Metabolic effects of pulsatile insulin infusion in the elderly

The present study investigated the metabolic effects of pulsatile insulin delivery at a pulse rate of 2 + 11 and 2 + 18 min in 7 healthy, elderly subjects (71.4 +/- 2.1 years), submitted to 260 min controlled iv glucose infusion via the Biostator. The endogenous secretion of pancreatic hormones was inhibited by somatostain (3 micrograms/min) and glucagon was replaced (67 ng/min) to basal levels. The same total insulin dose was delivered on both occasions. Insulin infusion rate was 1.3 and 2.0 mIU. kg-1. min-1 during switching on/off of 2 + 11 and 2 + 18 min, respectively. Blood glucose levels and glucose infusion rate were monitored continuously by the Biostator; [D-3-3H]glucose infusion allowed determination of glucose turnover. During the last 60 min of the experiment, pulsatile insulin at a pulse rate of 2 + 11 vs 2 + 18 min produced a stronger inhibition of endogenous glucose production, whereas glucose disappearance rate and glucose metabolic clearance rate were similarly affected. Plasma triglycerides, apolipoprotein B, and free fatty acids levels were also more suppressed during insulin delivery at pulse rate of 2 + 11 than at 2 + 18 min.

Insulin resistance as cause of increased blood pressure in the elderly: effects on intracellular ion contents

Previous reports have evidenced a strong relationship between high plasma insulin levels and blood pressure in diabetic and obese subjects but not in the elderly. During aging many patho-physiological changes in cardiovascular functions and autonomic nervous system occur, so that aging per se might be a cause of a 'physiological' increase in blood pressure. Nevertheless, an insulin resistance also develops during aging. The present study investigates the possible role of age-dependent insulin resistance in the genesis of increased blood pressure. Our data show that insulin resistance calculated by the glucose infusion rate during a euglycemic hyperinsulinemic glucose clamp procedure is significantly correlated with the insulin-mediated net decrease in erythrocyte Na+ content (r = 0.58, P < 0.05), as well as with net increase in erythrocyte K+ (r = 0.64, P < 0.05) and Mg2+ (r = 0.67, P < 0.01) content and to basal diastolic blood pressure (r = -0.63, P < 0.05). We conclude that in elderly subjects the age-related and normally occurring insulin resistance might contribute to the increase of arterial blood pressure through its effect on cell cation content.

Pulsatile glucagon has greater hyperglycaemic, lipolytic and ketogenic effects than continuous hormone delivery in man: effect of age

The present study aimed at investigating the hyperglycaemic, lipolytic and ketogenic effects of small doses of glucagon delivered continuously or in a pulsatile manner. The study was performed in eight healthy young volunteers (24.2 +/- 1.2 years) and in eight healthy aged subjects (69.4 +/- 2.0 years). In all the subjects, endogenous pancreatic hormone secretion was inhibited by somatostatin and only glucagon was replaced. Consequently, the effects of pulsatile and continuous glucagon delivery were studied in conditions of progressive somatostatin-induced insulin deficiency. In both the young and the aged subjects, pulsatile glucagon delivery resulted in increases in plasma glucose, non-esterified fatty acid, glycerol and beta-hydroxybutyrate levels greater than those observed when the same amount of glucagon was delivered in a continuous manner. The net increases in plasma glucose, glycerol and non-esterified fatty acid levels were similar between the young and the aged subjects when glucagon was infused continuously; in contrast, the rise in plasma beta-hydroxybutyrate in the aged was only about half that observed in the young subjects. Surprisingly, when glucagon was infused in a pulsatile manner, the rises in plasma glycerol, non-esterified fatty acid and beta-hydroxybutyrate levels were all significantly smaller in the aged subjects, while no significant differences were observed in the blood glucose responses. We conclude that, in the presence of somatostatin-induced insulin deficiency, pulsatile glucagon exerts greater effects on blood glucose, plasma non-esterified fatty acid, glycerol and beta-hydroxybutyrate levels than its continuous delivery. In the elderly, the lipolytic and ketogenic, but not the hyperglycaemic, responses to pulsatile glucagon are significantly reduced.

Pulsatile rather than continuous glucagon infusion leads to greater metabolic derangements in insulin-dependent diabetic subjects

The present study aimed at investigating the respective effects of continuous and pulsatile intravenous delivery of glucagon in insulin-dependent diabetic subjects. The study was performed in seven insulin-dependent diabetic subjects proven to have no residual insulin secretion. In random order and in different days each subject was submitted to glucagon delivery given continuously (58 ng/min) and in a pulsatile (377 ng/min during 2 min followed by 11 min during which no glucagon was infused) manner. In this conditions plasma glucose levels were significantly higher during pulsatile glucagon delivery. In particular in the last 65 min plasma glucose levels reached 10.8 +/- 0.3 vs 12.9 +/- 0.4 mmol/l (p less than 0.05) during continuous and pulsatile glucagon delivery respectively. Similarly plasma lipid changes also evidenced a greater effects of pulsatile rather than continuous hormone administration in producing the metabolic derangements classically encountered in insulin-dependent diabetic subjects. In conclusion, pulsatile glucagon delivery seem to produce greater metabolic effects than continuous hormone delivery.

Exaggerated orthostatic hypotension as first sign of diabetic autonomic neuropathy in the elderly

Long-standing diabetic subjects have an impaired sympathetic nervous system activity as a consequence of autonomic neuropathy. Moreover, in this latter group of subjects the parasympathetic rather than the sympathetic nervous system seems firstly impaired by glucose metabolism derangements. In the present study we show that, in aged diabetic subjects with a short duration of the disease (less than 5 years), and who are free from diabetic complications, it is possible to evidence a primary compromise of sympathetic rather than parasympathetic nervous system activity since a greater rate of orthostatic hypotension occurred. In the light of the well-known age-related changes in the physiopathology of cardiovascular activity, we hypothesize that in aged diabetic patients, even after a short duration of disease, sympathetic compromise precedes the derangement of parasympathetic nervous system activity.

Dietary magnesium supplements improve B-cell response to glucose and arginine in elderly non-insulin dependent diabetic subjects

Hypomagnesemia and low erythrocyte magnesium content are both common findings in non-insulin-dependent diabetic subjects. Moreover, intracellular magnesium may play a crucial role in modulating B-cell response to glucose by interfering with potassium permeability. Eight elderly, moderately obese, non-insulin-dependent diabetic subjects were treated with either magnesium supplementation (3 g/day) to the diet or placebo. Both treatment schemes lasted 4-weeks and were separated by a 'wash-out' of 3 weeks. At the end of each treatment period, in glucose test (0.33 g/kg for 3 min) and an iv arginine (5 g) test were performed to determine the B-and A-cell responses. Dietary magnesium supplementation vs placebo produced a slight but significant decrease in basal plasma glucose (8.6 +/- 0.3 vs 8.0 +/- 0.1 mmol/l, p less than 0.05) and an increase in acute insulin response after iv glucose (3.7 +/- 2.3 vs - 14.7 +/- 0.9 pmol.l 1. (10 min)-1, p less than 0.01) and after iv arginine (151 +/- vs 81 +/- 15 pmol.l-1. (10 min)-1, p less than 0.01), respectively. Plasma glucagon levels were unaffected by chronic dietary magnesium supplementation as well under basal conditions as in response to arginine. Net increase in acute insulin response after iv glucose and after iv arginine was significantly correlated to the net increase in erythrocyte magnesium content after dietary magnesium supplementation. We conclude that magnesium administration may be a useful adjuvant to the classic hypoglycemic agents in the treatment of non-insulin-dependent diabetic subjects.

Improved insulin response and action by chronic magnesium administration in aged NIDDM subjects

In eight aged non-insulin-dependent diabetes mellitus (NIDDM) subjects, insulin response and action were studied before and after chronic magnesium supplementation (2 g/day) to diet. Chronic magnesium supplementation to diet versus placebo produced 1) a significant increase in plasma (0.83 +/- 0.05 vs. 0.78 +/- 0.06 mM, P less than .05) and erythrocyte (2.03 +/- 0.06 vs. 1.88 +/- 0.09 mM, P less than .01) magnesium levels, 2) an increase in acute insulin response (AIR) (4.0 +/- 0.6 vs. -1.6 +/- 0.6 mU/L, P less than .05) to glucose pulse, and 3) an increase in glucose infusion rate (GIR) (3.6 +/- 0.6 vs. 2.9 +/- 0.5 mg.kg-1.min-1, P less than .025) calculated in the last 60 min of a euglycemic-hyperinsulinemic (100 mU.m2.min-1 during 180 min) glucose clamp. Net increase in AIR, glucose disappearance rate after glucose pulse, and GIR were significantly and positively correlated to the net increase in erythrocyte magnesium content calculated after chronic magnesium supplementation to diet. In conclusion, our data suggest that NIDDM subjects may benefit from therapeutic chronic administration of magnesium salts.

Lack of diabetogenic action of calcitonin in subjects affected by insulinoma

Calcitonin has been shown to affect calcium handling within cells thus impairing insulin secretion and glucose tolerance in healthy subjects. In the present study we investigate the effects of calcitonin on basal and nutrients-induced plasma glucose and insulin levels variations in healthy subjects (n = 10) and in patients affected by islet cell tumor (n = 6). In healthy subjects calcitonin markedly decreased basal and nutrients-induced plasma insulin levels while in patients with islet cell tumor this calcitonin-mediated effect was lost. So we conclude that the lack of calcitonin effect upon insulin secretion in patients with insulinoma is probably due to the autonomous insulin secretion characterizing islet cell tumor.

Effects of oxytocin delivery on counter-regulatory hormone response in insulin-dependent (type 1) diabetic subjects

In insulin-dependent (type 1) diabetic subjects (n = 7) with intact hormone response to hypoglycaemia, oxytocin infusion (0.2 mU/min over 60 min) produced significant rises in basal plasma glucagon and adrenaline levels, while it reduced basal plasma cortisol levels. During insulin-induced hypoglycaemia, oxytocin potentiated the increases in plasma glucagon and adrenaline, while an inhibitory effect on plasma cortisol levels was still present. In insulin-dependent (type 1) diabetic subjects (n = 7) with blunted counter-regulatory hormone response to hypoglycaemia, the same dose of oxytocin (0.2 mU/min over 60 min) increased basal plasma glucose and glucagon concentrations and lowered basal plasma cortisol concentration. In the same group of patients, oxytocin delivery (0.2 mU/min), simultaneously to an insulin-induced hypoglycaemia, produced a significant elevation of plasma glucagon and adrenaline concentrations thus enhancing glucose recovery from hypoglycaemia. In conclusion, in insulin-dependent (type 1) diabetic patients, oxytocin delivery enhances plasma glucagon and adrenaline levels in basal conditions and during insulin-induced hypoglycaemia.

Impaired insulin-induced erythrocyte magnesium accumulation is correlated to impaired insulin-mediated glucose disposal in type 2 (non-insulin-dependent) diabetic patients

Plasma and erythrocyte magnesium levels were measured by atomic absorption spectrometry in 12 healthy subjects and 12 moderately obese patients with Type 2 (non-insulin-dependent) diabetes mellitus. Basal plasma and erythrocyte magnesium levels were significantly lower in diabetic patients than in control subjects. In vitro incubation in the presence of 100 mU/l insulin significantly increased magnesium erythrocyte levels in both control subjects (p less than 0.001) and patients with diabetes (p less than 0.001). However, even in the presence of 100 mU/l insulin, the erythrocyte magnesium content of patients with Type 2 diabetes was lower than that of control subjects. The in vitro dose-response curve of the effect of insulin on magnesium erythrocyte accumulation was shifted to the right when red cells of diabetic patients were used, with a highly significant reduction of the maximal effect. Such reduction of the maximal effect of insulin suggests that the impairment of insulin-induced erythrocyte magnesium accumulation observed in Type 2 diabetic patients results essentially from a post-receptor defect.(ABSTRACT TRUNCATED AT 250 WORDS)

[Prostaglandins, insulin secretion and diabetes mellitus]

The islets of Langerhans have the enzymatic equipment permitting the synthesis of the metabolites of arachidonic acid: cyclo-oxygenase and lipo-oxygenase. Numerous studies have shown that cyclo-oxygenase derivatives, mainly PGE2, reduce the insulin response to glucose whereas lipo-oxygenase derivatives, mainly 15-HPETE, stimulate insulin secretion. So, for instance, drugs that increase prostaglandins synthesis as colchicine or furosemide inhibit insulin secretion while non steroid anti-inflammator drugs, mainly salicylates, which inhibit cyclo-oxygenase, enhance the insulin response to various stimuli. In type-2 (non insulin-dependent) diabetes, an increased sensitivity to endogenous prostaglandins has been proposed as a possible cause for the insulin secretion defect which characterizes this disease. Play in favor of this hypothesis the fact that the administration of PGE inhibits the insulin response to arginine in type-2 diabetics but not in normal subject and the fact that the administration of salicylates could improve the insulin response to glucose in some of these patients.

Diabetes and hypertension in the elderly

Hypertension combined with diabetes in the elderly is characterized by many important metabolic and cardiovascular changes, among which insulin resistance, hyperinsulinaemia and increased total peripheral resistance appear to be the most relevant. Non-insulin dependent diabetes mellitus is also characterized by insulin resistance and hyperinsulinaemia. Moreover, hyperinsulinaemia itself has been shown to increase total peripheral resistance. Hyperinsulinaemia thus seems to play a key role in the pathophysiology of hypertension in elderly diabetic subjects. Therefore elderly hypertensive diabetic patients should be treated with thiazide diuretics in low doses, calcium channel blockers and alpha-adrenergic blockers.

Advantageous metabolic effects of pulsatile insulin delivery in noninsulin-dependent diabetic patients

This study was done to compare the actions of pulsatile and continuous insulin administration in eight noninsulin-dependent diabetic patients. Human insulin was delivered in a pulsatile manner (1.3 mU/kg.min for 2 min, followed by 11 min during which no insulin was infused) or continuously (0.2 mU/kg.min) for 325 min. Endogenous hormone secretion was inhibited by somatostatin (125 micrograms/h), and glucagon was replaced at rate of 3.5 micrograms/h. Under these conditions plasma C-peptide levels fell progressively to extremely low values at the end of the experiment. Continuous insulin infusion resulted in steady plasma insulin levels, averaging 86 pmol/L, while during intermittent insulin administration plasma insulin levels were 5.7 and 158 pmol/L before and 3 min after the start of the insulin injection, respectively. Basal plasma glucagon [mean 158 +/- 11 (+/- SE) vs. 163 +/- 21 ng/L; P = NS] levels were similar on both occasions. During replacement peripheral plasma glucagon levels were no different whatever the mode of insulin administration, nor did they differ from the basal values. The mean plasma glucose concentrations were similar before both studies and rose to 9.5 and 8.6 mmol/L in the first 65 min during continuous and pulsatile insulin administration, respectively. In contrast, during the last 65 min, plasma glucose averaged 6.2 mmol/L during both studies. The glucose infusion rate initially increased, but then rapidly fell to values close to zero at the end of the first 65 min during the continuous insulin infusion, whereas during this time it averaged 0.59 +/- 0.10 mg/kg.min (32.5 +/- 5.5 mumol/kg.min) during pulsatile insulin administration. In the last 65 min the glucose infusion rate was significantly higher during pulsatile than during continuous insulin delivery. Furthermore, pulsatile rather than continuous insulin administration significantly reduced plasma triglyceride, very low density lipoprotein triglyceride, and FFA levels and increased high density lipoprotein cholesterol and apolipoprotein-B levels. We conclude that pulsatile insulin delivery has advantageous metabolic effects compared to continuous hormone administration in patients with noninsulin-dependent diabetes mellitus.

Beta-endorphin-induced inhibition and stimulation of insulin secretion in normal humans is glucose dependent

This study evaluated the effect of human beta-endorphin on pancreatic hormone levels and their responses to nutrient challenges in normal subjects. Infusion of 0.5 mg/h beta-endorphin caused a significant rise in plasma glucose concentrations preceded by a significant increase in peripheral glucagon levels. No changes occurred in the plasma concentrations of insulin and C-peptide. Acute insulin and C-peptide responses to intravenous pulses of different glucose amounts (0.33 g/kg and 5 g) and arginine (3 g) were significantly reduced by beta-endorphin infusion (P less than .01). This effect was associated with a significant reduction of the glucose disappearance rates, suggesting that the inhibition of insulin was of biological relevance. beta-Endorphin also inhibited glucose suppression of glucagon levels and augmented the glucagon response to arginine. To verify whether the modification of prestimulus glucose level could be important in these hormonal responses to beta-endorphin, basal plasma glucose concentrations were raised by a primed (0.5 g/kg) continuous (20 mg kg-1.min-1) glucose infusion. After stabilization of plasma glucose levels (350 +/- 34 mg/dl, t = 120 min), beta-endorphin infusion caused an immediate and marked increase in plasma insulin level (peak response 61 +/- 9 microU/ml, P less than .01), which remained elevated even after the discontinuation of opioid infusion. Moreover, the acute insulin response to a glucose pulse (0.33 g/kg i.v.) given during beta-endorphin infusion during hyperglycemia was significantly higher than the response obtained during euglycemia (171 +/- 32 vs. 41 +/- 7 microU/ml, P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Altered metabolic and hormonal responses to epinephrine and beta-endorphin in human obesity

Catecholamines and endogenous opioid peptides are released in response to stress. Exogenous infusions of epinephrine and beta-endorphin (both in doses of 15, 50, and 80 ng/kg.min sequentially, each dose lasting 30 min) were used to mimic short term stress in both normal weight (body mass index, less than 25 kg/m2) and obese (body mass index, greater than 30 kg/m2) subjects. Fasting plasma insulin, C-peptide, and beta-endorphin concentrations were significantly higher in the obese than in the normal subjects (P less than 0.01-0.005). In lean subjects epinephrine produced significant increases in plasma glucose levels, but no appreciable changes in plasma insulin, C-peptide, or glucagon. Infusion of beta-endorphin in the same subjects caused plasma glucose and glucagon to rise, but insulin and C-peptide levels did not change. The simultaneous infusion of epinephrine and beta-endorphin produced a glycemic response which, although greater, was not significantly different than the sum of the responses to the individual hormone infusions. However, the two hormones had a synergistic interaction on plasma glucagon levels [total glucagon response, 2275 +/- 370 pg/min.mL (ng/min.L); sum of single effects, 750 +/- 152 (+/- SE) pg/min.mL (ng/min.L); P less than 0.01]. The plasma epinephrine [207 +/- 21, 607 +/- 70, and 1205 +/- 134 pg/mL (1130 +/- 115, 3640 +/- 382, and 6577 +/- 691 pmol/L] and beta-endorphin [875 +/- 88, 1250 +/- 137, and 1562 +/- 165 pg/mL (250 +/- 25, 358 +/- 39, and 447 +/- 47 pmol/L] concentrations attained during the infusions of each single hormone were not different from those recorded during the combined hormonal infusion. In obese subjects epinephrine raised plasma glucose levels and caused dose-related increments of plasma glucagon concentrations. Plasma insulin and C-peptide concentrations remained low and rebounded at the end of the infusions. In the same subjects, beta-endorphin produced elevations of plasma glucose, insulin, C-peptide, and glucagon. When the combined hormonal infusion was given to obese subjects, the plasma epinephrine and beta-endorphin concentrations rose to values not significantly different from those in normal weight subjects. However, there was a dramatic increase in plasma glucose exceeding 200 mg/dL (11.1 mmol/L), which remained elevated 30 min after the infusion. The glucagon response was not greater than the sum of the single effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulsatile insulin delivery is more efficient than continuous infusion in modulating islet cell function in normal subjects and patients with type 1 diabetes

The respective modulating effects of continuous and intermittent insulin delivery on pancreatic islet cell function were studied in seven normal men and nine insulin-dependent (type 1) diabetic patients. In the normal men, saline or continuous (0.8 mU kg-1 min-1) or pulsatile (5.2 mU kg-1 min-1, with a switching on/off length of 2/11 min) human insulin were delivered on different days and in random order. Despite hyperinsulinemia, blood glucose was kept close to its basal value by the glucose clamp technique. The diabetic patients also were infused in random order and on different days with either saline or a smaller amount of insulin delivered continuously (0.15 mU kg-1 min-1) or in a pulsatile manner (0.97 mU kg-1 min-1 for 2 min, followed by 11 min during which no insulin was infused). In all experiments, 5 g arginine were given iv as a bolus dose 30 min before the end of the study, and plasma C-peptide and glucagon levels were determined to assess islet cell function. In the normal men, insulin administration resulted in a significant decline of basal plasma glucagon and C-peptide levels and in a clear-cut decrease in the arginine-induced glucagon response. These effects of insulin were significantly more marked when insulin was delivered in a pulsatile rather than a continuous manner. In the insulin-dependent diabetic patients, the lower dose of insulin infused continuously did not alter the basal or arginine-stimulated glucagon response. In contrast, when the same amount of insulin was delivered intermittently, arginine-induced glucagon release was greatly reduced. Thus, these data support the concept that insulin per se is a potent physiological modulator of islet A- and B-cell function. Furthermore, they suggest that these effects of insulin are reinforced when the hormone is administered in an intermittent manner in an attempt to reproduce the pulsatile physiological release of insulin.

Plasma glucose lowering effect of sparteine sulphate infusion in non-insulin dependent (type 2) diabetic subjects

Sparteine sulphate, given i.v. as a bolus of 15 mg/ml plus 90 mg in 0.9% NaCl 100 ml over 60 min, increases plasma insulin and decreases plasma glucose and adrenaline in non-insulin dependent (Type II) diabetic subjects. The hypoglycaemic effect was also evident in the presence of a high plasma glucose level produced by Biostator changing glucose infusion from 20.2 +/- 2.8 to 26.4 +/- 4.2 mg.kg-1.min-1 (p less than 0.01), and it was potentiated by simultaneous infusion of arginine. No additional effect of sparteine on the peripheral sensitivity to insulin were detected by the euglycaemic, hyperinsulinaemic glucose clamp technique, as the glucose infusion rate (3.1 +/- 0.8 vs 2.6 +/- 1.2 mg.kg-1.min-1) was not statistically significant different in the last 60 min of the experiment. It is concluded that sparteine sulphate enhances beta-cell secretion, causing a fall in the plasma glucose concentration.

Oxytocin increases arginine-induced A and B cell secretion in normal man and in diabetic subjects

In previous in Vitro and in Vivo studies oxytocin was shown to stimulate A and B cell secretion. In the present study we show that oxytocin is also able to increase arginine-induced glucagon and insulin secretion in healthy human beings. Similar results were obtained in both insulin-dependent (type-1) and non-insulin dependent (type-2) diabetic subjects.

Pharmacological doses of oxytocin affect plasma hormone levels modulating glucose homeostasis in normal man

Pharmacological doses of oxytocin administered in basal conditions evoked a rapid surge in plasma glucose and glucagon levels followed by a later increase in plasma insulin and adrenaline levels. The effects of oxytocin on plasma glucagon and adrenaline levels were potentiated by hypoglycemia. When the endogenous pancreas secretion was suppressed by cyclic somatostatin (150 micrograms/h) and exogenous glucagon (3.5 micrograms/h) and insulin (0.2 mU/kg.min) were both replaced, oxytocin (0.2 U/min) evoked a transient but significant increase in plasma glucose levels suppressing the glucose infusion rate (GIR) in the first 60 min. On the contrary at higher insulin infusion rate (0.6 mU/kg.min) plasma glucose levels and GIR remained unaffected throughout the study. Oxytocin seems also to potentiate glucose-induced insulin secretion as evidenced by hyperglycemic glucose clamp. In conclusion, pharmacological doses of oxytocin seem to exert a prevalent hyperglycemic effect by a combined action at the liver site (as glycogenolytic agent) and at the endocrine pancreas (as a stimulatory agent of A cell secretion).