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Biomedical subjects

R Navalesi

Publications and source records attributed to R Navalesi.

At least 73 records · Page 4Linked to original sources
PubMed1995

Insulin inhibits its own secretion from isolated, perifused human pancreatic islets.

It is still a controversial question whether insulin suppresses its own secretion. We prepared pure human islets from three pancreases by collagenase digestion and density gradient purification. Aliquots of 200 islet equivalents (IE, 150-microns sized-islets) were sequentially perifused at 37 degrees C with 3.3 mmol/l glucose (3.3G, 40 min), 16.7 mmol/l glucose (16.7G, 30 min) and again 3.3G (30 min) after 24 h, 37 degrees C culture in CMRL 1066 medium with or without the addition of either 200 or 400 microU/ml human insulin in the incubation medium (6 replicates each). Insulin secretion was assessed by C-peptide (Cp) measurement in the perifusate. Without added insulin (C) and with 200 (Ins200) or 400 (Ins400) microU/ml added insulin, basal Cp release was 0.12 +/- 0.03, 0.14 +/- 0.02 and 0.14 +/- 0.04 ng/ml, respectively. At 16.7G, the first-phase secretion peak (expressed as Cp value) was significantly lower with Ins200 (0.47 +/- 0.13 ng/ml, P < 0.02) and Ins400 (0.68 +/- 0.15 ng/ml, P < 0.05) than C (0.83 +/- 0.15 ng/ml). The second-phase secretion peak was also significantly (P < 0.05) reduced with added insulin (Ins200: 0.47 +/- 0.08 ng/ml; Ins400: 0.45 +/- 0.07 ng/ml) than in its absence (C: 0.65 +/- 0.09 ng/ml). Accordingly, total Cp secretion was lower with Ins200 (10.6 +/- 2.3 ng/ml, P = 0.03) and Ins400 (11.8 +/- 2.3 ng/ml) than with C (16.0 +/- 2.2 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

C-Peptide↗
PubMed1995

Massive isolation, morphological and functional characterization, and xenotransplantation of bovine pancreatic islets.

The limited availability of human donors makes the search for alternative islet sources mandatory for future developments in pancreatic islet transplantation. In this study, we report on the massive isolation of bovine islets of proven in vitro and in vivo viability. The islets were prepared by collagenase digestion, sequential filtrations, and density-gradient purification by modifying a technique previously developed in our laboratory for the porcine pancreas. The prepurification yield was 2,743 +/- 78 islet equivalents (IE)/g pancreas (mean +/- SE), with a postpurification recovery of 78.7 +/- 2.2%. Purity ranged from 80 to 90%. The histological and immunocytochemical studies demonstrated the identity and integrity of the islets with well-preserved insulin-, glucagon-, and somatostatin-containing cells. The morphological integrity of cultured bovine islets was demonstrated for up to 4 weeks from isolation. Insulin secretion from freshly isolated islets was similar at 3.3 mmol/l glucose (0.36 +/- 0.06 pmol.IE-1.min-1) and at 14 mmol/l glucose (0.42 +/- 0.00 pmol.IE-1.min-1), and it increased significantly (P < 0.01) at 25 mmol/l glucose (1.44 +/- 0.12 pmol.IE-1.min-1). Arginine, theophylline, and propionic acid increased insulin secretion from freshly isolated islets at 3.3 and 14 mmol/l glucose, but not at 25 mmol/l glucose. Islets cultured at 37 degrees C in CMRL 1066 culture medium for at least 10 days were shown to become responsive to a lower glucose concentration, as demonstrated by the significant increase of insulin release in response to 14 mmol/l glucose, when compared with basal secretion. This recovered responsivity to glucose was maintained after 4 weeks of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Increased transcapillary escape rate of albumin in microalbuminuric type II diabetic patients.

OBJECTIVE: To evaluate microvascular permeability by the transcapillary escape rate of albumin (TERalb) in type II diabetic patients with normo- and microalbuminuria. RESEARCH DESIGN AND METHODS: The TERalb has been measured following intravenous injection of 125I-labeled human serum albumin in 32 normotensive type II diabetic patients and 9 healthy control subjects matched for sex and age. Type II diabetic subjects were grouped in normoalbuminuric, albumin excretion rate (AER) < 20 micrograms/min (n = 18), and microalbuminuric, AER 20-200 micrograms/min (n = 14) categories. RESULTS: In type II diabetic patients, no differences were noted between normo- and microalbuminuric groups for known diabetes duration (8.3 +/- 5.9 vs. 11.7 +/- 8.0 years), blood pressure (BP) (129/76 +/- 16/8 vs. 131/76 +/- 14/5 mmHg), current metabolic control (HbA1c: 8.0 +/- 1.4 vs. 8.5 +/- 1.6%), and serum lipids. However, previous 2-year mean HbA1c levels were significantly higher in microalbuminuric patients (8.7 +/- 1.45 vs. 7.6 +/- 1.29%; P < 0.05). The TERalb was similar in control subjects and normoalbuminuric patients (5.16 +/- 1.09 vs. 5.71 +/- 1.66 %/h) and significantly higher in the microalbuminuric group (8.98 +/- 1.35 %/h; P < 0.0001). The increased leak of albumin was not explained by differences in diabetes duration, BP, or metabolic control at the time of investigation and was independently related to the presence of microalbuminuria (r = 0.63, percent explained variance approximately 40) and mean "historical" HbA1c (multiple r = 0.705; total explained variance approximately 50%). CONCLUSIONS: Type II diabetic patients with microalbuminuria show an increased TERalb, i.e., a widespread microvascular damage that may be important in the pathogenesis of long-term complications. Our findings may contribute to the explanation of why albuminuria seems to be an independent cardiovascular risk factor in type II diabetes.

Albuminuria↗
PubMed1995

[Hypertension and diabetes].

The prevalence of hypertension in diabetes is significantly higher than in non-diabetics, perhaps twice as common. The excess is related to diabetic nephropathy, mainly in type 1 diabetes, to obesity, mainly in type 2 diabetes, but also to increased sympathetic activity. Furthermore, the increased prevalence of hypertension may relate to insulin resistance and its sequelae. Insulin resistance leads to hyperinsulinemia, relates to increased LDL and reduced HDL levels, causes the development of impaired glucose tolerance and type 2 diabetes and might also be causally related to the onset of hypertension. Syndrome X has relevant therapeutic implications in the management of hypertension. Hypertension is a major risk factor for large vessel disease in diabetics and also a risk factor for microangiopathy, particularly nephropathy. The incidence of atherosclerotic disease is dramatically increased in both type 1 and type 2 diabetics and is the major cause of morbidity and premature death mainly in patients with raised urinary albumin excretion. Thus, diabetics show a two-fold increased risk of coronary heart disease, 2-6 fold increased risk of stroke and a several-fold increased risk of peripheral vessel disease. Some evidence suggests that hypertension may be a risk factor for retinopathy, particularly its progression, but surely hypertension is a significant risk factor for nephropathy, accelerating its progression and perhaps even causing the onset of the glomerulopathy. The mechanisms by which hypertension might contribute to the evolution of both large vessel as well as small vessel disease is still unknown, although increased capillary leakage and vascular endothelium alterations might be important factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive Agents↗
PubMed1994

Arterial hypertension and microalbuminuria in IDDM: the Italian Microalbuminuria Study.

Arterial hypertension and poor glycaemic control are central to the development of microalbuminuria in insulin-dependent diabetes mellitus (IDDM). Recent consensus has established sensitive criteria for their detection and treatment, although the proportion of patients who may benefit is unclear. Between 1988 and 1990, we measured urinary albumin to creatinine concentration ratio (A/C) in 3,636 adult out-patients with IDDM of more than 3 years duration, serum creatinine under 133 mumol/l and who were not undergoing antihypertensive treatment. A/C indicating microalbuminuria (> or = 2.38/2.96 mg/mmol, male/female) was found in 620 of 3,451 patients without proteinuria, and associated with hypertension (blood pressure > or = 140 and/or 90 mmHg; p = 0.0016; rate: 39.6%), independent of diabetes duration (p = 0.0082) and male gender (p = 0.0350; relative risk = 1.16; 95% confidence interval: 1.01-1.32). Hypertension was less common among those with normal A/C (27.5%, p < 0.0001) but was positively related with diabetes duration. Of the 1,015 patients with A/C > or = 2.0 mg/mmol 529 were reexamined. Glycated haemoglobin levels exceeded 3 SD above the mean of normal in 84.3% of the 198 microalbuminuric patients (AER = 20-200 micrograms/min), but were comparably poor (79.2%) in normoalbuminuria. Duration of diabetes was inversely related to glycated haemoglobin only in microalbuminuria (0.05 < p < 0.1). Intervention to lower blood pressure remains mainly restricted to those patients with long-term diabetes and slower development of kidney disease. Near-normalisation of glycaemia remains the priority for the majority of patients with microalbuminuria.

Adolescent↗
PubMed1994

A prevalence study of known diabetes mellitus in Tuscany assessed from pharmaceutical prescriptions and other independent sources.

This study evaluates the prevalence of diabetes mellitus (DM) in Pisa (Tuscany, Italy) using four independent data sources. The main source, represented by computerized prescriptions for anti-diabetic agents collected over a 4-month period, was validated using three secondary sources: (a) the list of diabetic patients who receive material of self-care from the National Health Service; (b) the clinical records of diabetic patients obtained from a random sample of family doctors; (c) the clinical records of diabetic patients attending our outpatient clinic. The main source provided 3806 patients, and 697 patients were added from the secondary sources, thus identifying a total number of 4503. The prevalence of known DM in the "Pisa area" exclusively reckoned by the main source, was 2.01%, and the prevalence corrected by the addition of the various sources resulted in 2.4%. The capture-recapture method showed a completeness of ascertainment of the survey of 90.1%, and thus an estimated prevalence of known diabetes of 2.64%. Of these, 141 patients had insulin-dependent diabetes mellitus (IDDM) corresponding to 3.2% of identified diabetic subjects (prevalence 0.07% inhabitants); 4362 patients had non-insulin-dependent diabetes mellitus (NIDDM), 96.8% of identified diabetic subjects (prevalence 2.36%). Of patients with NIDDM 10.5% was treated by diet, 65% with oral hypoglycaemic agents (OHA), 23% with insulin and 1.5% with insulin plus OHA. This study shows that the method used in this survey is suitable for epidemiological studies because it does not demand the cooperation of the diabetic patients, is addressed to the entire diabetic population without age discrimination and singles out the diabetic population in a very reliable way.

Adult↗
PubMed1994

Insulin degradation in vitro and in vivo: a comparative study in men. Evidence that immunoprecipitable, partially rebindable degradation products are released from cells and circulate in blood.

The products of insulin metabolism generated in vitro and in vivo were compared in this study. Monocytes from 10 control subjects were incubated with 125IA14-labeled insulin, acid washed, and solubilized or reincubated in insulin-free binding buffer to study both intracellular radioactivity or radioactivity released from cells to medium. To evaluate in vivo insulin metabolism, labeled insulin (100-120 microCi) was injected as a single intravenous bolus in 5 of the 10 subjects. Cellular and plasma radioactivity was characterized by high-performance liquid chromatography (HPLC). The results of the study show the following: 1) Products with superimposable HPLC elution profiles are found within cells and in medium. Two new labeled products are observed in the latter, suggesting that a membrane degradation process exists in monocytes. 2) Intermediates found within monocytes, in medium from monocytes, and in plasma have identical elution profiles, supporting the possibility that insulin is metabolized in various cells by a common pathway. 3) Insulin metabolism produces intermediates that bind well to anti-insulin antibody. The presence in plasma of these products induces a significant difference in the value of the metabolic clearance rate of insulin when HPLC or immunoprecipitation is used to detect intact insulin. 4) Immunoprecipitable products maintain, in part, the capacity to bind to insulin receptors and to be internalized into monocytes.

Chromatography, High Pressure Liquid↗
PubMed1994

Pulsatile insulin secretion from isolated human pancreatic islets.

Insulin secretion from the pancreas is pulsatile. The precise site and function of the pacemaker that regulates insulin periodicity in humans have not been determined. We isolated human pancreatic islets from five cadaver organ donors by collagenase digestion and density gradient purification. After 24 h of culture in CMRL-1066 medium at 37 degrees C, aliquots of 200 islets were perifused (1 ml/min for 120 min) with glucose and other secretagogues in oxygenated Krebs-Ringer bicarbonate solution at 37 degrees C. Samples for insulin measurement were taken every minute, and insulin secretion was analyzed by the Clifton and Steiner cycle detection technique. With 3.3 mM glucose (n = 17), insulin oscillations were demonstrated with a periodicity of 9.8 +/- 0.1 min (means +/- SE), mean amplitude was 16.8 +/- 1.8 pM, and overall mean insulin release was 43.8 +/- 4.2 pM. With 16.7 mM glucose (n = 14), no change of insulin periodicity was observed (10.2 +/- 0.9 min), mean amplitude was 41.4 +/- 10.2 pM (P < 0.01 vs. 3.3 mM glucose), and mean insulin release was 118.2 +/- 19.2 pM (P < 0.01 vs. 3.3 mM glucose). Both at 3.3 and 16.7 mM glucose, the addition of 1.4 mM glucagon (n = 4), 15 mM arginine (n = 4), or 100 micrograms/ml tolbutamide (n = 4) caused no change of insulin periodicity but enhanced mean amplitude and mean insulin release compared with glucose alone. These results show that a pacemaker is located within the islets that regulates pulsatile insulin secretion in humans; the pacemaker is remarkably stable, because its periodicity is not affected by factors altering insulin secretion.

Adult↗