Catecholamines and diabetes mellitus

A High intensity Interval training (running and swimming) and resistance training intervention on heart rate variability and the selected biochemical factors in boys with type 1 diabetes

OBJECTIVE

The purpose of this research is to investigate the effect of High Intensity Interval Training and Resistance training (HIITR) on heart rate variability (HRV), blood glucose, and plasma biomarkers levels in adolescents with type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

24 boys with T1D (FBS: 274.66 ± 52.99, age: 15.2 ± 1.78 years, and BMI = 19.61 ± 1.11) and 12 healthy boys (FBS: 92.75 ± 5.22, age: 15.08 ± 1.67 years, and BMI = 20.26 ± 2.66) were divided into three groups: Diabetes Training (DT, n = 12), Diabetes Control (DC, n = 12), and Healthy Control (HC, n = 12). HRV (24 h) was computed in time and frequency domains, anthropometric, biochemical parameters at rest, and aerobic capacity (VO2peak) obtained during a graded exercise testing (GXT). All variables were evaluated at the baseline and following 12 weeks of exercise training, done 3 days weekly. The statistical method used for data analysis was analysis of covariance (ANCOVA) test.

RESULTS

HRV, Hemoglobin A1c (HbA1c) and Fasting blood sugar (FBS), VO2peak, norepinephrine (NEP), and HDL-C indicated significant differences between both T1D groups compared to HC at baseline (p < 0.001). BMI, LDL-C, TC, and TG parameters were similar in all groups. HRV parameters, VO2peak and HDL-C, and NEP were significantly improved by exercise training, and HbA1c and FBS levels were significantly reduced (p < 0.001). There is a negative and significant correlation between LF/HF Ratio Difference (post-test minus pre-test) and VO2Peak Difference variables (post-test minus pre-test) (p < 0.001).

CONCLUSIONS

The present study suggests the importance of early screening for CVD risk factors in adolescent males with T1D. Also, it was revealed HIITR training compared to other training patterns, and cardiovascular health improves via enhancement of autonomic modulation, VO2peak, plasma lipids, and catecholamine levels.

Sympathetic neural abnormalities in type 1 and type 2 diabetes: a systematic review and meta-analysis

BACKGROUND

Microneurographic recordings of muscle sympathetic nerve activity (MSNA) have shown that sympathetic activation may characterize diabetes mellitus. However, it is recognized that comorbidities and metabolic abnormalities frequently associated with both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) diabetes affect MSNA, generating potential confounding effects and making the association between sympathetic activation and diabetes mellitus still a controversial matter.

METHODS

The present meta-analysis evaluated 11 microneurographic studies enrolling 314 diabetes mellitus patients and healthy controls, and MSNA was chosen as the main variable of interest. Collection of the data included indirect adrenergic markers such as heart rate and venous plasma noradrenaline, together with hemodynamic, anthropometric and metabolic variables.

RESULTS

A total of 11 microneurographic studies were evaluated including 314 diabetes mellitus patients and controls. Diabetes mellitus displayed MSNA significantly greater than controls (mean difference amounting to 8.1, 95% confidence interval 1.21-15.08, P < 0.05). This difference was ascribed to T2DM, since T1DM patients displayed MSNA values superimposable to controls. In T2DM MSNA was directly related to age (r = 0.83, β = 0.82, P < 0.04) and plasma insulin (r = 1.00, β = 2.25, P < 0.01) but not to other variables.

CONCLUSION

T2DM-related sympathetic activation is detectable even when obesity, hypertension and metabolic syndrome are excluded; not found in T1DM; not associated with anthropometric and hemodynamic variables; and related to plasma insulin.

Peripheral Neuropathy as a Component of Skeletal Disease in Diabetes

PURPOSE OF REVIEW

The goal of this review is to explore clinical associations between peripheral neuropathy and diabetic bone disease and to discuss how nerve dysfunction may contribute to dysregulation of bone metabolism, reduced bone quality, and fracture risk.

RECENT FINDINGS

Diabetic neuropathy can decrease peripheral sensation (sensory neuropathy), impair motor coordination (motor neuropathy), and increase postural hypotension (autonomic neuropathy). Together, this can impair overall balance and increase the risk for falls and fractures. In addition, the peripheral nervous system has the potential to regulate bone metabolism directly through the action of local neurotransmitters on bone cells and indirectly through neuroregulation of the skeletal vascular supply. This review critically evaluates existing evidence for diabetic peripheral neuropathy as a risk factor or direct actor on bone disease. In addition, we address therapeutic and experimental considerations to guide patient care and future research evaluating the emerging relationship between diabetic neuropathy and bone health.

Effect of yoga on cardiac autonomic dysfunction and insulin resistance in non-diabetic offspring of type-2-diabetes parents: A randomized controlled study

OBJECTIVE

The present study was aimed to determine the effect of yoga program on cardiac autonomic dysfunction and insulin resistance in non-diabetic offspring of diabetes parents.

METHODS

A randomized passive-controlled study was conducted on 64 non-diabetic offspring of type-2-diabetes parents (mean-age:25.17years). Yoga group participants received yoga training for 8 weeks. Heart-rate variability (HRV) indices: low frequency (LF), high frequency (HF) and LF/HF ratio; fasting blood glucose (FBG), oral glucose tolerance test (OGTT) and insulin resistance (IR) were estimated at baseline and after 8-weeks of intervention.

RESULTS

We found a significant decrease in LF (p = 0.005), LF/HF ratio (p = 0.004), IR (p < 0.001), OGTT (p = 0.003) and increase in HF (p = 0.022) in yoga group participants. Control group participants did not show any significant change in any variables.

CONCLUSIONS

Improvement in cardiac autonomic function and insulin resistance by yoga training implies that yoga can reduce the risk of development of diabetes in offspring of diabetes parents.

An influence of adrenaline (1:80,000) containing local anesthesia (2% Xylocaine) on glycemic level of patients undergoing tooth extraction in Riyadh

OBJECTIVE

Aim is to compare the glycemic level among patients before, and after local anesthesia containing adrenaline 1:80,000 among patients who need dental extraction.

MATERIALS AND METHODS

60 patients were randomly selected including 30 healthy and 30 with a diabetes history for this study in Riyadh city. First the blood glucose level was measured before administering local anesthesia containing adrenaline after taking their history with glucocheck according to instructions, then blood Sugar level was recorded after administering local anesthesia containing adrenaline 1:80,000 concentrations. Blood sugar level was also checked 5 min after the tooth extraction procedure.

RESULTS

There were no significant results found after the administration of local anesthesia containing adrenaline in both healthy and diabetic patients (p > 0.05). However, change of significance (p < 0.05) was noticed in diabetic patients who had not taken their hypoglycemic medication; there was a rise in their blood glucose level after extraction.

CONCLUSION

The study concluded no significant effect on the glycemic level of patients after the administration of local anesthesia containing adrenaline 1:80,000 in healthy and diabetic patients whether hypoglycemic medication was taken or not but a rise in blood sugar level was found among diabetic patients who did not take their hypoglycemic medications undergoing tooth extraction.

Differential sensitivity to adrenergic stimulation underlies the sexual dimorphism in the development of diabetes caused by Irs-2 deficiency

The diabetic phenotype caused by the deletion of insulin receptor substrate-2 (Irs-2) in mice displays a sexual dimorphism. Whereas the majority of male Irs-2(-/-) mice are overtly diabetic by 12 weeks of age, female Irs-2(-/-) animals develop mild obesity and progress less rapidly to diabetes. Here we investigated β-cell function and lipolysis as potential explanations for the gender-related differences in this model. Glucose-stimulated insulin secretion was enhanced in islets from male null mice as compared to male WT whereas this response in female Irs-2(-/-) islets was identical to that of female controls. The ability of α(2)-adrenoceptor (α(2)-AR) agonists to inhibit insulin secretion was attenuated in male Irs2 null mice. Consistent with this, the expression of the α(2A)-AR was reduced in male Irs-2(-/-) islets. The response of male Irs-2(-/-) islets to forskolin was enhanced, owing to increased production of cAMP. Basal lipolysis was increased in male Irs-2(-/-) but decreased in female Irs-2(-/-) mice, concordant with the observation that adipose tissue is sparse in males whereas female Irs2 null mice are mildly obese. Adipocytes from both male and female Irs-2(-/-) were resistant to the anti-lipolytic effects of insulin but female Irs-2(-/-) fat cells were additionally resistant to the catabolic effects of beta-adrenergic agonists. This catecholamine resistance was associated with impaired generation of cAMP. Consequently, targets of cAMP-dependent protein kinase (PKA) which mediate lipolysis were not phosphorylated in adipose tissue of female Irs-2(-/-) mice. Our findings suggest that IRS-2 deficiency in mice alters the expression and/or sensitivity of components of adrenergic signaling.

Impaired counter regulation of hypoglycemia in a group of insulin-dependent diabetics with recurrent episodes of severe hypoglycemia

The counterregulatory response to insulin-induced hypoglycemia was investigated in 22 insulin-dependent diabetics (IDD) with recurrent hypoglycemia and in 6 healthy volunteers. Hypoglycemia was induced by a constant rate infusion of insulin (2.4 U/h) up to four hours. Conventional insulin therapy was changed to an i.v. infusion of regular insulin 24 hours prior to the experiment. The presence of diabetic autonomic neuropathy was evaluated by respiratory sinus arrhythmia and Valsalva maneuver. In healthy subjects, blood glucose was decreased to 2.5 mmol, here reaching steady state level and giving rise to marked glucagon and growth hormone (GH) responses. The majority of IDD (group A) reached a slightly lower steady state glucose level and exhibited similar glucagon and GH responses while the epinephrine response was augmented. Six IDD (group B) showed a continuous decrease in blood glucose to 1.2 +/- 0.1 mmol/l at which level the infusion of insulin was discontinued due to neuroglucopenic symptoms. These subjects had no glucagon and epinephrine responses while their GH and cortisol responses were normal. A comparison of the diabetic groups revealed a longer duration of diabetes and a more impaired autonomic nervous function in group B while glycosylated hemoglobin was similar. It is concluded that most IDD have normal hormonal responses (epinephrine, glucagon, GH, cortisol) and normal counterregulartory capacity to hypoglycemia induced by a prolonged infusion of a moderate dose of insulin. Some patients with long-term diabetes and impaired capacity to counteract hypoglycemia exhibit deficient glucagon and epinephrine responses to hypoglycemia.

Factors contributing to left ventricular diastolic dysfunction in long-term type I diabetic subjects

Although non-invasive studies in type I diabetic subjects indicate left ventricular (LV) diastolic dysfunction, the contribution of borderline or mild hypertension to such changes is obscure. Thus, digitized M-mode echocardiograms were obtained in 32 (18 men) young (less than 50 years) normotensive controls and 32 (21 men) long-term (greater than or equal to 12 years) type I diabetics with blood pressures ranging from normal to hypertensive. All diabetics were without clinical heart disease, none were previously treated for hypertension or using cardioactive drugs. Heart rate, systolic and diastolic blood pressures were higher in diabetic than control subjects. Their LV end-diastolic dimension was smaller, whereas wall thickness, LV mass index and fractional shortening were similar to controls. In diabetics, however, the normalized peak filling rate was decreased and the rapid filling period fraction of diastole increased. In multivariate analysis, diabetes and LV mass independently and inversely influenced the normalized peak filling rate, while fractional shortening did so positively. Furthermore, diabetes and systolic blood pressure independently influenced the rapid filling period fraction of diastole. This study is the first to demonstrate systolic blood pressure and LV mass as independent contributors to subclinical LV diastolic abnormalities in diabetics. These findings may therefore indicate the need to treat even mild hypertension in diabetics in an effort to delay the development of cardiopathy.

An etiologic model proposing that non-insulin-dependent diabetes mellitus is chronic hypoxic stress hyperglycemia

This etiologic model equates non-insulin-dependent diabetes mellitus (NIDDM) to chronic hypoxic stress hyperglycemia produced by increased stimulation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. In the initial stages of the disease, hypoxia is believed to result from hemodilutional anemia precipitated by a reduction in vascular smooth muscle tone. The reduction increases lumen diameter necessitating an increased blood volume to maintain pressure. Increased lumen diameter may also trigger atherosclerotic changes that characterize the later stages of NIDDM. The increased diameter decreases the shear stress experienced by endothelial cells and they respond by releasing endothelin, a smooth muscle constrictor and mitogen. The constricting action is hypothesized to be relatively ineffective in NIDDM leading to long-term endothelin release and activation of its mitogenic properties. The resulting increase in the number of smooth muscle cells may explain the intimal thickening of atherosclerosis. Restoration of vascular muscle tone is proposed as a treatment strategy for mild NIDDM.

Morphological changes in the sciatic nerve of diabetic rats treated with low molecular weight heparin OP 2123/parnaparin

This study points out the early alterations that affect the sciatic nerve of rats with experimentally induced diabetes. It emphasizes the advantages deriving from treatment with low molecular weight heparin (LMWH) OP 2123/parnaparin and correlates these findings with observations emerging from a review of the relevant literature. In fact, the number and diameter of the capillaries within the sciatic nerve of diabetic rats appear to be increased consistent with a microangiopathy (the main characteristic of which is the fragility of new vessels), that is related to the evolution of diabetes in humans and animals. Our results suggest a possible therapeutic role for OP 2123/parnaparin in both diabetic neuropathy and microangiopathy, frequent complications of diabetes.

Differential alterations of spontaneous and stimulated 45Ca(2+) uptake by platelets from patients with type I and type II diabetes mellitus

Diabetes mellitus (DM) is associated with hyperaggregability of platelets. Although the mechanisms underlying this abnormality remain unknown, Ca(2+) imbalance has been implicated. Both activators (alpha-adrenoceptor agonists, collagen, and ADP) and inhibitors (beta-adrenoceptor agonists, iloprost and dibutyryl cAMP) of platelet function, respectively, elicit the uptake of [45Ca(2+)] in human platelets. It was determined that the [45Ca(2+)] uptake methods employed reflected signal transduction events at the plasma membrane rather than absolute changes of Ca(2+) fluxes or levels of cytosolic Ca(2+). In the present study, basal (unstimulated) [45Ca(2+)] uptake by platelets from both type I and type II diabetic patients was significantly enhanced when compared to age-matched controls. When basal values were subtracted from stimulated values, there were highly significant decreases in [45Ca(2+)] uptake in platelets from type I diabetic patients compared to controls when stimulated with adrenaline, isoprenaline, noradrenaline, collagen, A23187, or iloprost. In contrast, when basal values were subtracted from stimulated values there were significant increases in [45Ca(2+)] uptake by platelets from type II diabetic patients when stimulated with adrenaline, isoprenaline, noradrenaline, A23187, iloprost, and collagen. It is concluded that in type I and type II DM there are differential alterations in [45Ca(2+)] sequestration linked to inhibitors and stimulators of platelet activation. These data indicate that the hyperaggregability of platelets that is associated with both type I and type II DM may be due to an aetiology other than Ca(2+) mobilization linked to signal transduction.

Evaluation of the elderly patient with weakness: an evidence based approach

Because of the altered physiology of the elderly population, either as a result of aging or as a result of other disease processes, many illnesses may present with features that are either atypical or nonspecific in nature. Difficult and nonspecific complaints such as weakness in an elderly patient must be handled in a judicious, cost-effective, comprehensive, and expeditious manner that benefits both the patient and the emergency department. This article addresses the evaluation of the elderly patient who presents to the ED complaining of weakness.

Evaluation of the cardiac autonomic nervous system in spontaneously non-insulin-dependent diabetic rats by 123I-metaiodobenzylguanidine imaging

OBJECTIVE

To evaluate the sensitivity of 123I-labeled metaiodobenzylguanidine (123I-MIBG) scintigraphy in detecting diabetic autonomic nervous system disorders.

MATERIALS AND METHODS

Thirty-one-week-old male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of spontaneous non-insulin-dependent diabetes mellitus, were maintained for 8 weeks with or without 30% sucrose solution as a drinking water (n = 3 each). Long-Evans Tokushima Otsuka (LETO) rats (n = 3), served as controls. Plasma glucose and insulin levels were measured, and 123I-MIBG scintigraphy was performed with a gamma camera equipped with a pinhole collimator for animals. Plasma and cardiac tissue cathecolamine levels were also determined.

RESULTS

Plasma glucose levels of OLETF rats with and without sucrose loading (554+/-106 and 141+/-1.5 mg/dl respectively) were significantly higher than those of LETO rats (116+/-3.7 mg/dl). Norepinephrine concentrations in heart and plasma tended to be lower in diabetic rats. The washout rate of 123I-MIBG in diabetic rats was significantly higher than the rate in control rats. Cardiac uptake of 123I-MIBG, calculated as % dose/g of tissue, was significantly lower in diabetic rats than in control rats.

CONCLUSION

These results suggest that myocardial 123I-MIBG scintigraphy is suitable for assessing cardiac sympathetic activity noninvasively in diabetic states, even in the early stages.

Altered activity of the autonomous nervous system as a determinant of the impaired beta-cell secretory response after protein-energy restriction in the rat

Glucose-induced insulin secretion in vivo is known to be severely blunted in the rat as a consequence of protein-energy restriction starting early in life. We have recently reported in such malnourished rats (M rats) that the release of the counterregulatory hormones that defend against hypoglycemia was severely disturbed, and their plasma levels of epinephrine and norepinephrine were prominently increased. Knowing that the autonomic nervous system has the potential to play a major role in the control of insulin secretion in response to glucose in vivo, we therefore determined whether protein-energy restriction starting after weaning could alter sympathetic and/or parasympathetic nerve activities, and whether these changes could be responsible for the lack of response to glucose of their beta-cells in vivo. When tested in the basal postabsorptive state, the malnourished rats exhibited profound alterations of both parasympathetic and sympathetic nerve activities; the firing rates of the vagus nerve and the superior cervical ganglion were dramatically decreased and increased, respectively. Under the same conditions, insulin secretion in vivo in response to a glucose load (deltaI/deltaG) was severely decreased in M rats compared with that in control (C) rats. When evaluated after administration of acetylcholine, deltaI was amplified to the same extent in M rats as in C rats. After administration of the alpha2A-adrenergic agonist oxymetazoline, glucose-induced insulin release in M rats was not significantly affected, whereas it was sharply decreased in C rats. Finally, administration of yohimbine, an alpha2-adrenergic antagonist, partially restored the lack of reactivity of the beta-cells to glucose in the M rats, as deltaI/deltaG was amplified by 6-fold in the M group and by 3.3-fold in the C group. We conclude that protein-energy restriction starting early in life in rats brings about changes in the overall activity of the autonomic nervous system that, in turn, are responsible at least in part for the acquisition/maintenance of decreased beta-cell reactivity to glucose in vivo.

Decreased sympatho-adrenal activity in diabetic patients with autonomic dysfunction following mental stress

The sympathetic nervous system is of major importance in the regulation of numerous physiological functions. While it is clearly established that there is a decreased noradrenergic status in people with autonomic neuropathy, the epinephrine secretion is much more controversial. Basal and mental stress-stimulated plasma catecholamine levels were measured in 42 diabetic patients with and without pathological cardiovascular function tests and in 13 healthy, non-diabetic control subjects. In addition, the excretion of catecholamines was measured in a 24 h urine collection and compared with the stress stimulated plasma levels. During mental stress exposure a diminished epinephrine secretion was found in diabetic patients with autonomic neuropathy compared with diabetic patients without neuropathy and the healthy control group (p < 0.05: respectively). The decreased epinephrine response to mental stress was strongly correlated with a diminished urinary excretion of this "neurotransmitter' (r = 0.46; p < 0.01). Diabetic patients suffering from cardiovascular autonomic neuropathy exhibit a diminished sympatho-adrenal response following mental stress exposure. Both measurement of urinary and mental stress stimulated plasma epinephrine levels following mental stress provide reliable information regarding sympatho-adrenal activity in diabetic patients.

Effects of streptozotocin-induced diabetes on the response of male rats to immobilization stress

The effects of streptozotocin-induced (STZ) diabetes on the response to immobilization stress were evaluated in adult male rats. Rats were injected with STZ or vehicle and handled daily to minimize stress. Four weeks later, half of the animals were lightly anesthetized with ether and immobilized for 20 min. At that time the stressed and nonstressed controls were sacrificed, and blood and tissue collected for hormone and amine determinations. Immobilization caused an increase in plasma glucose levels in the controls, but caused no further increase in the already high levels seen in the diabetic rats. Basal corticosterone levels did not differ between the STZ and control rats, and the increase after immobilization was of similar magnitude. The stress-induced increase in prolactin was attenuated in the diabetic rats. Immobilization caused a significant rise in plasma norepinephrine (NE) levels in control, but not in diabetic rats. Adrenal NE content and tyrosine hydroxylase activity were not significantly affected by stress or STZ treatment. Dopamine (DA) and NE content was increased in the hypothalamus of immobilized diabetic rats as compared to nondiabetic immobilized controls. These results demonstrate that diabetic rats respond to immobilization stress, but the endocrine and sympathetic nervous system response is impaired. Changes in the stress response may be related to changes in hypothalamic amine metabolism.

Plasma met-enkephalin levels in diabetic patients: influence of autonomic neuropathy

The presence of opioid peptides within pancreatic islets in several animal species and in humans suggests that these peptides could play a role in pancreatic endocrine secretion, influencing glucose metabolism. We measured plasma met-enkephalin (met-Enk) levels in eight neuropathic (four with insulin-dependent diabetes mellitus [IDDM] and four with non-insulin-dependent diabetes mellitus [NIDDM]) and eight nonneuropathic (four IDDM and four NIDDM) diabetic patients to study met-Enk secretion in diabetic patients with asymptomatic autonomic neuropathy. Plasma met-Enk levels were significantly lower in neuropathic compared with nonneuropathic patients both in the IDDM group (28.7 +/- 4.8 v 61.6 +/- 4.1 pg/mL, P < .0025) and in the NIDDM group (26.5 +/- 3.6 v 44.3 +/- 4.6 pg/mL, P < .0125). This study suggests that the presence of neuropathy in diabetic patients, even if asymptomatic, is associated with a significant decrease of plasma met-Enk levels, thus contributing to a worsening of metabolic control under stress conditions.

Blockade of muscarinic transmission increases the frequency of diabetes after low-dose alloxan challenge in the mouse

The diabetogenic action of the beta-cell toxin, alloxan, is transient when administered to mice at a dosage of 50 mg/kg. We examined whether increased cholinergic activity is involved in the compensatory mechanisms. Therefore, following administration of alloxan, methylatropine (32 mumol/kg) was given intraperitoneally once daily for 5 consecutive days. Methyl atropine worsened the degree of hyperglycaemia during the first week after alloxan administration. Recovery from the diabetes mellitus was observed in a substantial number of animals given alloxan without methyl atropine, whereas the risk of developing manifest diabetes was markedly enhanced by methyl atropine. At 35 days after alloxan administration, 33% of the animals, which were given alloxan alone and were diabetic after 4 days, still had diabetes. In contrast, of the animals rendered diabetic by alloxan with concomitant atropinization, 92% remained diabetic throughout the study (p = 0.0145 vs alloxan alone). Glucose-stimulated insulin secretion and pancreatic insulin content were markedly reduced in animals with diabetes while being less reduced in alloxan-injected animals without diabetes. Moreover, in situ hybridization and immunocytochemistry revealed markedly decreased levels of insulin mRNA and number of insulin cells in alloxan-treated animals. With regard to insulin secretion, pancreatic insulin content, insulin mRNA and insulin cell number, the reduction was the same irrespective of whether methyl atropine had been given. Thus, 5 days of atropinization increases the incidence of diabetes following alloxan at 50 mg/kg in mice. We suggest that cholinergic activity protects insulin cells from glucotoxicity during the first week after alloxan administration and therefore, reduces the frequency of diabetes.

Cholecystokinin (CCK) and C-terminal fragments of CCK: effects of CCK-33, CCK-8 and CCK-4 in the cardiovascular system of diabetic rats

The effect of cholecystokinin (CCK-33) and its fragments, CCK-8 and CCK-4, on arterial blood pressure and the function of isolated rat heart and catecholamine levels in plasma and from isolated heart tissue in diabetes mellitus were studied. The results indicated that, in diabetes, cardiovascular effects of CCK-33 and CCK-8 are diminished or abolished. Diabetes can change the response of the alpha- and beta-adrenergic system to CCK-33 and CCK-8 and the contents of catecholamines in heart tissue.

Is bronchial asthma a pancreatic disease?

Bronchial asthma and diabetes mellitus seldom occur in the same patient. The exact mechanism of this mutual exclusion is still unknown and its elucidation can make clear the physiopathology of both diseases. Clinical and experimental evidences suggest that insulin is a proinflammatory hormone and glucagon an antiinflammatory and a bronchodilator one. We hypothesize that the relationship between plasma insulin and glucagon may play an important role in bronchial asthma.

Postural hypotension in diabetic autonomic neuropathy: a review

Postural hypotension is uncommon in diabetes but can occur secondary to autonomic neuropathy. Symptoms are rare and include dizziness, weakness, blurred vision, tiredness, and loss of consciousness. The pathophysiology of postural hypotension is not clear, but changes in intravascular volume, heart rate, cardiac output, and splanchnic vascular resistance are similar in patients and controls. The main factors producing hypotension are a blunted catecholamine response to standing, and failure of lower limb vascular resistance to increase adequately. Treatment for symptomatic postural hypotension includes avoidance of dehydration, adequate salt intake, and fludrocortisone. Other treatments are reviewed but are less helpful. Patients with postural hypotension have intermittent symptoms over the years but rarely become severely disabled. They have a poorer prognosis than patients with symptomatic autonomic neuropathy without postural hypotension.

Effect of diabetes, insulin, and glucose load on lipid peroxidation in the rat

Lipid peroxidative activity in rats made diabetic with streptozocin and rats made acutely hyperglycemic by intraperitoneal dextrose administration was determined by measurement of exhaled ethane during exposure in vivo to ethane-free air (EFA). Diabetic rats demonstrated increased ethane in the expired breath while breathing EFA (5.82 +/- 0.56 pmol/min/100 g) compared with control rats (4.02 +/- 0.23 pmol/min/100 g). Insulin treatment of diabetic rats attenuated the ethane produced (4.88 +/- 0.23 pmol/min/100 g). Acute hyperglycemia increased exhaled ethane to levels higher than those seen in diabetic rats (9.87 +/- 0.98 pmol/min/100 g). Saline injected intraperitoneally to control rats produced ethane levels similar to those of untreated nondiabetic controls (4.11 +/- 0.52 pmol/min/100 g). Chronic uncontrolled hyperglycemia and acute hyperglycemia are associated with increased in vivo ethane production.

Pathogenesis and treatment of hypertension associated with diabetes mellitus

The pathogenesis of hypertension associated with diabetes mellitus (DM) involves an interplay of hereditary and acquired mechanisms. A familial trait for essential hypertension appears to be a risk factor for the development of both hypertension and nephropathy in type I DM and coexists commonly with impaired insulin sensitivity, relative hyperinsulinemia, and dyslipidemia, which can already be detected before the appearance of hypertension, obesity, or upper abdominal redistribution of body fat. The latter finding helps explain the frequent development of hypertension as well as dyslipidemia and/or type II DM in given individuals. Obesity is an important factor promoting these complications. Type I or II DM but not uncomplicated essential hypertension is characteristically accompanied by excess body Na+. This abnormality complements a tendency toward vascular hyperreactivity and a presumably morphologic and functional vasculopathy, thereby promoting the pathogenesis of hypertension in diabetic patients. For the treatment of hypertension in diabetic patients, nonpharmacologic measures are indispensable. If drugs are needed, angiotensin-converting enzyme (ACE) inhibitors and some but not all calcium antagonists are the preferred agents. Monotherapy or a combination of these drug types allows effective blood pressure control in most diabetic patients without further metabolic impairment; ACE inhibitors even tend to improve glucose control. Ketanserin may be a potential alternative, and if a diuretic is also needed, the metabolically neutral indapamide is a reasonable choice. If these agents do not allow satisfactory blood pressure highly selective beta 1-blockers or alpha 1-blockers may be introduced as a second choice. In diabetic patients with nephropathy, effective antihypertensive therapy can reduce proteinuria and slow the progression of the nephropathy; ACE inhibitors may improve diabetic proteinuria even at unchanged systemic blood pressure levels. Unless diuretics are needed for reasons other than hypertension, the treatment of diabetic patients with thiazides or loop diuretics in conventional dosage should probably be avoided until clarification of their influence on prognosis. Nevertheless, whether and to what extent other agents and nonpharmacologic measures can modify the prognosis in diabetic patients is also unclear, and the approach to antihypertensive therapy is therefore still largely empiric.

Hypertension in individuals with insulin-dependent diabetes mellitus

Hypertension is known to place the individual with IDDM at high risk for the development of both renal and cardiovascular disease. Recent data suggest that aggressive antihypertensive therapy (angiotensin I converting enzyme inhibitors, prazosin, and calcium channel blockers) have significantly improved overall prognosis and long-term survival for individuals with IDDM. Because in individuals with IDDM the development of both hypertension and renal disease has its roots in childhood, it is important that early and effective antihypertensive treatment begin there.

Contraindications to vasoconstrictors in dentistry: Part II. Hyperthyroidism, diabetes, sulfite sensitivity, cortico-dependent asthma, and pheochromocytoma

Dentists are aware of contraindications to the use of vasoconstrictors in patients with cardiovascular diseases. However, there are some other noncardiac conditions we should know. This article discusses the absolute contraindications to the use of vasoconstrictors in patients with a history of hyperthyroidism, diabetes, allergy to sulfites, asthma, and pheochromocytoma.

Effects of alpha 2-adrenergic blockade on renal hemodynamics in patients with insulin dependent diabetes mellitus

The role of renal alpha 2-adrenoceptors in the regulation of glomerular filtration and renal perfusion is unknown. We studied the effects of alpha 2-adrenergic blockade on renal hemodynamics in six patients with insulin-dependent diabetes mellitus (IDDM) and in six healthy subjects. At the basal state, glomerular filtration rate (GFR) was higher in IDDM although the difference from control levels was not statistically significant. Volume expansion, achieved by infusion of isotonic sodium chloride solution, during placebo infusion induced a significant drop in GFR in healthy subjects but not in IDDM patients. Infusion of the alpha 2-adrenoceptor antagonist idazoxan did not further modify the effect of volume expansion on GFR. Renal plasma and blood flow as well as filtration fraction were not significantly changed by volume expansion or idazoxan infusion. Plasma renin activity and plasma aldosterone levels decreased during volume expansion in both IDDM and control subjects. In conclusion, volume expansion induced decreased GFR in healthy controls but not in IDDM patients. Since infusion of idazoxan did not affect GFR or other parameters of renal hemodynamics, renal alpha 2-adrenoceptors do not seem to be involved in the regulation of renal function. Hence, enhanced renal alpha 2-adrenoceptor activity is not likely to underlie hyperfiltration as seen in IDDM.

Are insulin and hypertension independently related?

Hyperinsulinemia has been proposed as the common pathogenetic mechanism of obesity, non-insulin-dependent diabetes mellitus, and hypertension. We examined the cross-sectional relationship between fasting and postchallenge insulin levels and hypertensive status in a population-based study of 653 men and 784 women, aged 50 to 93 years, in Rancho Bernardo, California. Hypertensive subjects had slightly but not significantly higher fasting plasma insulin levels than did normotensive subjects, but significantly higher postchallenge insulin levels. After stratification for obesity and glucose intolerance, there was no significant difference between the mean age-adjusted fasting or postchallenge insulin levels of those with and those without hypertension in 12 possible subgroups. Analysis of variance of both fasting and postchallenge insulin levels also failed to reveal a significant relationship between insulin and hypertensive status after adjusting for age, sex, body mass index, and diabetes. The current study does not support the hypothesis that insulin is independently associated with hypertension.

Cardiovascular autonomic dysfunction: diagnosis and prognosis

The symptoms of cardiovascular autonomic dysfunction may be subtle and occur late in the course of diabetes. They include abnormal exercise-induced cardiovascular performance, postural hypotension, and cardiac denervation syndrome. Autonomic nervous system testing involves an evaluation of the responses of complex reflex pathways. Some of the most commonly used and validated cardiovascular autonomic tests are RR-variation, the Valsalva manoeuvre, and postural testing. Sinus arrhythmia during breathing is termed RR-variation. In diabetic patients with autonomic neuropathy the magnitude of the RR-variation is decreased. Abnormal exercise-induced cardiovascular performance has been observed in diabetic subjects with abnormal RR-variation due to autonomic neuropathy. The Valsalva manoeuvre consists of forced expiration against a standardized resistance for a specified period of time. The reflex bradycardia that follows the Valsalva period in normal subjects is lacking in diabetic patients with clinical evidence of autonomic neuropathy. Postural hypotension in diabetics may be due to neuropathy or to a variety of secondary causes. An algorithm is presented to facilitate assessment of diabetic patients with postural symptoms. Treatment of postural hypotension should be directed primarily to the correction of secondary causes, in the absence of which the symptoms can be controlled by mechanical measures, plasma volume expansion, and vasoconstriction. Cardiac denervation syndrome may result in denervation supersensitivity and afferent (pain) nerve dysfunction. The RR-variation is a sensitive indicator of impairment of cardiac autonomic innervation and is a simple method for identifying asymptomatic patients at risk for painless ischaemia. Formal cardiovascular stress testing may be prudent before initiating an exercise programme in such individuals.

QT interval prolongation in type 2 (non-insulin-dependent) diabetic patients with cardiac autonomic neuropathy

QT interval alterations were measured in 41 non-insulin-dependent (type 2) diabetic patients and 14 age- and sex-matched control subjects. Cardiac autonomic neuropathy (CAN) was assessed by noninvasive tests (deep breathing, Valsalva maneuver and lying-to-standing) and diabetics were divided into three groups according to the results of these tests: diabetics with definitive (n = 14), early (n = 13) and without (n = 14) CAN. The corrected values of QT intervals (QTc) at rest were significantly longer in diabetics with definitive (447 +/- 5 ms; p less than 0.001), early (426 +/- 5 ms; p less than 0.05) and without (424 +/- 5 ms; p less than 0.05) CAN than in controls (407 +/- 5 ms). Moreover, QTc intervals at rest were significantly (p less than 0.01) longer in diabetics with definitive CAN than in diabetics with early and without CAN. QTc intervals at maximum tachycardia, induced by Valsalva maneuver, were considerably longer in diabetics with definitive CAN (451 +/- 6 ms) than in controls (407 +/- 6 ms; p less than 0.001) and in diabetics with early (434 +/- 6 ms; p less than 0.05) or without (422 +/- 6 ms; p less than 0.01) CAN. Furthermore, QTc intervals at maximum tachycardia were significantly (p less than 0.01) longer in diabetics with early CAN than in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes mellitus: stress, neurochemistry and behavior

Neurochemical alterations in several rodent models of insulin-dependent diabetes are compared and their relevance to behavioral and physiological pathology in the clinical disorder is discussed. In the majority of rodent models, reductions in metabolism of norepinephrine (NE), dopamine (DA) and serotonin (5HT) in the central nervous system (CNS) have been reported. While there are two reports of increased 5HT turnover in CSF or post-mortem brains of diabetic humans experiencing severe ketoacidosis, these patients were receiving insulin therapy. Insulin appears to have effects on monoamines opposite to that of chronic hyperglycemia. Both in rodent models and in clinical populations, there is widespread evidence of enhanced hormonal and behavioral responsiveness to stress. There are findings in rodent models indicating that hormonal responses to stress are related to CNS monoamine activity. The mechanisms responsible for both hormonal and CNS alterations in diabetes, as well as their involvement in behavioral pathology, can best be investigated further using animal models.

Alpha-adrenoceptors and insulin release from pancreatic islets of normal and diabetic rats

The role of alpha-adrenoceptors in the regulation of glucose-induced insulin release (GIR) was investigated in islets of normal and neonatally streptozotocin-injected non-insulin-dependent diabetic rats (STZ). In normal islets GIR was suppressed to approximately 50% by 10(-8) M of the alpha 2-adrenergic agonist UK 14304, whereas 10(-9) M of the agonist induced a similar inhibition in STZ islets. In normal islets, suppression of GIR by UK 14304 (10(-8) M) was totally antagonized by 10(6) M idazoxan (alpha 2-antagonist) or 10(6) M phentolamine (alpha 1 + alpha 2-antagonist). In STZ islets, the inhibitory effect of UK 14304 (10(-9) M) was entirely reversed by 10(-5) M idazoxan or 10(-6) M phentolamine. The alpha 1-antagonist prazosin (10(-7)-10(-5) M) was without effect on insulin release suppressed by UK 14304 in normal and STZ islets. Insulin release at 3.3, 8.3, or 16.7 mM glucose was augmented by phentolamine but not by idazoxan. It is concluded that the inhibitory effect of catecholamines on insulin release is mediated by alpha 2-receptors in normal and STZ islets. Phentolamine augments basal and glucose-induced insulin release by a mechanism that does not involve alpha 2-adrenoceptors.

Mental arithmetic stress as a test for evaluation of diabetic sympathetic autonomic neuropathy

The effects of a 1-min mental arithmetic stress test on heart rate change were studied in 72 Type 1 diabetic patients, 36 without and 36 with diabetic autonomic neuropathy (mean age 33 and 44 yr, respectively), and in 80 matched normal subjects. Variation in hand skin temperature was also recorded in 25 normal subjects and 30 diabetic patients without and 32 with autonomic neuropathy. While mental arithmetic rapidly reduced skin temperature of normal volunteers and of patients without autonomic neuropathy, no effect was found in autonomic neuropath (a drop of 0.63 +/- 0.05 (+/- SE), 0.52 +/- 0.04 and 0.16 +/- 0.02 degrees C (p less than 0.001), respectively). In control subjects and in diabetic patients without and with autonomic neuropathy the heart rate increase was 22.9 +/- 6.8 (+/- SD), 21.4 +/- 8.4 and 7.0 +/- 3.7 beats min-1, respectively (p less than 0.001). The ratio between maximum mental arithmetic-induced heart rate and basal heart rate was 1.29 +/- 0.10, 1.24 +/- 0.10 and 1.07 +/- 0.05 (p less than 0.001) for healthy subjects, non-neuropathic patients, and neuropathic patients. Cut-off values (the low normal limit for these variables) are proposed: skin temperature 0.23 degrees C, heart rate increase 11.6 beats min-1 and heart rate ratio 1.12. Anxiety state, blood glucose concentration (excluding hypoglycaemia), body position, basal heart rate, and age did not interfere with responses to mental arithmetic stress.

Adrenergic blocking agents and lipoprotein lipase activity

Lipoprotein lipase activity, total serum cholesterol and triglycerides, HDL cholesterol were determined before and after two weeks of treatment with a low dose of an alpha 1-blocking agent (prazosin) or of a beta-adrenergic-blocking drug (metoprolol). Lipoprotein lipase activity was almost doubled after prazosin (p less than 0.02) and practically unchanged after metoprolol, at a time and at a drug dosage when only minor changes in blood pressure and serum lipids were detectable. HDL cholesterol was slightly but significantly increased after prazosin (p less than 0.05). Heart rate was increased after prazosin (p less than 0.05) and decreased after metoprolol (p less than 0.01).

Helpless behavior (escape deficits) in streptozotocin-diabetic rats: resistance to antidepressant drugs

Using the learned helplessness model of depression in rats, the present study undertook to investigate the possibility of an impaired response to antidepressant drugs in diabetic animals. Experimental diabetes was induced by three intraperitoneal (IP) injections of streptozotocin (37.5, 37.5, 50 mg/kg, three days apart), four weeks before behavioral testing. Diabetic and non-diabetic rats were first exposed to 60 inescapable shocks. Forty-eight hours later and over three consecutive days, they were subjected to daily shuttle-box sessions for assessment of escape failures (helpless behavior). Twice daily (IP) injection of clomipramine (24 mg/kg), desipramine (24 mg/kg), imipramine (32 mg/kg) or clenbuterol (0.75 mg/kg) prevented escape deficits in the non-diabetic but not in the diabetic rats. However, this prevention was made possible in the diabetic rats by increasing the duration of the antidepressant treatment. Moreover, one week of insulin therapy restored operant escape responding to both the tricyclics and a beta-agonist. The inefficacy of clenbuterol (a central beta-agonist) in reversing helpless behavior in diabetic rats, along with the observation that triiodothyronine (T3) supplementation also restored the response to imipramine in the diabetic rats, suggests that thyroid-mediated alterations of central noradrenergic function might be a critical factor in the resistance or delayed response to antidepressants in experimental diabetes. These animal findings raise the possibility of a similar resistance to conventional antidepressants in depressed diabetic patients.

Diabetic autonomic neuropathy--Part I. Autonomic nervous system data analysis by a computerized central unit in a multicenter trial

To determine the feasibility of utilizing a central, computerized unit to analyze autonomic nervous system function tests for a 10-year, multicenter, clinical trial, the Autonomic Nervous System Reading Center was established. The Reading Center selected and standardized testing methods, designed the testing protocol, developed testing equipment, computerized data analysis, and instituted measures to monitor data quality. Three cardiovascular testing methods, RR-variation, Valsalva maneuver, and postural testing, were selected because each is a simple, non-invasive, quantitative, sensitive, and reproducible test. Furthermore, a hierarchy of sensitivity has been established with these cardiovascular autonomic nervous system measurements: RR-variation, Valsalva maneuver, and finally postural testing. Confounding variables were minimized by prescribing eligibility criteria. Testing equipment, designed to record time between RR intervals in a form easily read into a computer, has been in 21 clinics for three years and a total of 54 technicians have been trained. Over 85 percent of the autonomic nervous system tests performed have been usable at initial testing. A central reading center is an efficient and necessary means of collecting and analyzing data for a multicenter clinical trial.

Left ventricular performance during exercise in long-term type 1 diabetic men: an echocardiographic study

M-mode echocardiograms were recorded and digitized during semisupine bicycle exercise in 10 young (less than 40 years) long-term (greater than or equal to 12 years) type 1 diabetic men, without heart symptoms, and 10 controls. Recordings were done at rest, during workloads of 50 and 100 W and 1, 3 and 5 min post-exercise. The groups were comparable at rest. Exercise intervention caused a higher heart rate and systolic blood pressure response in the diabetics. Overall, diabetics had a smaller left ventricular (LV) end-diastolic dimension, but it did not change during exercise within either group; LV end-systolic dimensions (ESD), however, decreased in both. The fractional shortening, normalized peak shortening rate and systolic blood pressure/ESD ratio increased in both groups. However, fractional shortening was lower in the diabetics during peak exercise, while the two latter variables of LV systolic function were similar to the controls. Furthermore, fractional shortening during peak exercise remained lower in the diabetics even when adjusted for systolic blood pressure by covariance analysis. Therefore, the decreased LV performance during exercise in the diabetic subjects is most likely secondary to reduced LV diastolic filling, as indicated by their smaller end-diastolic dimension, rather than due to decreased contractility or a higher afterload.

Presynaptic changes promoted by alloxan diabetes in the cat isolated heart

Adrenergic presynaptic functions were evaluated in the cat isolated perfused heart preparation. The sympathetic nerve endings were labelled with [3H]noradrenaline ([3H]NA) and the effect of electric neural stimulation was determined in the presence of drugs which inhibit neuronal or extraneuronal uptake, or which antagonize alpha-adrenoceptors. [3H]NA overflow was measured in control and diabetic cats and was significantly increased by electric neural stimulation on both conditions. Perfusion with 0.1 microM phentolamine increased transmitter overflow in control hearts but failed to do so on organs obtained from alloxan-treated cats. The data provide evidence that in alloxan diabetic cats there is an abnormality of the adrenergic synapse.

Adrenal catecholamine metabolism and myocardial adrenergic receptors in streptozotocin diabetic rats

Adrenal medullary function and myocardial adrenergic receptors were investigated in streptozotocin-treated diabetic rats. The animals were rendered diabetic by a single i.v. injection of streptozotocin (STZ, 65 mg/kg) and killed 60 days after treatment. Adrenal tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) activities were increased by 52, 28 and 39%, respectively, in the STZ diabetic rats. In addition, adrenal concentrations of dopamine (+52%) norepinephrine (+46%), and epinephrine (+33%) were elevated significantly (P less than 0.05). Increased adrenal TH activity reflected an increased Vmax, but no change in Km. Receptor densities (Bmax), determined by [3H]prazosin and [3H]dihydroalprenolol binding, were decreased by 24 and 25%, respectively, in the myocardium of 60-day diabetic rats. Insulin-induced chronic hypoglycemia in the STZ diabetic rats produced a marked increase in the adrenal TH concentration (Vmax, +65% or +225%, respectively), as compared to control or diabetic rats, without changes in the affinity (Km) for the substrate. These results suggest that the STZ diabetic rat has abnormalities of catecholaminergic function of the adrenal medulla and myocardial adrenergic receptors, which may contribute to the development and maintenance of many of the hemodynamic and metabolic defects described in this animal model of diabetes mellitus.

Body mass, blood pressure, glucose, and lipids. Does plasma insulin explain their relationships?

Obesity, hypertension, a high plasma level of glucose, and some lipid abnormalities (high plasma levels of cholesterol and triglycerides) often occur in the same individuals. Some authors have postulated that the elevated levels of plasma insulin in obese individuals may explain this association. To explore this hypothesis further, the relationships between body mass index, fasting plasma glucose and insulin, blood pressure, serum lipids, and apoproteins were investigated in a group of 2144 healthy middle-aged men. Analysis of the data show that the associations between body mass index and blood pressure or lipid variables are largely independent of plasma glucose and insulin. Plasma glucose is strongly related to blood pressure in nonobese subjects. Plasma insulin is not associated with blood pressure independently of body mass index and plasma glucose; however, the simultaneous elevation of body mass index, plasma glucose, and insulin is strongly associated with blood pressure. The results also confirm that plasma insulin is positively related to triglycerides and negatively related to high density lipoprotein cholesterol independently of plasma glucose and body mass index.

The diabetic foot: pathophysiology and treatment

The diabetic foot can be classified into the neuropathic foot, characterized by the neuropathic ulcer, the Charcot joint and neuropathic oedema associated with a good circulation, in which neuropathy predominates, and the ischaemic foot in which atherosclerosis is the dominant factor leading to a reduction in blood flow with absent pulses. In the neuropathic foot, blood flow is increased, the vessels are still and dilated as a result of medial wall calcification and there is evidence for arteriovenous shunting. The neuropathic ulcer characteristically develops on the plantar surface following inflammatory autolysis and haematoma formation under neglected callosities. Chiropody is therefore the mainstay of treatment and recurrence is prevented by redistribution of weight bearing forces by moulded insoles in special footwear. Charcot osteoarthropathy is often preceded by fracture which is a further complication of diabetic neuropathy and which precipitates the rapid bone and joint destruction of the Charcot joint. Neuropathic oedema responds to ephedrine with a reduction in peripheral flow and an increase in urinary sodium excretion. The ischaemic foot is characterized by rest pain, ulceration and gangrene. Medical management can be successful in up to 72%, the remainder needing arteriography to assess suitability for arterial reconstruction or angioplasty. In the diabetic leg, atherosclerosis is predominant in the branches of the popliteal artery making arterial reconstruction difficult. Optimum care of the diabetic foot is provided in a diabetic foot clinic where the skills of chiropodist, shoe-fitter and nurse receive full support from physician and surgeon. Many lesions of the diabetic foot are avoidable and thus patient education is the cornerstone of prevention.

Plasma levels of immunoreactive atrial natriuretic hormone in patients with diabetes mellitus

In order to determine whether atrial natriuretic hormone (ANH) secretion is altered in diabetic patients with autonomic neuropathy, plasma immunoreactive ANH (IR-ANH) levels were measured in 23 patients with insulin-dependent diabetes mellitus, 12 of whom had definite cardiac autonomic neuropathy determined by noninvasive maneuvers. Levels were also measured in 31 healthy control subjects. Whereas only one of the 11 diabetics without cardiac autonomic neuropathy had elevated IR-ANH levels, four of the 12 diabetics with cardiac autonomic neuropathy had elevated IR-ANH levels (P = 0.03 compared to control subjects). 24-h urinary sodium excetion was not different among the groups. There was no significant correlation between IR-ANH levels and diabetes control and any of the parameters of autonomic nervous system activity nor between IR-ANH levels and plasma norepinephrine or epinephrine levels. Furthermore, no relationship was observed in the diabetic subjects between IR-ANH levels and left ventricular ejection fraction determined by radionuclide ventriculography. Thus, elevated IR-ANH levels occur with greater frequency in diabetic patients with autonomic neuropathy. These elevations do not appear to be due to alterations in dietary sodium intake or left ventricular dysfunction.

Autonomic neuropathy: its diagnosis and prognosis

Autonomic neuropathy is now well established as a relatively common and significant complication of diabetes mellitus. Its importance has been clarified in recent years during which the extent of autonomic control over all areas of body function has been defined. Using simple cardiovascular reflex tests, autonomic abnormalities can be demonstrated without any corresponding symptoms. The often stated concept of 'patchy' involvement in diabetic autonomic neuropathy should now be rejected as too should the view that autonomic neuropathy is either 'present' or 'absent' based on a single test result. When generalized and predominantly metabolic disturbances, as in diabetes, give rise to impaired nerve function, autonomic as well as somatic components of the nerve are affected. Where damage is severe this leads to the characteristic florid picture of symptomatic autonomic neuropathy with its particularly poor prognosis. For the physician in a busy clinic, much of the theoretical and experimental basis for autonomic neuropathy may not appear of direct relevance. However, he has now to be aware of the clinical implications of autonomic damage in the diabetic. This may have particular relevance in the care of the diabetic foot (see Chapter 10), the recognition of many of the vague symptoms associated with autonomic damage, the treatment of disabling features such as postural dizziness and nocturnal diarrhoea, and an awareness of the poor prognosis associated with symptomatic autonomic neuropathy. He will also need to be alert to the dangers of general anaesthesia in such patients, and the possibility of sudden unexpected deaths. Diabetic autonomic neuropathy causes widespread abnormalities, some of which are clinically apparent, some of which can be detected by sensitive tests, and others which have yet to be discovered. Inclusion of the neuropeptides and other hormones within the compass of autonomic control has opened up a whole new area of investigative interest, with many complex interrelationships which still need to be unravelled. This should lead to better understanding of the pathophysiological processes that cause damage to diabetic nerves. With so much research effort directed towards better glycaemic control and aldose reductase inhibitors (see Chapter 8), it may eventually be possible to reverse or prevent this potentially disabling and lethal complication of diabetes.

The effect of insulin and catecholamines on the activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyltransferase in isolated rat hepatocytes

This study was concerned with the effect of insulin and catecholamines on the rate limiting enzymes of cholesterol metabolism in rat hepatocytes. Insulin was found to increase the activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and to have no effect on the activity of acyl-coenzyme A: cholesterol-o-acyltransferase. Noradrenaline and isoprenaline increased the activities of both 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyltransferase. The effect of noradrenaline or isoprenaline in the presence of insulin was that of a lower stimulatory response on 3-hydroxy-3-methyl glutaryl coenzyme A reductase but comparable to that found with either catecholamine alone. The combination of either catecholamine with insulin had no effect on the activity of acyl-coenzyme A: cholesterol-o-acyltransferase. These observations suggest that the activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and acyl-coenzyme A: cholesterol-o-acyl-transferase are regulated independently by insulin in the presence or absence of catecholamines. By contrast, catecholamines appear to regulate both enzyme activities in a similar fashion.

Reduced noradrenaline turnover in streptozotocin-induced diabetic rats

To clarify whether activity of the sympathetic nervous system is decreased in streptozotocin-induced diabetic rats, noradrenaline turnover, which is a reliable indicator of sympathetic nervous system activity, was measured in the interscapular brown adipose tissue, heart and pancreas of streptozotocin diabetic rats. Results from studies using inhibition of noradrenaline biosynthesis with alpha-methyl-p-tyrosine demonstrated significant reductions (p less than 0.05-0.001) in sympathetic nervous system activity in the interscapular brown adipose tissue, heart and pancreas of streptozotocin (65 mg/kg) diabetic rats, compared with measurements in streptozotocin (35 mg/kg) diabetic and saline-control rats. The daily injections of neutral protamine Hagedorn insulin to streptozotocin (65 mg/kg) diabetic rats prevented the decrease of noradrenaline turnover in the interscapular brown adipose tissue and heart significantly (p less than 0.02), but this was less marked in pancreas, compared with non-treated streptozotocin (65 mg/kg) diabetic rats. Furthermore reduced noradrenaline turnover was also observed in the control rats which showed comparable changes in body weight to the rats injected with streptozotocin (65 mg/kg). These results suggest that poorly controlled streptozotocin diabetic rats may have reduced sympathetic nervous function, and that insulin therapy might prevent this.

Identification of an alpha-adrenoceptor binding inhibitor: possible implications in diabetes mellitus

An endogenous adrenergic antagonist extracted from porcine duodenal mucosa was tested for 3H-yohimbine (5 nM) binding inhibitory activity using whole brain membranes. Duodenal mucosa was scraped into liquid N2 and extracted in 2M acetic acid (HAc) + 1 mg/ml ascorbic acid. The supernatant was fractionated on SP-Sephadex C-25 with a stepwise pH gradient. The peak adrenoceptor binding inhibitory (ABI) activity eluted at pH 4.5 and fractionation of this material on Sephadex G-25 SF indicated a relative molecular mass (Mr) of 2000 to 3000. The ABI did not bind to a Pharmacia Pro RPC 5/5 column which resulted in further purification and indicated that the peptide is hydrophilic. ABI activity was specific for 3H-yohimbine and did not affect 3H-dihydroalprenolol binding to beta receptors. Incubation of pancreatic islets isolated from fasted rats with ABI completely reversed the effect of 2.5 X 10(-6)M norepinephrine (NE) on insulin release in the presence of 300 mg/dl glucose. I.v. injection of ABI in rats also prevented the increased serum glucose response to a glucose bolus caused by NE. Preliminary experiments indicate that ABI blocks the stimulation of platelet aggregation by epinephrine as well. The peptide identified in this study causes specific inhibition of binding to alpha-2 adrenergic receptors and exerts a potent glucose dependent effect on adrenergic inhibition of insulin release. Possible implications in diabetes mellitus are discussed.

Streptozotocin-induced diabetes and hormone sensitivity of adenylate cyclase in rat myocardial sarcolemma, aorta and liver

Adenylate cyclase activity was investigated in myocardial sarcolemma, aorta particulate fractions, and liver plasma membranes from control and 5-day streptozotocin-induced diabetic rats. The basal adenylate cyclase activity was increased in heart sarcolemma from diabetic rats, whereas the extent of stimulation by glucagon, dopamine, isoproterenol, epinephrine, sodium fluoride and forskolin was decreased markedly. The decreased responsiveness was associated with a decrease in Vmax but not in the activation constant. In contrast, GTP stimulated adenylate cyclase in control and diabetic myocardial sarcolemma to the same extent. In addition, the basal adenylate cyclase activity was not altered significantly in aorta particulate fraction of liver plasma membranes from diabetic rats, but the stimulation of adenylate cyclase by catecholamines and forskolin (in the case of aorta) and by adenosine, glucagon, NaF and forskolin (in the case of liver) was diminished markedly. These data suggest that, in streptozotocin-induced diabetes, the responsiveness of adenylate cyclase to various hormones and agents (fluoride and forskolin) which act through receptor-independent mechanisms is decreased.