The acute effect of insulin on tissue plasminogen activator and plasminogen activator inhibitor in man

The present study was performed to elucidate the acute effect of insulin on levels of tissue plasminogen activator (t-PA) and plasminogen activator inhibitor of endothelial cell type (PAI-1). Nine middle-aged, non-obese and non-smoking men were studied during a hyperinsulinemic, euglycemic glucose clamp for 2 h. Plasma insulin level during the clamp averaged 84 +/- 12 mU/l and euglycemia was maintained at 4.9 +/- 0.6 mmol/l. The t-PA activity gradually increased (75% mean increase after 2 h, p less than 0.001) and the PAI-1 activity decreased (49% mean decrease after 2 h, p less than 0.001) during the clamp. t-PA activity decreased and PAI-1 activity increased after the insulin infusion was ceased, but they were still 48% higher and 38% lower, respectively, after 60 min. PAI-1 and t-PA activities were not affected by saline infusion for 2 h. Thus, acute changes in the insulin levels lead to rapid alterations in the fibrinolytic system even when euglycemia is maintained. These effects may be induced by insulin itself or by the concomitant activation of the sympatho-adrenal system during the euglycemic clamp.

Treating insulin resistance in hypertension with metformin reduces both blood pressure and metabolic risk factors

Insulin resistance and hyperinsulinaemia may play an important role in both the development of hypertension and its accompanying metabolic aberrations. In order to investigate this possibility, nine non-obese, non-diabetic, non-smoking, middle-aged men with untreated hypertension were treated with metformin 850 mg b.i.d. for 6 weeks as a pilot study and within-patient comparison. Metformin decreased total and LDL-cholesterol (P less than 0.01), triglyceride (P less than 0.01), fasting plasma insulin (P less than 0.01) and C-peptide levels (P less than 0.02). Glucose disposal, an indicator of insulin action measured by means of the euglycaemic clamp technique, increased (P less than 0.001). Tissue plasminogen activator (t-PA) activity increased (P less than 0.02), and t-PA antigen decreased (P less than 0.01), whereas plasminogen activator inhibitor (PAI-1) and fibrinogen were unaffected by metformin treatment. Body weight remained unchanged. Withdrawal of metformin was associated with the return of both blood pressure and metabolism towards the initial levels. In conclusion, metformin treatment increased insulin action, lowered blood pressure, improved the metabolic risk factor profile and tended to increase the fibrinolytic activity in these mildly hypertensive subjects. These results support the view that insulin resistance plays a role in hypertension, and may open up a new field for the alleviation of abnormalities associated with cardiovascular disease.

The skeletal muscle Na:K ratio is not increased in hypertension: evidence for the importance of obesity and glucose intolerance

Several previous studies have suggested that hypertension is associated with altered sodium transport across the cell membrane. The aim of the present study was to study the skeletal muscle Na:K ratio in relation to blood pressure and glucose tolerance in obese and non-obese men. Muscle biopsies were taken from the femoral vastus lateralis muscle in men aged 52 +/- 5 years and the electrolytes were analyzed. Ten obese men with impaired glucose tolerance and hypertension, 10 obese normotensive controls, 10 lean men with hypertension and 10 lean normotensive controls participated in the study. Higher insulin levels were found in both hypertensive groups compared with the respective normotensive groups. Increased muscle Na:K ratio was found in obesity (P less than 0.01) and this was further enhanced when combined with hypertension and impaired glucose tolerance (P less than 0.001). However, hypertension in lean individuals was not associated with an increased muscle Na:K ratio. These data suggest that the increased muscle Na:K ratio in obese subjects and those with impaired glucose tolerance is not solely due to insulin resistance and hyperinsulinemia. Furthermore, the data clearly suggest that there is no important general perturbation of the Na-K pump in hypertension per se.

Abdominal obesity is associated with an impaired fibrinolytic activity and elevated plasminogen activator inhibitor-1

Recent epidemiologic studies have shown that abdominal obesity, characterized by a high waist to hip circumference ratio (WHR), is associated with increased cardiovascular morbidity and mortality. The present study examines components of the fibrinolytic system in obese and lean middle-aged women with a high and low WHR. Ten women in each group were carefully matched with respect to age, body weight, lean body mass, and body fat. Fibrinogen and endothelial type of plasminogen activator inhibitor -1 (PAI-1) were significantly elevated in the obese women with a high WHR compared with the obese women with a low WHR or with both groups of lean women. In addition, obese women with a high WHR exhibited a greater metabolic risk profile (elevated glucose, insulin, and triglyceride levels). When all subjects were pooled for the analyses, both fibrinogen and PAI-1 levels correlated positively with glucose and insulin levels. PAI-1 was also negatively related to degree of insulin sensitivity measured with the euglycemic clamp technique. In the obese groups, WHR but not body mass index (BMI), correlated with PAI-1 levels. No such correlations were seen in the lean groups. In conclusion, the data show that a high WHR in obese, but not lean middle-aged women, is associated with an impaired fibrinolytic activity. This perturbation becomes enhanced when it is associated with hyperinsulinemia and insulin resistance, which is a typical feature of abdominal obesity.

Increased insulin resistance and fat cell lipolysis in obese but not lean women with a high waist/hip ratio

Increased lipolysis in abdominal adipocytes has been suggested to be of importance for the insulin resistance typical for abdominal obesity. In order to differentiate between fat distribution, measured as waist/hip ratio (WHR), and amount of body fat, glucose disposal during a euglycaemic clamp as well as lipolysis in isolated cells from abdominal and gluteo-femoral regions were studied in 20 obese and 20 lean postmenopausal women with a high (n = 10) and low (n = 10) WHR, respectively. The lipolytic response was increased in cells from obese women irrespective of region. Furthermore, lipolysis was enhanced in abdominal compared with the gluteo-femoral cells in obese women with a high WHR. Fasting blood glucose and insulin were increased in both groups of obese women while the degree of insulin resistance was most pronounced in the obese women with a high WHR. It is concluded that increased body fat is associated with both insulin resistance and increased lipolysis, and that this relationship is stronger in the presence of a high WHR. A high WHR may increase the expression of obesity as a risk for insulin resistance and this may be mediated through an increased lipolytic rate.

Characterization of the late posthypoglycemic insulin resistance in insulin-dependent diabetes mellitus

The insulin effect (6.5 to 7.5 hours) following hypoglycemia was studied with the euglycemic clamp technique in eight patients with insulin-dependent diabeteses mellitus (IDDM). The results were compared with a control study with the same insulin infusion, but where hypoglycemia was prevented by a glucose infusion. Glucose production (Ra) and utilization (Rd) were evaluated with D-(3-3H) glucose infusion. Hypoglycemia (glucose nadir, 1.5 +/- 0.1 mmol/L) caused a marked increase in cortisol and growth hormone, whereas the release of adrenaline and, in particular, glucagon was low. The plasma free insulin levels were similar in the studies, including during the clamp periods. The glucose infusion rates (GIR) were significantly lower after the hypoglycemia as compared with the control study (control, 2.4 +/- 0.3; hypoglycemia, 1.5 +/- 0.3 mg/kg x min; P less than .05). Thus, hypoglycemia induces prolonged insulin resistance. The posthypoglycemic insulin resistance during a moderate hyperinsulinemic (approximately 30 mU/L) clamp was mainly due to a decreased insulin effect on glucose utilization (control, 2.9 +/- 0.2; hypoglycemia, 2.2 +/- 0.2 mg/kg x min; P less than .02), whereas the insulin effect on glucose production was not significantly different after hypoglycemia.

The insulin-like effect of growth hormone on insulin-like growth factor II receptors is opposed by cyclic AMP. Evidence for a common post-receptor pathway for growth hormone and insulin action

The counter-regulatory effects of beta-adrenergic stimulation and cyclic AMP on the insulin-like action of growth hormone (GH) on the subcellular distribution of insulin-like growth factor II (IGF-II) receptors were studied in fat cells from hypophysectomized (Hx) and sham-operated rats. For comparison, the effect of insulin on this process was also studied. Basal IGF-II binding was increased by approx. 2-fold in cells from Hx as compared with sham-operated animals. The stimulatory effect of insulin was decreased in Hx cells, mainly due to a basal redistribution but also to a reduced total number of receptors. GH exerted an acute insulin-like effect in cells from Hx rats and stimulated the translocation of IGF-II receptors from an intracellular pool to the plasma membrane. beta-Adrenergic stimulation with isoprenaline or addition of the non-metabolizable cyclic AMP-analogue N6-monobutyryl cyclic AMP induced a cellular resistance to both GH and insulin and also reduced the responsiveness to these hormones. Adenosine exerted a modulatory effect on both hormones. Binding of 125I-labelled GH to its receptors was not significantly changed by any of these factors. It is concluded that: (1) beta-adrenergic stimulation and cyclic AMP induce a cellular GH resistance at a level distal to the GH-binding site, and (2) the insulin-like effect of GH shares a common pathway with insulin which occurs at the post-binding level.

Interstitial glycerol concentration measured by microdialysis in two subcutaneous regions in humans

Interstitial glycerol concentrations were measured in the abdominal and femoral subcutaneous tissue in 10 lean and 6 obese subjects. In the lean subjects [waist-hip circumference ratio (WHR) 0.89 +/- 0.01] the fasting interstitial glycerol concentrations in the abdominal and femoral regions were 185 +/- 20 and 160 +/- 15 (SE) microM, respectively, whereas glycerol in venous plasma was considerably lower (66 +/- 5 microM). After an oral glucose load (100 g) the interstitial glycerol concentrations declined but remained higher than in plasma. In obese subjects (WHR 1.1 +/- 0.03) the fasting interstitial glycerol levels were higher, in both regions, than in lean individuals. Furthermore, interstitial glycerol in the abdominal site (291 +/- 32 microM) was significantly higher than in the femoral fat (210 +/- 13 microM; P less than 0.05), while plasma glycerol was similar to that in lean subjects (80 +/- 12 microM). Interstitial glycerol remained higher in the obese than in the lean subjects also after an oral glucose load, but the regional differences were less apparent. Thus interstitial glycerol is higher in the subcutaneous tissue than in venous blood. The data also suggest that lipolysis is enhanced in the abdominal subcutaneous tissue as compared with the femoral site in obese subjects and that lipolysis is exaggerated in both regions in obese as compared with lean individuals.

Microdialysis--a novel technique for clinical investigations

Microdialysis is a novel, non-traumatic technique which, when properly performed, allows continuous direct measurements of substances in the interstitial space of a tissue or organ. It also makes it possible to obtain protein-free fluid for analyses, while contaminating bacteria or viruses are excluded. The measurements provide us with an insight into metabolic and pharmacological events at the cellular level in a target organ. Apart from its usefulness for experimental work, it is likely to become an important tool for defined areas in clinical practice.

Free-fatty acid inhibition of insulin binding, degradation, and action in isolated rat hepatocytes

The effect of free fatty acids (FFAs) on insulin binding and action was investigated in isolated rat hepatocytes. Oleic acid (0.4 mM) added to the cells rapidly (within 45 min) reduced insulin binding and degradation (each by 45%; P less than 0.001, n = 7) without changing the apparent receptor affinity. The effect was concentration dependent; a half-maximal inhibitory effect occurred at 0.150 +/- 0.050 mM (mean +/- SE). Oleic acid exerted no effect on insulin binding in energy-depleted (KCN-treated) cells. Oleic, palmitic, stearic, palmitoleic, and eicosapentaenoic acids were equally effective in reducing insulin binding. FFA did not change insulin binding to partially purified insulin receptors, thus excluding a direct effect on the insulin receptor. Furthermore, binding to partially purified receptors from solubilized cells pretreated with 0.2 mM oleic acid was not changed, indicating the effect of FFA in intact cells is on the rate of receptor internalization and/or recycling. Concomitant with the effect on insulin binding, oleic acid elicited a concentration-dependent reduction in nonstimulated cellular [14C]aminoisobutyric acid uptake (AIB; 29 +/- 8%, P less than 0.05) and decreased the maximal effect of insulin (39 +/- 7%, P less than 0.05). Thus, in a concentration-dependent manner, different fatty acids can reduce the number of binding sites for insulin and the degradation of insulin by isolated liver cells. Basal and insulin-stimulated AIB transport was reduced, suggesting the presence of postbinding perturbations. These data suggest that FFA exerts an important modulating effect on insulin action in the liver.

Elevated fibrinogen and plasminogen activator inhibitor (PAI-1) in hypertension are related to metabolic risk factors for cardiovascular disease

The relationship between hypertension, glucose metabolism, fibrinogen and plasminogen activator inhibitor of endothelial cell type (PAI-1) was studied under conditions in which the influence of obesity and adipose tissue distribution (waist/hip ratio) were controlled. Twenty-two non-obese, middle-aged men with normal blood pressure (n = 11) and untreated mild hypertension (n = 11), respectively, participated in the study. Cholesterol, triglyceride and insulin levels were higher in hypertensive men than in the control group. Glucose disposal was studied as an indicator of insulin sensitivity using the euglycaemic clamp technique. The insulin effect tended to be less marked in men with hypertension. PAI-1 was higher in hypertensive men compared to the controls. A strong positive correlation was observed between PAI-1 and insulin levels as well as blood pressure. PAI-1 and fibrinogen levels correlated negatively with the rate of glucose disposal. Thus, even in these non-obese and mildly hypertensive individuals, an enhanced metabolic risk factor profile for cardiovascular disease was found. The metabolic aberrations were related to elevated fibrinogen and PAI-1 levels which, in turn, increase the risk of thrombus formation.

Evidence for lactate production by human adipose tissue in vivo

Microdialysis of the abdominal subcutaneous tissue was performed in seven healthy normal weight subjects after an overnight fast and also after oral ingestion of 100g glucose. The lactate concentration in the interstitial water was compared with that in the venous and arterialized plasma from the cubital veins. In the postabsorptive state the lactate concentration in the subcutaneous tissue (1128 +/- 72 mumol/l, mean +/- SEM) was significantly higher (p less than 0.01) than that in both arterialized (722 +/- 72 mumol/l) and venous plasma (798 +/- 41 mumol/l). The oral glucose load further increased the lactate level in the subcutaneous tissue throughout the observation period of 2h. The kinetics for the increase in the lactate concentration was not apparently different in blood or tissue. The highest lactate levels were 1798 +/- 173 mumol/l in the subcutaneous tissue and 1199 +/- 150 mumol/l and 1275 +/- 123 mumol/l in arterialized and venous plasma, respectively. It is concluded that abdominal adipose tissue produces lactate both in the fasting state and after an oral glucose load. The data emphasize the importance of the adipose tissue as a significant source of lactate production in the body.

Probing the bacteriochlorophyll binding site by reconstitution of the light-harvesting complex of Rhodospirillum rubrum with bacteriochlorophyll a analogues

Structural features of bacteriochlorophyll (BChl) a that are required for binding to the light-harvesting proteins of Rhodospirillum rubrum were determined by testing for reconstitution of the B873 or B820 (structural subunit of B873) light-harvesting complexes with BChl a analogues. The results indicate that the binding site is very specific; of the analogues tested, only derivatives of BChl a with ethyl, phytyl, and geranylgeranyl esterifying alcohols and BChl b (phytyl) successfully reconstituted to form B820- and B873-type complexes. BChl analogues lacking magnesium, the C-3 acetyl group, or the C-13(2) carbomethoxy group did not reconstitute to form B820 or B873. Also unreactive were 13(2)-hydroxyBChl a and 3-acetylchlorophyll a. Competition experiments showed that several of these nonreconstituting analogues significantly slowed BChl a binding to form B820 and blocked BChl a-B873 formation, indicating that the analogues may competitively bind to the protein even though they do not form red-shifted complexes. With the R. rubrum polypeptides, BChl b formed complexes that were further red-shifted than those of BChl a; however, the energies of the red shifts, binding behavior, and circular dichroism (CD) spectra were similar. B873 complexes reconstituted with the geranylgeranyl BChl a derivative, which contains the native esterifying alcohol for R. rubrum, showed in-vivo-like CD features, but the phytyl and ethyl B873 complexes showed inverted CD features in the near infrared. The B820 complex with the ethyl derivative was about 30-fold less stable than the two longer esterifying alcohol derivatives, but all formed stable B873 complexes.

Postprandial hyperglycaemia following a morning hypoglycaemia in type 1 diabetes mellitus

The occurrence of hyperglycaemia following a morning hypoglycaemic episode was studied in nine patients with Type 1 diabetes. Each patient was studied twice, once following induced hypoglycaemia and once in a control study when hypoglycaemia was prevented by glucose infusion. After the initial hypoglycaemic/control period the patients were maintained on their regular insulin regimens and were given standard meals. Hypoglycaemia induced postprandial hyperglycaemia (3.1 +/- 0.8 mmol l-1 above control) which lasted for about 8 h. Maximal growth hormone levels were seen 40 min after glucose nadir (control 7.8 +/- 3.2, hypoglycaemia 74.0 +/- 12.3 mU l-1) and the magnitude of the hyperglycaemia was related to the growth hormone levels following the hypoglycaemia (r = 0.80, p less than 0.01).

Combined effect of growth hormone and cortisol on late posthypoglycemic insulin resistance in humans

The occurrence and mechanisms for late (6.5- to 7.5-h) posthypoglycemic insulin resistance were studied with the euglycemic clamp in 19 healthy subjects. Comparisons were made with a control study with the same insulin infusion rate but where hypoglycemia was prevented by glucose infusion. Glucose production and utilization were studied with D-[3-3H] glucose infusions. Hypoglycemia induced marked insulin resistance shown by lower glucose infusion rates compared with the control study 3.1 +/- 0.3 vs. 6.0 +/- 0.7 mg.kg-1.min-1, P less than .001). This late posthypoglycemic insulin resistance was mainly due to a decreased insulin effect on glucose utilization. Infusion of propranolol did not prevent insulin resistance, whereas somatostatin partially prevented its appearance. Somatostatin plus metyrapone completely normalized posthypoglycemic insulin resistance. A positive correlation (r = .72, P less than .001) was found between initial insulin sensitivity and percent reduction of the insulin effect after hypoglycemia. Thus, hypoglycemia is followed by prolonged (6- to 8-h) insulin resistance. In contrast to early-phase (2- to 3-h) resistance, long-term resistance is not due to beta-adrenergic stimulation but to the combined effect of growth hormone and cortisol. This resistance is also more pronounced in subjects with initially high insulin sensitivity.

Importance of obesity for the metabolic abnormalities associated with an abdominal fat distribution

Obese people with a high waist/hip ratio (W/H ratio) have an increased risk for cardiovascular disease. The present study was designed to separately analyze the importance of obesity and the regional fat distribution for the metabolic risk factors. Blood pressure, glucose tolerance, insulin, and plasma lipid levels were studied in lean and obese postmenopausal women with a high or low W/H ratio. The individuals within each group were carefully matched for age, lean body mass, and body fat. The risk factors associated with a high W/H ratio (elevated blood pressure, blood lipids, and glucose levels) were found in the obese but not in the lean women. Furthermore, lean women with a high W/H ratio tended to have a lower metabolic risk factor profile than obese women with a low W/H ratio. These findings document the importance of obesity in expressing the metabolic risk factors for cardiovascular disease associated with a high W/H ratio.

Microdialysis of intercellular adenosine concentration in subcutaneous tissue in humans

To determine the intercellular adenosine concentration the periumbilical subcutaneous interstitial fluid was investigated in five healthy subjects with two single dialysis fiber catheters perfused with isotonic saline at a rate of 2.5 mul/min. A newly developed in situ calibration technique (29) allows an estimation of the adenosine concentration in the perfusate equilibrating with the surrounding medium, i.e., the concentration in the interstitial fluid. The mean interstitial adenosine concentration was 128 +/- 26 nM (range 25-300 nM). The effect of these adenosine concentrations on adipose tissue metabolism was investigated in isolated human fat cells. The influence of 5 and 10 nM 2-chloroadenosine, which is equipotent to 150 and 300 nM adenosine, on the dose-response curve for the lipolytic effect of norepinephrine and the stimulatory effect of insulin on glucose transport was studied. 2-Chloroadenosine at 10 nM decreased basal lipolysis 53 +/- 8% and shifted the dose-response curve for norepinephrine approximately twofold to the right. At 5 nM, 2-chloroadenosine only slightly shifted the dose-response curve, whereas basal lipolysis was not significantly reduced. 2-Chloroadenosine at either concentration had no significant effect on basal or insulin-stimulated glucose transport. In conclusion, endogenous adenosine can reach concentrations in human subcutaneous tissue sufficient for an important modulating effect on lipolysis in vivo.

Insulin-induced subcellular redistribution of insulin-like growth factor II receptors in the rat adipose cell. Counterregulatory effects of isoproterenol, adenosine, and cAMP analogues

Insulin shifts the steady-state subcellular distribution of insulin-like growth factor II (IGF-II) receptors from a large intracellular pool to the plasma membrane in the rat adipose cell (Wardzala, L. J., Simpson, I. A., Rechler, M. M., and Cushman, S. W. (1984) J. Biol. Chem. 259, 8378-8383). In the present study, the counterregulatory effects of adrenergic stimulation, adenosine deaminase, and cAMP on this process were studied. Both isoproterenol (10(-6) M) and adenosine deaminase reduced insulin sensitivity and also rapidly (t1/2 approximately 1.5 min) decreased the effect of a maximal insulin concentration on the number of cell surface IGF-II receptors by 35-50%, and by 70% when added together. The marked reduction in binding was retained in isolated and solubilized plasma membranes. Both isoproterenol and adenosine deaminase alone increased the EC50 for insulin from 0.06 to 0.17 nM and, when combined, to 0.6 nM. N6-Monobutyryl-cAMP and 8-bromo-cAMP were equally potent in reducing IGF-II binding in the absence of insulin and inhibited maximal insulin-stimulated IGF-II binding by 60 and 30%, respectively. However, only the nonhydrolyzable cAMP analogue, N6-monobutyryl-cAMP, reduced the insulin sensitivity (EC50 0.7 nM). An important stimulatory role for Gi (guanine nucleotide-binding regulatory protein that inhibits adenylate cyclase) was indicated by the altered activities of cells from pertussis toxin-treated animals. The results suggest that beta-adrenergic stimulation through a cAMP-dependent mechanism markedly alters the insulin-stimulated redistribution of IGF-II receptors. This effect is additional to the potent antagonistic action of cAMP on insulin's signalling mechanism.

Characterization by microdialysis of intracellular glucose level in subcutaneous tissue in humans

The subcutaneous intercellular glucose concentration was measured with a microdialysis method in 14 healthy volunteers and compared with that in venous blood. Under steady-state fasting conditions the intercellular glucose concentration was similar to that in the blood. During an oral glucose tolerance test the absorption phase was slightly delayed (approximately 2 min) in the intercellular space compared with the blood. However, the kinetics for the decline in glucose was similar in the two compartments. The interstitial glucose concentration was similar to that in venous blood during both a eu- and a hyperglycemic clamp. However, a rapid change from euglycemia to hyperglycemia was associated with a significant delay (approximately 8 min) in the intercellular glucose. The data demonstrate that the subcutaneous tissue glucose concentration under non-steady-state conditions closely resembles that in venous blood.