycemia. Steady-state glucose disposal during hyperglycemia averaged (+/- SE) 33.8 +/- 3.2 mumol.kg fat-free mass-1.min-1, and approximately 70% of the glucose disposal was accounted for by skeletal muscle. Intracellular glucose increased from 0.9 +/- 0.2 mmol/kg dry wt during S to 9.5 +/- 2.5 during hyperglycemia (P less than 0.01). It was estimated that approximately 35% of the glucose taken up by muscle during 120 min of hyperglycemia was not phosphorylated. Muscle contents of alpha-D-glucose 1,6-diphosphate, D-glucose 6-phosphate, ATP, ADP, and AMP (both of which are based on the phosphocreatine-to-creatine ratio), which have been shown to inhibit hexokinase in vitro, did not change significantly during hyperglycemia, nor were there any significant changes in any of the other postphosphofructokinase intermediates, D-fructose 2,6-diphosphate, and citrate. Hyperglycemia did not alter the fractional activities of glycogen synthase or phosphorylase, nor total phosphorylase activity. However, hyperglycemia resulted in a 55% increase in glycogen synthase-specific activity (P less than 0.01). It is concluded that hyperglycemia results in a marked increase in muscle glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Defective insulin response of cyclic adenosine monophosphate-dependent protein kinase in insulin-resistant humans.

Insulin-stimulated glycogen synthase activity in human muscle correlates with insulin-mediated glucose disposal and is reduced in insulin-resistant subjects. Inhibition of the cyclic AMP-dependent protein kinase (A-kinase) is considered as a possible mechanism of insulin action for glycogen synthase activation. In this study, we investigated the time course of insulin action on human muscle A-kinase activity during a 2-h insulin infusion in 13 insulin-sensitive (group S) and 7 insulin-resistant subjects (group R). Muscle biopsies were obtained from quadriceps femoris muscle at times 0, 10, 20, 40, and 120 min. Insulin infusion resulted in significant inhibition of A-kinase activity at 20 and/or 40 min using 0.2, 0.6, and 1.0 microM cyclic AMP in group S. A-kinase activities both before and after insulin administration were lower in group S than in group R using 0.6 microM cyclic AMP. The decrease in apparent affinity for cyclic AMP during insulin infusion was larger for group S compared with group R. Glycogen synthase activity increased significantly after insulin infusion in both groups and was higher in group S compared with group R. The data suggest that a defective response of A-kinase to insulin in insulin-resistant subjects could contribute to their reduced insulin stimulation of skeletal muscle glycogen synthase.

Adult↗

PubMed1991

Deficiency in phosphorylase phosphatase activity despite elevated protein phosphatase type-1 catalytic subunit in skeletal muscle from insulin-resistant subjects.

Glycogen synthase is activated by protein phosphatase type-1 (PP-1). The spontaneous PP-1 activity accounts for only a small fraction of total PP-1 activity, which can be exposed by trypsin digestion of inhibitor proteins in the presence of Mn2+. We determined total PP-1 activity in muscle biopsies from insulin-sensitive and -resistant nondiabetic Pima Indians. Inhibitor-2 sensitive PP-1 represented 90% of total phosphatase activity. Spontaneous and total PP-1 activities were reduced in insulin resistant subjects (P less than 0.05-0.01), suggesting that the reduced PP-1 activity is not the result of inhibition by trypsin-labile phosphatase regulatory subunits. This difference was further investigated by Western blots using two different antibodies. An antibody raised against the rabbit muscle PP-1 catalytic subunit was used to analyze muscle extracts concentrated by DEAE-Sepharose adsorption. An antibody raised against a peptide derived from the COOH-terminal end of the PP-1 catalytic subunit was used to analyze crude muscle extracts. Both antibodies recognized a PP-1 catalytic subunit of approximately 33 kD, which unexpectedly was more abundant in insulin-resistant subjects (P less than 0.05-0.01). The increase in the tissue PP-1 protein content may be a response to compensate for the impairment in the enzyme activity.

Adult↗

PubMed1991

Insulin-sensitive tyrosine kinase activity changes in parallel with plasma insulin and glucose concentrations in humans.

Insulin receptor tyrosine kinase is an important step in insulin action. We examined the relationship between diet-induced changes in glucose metabolism and changes in skeletal muscle insulin-sensitive tyrosine kinase activity in 12 nondiabetic subjects. Subjects were fed a traditional, high carbohydrate Pima Indian diet and a modern, high fat western diet for 2 weeks in a randomized cross-over design. At the end of each dietary period, glucose tolerance was assessed, insulin sensitivity (SI) was estimated by Bergman's minimal model method, and insulin receptor concentration and tyrosine kinase activity were determined on lectin-purified extracts from quadriceps femoris muscle. Compared to the traditional diet, the modern diet was associated with a deterioration of glucose tolerance and an increase in glucose-induced plasma insulin levels. As expected, SI changes were associated with opposite changes in plasma insulin levels. However, the changes in maximal tyrosine kinase activity were negatively correlated with changes in SI (r = -0.69; P less than 0.01) and positively correlated with changes in plasma glucose (r = 0.70; P less than 0.01) and insulin response to glucose (r = 0.57; P less than 0.025). These results suggest that the site of diet-induced changes in insulin action is beyond the insulin-sensitive tyrosine kinase. The results further suggest that the kinase activity is modulated by prevailing plasma insulin levels.

Blood Glucose↗

PubMed1990

Skeletal muscle glycogen synthase activity in subjects with non-insulin-dependent diabetes mellitus after glyburide therapy.

Sulfonylureas are used in the treatment of non-insulin-dependent diabetes mellitus (NIDDM) largely because of their ability to enhance insulin secretion and possibly to potentiate insulin action. In this study, we investigated the effects of chronic glyburide treatment on glycogen synthase activity determined in skeletal muscle biopsies taken during euglycemic hyperinsulinemic clamps in nine Pima Indians with NIDDM. Insulin was infused at the rate of 40 mU/m2/min (low dose) followed by 400 mU/m2/min (high dose). Compared with the fasting value, the mean glycogen synthase activity assayed at low glucose-6-phosphate (G6P) concentration (active glycogen synthase) showed no significant changes during insulin infusion before glyburide treatment. After glyburide treatment, the mean active glycogen synthase increased by 39% (P less than .05) above the fasting value during the high-dose insulin infusion. Total glycogen synthase activity assayed at high G6P concentration did not change after glyburide treatment. Changes of insulin-stimulated active glycogen synthase associated with glyburide treatment correlated with changes in total body glucose disposal rates (r = .70, P less than .05) during euglycemic clamps. We conclude that glyburide treatment of subjects with NIDDM is associated with an increase in insulin action in vivo and concomitantly with improved insulin action on skeletal muscle glycogen synthase.

Adult↗

PubMed1990

Insulin-sensitive tyrosine kinase: relationship with in vivo insulin action in humans.

To investigate the relationship of insulin receptor kinase with insulin resistance in humans, we studied insulin-sensitive tyrosine kinase activity in muscle biopsies taken from 20 Pima Indians [14 nondiabetics, 6 with non-insulin-dependent mellitus (NIDDM)] during euglycemic clamps, at insulin concentrations of approximately 68 microU/ml (low dose) and approximately 1,170 microU/ml (high dose). In the nondiabetics, the low dose, insulin-induced kinase activation in vivo was 1.5-fold the activity in the fasting state (P less than 0.05), whereas in the diabetics, the kinase activity actually decreased by 40% relative to fasting (P less than 0.05). The difference in delta-kinase in vivo was significant (P less than 0.01) between the two groups. Similarly, the kinase activation in vitro in response to 1 nM insulin was lower in diabetic subjects compared with nondiabetics (P less than 0.01). These data indicate that, in NIDDM, both in vitro and in vivo insulin-stimulated tyrosine kinase activity is impaired. Among nondiabetics, the kinase sensitivity to insulin, calculated as the ratio of the kinase activity at 1 nM insulin in vitro to the kinase activity at 100 nM insulin, was positively correlated with plasma insulin concentrations 2 h after an oral glucose load (r = 0.69, P less than 0.01). Thus, in nondiabetic subjects with insulin resistance, insulin activation of the kinase is not reduced, but the kinase sensitivity to insulin increases with increasing plasma insulin levels. Therefore, the site of insulin resistance in nondiabetic subjects is distal to the insulin receptor kinase. Furthermore, it is possible that circulating insulin, by increasing the kinase sensitivity to insulin, is a determinant of the receptor kinase activity.

Adult↗

PubMed1990

Insulin resistance is associated with reduced fasting and insulin-stimulated glycogen synthase phosphatase activity in human skeletal muscle.

Insulin-stimulated glycogen synthase activity in human skeletal muscle correlates with insulin-mediated glucose disposal rate (M) and is reduced in insulin-resistant subjects. We have previously reported reduced insulin-stimulated glycogen synthase activity associated with reduced fasting glycogen synthase phosphatase activity in skeletal muscle of insulin-resistant Pima Indians. In this study we investigated the time course for insulin stimulation of glycogen synthase and synthase phosphatase during a 2-h high-dose insulin infusion (600 mU/min per m2) in six insulin-sensitive caucasians (group S) and in five insulin-resistant Pima Indians (group R). Percutaneous muscle biopsies were obtained from the quadriceps femoris muscle after insulin infusion for 0, 10, 20, 40, and 120 min. In group S, insulin-stimulated glycogen synthase activity increased with time and was significantly higher than in group R. In group S, synthase phosphatase activity increased significantly by 25% at 10 min and then decreased gradually. No significant change in synthase phosphatase was seen in group R and activity was lower than group S at 0 to 20 min. These data suggest that a low basal synthase phosphatase activity and a defect in its response to insulin explain, at least in part, reduced insulin stimulation of skeletal muscle glycogen synthase associated with insulin resistance.

Adenosine Triphosphate↗

PubMed1990

Insulin and hypertension. Relationship to obesity and glucose intolerance in Pima Indians.

The relationships among blood pressure, obesity, glucose tolerance, and serum insulin concentration were studied in 2873 Pima Indians aged 18-92 yr (mean 37 yr). Age- and sex-adjusted to the Pima population, the prevalence of hypertension (systolic blood pressure greater than or equal to 160 mmHg, diastolic blood pressure greater than or equal to 95 mmHg, or receiving drug treatment) was 7.1% for subjects with normal glucose tolerance compared with 13.0% for subjects with impaired glucose tolerance (IGT) and 19.8% for those with non-insulin-dependent diabetes mellitus (NIDDM) (P less than 0.001). The prevalence ratio of hypertension was 1.8 (95% confidence interval [CI] 1.2-2.5) for IGT and 2.6 (95% CI 2.0-3.2) for NIDDM compared with normal glucose tolerance, controlled for age, sex, and body mass index (BMI). In logistic regression analysis, hypertension was positively related to age, male sex, BMI, glucose tolerance, and fasting but not 2-h postload serum insulin concentration. Among subjects not taking antihypertensive drugs, however, neither fasting nor 2-h postload serum insulin was significantly related to hypertension. Furthermore, in 2033 subjects receiving neither antihypertensive nor antidiabetic drugs, blood pressure was not significantly correlated to fasting insulin concentration, and 2-h postload serum insulin was negatively correlated with diastolic blood pressure. In conclusion, insulin is not significantly related to blood pressure in Pima Indians not receiving antihypertensive drugs. Higher insulin concentrations in drug-treated hypertensive patients might result from the treatment rather than contribute to the pathogenesis of hypertension. Thus, these data do not support a major role for insulin in determining the occurrence of hypertension or regulation of blood pressure in Pima Indians.

Adolescent↗

PubMed1989

Sequential changes in serum insulin concentration during development of non-insulin-dependent diabetes.

Changes in serum insulin concentrations during deterioration of glucose tolerance were studied in 81 Pima Indians who worsened from normal to impaired glucose tolerance (IGT); 44 who changed from IGT to non-insulin-dependent diabetes mellitus (NIDDM); 27 who were seen at diagnosis of NIDDM and 1.4-8.5 years later; and 11 subjects who were seen at each of these stages. When their glucose tolerance was normal, subjects who later developed NIDDM had higher fasting and post-load insulin concentrations than controls of similar age and body mass index who did not become diabetic. Onset of IGT or NIDDM was associated with a further increase in fasting insulin concentrations, although a deterioration from IGT to NIDDM was associated with little change in insulin responses to oral glucose in spite of increased blood glucose. After the onset of NIDDM, both fasting and post-load insulin concentrations diminished. These longitudinal data show that, as glucose tolerance worsens, insulin and glucose concentrations in individuals follow the inverted-U-shaped relation previously reported in cross-sectional population studies.

Adolescent↗

PubMed1989

Contraction-mediated inactivation of glycogen synthase is accompanied by inactivation of glycogen synthase phosphatase in human skeletal muscle.

Activities of glycogen synthase (GS) and GS phosphatase were determined on human muscle biopsies before and after isometric contraction at 2/3 maximal voluntary force. Total GS activity did not change during contraction (4.92 +/- 0.70 at rest versus 5.00 +/- 0.42 mmol/min per kg dry wt.; mean +/- S.E.M.), whereas both the active form of GS and the ratio of active form to total GS decreased by approximately 35% (P less than 0.01). GS phosphatase was inactivated in all subjects by an average of 39%, from 5.95 +/- 1.30 to 3.63 +/- 0.97 mmol/min per kg dry wt. (P less than 0.01). It is suggested that at least part of the contraction-induced inactivation of GS is due to an inactivation of GS phosphatase.

Adult↗

PubMed1989

Adenosine 3',5'-monophosphate-dependent protein kinase activity decreases in human muscle after insulin infusion.

We have previously reported that the increase in glycogen synthase activity in human muscle during a euglycemic clamp was not associated with a measured increase in glycogen synthase phosphatase activity after a 200-min insulin administration. To investigate further the mechanism of the regulation of human muscle glycogen synthase by insulin, we measured the activity of cAMP-dependent protein kinase before and after a 200-min hyperinsulinemic euglycemic clamp in Southwest American Indians. Insulin infusion resulted in a decreased cAMP-dependent protein kinase activity assayed at physiological cAMP concentration with increased glycogen synthase activity in all subjects (n = 5; P less than 0.01). No significant change was observed in cAMP-independent protein kinase activity. These results suggest that 200 min of insulin administration during a euglycemic clamp may regulate human muscle glycogen synthase activity by mechanisms other than the stimulation of phosphatase; one probable mechanism is by decreasing the activity of cAMP-dependent protein kinase.

Adult↗

PubMed1989

Distribution of in vivo insulin action in Pima Indians as mixture of three normal distributions.

If a single gene produced insulin resistance, with environmental effects creating some additional variance, insulin action might be distributed as a mixture of two normal distributions if the gene is dominant or recessive or as a mixture of three normal distributions if the gene is codominant. To estimate maximal insulin-stimulated glucose uptake rates (MaxMs), hyperinsulinemic-euglycemic clamps were performed on 245 nondiabetic Pima Indians (126 men, 119 women). Five models (for 1, 2, 3, 4, or 5 components each, normally distributed with a common variance) were fitted to the frequency distribution of MaxM by iterative maximum-likelihood estimation. The three-component model fit the data significantly better than a single normal distribution (chi 2 = 14.3 with 4 df P less than .01) or a mixture of two normal distributions (chi 2 = 9.9 with 2 df, P less than .01). Mixtures of four or five normal distributions did not fit the data significantly better than a mixture of three normal distributions. The first component of the distribution comprised 23%, the second 48%, and the third 29% of the total distribution. Similarly, the frequency distributions of fasting plasma insulin concentrations and a principal component score derived from MaxM and fasting insulin were best fitted by a mixture of three normal distributions. These results are consistent with the hypothesis that among Pimas, insulin resistance is determined by a single gene with a codominant mode of inheritance. Segregation analyses of studies performed in pedigrees are indicated to prove or disprove this genetic hypothesis.

Adult↗

PubMed1988

The natural history of impaired glucose tolerance in the Pima Indians.

Among 384 Pima Indians with impaired glucose tolerance according to World Health Organization criteria who were followed for 1.6 to 11.5 years (median, 3.3), non-insulin-dependent diabetes mellitus (NIDDM) developed in 118 (31 percent), glucose tolerance remained impaired in 100 (26 percent), and glucose tolerance returned to normal in 166 (43 percent). The cumulative incidence of NIDDM was 25 and 61 percent at 5 and 10 years, respectively. The risk of development of diabetes was 6.3 times (95 percent confidence interval, 3.8 to 10.6) as high as in a normoglycemic control group (n = 752). Variables predicting deterioration to NIDDM were age up to the age of 40, after which increasing age had a beneficial effect; higher plasma glucose levels during fasting and after carbohydrate loading; and higher serum insulin levels after fasting and lower levels after carbohydrate loading, suggesting that insulin resistance and decreased beta-cell responsiveness are important determinants of the clinical outcome of impaired glucose tolerance. Obese subjects had 2.9 times (95 percent confidence interval, 2.0 to 10.9) the incidence of NIDDM as the nonobese. Obesity was not, however, predictive of progression to NIDDM after an adjustment for plasma glucose and serum insulin levels. We conclude that in this population approximately one fourth of subjects with impaired glucose tolerance have NIDDM at five years and two thirds at 10 years (approximately one third revert to normal) and that age and plasma glucose and insulin levels are the best predictors of clinical outcome.

Adult↗