The effects of different plasma insulin concentrations on lipolytic and ketogenic responses to epinephrine in normal and type 1 (insulin-dependent) diabetic humans

This study was performed to verify: (1) the ability of different insulin concentrations to restrict the lipolytic and ketogenic responses to exogenous epinephrine administration; (2) whether the ability of insulin to suppress the lipolytic and ketogenic responses during epinephrine administration is impaired in Type 1 (insulin-dependent) diabetic patients. Each subject was infused on separate occasions with insulin at rates of 0.2, 0.4, and 0.8 mU.kg-1.min-1 while normoglycaemic. To avoid indirect adrenergic effects on endocrine pancreas secretions, the so-called "islet clamp" technique was used. Rates of appearance of palmitic acid, acetoacetate, and 3-hydroxybutyrate were simultaneously measured with an infusion of 13C-labelled homologous tracers. After a baseline observation period epinephrine was exogenously administered at a rate of 16 ng.kg-1.min-1. At low insulin levels (20 microU/ml) the lipolytic response of comparable magnitude was detected in normal and Type 1 diabetic patients. However, the ketogenic response was significantly higher in Type 1 diabetic patients. During epinephrine administration, similar plasma glucose increments were observed in the two groups (from 4.74 +/- 0.53 to 7.16 +/- 0.77 mmol/l (p less than 0.05) in Type 1 diabetic patients and from 4.94 +/- 0.20 to 7.11 +/- 0.38 mmol/l (p less than 0.05) in normal subjects, respectively). At intermediate insulin levels (35 microU/ml) no significant differences were found between Type 1 diabetic patients and normal subjects, whereas plasma glucose levels rose from 4.98 +/- 0.30 to 6.27 +/- 0.66 mmol/l (p less than 0.05) in Type 1 diabetic patients, and from 5.05 +/- 0.13 to 6.61 +/- 0.22 mmol/l (p less than 0.05) in normal subjects. At high insulin levels (70 microU/ml) the lipolytic response was detectable only in Type 1 diabetic patients; the ketogenic response was reduced in both groups. During the third clamp, a significant rise in plasma glucose concentration during epinephrine infusion was observed in both groups. In conclusion this study shows that at low insulin levels Type 1 diabetic patients show an increased ketogenic response to epinephrine, despite their normal nonesterified fatty acid response. Instead, high insulin levels are able to restrict the ketogenic response to epinephrine in both normal and Type 1 diabetic subjects, although there is a still detectable lipolytic response in the latter. In the presence of plasma free insulin levels that completely restrict the ketogenic response in the same group, there is still a distinct glycaemic response. Plasma insulin levels in Type 1 diabetic patients are a major determinant of the metabolic response to epinephrine.

Various Ca2+ entry blockers prevent glutamate-induced neurotoxicity

In the present study we investigated the effect of different Ca2+ entry blockers on the onset of neuronal damage induced by glutamate, kainate or alpha-amino-3-hydroxy-5-methyl-5-isoxazolo propionate (AMPA) in primary culture of rat cerebellar granule cells. We found that the dihydropyridine derivative, nifedipine used at 100 nM concentration, significantly counteracted the neuronal death induced by 15 min application of 50 microM glutamate. This effect was dependent on the presence of nifedipine before the exposure of granule cells to glutamate and was dose-related (IC50 = 10 nM). The nifedipine response was reproduced by isradipine and by verapamil with IC50 values of 9 and 100 nM, respectively. The activation of voltage sensitive Ca2+ channels elicited by 100 nM Bay K 8644, greatly enhanced glutamate-mediated neurotoxicity. Moreover, 100 nM isradipine was significantly active in blocking the neuronal death produced by 24 h exposure of cerebellar granule cells to 10 microM AMPA or 60 microM kainate. These results reveal a 'preventive' role of the Ca2+ entry blockers on the development of the neurodegeneration induced by overstimulation of various glutamate receptor subtypes.

Reduced beta-cell secretion and insulin hepatic extraction in healthy elderly subjects

One factor responsible for the altered carbohydrate metabolism in elderly subjects is impaired insulin release; however, difficulties in directly measuring insulin secretion have limited studies on pancreatic activity and on the contribution of the liver to insulin delivery. This study investigated beta-cell performance and insulin hepatic extraction under dynamic conditions in normal elderly subjects. Two strictly comparable groups of 12 young controls (Y, 27 +/- 1 (SE) years, 73 +/- 3 kg) and 12 elderly men (E, 69 +/- 2 years, 73 +/- 3 kg) were chosen on the basis of normal OGTT and normal insulin sensitivity in order to investigate a "pure" age effect. The subjects underwent a 4-hour frequently sampled intravenous glucose tolerance test (FSIGT) (dose 0.3 g/kg). Although no significant differences were found between the fasting levels of glucose and insulin (respectively: E: 89 +/- 3 mg/dL versus Y: 87 +/- 2, P greater than .1; and E: 5.0 +/- 0.5 microU/mL versus Y: 6.8 +/- 1.0, P greater than .05), basal C-peptide was found to be lower in the old subjects: 0.43 +/- 0.06 ng/mL versus 0.70 +/- 0.11 (P less than .025). The patterns of glucose and insulin during the FSIGT were similar, whereas C-peptide concentration in E was systematically lower, suggesting a reduced insulin secretion. To verify this hypothesis, we analyzed FSIGT data with a mathematical model-based method that provides a noninvasive direct measurement of the time courses of insulin secretion and hepatic extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Age and glucose tolerance in healthy subjects

An important and still controversial issue is the role played by the aging process itself in the metabolic alterations observed in aged people. We previously reported that a group of normal elderly people exhibited glucose disposal comparable to that of young controls. In the present study we investigated the effect of age on beta-cell secretion, by analyzing C-peptide measurements. Ten elderly men (E, 70 +/- 2 years) with normal oral glucose test and ten young subjects (Y, 27 +/- 1 years) with matching ideal body weight formed the study group. They were studied under highly dynamic conditions by means of a 0.3 g/kg i.v. glucose tolerance test. Fasting glucose and insulin were not different in the two groups (Y: 87 +/- 2 mg/di, E: 88 +/- 3, p greater than 0.1; Y: 50 +/- 7 pM, E: 36 +/- 7, p greater than 0.05). Glucose-insulin data set was analyzed by means of the minimal model of glucose disappearance which provided two parameters for every individual, yielding a quantitative description of glucose utilization: i.e., SI, the index of insulin sensitivity, and SG, the fractional glucose disappearance at basal insulin (glucose effectiveness). Both parameters were unaltered by age (SI = Y: 6.30 +/- 0.41 10(-4)min-1/(microU/ml), E: 7.11 +/- 0.72, p greater than 0.1; SG = Y: 0.020 +/- 0.003 min-1, E: 0.019 +/- 0.002, p greater than 0.1). C-peptide time course in elderly people was systematically lower than in the control group (basal levels: Y: 252 +/- 36 pM, E: 129 +/- 17, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Very early nutrition supplementation in burned patients

We studied some metabolic and hormonal effects of a very early nutrition supplementation in burned patients. The patients were divided into two groups of 10 patients each. Supplementation in the first group, the very early nutritionally supplemented (VENS) group, was started immediately after admission, ie, after 4.4 +/- 0.5 h (mean +/- SEM) from the injury; it was started after 57.7 +/- 2.6 h from the injury in the second group (control group). Hormonal and metabolic indices were recorded every 4 d up to 28 d. In the VENS group, the nitrogen balance became positive in 8.8 +/- 4.1 d whereas it took 24.1 +/- 6.9 d in the control group (p less than 0.05). Urinary catecholamine excretion and plasma glucagon concentrations were lower during the first 2 wk of observation in the VENS group compared with the control group. Insulin concentrations were significantly higher on the fourth and eighth days in VENS patients and plasma cortisol concentrations were similar in both groups.

Impaired renal response to a meat meal in insulin-dependent diabetes: role of glucagon and prostaglandins

The renal response to 100 g/1.73 m2 protein load in the form of a meat meal was studied in 19 normal subjects and 35 normoalbuminuric insulin-dependent diabetic patients (IDDs) under conditions of sustained euglycemia. The area under the glomerular filtration rate (GFR) curve rose above base line by 1,904 +/- 292 in normals and 502 +/- 237 ml/1.73 m2 in IDDs (P less than 0.01). The meat meal induced a greater increment in the area under the glucagon curve in normals (14,930 +/- 186 pg.ml-1.min-1) than in IDDs (7,227 +/- 67, P less than 0.01); similarly urinary excretion of prostaglandin E2 and 6-ketoprostaglandin F1 alpha rose by 119 and 98%, respectively, in normals but only by 2% (P less than 0.01 vs. normals) and 10% (P less than 0.01 vs. normals) in IDDs. The fractional albumin clearance rose by 102 and 251% in normals and IDDs, respectively. In five normal subjects indomethacin administration abolished the GFR, glucagon, prostaglandin, and albuminuric response to meat ingestion. Glucagon replacement under indomethacin treatment failed to restore these responses. In five diabetic patients, selected for having a flat glucagon and GFR response to a meat meal, replacement of glucagon to postprandial levels increased urinary vasodilatory prostaglandins and restored a normal GFR response. Thus in normal subjects renal vasodilatory prostaglandins appear to be the final effector of the renal hemodynamic and albuminuric response to a meat meal. The prostaglandin increase is likely to be mediated under physiological conditions by a glucagon rise, which, however, has no effect per se on renal hemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of ticlopidine on platelet function at rest and after exercise in patients with previous myocardial infarct. An acute crossover double-blind study]

The effects of Ticlopidine on platelet function at rest and after exercise test in 12 patients with a history of myocardial infarction but no risk factors and/or residual angina, were investigated. The patients were treated with 500 mg per diem Ticlopidine or placebo for 15 days in a crossover double-blind study. Blood samples were taken before and 3 minutes after maximum effort exercise cycle tests. Blood samples from 25 healthy volunteers of comparable age and sex were used for control purposes. The parameters examined were: platelet aggregation induced by ADP (1 and 3 mumol/l), Arachidonic Acid (AA) (1.3 mmol/l) and collagen (2 micrograms/ml); the presence of circulating platelet aggregates and plasmatic fibrinogen levels. When compared with the controls, the patients showed higher levels of aggregation caused by ADP, AA and collagen as well as circulating aggregates. Exercise produced a statistically significant increase in platelet activation, while Ticlopidine significantly inhibited the platelet aggregation induced by ADP, AA and collagen as well as circulating aggregates both at rest and after the exercise test. Fibrinogen levels were higher in the heart attack patients than the controls especially after exercise, but not to a statistically significant degree. Treatment with Ticlopidine did not influence plasma fibrinogen levels. It is not known whether the patients with signs of effort-induced platelet aggregation run a higher risk of ischaemic cardiopathy or whether drug treatment could prevent this eventuality.

Ketone body kinetics in vivo using simultaneous administration of acetoacetate and 3-hydroxybutyrate labelled with stable isotopes

Isotope dilution studies of ketone body (KB) turnover have usually been performed using a single 14C tracer and the so called 'combined KB specific activity'. By definition, this approach does not allow to evaluate the individual kinetics of acetoacetate (AcAc) and 3-hydroxybutyrate (R-BHB) which is feasible only using the separate administration of 14C tracer AcAc and R-BHB. In the present study we followed a different approach using the simultaneous administration in vivo of [1,2,13C2] AcAc and m [1,2,3,4(13)C4] R-BHB which allows to evaluate the individual kinetics of the two KB in the some study, thus minimizing the magnitude of blood sampling and the potential changes in the metabolic conditions of each subject. The four isotopic 13C/12C KB ratios of AcAc and R-BHB tracer and tracee blood concentrations along with the fluorimetric measurement of 12C concentrations were determined in each blood sample. Using compartmental analysis following single dose bolus injection the production rate of KB was 206 +/- 57 mumol/min/1.73 m2 (mean +/- SD). The turnover rate of KB using noncompartmental analysis, during continuous infusion in a separate study was 294 +/- 41. The plasma clearance rates of AcAc and R-BHB were 1966 +/- 502 and 1443 +/- ml/min/1.73 m2, respectively. The mean residence time was 17 +/- 3 min and the total distribution volume 20 +/- 9.7 l/m2. We conclude that: (1) stable isotope tracer infusion allows the contemporary in vivo administration of the two KB and the simultaneous assessment of individual AcAc and R-BHB kinetics; (2) the estimated compartmental and noncompartmental parameters of KB turnover were similar to those observed in normal overnight fasting subjects following separate radioactive tracer injections.

Red cell sorbitol concentration in relation to short- and medium-term variation of plasma glucose

To evaluate the time course of changes in red cell sorbitol (RCS) concentration in relation to variations of plasma glucose levels, RCS was determined in 7 normal subjects during i.v. glucose infusion (IVGTT); in 6 hyperglycemic insulin-dependent diabetic subjects while glycemia was normalized with Biostator GC 115 and in 4 diabetic patients in previously poor metabolic control, in whom normal glycemia was obtained in 8-10 days by intensive insulin therapy. During IVGTT, plasma glucose levels increased with significant differences from baseline at 5, 10, 16, 25, 60, 100 and 160 min and returned to basal levels after 3h; RCS concentration showed small and insignificant increases. During i.v. insulin infusion, plasma glucose fell to almost normal levels within roughly 3h; RCS levels showed a gradual reduction becoming significant at 180 min. In the third study, decrease in plasma glucose was always associated with a fall in RCS level which became significant between the 2nd and the 3rd day of the study. Thus, RCS levels were not affected by very short-term variations of glycemia but by a previous hyperglycemic crisis that lasted a few hours. There were therefore medium-term variations of RCS level. In conclusion, RCS determination is not useful as an index of metabolic control in diabetes.

Potassium channels involved in the transduction mechanism of dopamine D2 receptors in rat lactotrophs

1. Radioactive rubidium (86Rb+) efflux was used to measure potassium (K+) permeability in a study designed to asses both the presence and the sensitivity to ions and drugs of the K+ channels in the plasma membrane of rat lactotrophs. 2. Rb+ efflux from Rb+-pre-loaded lactotrophs into nominally calcium-free solution containing 5 mM-K+ was linear from 1 to 60 s, with a calculated rate of about 0.1%/s. Raising K+ concentrations to depolarize the cells stimulated the Rb+ efflux (0.2%/s), which was already significant after 1 s of exposure of the cell to 100 mM-K+. This component of Rb+ efflux has been designated component V (sensitive to voltage and Ca2+ independent). 3. Addition of Ca2+ to 5 mM-K+ solution had no effect on resting Rb+ efflux (0.1%/s), but did further stimulate Rb+ efflux into K+-rich solutions. This component, which has been designated component C, was completely inhibited by 0.5 mM-cadmium. These data fit the view that the increase in intracellular Ca2+ concentration during depolarization opens certain (Ca2+-activated) K+ channels. 4. K+ efflux was differently affected by K+ channel blockers. Tetraethylammonium (TEA) inhibited both V and C components while 4-aminopyridine (4-AP) inhibited the component V without modifying the C component of Rb+ efflux. 5. Dopamine appears to affect both types of Rb+ efflux components. Dopamine increased the efflux of Rb+ in a nominally Ca2+-free medium containing 5 mM-K+ (component V). This effect was statistically significant 15 s after exposure of the cells to 10 nM-dopamine. Increasing the concentrations of K+ to gradually depolarize the cells enhanced the rate of increase of Rb+ efflux induced by dopamine, being evident in the initial 2-5 s of incubations. Dopamine also increased Rb+ efflux in a 5 mM-K+ solution containing 1 mM-Ca2+ (component C). This effect was rapid (2-5 s) and inhibited by 0.5 mM-cadmium. The combined action of dopamine on both component C and V caused the cells to be less sensitive to depolarizing concentrations of K+. The increase in Rb+ efflux and the enhancement of prolactin release induced by high concentrations of K+ were, indeed, prevented by exposure of the cells to 10 nM-dopamine. 6. The effects of dopamine on either component V or component C were pharmacologically characterized as D2 receptor mediated, being mimicked by selective D2 receptor agonists (quinpirole and RU 24213) and stereospecifically blocked by the D2 receptor antagonist sulpiride.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopamine D2 receptor stimulation inhibits inositol phosphate generating system in rat striatal slices

Previous studies on the transduction mechanisms triggered by dopamine receptor stimulation have established that both D1 and D2 subtypes of dopamine receptors are linked to the adenylate cyclase system, the former in a stimulatory and the latter in an inhibitory manner. The present report provides the first evidence that stimulation of D2 receptors in rat brain tissue affects the turnover of polyphosphoinositides, as revealed by changes of the content of inositol phosphates. We found that the basal level of [3H]inositol trisphosphate, [3H]inositol bisphosphate and [3H]inositol monophosphate decreased following the stimulation of the D2 receptor. The rank order of potency was quinpirole (IC50 5 nM) greater than lisuride (IC50 8 nM) greater than RU 24213 (IC50 50 nM) greater than dopamine (IC50 200 nM). In contrast, selective D1 receptor stimulation by fenoldopam did not alter the inositol monophosphate, inositol bisphosphate and inositol trisphosphate content. The quinpirole effect was prevented by selective D2 antagonists, such as domperidone and L-sulpiride (both 5 microM) while it was unaffected by the selective D1 antagonist SCH 23390 (100 nM) and by the pharmacologically inactive D-isomer of sulpiride. Our data indicate that the activation of striatal D2 receptors leads to the inhibition of inositol phosphate production.

Reduced in vivo biological activity of in vitro glycosylated insulin

We evaluated the in vivo biological activity of in vitro extensively glycosylated insulin (GI) with the euglycemic-hyperinsulinemic glucose-clamp technique in postabsorptive nondiabetic subjects. Insulin-mediated glucose disposal was approximately 30% lower (P less than .03) with GI (9.2 +/- 1.2 mg.kg-1.min-1, mean +/- SE) than with the nonglycosylated hormone (12.6 +/- 0.7 mg.kg-1.min-1) at comparable plasma insulin concentrations (approximately 90 microU/ml). Binding of GI to a specific receptor on circulating cells (erythrocytes and monocytes) was normal. We conclude that in vitro extensive glycosylation of insulin reduces its biological activity in vivo, as reflected by insulin-mediated glucose disposal, probably at a postreceptor level.

A superfusion method for the study of calcium fluxes from pituitary cells

This paper describes a superfusion technique that allows the study of calcium fluxes from a preparation of anterior pituitary cells. There is easy reproducibility, high sensitivity, controlled conditions that closely resemble those in vivo, possibility to operate sequential treatments on the same sample. These are some of the advantages of this method. An interesting application consists of the possibility of simultaneous measurement of calcium fluxes and hormone release.

Insulin sensitivity and beta-cell responsivity are not decreased in elderly subjects with normal OGTT

Glucose intolerance has been observed often in elderly subjects, but it is not yet clear whether this impaired metabolic state is due to the aging process itself or is secondary to the appearance of other age-related variables. This study attempts to elucidate the effect of age in itself on factors controlling glucose tolerance. Several metabolic parameters were measured in 10 young male controls (23-29 yr) and 17 nonhospitalized, healthy, nonobese, old (60-80 yr) male subjects. Insulin binding to circulating cells was performed along with the intravenous glucose tolerance test, and the data were analyzed by the minimal model method. This approach yields the following measures: tissue insulin sensitivity (SI), fractional glucose disappearance at basal insulin (glucose effectiveness, SG), and first (phi 1) and second (phi 2) phase beta-cell responsiveness to glucose. Insulin-binding capacity to monocytes and erythrocytes was respectively 6.03% +/- 0.57% and 5.96% +/- 0.53% (elderly), 5.97% +/- 0.39% and 5.36% +/- 0.57% (young); SI was 6.20 +/- 0.59 X 10(4) min-1/(microU/mL) (elderly) and 6.35 +/- 0.30 (young); SG was 0.016 +/- 0.002 min-1 (elderly) and 0.019 +/- 0.003 (young); phi 1 was 1.84 +/- 0.29 min-1 (microU/mL)/(mg/dL) (elderly) and 3.37 +/- 0.84 (young); phi 2 was 13.80 +/- 1.78 X 10(4) min-2 (microU/mL)/(mg/dL) (elderly) and 9.59 +/- 2.65 (young). These results show no change with aging of tissue insulin sensitivity and an intact beta-cell activity, suggesting that age per se does not contribute to the deterioration of glucose tolerance when the effect of other age-related variables, eg, obesity and physical inactivity, is precluded.

Modifications of brain electrical activity after activation of the benzodiazepine receptor types in rats and rabbits

The present study reports a comparative electroencephalographic (EEG) study of drugs belonging to different chemical classes which share the property to bind at benzodiazepine (BDZ) recognition sites. The EEG patterns are recorded from the neocortex of rats and rabbits as well as from dorsal hippocampus and red nucleus in rabbits after intravenous administration of diazepam (0.1-10 mg/kg), clonazepam (0.02-2.5 mg/kg), zopiclone (0.3-3 mg/kg), flunitrazepam (0.03-2.5 mg/kg), CGS 9896 (0.1-3 mg/kg), zolpidem (0.1-3 mg/kg) and Cl 218,872 (0.1-10 mg/kg). The most relevant differences are observed at the level of the neocortex. All drugs induced appearance of 7-12 Hz spindle bursts. On the contrary, the presence of 15-30 Hz waves (defined beta-like activity) mainly occurs after diazepam, clonazepam and zopiclone. Scarce beta-like activity is present after CGS 9896, zolpidem and Cl 218,872. According to the selectivity of these drugs for the various types of BDZ receptor, one can speculate that activation of BDZ2 is relevant for the appearance of the beta-like activity. Flunitrazepam, diazepam, and zolpidem increase the amplitude of the red nucleus waves. Such an effect is less marked after zopiclone and CGS 9896, whereas is almost absent after clonazepam and Cl 218,872. A reduction of the frequency is observed after flunitrazepam, diazepam, clonazepam, CGS 9896 and zolpidem, whereas it is almost absent after zopiclone and Cl 218,872. Finally, all drugs induce a reduction of the amplitude of the hippocampal theta rhythms, whereas after diazepam, flunitrazepam, zolpidem and CGS 9896 a slowing of the record also occurs.

Electroencephalographic changes after short-term exposure to agonists of benzodiazepine receptors in the rat

Naive rats receiving IV diazepam (10 mg/kg), flunitrazepam (2.5 mg/kg) and clonazepam (2 mg/kg) show electroencephalographic (EEG) changes consisting of lengthening of the spindle bursts (7-12 Hz; 200-300 microV) and appearance of 15-30 Hz waves (beta-like activity). These EEG manifestations are associated with signs of behavioral sedation (crouched, eyes open and myorelaxation) and stimulation (gnawing, running, ear twitches and sometimes wet-dog shakes), respectively. Bursts of 2-4 Hz waves can be occasionally observed associated with either marked sedation (lying down, eyes closed and presence of righting reflex) or sleep (stretched in the side with absence of righting reflex). Measurements of the periods spent by the animals in the two EEG patterns within the first hour after intravenous injection show the large preponderance of the spindle bursts over the beta-like activity. After the triazolopyridazine Cl 218,872 (10 mg/kg) the beta-like activity is almost absent, and in no case loss of the righting reflex can be observed. These agonists of BDZ receptors have been injected at the above reported doses for 5 days, once-a-day. At the 5th day, animals receiving diazepam exhibit a preponderance of the EEG and behavioral activation within the first hour after injection. Rats receiving flunitrazepam show a significant increase of the periods of stimulation and a slight decrease of the periods of sedation. These phenomena of "habituation" are absent in animals treated with clonazepam and Cl 218,872.

Type I insulin-dependent diabetic patients show an impaired renal hemodynamic response to protein intake

Human kidney responds to a meat meal with an increase in glomerular filtration rate (GFR), but the mechanisms regulating kidney hemodynamics following protein intake are poorly understood in Type I insulin-dependent diabetes. In the present study we investigated GFR response to protein intake (600 gr/1.73 m2 meat meal) in nine normal subjects and 21 Type I insulin-dependent diabetic patients with normal albumin excretion rates as well as proximal tubular sodium reabsorption rates and distal sodium delivery (PRNa and DDNa). The same study was reperformed in normal subjects and diabetic patients, with less than a 5 year diabetes duration, following one week of indomethacin treatment. Normal subjects showed a 38% increase in GFR following protein intake, whereas diabetic patients showed a significantly lower response (18%, p less than 0.01). The response of GFR to protein challenge was negatively related to diabetes duration but not to baseline glomerular filtration rate. Indomethacin treatment completely prevented the protein induced GFR increase in normal subjects but not in diabetic patients. Sodium reabsorption rate was increased following protein challenge both at the proximal and distal tubular level, as was net natriuresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic control of kidney hemodynamics in normal and insulin-dependent diabetic subjects. Effects of acetoacetic, lactic, and acetic acids

Diabetes mellitus is associated with important changes in renal hemodynamics. The purpose of this study was to determine whether an increase in blood concentration patterns of ketone bodies and lactic acid, organic acids often elevated in poorly controlled insulin-dependent diabetes mellitus (IDDM), could contribute to increase glomerular filtration rate (GFR) and renal plasma flow (RPF) regardless of changes in circulating levels of glucose and insulin. Six IDDM patients and six normal subjects were given a saline infusion (15 mumol.min-1.kg-1) for 2 h, an acetoacetic acid infusion (15 mumol.min-1.kg-1) for another 2 h, and then a saline infusion after an overnight fast during euglycemic insulin-glucose clamp. Acetoacetic acid infusion resulted in an increase of blood ketone bodies in the range of 0.7-1.5 mM from a basal value of 0.1-0.3 mM. GFR was 125 +/- 16 and 136 +/- 17 ml.min-1.1.73 m-2 in normal and IDDM subjects, respectively, during baseline saline infusion and 138 +/- 21 (P less than .01 vs. basal level) and 158 +/- 15 ml.min-1.1.73 m-2 (P less than .001 vs. basal level) during acetoacetic acid infusion. During the last saline infusion, renal hemodynamic patterns decreased again to baseline levels. Another six IDDM patients and six normal subjects were given saline, lactic acid, and saline infusions at the same rates of infusion after an overnight fast during euglycemic insulin-glucose clamp. Lactic acid concentration increased from approximately 0.5-0.8 to 1.0-1.5 mM in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin receptors on circulating blood cells from patients with pancreatogenic diabetes: a comparison with type I diabetes and normal subjects

We studied 125I-insulin binding to erythrocytes from 14 patients with diabetes secondary to chronic pancreatitis or pancreatectomy and compared the results with those found in 10 patients with type I diabetes and 25 normal controls. Patients with pancreatogenic diabetes had higher 125I-insulin binding and enhanced tissue sensitivity to exogenous insulin measured with the glucose clamp technique as compared with patients with type I diabetes. Similar binding data were obtained with monocytes from 3 patients with pancreatogenic diabetes. The increase in insulin binding seemed due mainly to an increase in receptor number. The increase in insulin binding to cells from patients with pancreatogenic diabetes in comparison with cells from normal subjects was also seen in young-erythrocyte-rich fractions and in old-erythrocyte-rich fractions obtained from the mixed population of circulating erythrocytes by centrifugation in density gradient of Percoll-Pielografin. These data, in the absence of any sign of major hematological disorders, suggest that the increase in insulin receptors seen in erythrocytes and in monocytes from patients with pancreatogenic diabetes, can mirror a general phenomenon on tissues throughout the body, including major target cells for insulin and correlate with the heightened sensitivity to insulin characteristic of these patients. In conclusion, patients with pancreatogenic diabetes have increased insulin binding as compared to controls and to patients with type I diabetes with chronic hypoinsulinemia of the same degree. Thus, in addition to insulin deficiency, other factor (s), such as glucagon deficiency, are responsible for the clinical and metabolic differences between these two conditions of insulin deficiency.

Alcohol impairs insulin sensitivity in normal subjects

The effects of alcohol on insulin action are not yet clearly established. To assess the effects of intravenously administered ethanol on insulin mediated glucose disposal, euglycaemic clamps at 3 different plasma insulin levels and insulin receptor binding studies on circulating monocytes after alcohol infusion were performed. Ethanol infusion leads to a significant reduction of insulin mediated glucose disposal (7.08 +/- 0.4 vs 8.6 +/- 0.6 mg/Kg/min; 9.8 +/- 0.7 vs 13.4 +/- 0.7; 14.7 +/- 0.7 vs 18.1 +/- 0.7 at 33, 73 and 760 mU/m2/min insulin infusion rate respectively). Monocyte insulin-receptor binding was decreased in all the subjects from 30 to 60% after ethanol infusion. These results demonstrate that alcohol can adversely influence the insulin mediated glucose disposal.

Ketone bodies increase glomerular filtration rate in normal man and in patients with type 1 (insulin-dependent) diabetes mellitus

The purpose of this study was to investigate whether the administration of acetoacetic and hydrochloric acids in a group of control and Type 1 (insulin-dependent) diabetic patients influenced renal haemodynamics. Renal plasma flow increased from 657 +/- 88 to 762 +/- 81 ml X min-1. 1.73 m-2 in diabetic patients (p less than 0.01) and from 590 +/- 71 to 691 +/- 135 in control subjects (p less than 0.01). Glomerular filtration rate increased from 135 +/- 9 to 180 +/- 8 ml X min-1. 1.73 m-2 in diabetic patients (p less than 0.001) and from 117 +/- 8 to 145 +/- 7 in control subjects (p less than 0.01). Similar effects on renal haemodynamics, even if less pronounced, were observed with low dose acetoacetic but not with hydrochloric acid infusion. Total protein, beta 2-microglobulin but not albumin excretion rates were increased by acetoacetic acid. We conclude that an acute increase in blood concentration of ketone bodies within the range found in diabetic patients with poor metabolic control increases renal plasma flow and glomerular filtration rate both in control subjects and diabetic patients and causes a tubular proteinuria.

Effect of metformin on insulin-stimulated glucose turnover and insulin binding to receptors in type II diabetes

Euglycemic insulin glucose-clamp and insulin-binding studies on erythrocytes and monocytes were performed in seven type II (non-insulin-dependent) diabetic subjects before and after 4 wk of metformin treatment (850 mg 3 times/day) and in five obese subjects with normal glucose tolerance. Glucose turnover was also measured at basal insulin concentrations and during hyperinsulinemic euglycemic clamps. During euglycemic insulin-glucose clamps, diabetic subjects showed glucose disposal rates of 3.44 +/- 0.42 and 7.34 +/- 0.34 mg X kg-1 X min-1 (means +/- SD) before metformin at insulin infusion rates of 0.80 and 15.37 mU X kg-1 X min-1, respectively. With the same insulin infusion rates, glucose disposal was 4.94 +/- 0.55 (P less than .01) and 8.99 +/- 0.66 (P less than .01), respectively, after metformin treatment. Glucose disposal rates in normal obese subjects were 5.76 +/- 0.63 (P less than .01) and 10.92 +/- 1.11 (P less than .01) at 0.80 and 15.37 mU X kg-1 X min-1, respectively. Insulin maximum binding to erythrocytes in diabetics was 9.6 +/- 4.2 and 5.8 +/- 2.6 X 10(9) cells (means +/- SD) before and after metformin treatment, respectively (NS). Insulin maximum binding to monocytes in diabetics was 6.2 +/- 2.3 X 10(7) cells before and 5.0 +/- 1.6% after metformin. Hepatic glucose production was higher in the diabetic patients at basal insulin levels, but not at higher insulin concentrations, and was not significantly changed by drug treatment. Basal glucose and insulin concentrations decreased with metformin. Thus, metformin treatment improved glucose disposal rate without significant effect on insulin-binding capacity on circulating cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopaminergic inhibition of prolactin release and calcium influx induced by neurotensin in anterior pituitary is independent of cyclic AMP system

The present study demonstrates that 3,4-dihydroxyphenylethylamine (DA, dopamine) prevents neurotensin (NT) stimulation of both prolactin (PRL) release and calcium influx by interacting with specific receptors that are functionally linked to calcium channels. As shown by the studies with dispersed cells from rat anterior pituitary, the pharmacology of the control of PRL release and calcium influx, both induced by NT, was found to be typical of a DAergic process. This was demonstrated by the order of potency of agonists in inhibiting PRL release and calcium influx (DA greater than epinephrine greater than norepinephrine much greater than isoproterenol); by the high affinity of antagonists such as haloperidol and fluphenazine for this process; and by the high degree of stereoselectivity of sulpiride. Specific D2 receptor agonists, such as bromocriptine and lisuride, and the specific D2 receptor antagonist (-)-sulpiride were found to be highly potent on the DA receptors negatively coupled with calcium channels and PRL release. DA was found to lack the capacity to change the influx of calcium induced by either the sodium channel activator veratridine or high extracellular potassium levels, thus indicating a specific action of this amine on calcium channels sensitive to NT. In a range of concentrations that are effective in inhibiting either the calcium influx or the PRL release, both induced by NT, DA did not alter the cyclic AMP generating system. DA (from 1.0 nM to 50 nM) did not affect adenylate cyclase activity in rat pituitary gland homogenates and did not modify intracellular cyclic AMP levels in pituitary cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of neurotensin receptors associated with calcium channels and prolactin release in rat pituitary

Neurotensin (NT) is now reasonably well established as a neurotransmitter or neuromodulator candidate in the CNS. In the present study, we characterized the NT receptors in dispersed cells from the anterior lobe of rat pituitary and investigated the involvement of both cyclic AMP and calcium in the release of prolactin (PRL) induced by NT receptor stimulation. The [3H]NT binding to membranes from anterior pituitary dispersed cells was found saturable and stereospecific. Scatchard analysis of the data gave a straight line indicating a Bmax value of 121 +/- 11 fmol/mg protein and a KD value of 1.4 +/- 0.2 nM. The calculated IC50 values for [3H]NT binding were 5.8 nM for NT, 7.8 nM for L-Phe-NT, and 3,000 nM for the pharmacologically inactive form D-Phe-NT. NT, up to a concentration of 1 microM, did not affect the cyclic AMP generating system in homogenates of anterior pituitary from male or lactating female rats. The same pattern of results was obtained for cyclic AMP formation in intact cells. NT and its analogs stereospecifically enhanced the influx of calcium into dispersed cells from rat anterior pituitary. The effect was time- and dose-dependent. It appeared to be associated with neurotransmitter-operated calcium channels since: preincubation of the cells with tetrodotoxin did not affect the increase in calcium influx induced by NT; concentrations of verapamil that counteract the influx of calcium induced by potassium lacked the capacity to modify the influx of calcium induced by NT; and NT lost its capacity to release PRL in the absence of extracellular calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha cell autoantibodies: immunological and metabolic follow-up study

We studied glucagon responses to OGTT and insulin and arginine stimulation in 12 out of 21 patients who were found positive for alpha cell autoantibodies (ACA) during routine screening procedures for autoimmunity in a group of 4080 individuals. The study was repeated in 8 subjects after an average observation period of 42 months. In both studies glucagon plasma levels were normal and independent of ACA titres, ACA ability to fix complement and ACA ability to cross-react with duodenal alpha cells. The clinical significance of ACA remains to be elucidated.

Is red cell sorbitol content a good marker of glycemic control in diabetic patients?

Red cell sorbitol (RCS) concentration and some metabolic parameters were evaluated in 62 diabetic patients. 42 normal subjects were studied as controls. RCS levels were 66.1 +/- 2.0 nmol/gHb in diabetic patients and 41.8 +/- 2.0 nmol/gHb in controls (p less than 0.001). RCS levels were positively correlated with all metabolic parameters evaluated in diabetic patients and in controls. To evaluate RCS distribution, diabetic subjects were subdivided in 3 groups according to fasting plasma glucose (FPG) (less than or equal to 150; 151-200; greater than 200 mg/dl) and glycosylated hemoglobin (GHb) levels (less than or equal to 8; 8.1-10; greater than 10%). 31 patients with FPG less than or equal to 150 mg/dl, all except 7, had RCS levels in the normal range. These 7 patients however had GHb levels greater than 10%. 18 patients with FPG between 151-200 mg/dl had RCS levels in the normal range. Of 13 patients with FPG greater than 200 mg/dl all, except 3, had RCS levels above the normal range. These 3 patients had GHb levels greater than 10%. 45 patients with GHb less than or equal to 10% had RCS values in the normal range. 17 patients with GHb levels greater than 10%, had RCS levels over the normal range. Our data show that RCS levels seem to be related more strictly with GHb. RCS levels increase significantly only in patients with bad metabolic control. Even if RCS levels seem to be a medium-term index of metabolic "equilibrium" they cannot be useful in the routine monitoring of metabolic control in diabetic patients.

Glycosylated serum proteins in diabetic patients and their relation to metabolic parameters

Glycosylated plasma proteins (GSP) and some metabolic parameters (plasma glucose profile, urine glucose excretion, glycosylated hemoglobin, cholesterol, triglycerides) were evaluated in 70 diabetic and 70 normal subjects. Of the late diabetic complications, retinopathy, nephropathy and somatic neuropathy were evaluated. Proliferative retinopathy was observed in 41 of the 70 diabetics studied. No retinopathy or background retinopathy was observed in 29 diabetics. Nephropathy was diagnosed in 39 patients and somatic neuropathy in 44 patients; 26 diabetic subjects had no complications. GSP levels were 0.82 +/- 0.03 nmolHMF/mg prot in diabetics and 0.43 +/- 0.02 nmolHMF/mg prot in controls. GSP levels were positively correlated with metabolic parameters evaluated the same day and 14 days before. A positive correlation between GSP and triglycerides was seen for the first time. The patients with retinopathy showed levels of GSP significantly higher (p less than 0.001) in respect to patients with background retinopathy or absence of it (0.91 +/- 0.03 vs 0.74 +/- 0.04 nmolHMF/mg prot). GSP were significantly higher in the patients with somatic neuropathy (0.93 +/- 0.02 nmolHMF/mg prot) (p less than 0.001) than in the subjects without neuropathy (0.72 +/- 0.04 nmolHMF/mg prot). GSP levels were 0.92 +/- 0.03 nmolHMF/mg prot in diabetics with proteinuria and 0.75 +/- 0.04 nmolHMF/mg prot in diabetics without proteinuria (p less than 0.001). These results confirm the importance of GSP determination as another parameter of glycemic control and particularly as an index of the overall protein glycosylation processes.

Plasma and red cell sorbitol assay in diabetic subjects

Plasma and red cell sorbitol concentrations, fasting plasma glucose, glycosylated hemoglobin (GHb) were evaluated in 30 diabetic patients and 42 normal subjects. Red cell sorbitol levels were evaluated in hemolysate and non-hemolyzed samples. Mean red cell sorbitol concentrations evaluated after hemolysis were 21.5 +/- 5 nmol/ml in diabetics and 12.2 +/- 4 nmol/ml in controls (p less than 0.001). Mean values of red cell sorbitol determined in non-hemolyzed samples were 13.9 +/- 3 nmol/ml in diabetics and 8.1 +/- 3 nmol/ml in controls (p less than 0.001). Mean plasma sorbitol concentrations were 8.4 +/- 3 nmol/ml in diabetics and 5.2 +/- 1 nmol/ml in controls (p less than 0.001). The within and between run reproducibilities evaluated in plasma, hemolysate and non-hemolyzed red cells gave the lowest values for hemolyzed red cell samples. The studies on stability showed that samples neutralized and stored at -20 degrees C gave reproducible values if assayed within 3 days. A positive correlation was found between red cell hemolysate sorbitol concentrations and fasting plasma levels in both diabetics (r = 0.56; p less than 0.001) and controls (r = 0.62; p less than 0.001). Red cell hemolysate sorbitol concentrations were also positively correlated to GHb in both diabetics (r = 0.64; p less than 0.001) and controls (r = 0.36; p less than 0.05). We believe the most effective sorbitol assay to be that obtained in hemolyzed red cells and that these values related to glycemic levels could be a useful index of metabolic control and an indicator of tissue sorbitol levels in humans.

Insulin-mediated glucose disposal in type I diabetes: evidence for insulin resistance

To clarify whether type I diabetes is characterized by insulin resistance, insulin-mediated glucose metabolism (M; milligrams per kg/min) was estimated by means of the glucose clamp technique in five insulin-dependent diabetic patients and six normal subjects. Three glucose clamps were carried out under different metabolic conditions. Free insulin plateaux were similar during each clamp in both groups. The first clamp was performed in normal subjects after an overnight fast [blood glucose, 80 +/- 3 mg/dl (mean +/- SEM)] and in diabetic patients 18 h after insulin withdrawal (blood glucose, 366 +/- 47 mg/dl). Diabetic patients had a M value (4.25 +/- 0.74) not different from normals (5.38 +/- 0.63; P = NS). The second clamp was done with the same glycemic values (approximately 125 mg/dl) in both groups. M increased to 8.07 +/- 1.06 (P less than 0.01) in the normal subjects and decreased to 2.87 +/- 0.50 (P = NS) in the diabetic patients. The M value in the diabetic patients was lower than that in the normal subjects (P less than 0.05). The third clamp was performed in three diabetic patients after 1 month of treatment with continuous sc insulin infusion. The mean blood glucose level was 88 +/- 6 mg/dl, and M was 3.23 +/- 0.38, significantly lower than that of the normal subjects in the basal state (P less than 0.05). No differences were found in insulin binding to erythrocytes. The mean plasma clearance rate (milliliters per m2/min) of free insulin was the same in both groups (428 +/- 113 in normal subjects and 354 +/- 83 in diabetic patients). Basal endogenous glucose production was higher in the diabetics (3.13 +/- 0.48 mg/kg X min) than in the normal subjects (1.71 +/- 0.57). During the clamp, however, endogenous glucose production was similarly inhibited (approximately 95%) in both groups. Multiple glucose clamp studies were also performed at three different insulin infusion rates (21, 73, and 760 mU/m2 X min, respectively) to generate an insulin-dose response curve for glucose disposal in six diabetic patients treated with continuous sc insulin infusion for at least 6 months. This allowed investigation of the effect of chronic strict insulin therapy leading to normal glucose and intermediary metabolite levels and identification of the cellular mechanism of insulin resistance. A significant reduction of the maximal glucose disposal rate (10.7 +/- 0.5 mg/kg X min) was found in these diabetic patients compared to that in normal subjects (14.9 +/- 1.0; P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin resistance in Cushing's syndrome

It is well established that cortisol excess causes insulin resistance in man, but the mechanisms responsible for this insulin resistance are poorly understood. We studied five women with Cushing's syndrome with impaired oral glucose tolerance tests and seven normal subjects, plotting the shape of the insulin-induced disposal dose-response curve obtained by means of the euglycemic clamp procedure during four different plasma insulin plateaus at four infusion rates of 21, 73, 760, and 1200 mU/M2 . min. Glucose disposal (M = mg/M2 . min) was calculated as glucose amount infused to maintain euglycemia. In Cushing's syndrome the dose-response curve was shifted to the right in comparison with normal subjects, with a significantly lower M (337 +/- 35 vs. 657 +/- 76 P less than 0.01) during the highest insulin infusion rate [maximal glucose disposal (MGD)] without any significant difference in the levels of insulin half-maximally effective in the stimulation of glucose utilization. Neither erythrocyte nor monocyte maximum insulin receptor binding were different between the two populations. Four Cushing's syndrome patients were studied again after surgical treatment. A marked improvement of MGD was observed without any significant change in insulin-binding capacity. These results, particularly the marked decrease in MGD, a typical feature of postreceptor defects, indicate that cortisol-induced insulin resistance in man is due to an impairment of peripheral insulin action located beyond the hormone-receptor binding step.

Insulin receptor on monocytes from patients with acromegaly and fasting hyperglycemia

[125I]Insulin binding to insulin receptors on circulating monocytes was studied in 9 patients with acromegaly associated with fasting hyperglycemia and was compared to previously reported studies of 11 patients with acromegaly who had normal or nearly normal glucose tolerance and 29 normal volunteers. In the hyperglycemic acromegalic, as had been found in the normoglycemic acromegalic, the total receptor concentration per cell was decreased in proportion to the hyperinsulinemia, i.e. the receptor concentration was inversely related to the basal level of insulin, similar to what is found in patients with obesity, diabetes, and insulin-secreting tumors. However, the acromegalic patients with hyperglycemia failed to show the increase in affinity of the empty receptor that had previously been found in their normoglycemic counterparts. The failure to increase receptor affinity causes the cells of the hyperglycemic acromegalic patients to bind less insulin at each insulin concentration than do the cells of normoglycemic patients. Again, the abnormalities in the patients correlates very closely with abnormalities at the level of the insulin receptor, though the sequence of the molecular events that produce these changes remains to be determined.

Effect of ethanol, acetaldehyde, and acetate on insulin and glucagon secretion in the perfused rat pancreas

The effects of varying concentrations of ethanol (1, 10, and 30 mM) and its metabolites (1 mM acetate and 1 and 10 mM acetaldehyde) on insulin and glucagon secretion induced by glucose (11.1 mM) and arginine (20 mM) were studied in isolated perfused pancreas of Sprague-Dawley rats. Ethanol and its metabolites did not significantly modify basal secretion of the two hormones. Ethanol reduced glucose-induced insulin secretion by means of a dose-related effect. Arginine-induced insulin output did not seem to be influenced to any significant degree. Acetate and acetaldehyde significantly inhibited glucose and arginine-induced insulin secretion. While ethanol (10 and 30 mM ) did not modify glucagon output during arginine perfusion, acetate and acetaldehyde markedly enhanced it. The block of insulin secretion and the increased secretion of glucagon could explain the diabetogenic effect of ethanol demonstrated in vivo. The mechanism by which ethanol acts on the pancreatic beta- and alpha-cells is discussed.

Bromocriptine acute effect on insulin, glucagon and growth hormone levels in acromegalic patients

It has been shown that L-dopa or dopamine administration influences glucose metabolism, as well as insulin and glucagon release in man. In the present study, the effect of bromocriptine (CB-154), a long-acting dopamine agonist, on insulin, glucagon and growth hormone secretion in 32 acromegalic patients was investigated. Glucose, insulin and plasma glucagon levels were not modified following administration of bromocriptine or placebo. Moreover, plasma GH levels were decreased by more than 50% in 18 of the 32 acromegalics. Mean GH levels were significantly lower with respect to levels observed following placebo at 60 min to the end of the test (p less than 0.001). Administration of a double dose of CB-154 (5 mg po) one hour before arginine test did not affect insulin or glucagon secretion with respect to levels observed during arginine alone. In addition, there was a fall in GH levels similar to that observed following administration of bromocriptine alone. These findings suggest that bromocriptine in itself does not exert a direct action on insulin and glucagon release. Improvement in glucose tolerance and reduction in insulin secretion observed following prolonged CB-154 treatment in acromegalic patients are probably due to a simultaneous inhibition of GH secretion or to other peripheral effects of bromocriptine.