Impaired pancreatic polypeptide response to insulin hypoglycemia in obese subjects

We have studied the effect of insulin hypoglycemia on the secretion of pancreatic polypeptide (PP) in 14 obese subjects with normal glucose tolerance and in 6 normal controls. Infusion of insulin 0.1 U/kg/h in controls and 0.12 U/kg/h in the obese, for one hour, produced a progressive hypoglycemia, similar in both groups (nadir 2 mmol/l at 50 min). The secretion of PP was less in obese subjects than in controls (peak 116 mmol/l vs 184 pmol/l, P less than 0.01) (integrated secretion sigma delta PP 288 vs 472 pmol/l, P less than 0.01) and was also delayed in the obese subjects beginning at 50 min instead of 40 min. The secretion of glucagon and of C-peptide were not different in the two groups, but the integrated response of ACTH was higher in the obese (sigma delta ACTH 52 pmol/l vs 25 pmol/l, P less than 0.01). The secretory response of growth hormone (STH) was smaller in the obese group (peak 8.6 +/- 1.28 vs 21.4 +/- 6.4 ng/ml, P less than 0.01). The reduced secretion of PP in obese subjects could be due to impaired sensitivity to hypoglycemia of the central control mechanism for PP release. The similarity of the reductions in the secretion of both PP and STH support this hypothesis, although a reduction in the secretory capacity of pancreatic PP cells cannot be excluded.     

Unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation: no causal relation with diabetic autonomic neuropathy.

OBJECTIVE--To examine the traditional view that unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation in insulin dependent diabetes mellitus are manifestations of autonomic neuropathy. DESIGN--Perspective assessment of unawareness of hypoglycaemia and detailed assessment of autonomic neuropathy in patients with insulin dependent diabetes according to the adequacy of their hypoglycaemic counterregulation. SETTING--One routine diabetic unit in a university teaching hospital. PATIENTS--23 Patients aged 21-52 with insulin dependent diabetes mellitus (seven with symptoms suggesting autonomic neuropathy, nine with a serious clinical problem with hypoglycaemia, and seven without symptoms of autonomic neuropathy and without problems with hypoglycaemia) and 10 controls with a similar age distribution, without a personal or family history of diabetes. MAIN OUTCOME MEASURES--Presence of autonomic neuropathy as assessed with a test of the longest sympathetic fibres (acetylcholine sweatspot test), a pupil test, and a battery of seven cardiovascular autonomic function tests; adequacy of hypoglycaemic glucose counterregulation during a 40 mU/kg/h insulin infusion test; history of unawareness of hypoglycaemia; and response of plasma pancreatic polypeptide during hypoglycaemia, which depends on an intact and responding autonomic innervation of the pancreas. RESULTS--There was little evidence of autonomic neuropathy in either the 12 diabetic patients with a history of unawareness of hypoglycaemia or the seven patients with inadequate hypoglycaemic counterregulation. By contrast, in all seven patients with clear evidence of autonomic neuropathy there was no history of unawareness of hypoglycaemia and in six out of seven there was adequate hypoglycaemic counterregulation. Unawareness of hypoglycaemia and inadequate hypoglycaemic counterregulation were significantly associated (p less than 0.01). The response of plasma pancreatic polypeptide in the diabetic patients with adequate counterregulation but without autonomic neuropathy was not significantly different from that of the controls (change in plasma pancreatic polypeptide 226.8 v 414 pmol/l). The patients with autonomic neuropathy had a negligible plasma pancreatic polypeptide response (3.7 pmol/l), but this response was also blunted in the patients with inadequate hypoglycaemic counterregulation (72.4 pmol/l) compared with that of the controls (p less than 0.05). CONCLUSIONS--Unawareness of hypoglycaemia and inadequate glucose counterregulation during hypoglycaemia are related to each other but are not due to autonomic neuropathy. The blunted plasma pancreatic polypeptide responses of the patients with inadequate hypoglycaemic counterregulation may reflect diminished autonomic activity consequent upon reduced responsiveness of a central glucoregulatory centre, rather than classical autonomic neuropathy.     

Immediate heart-rate response to standing: simple test for autonomic neuropathy in diabetes.

The immediate heart-rate response to standing was measured in 22 normal controls and 25 patients with diabetes, 15 of whom had autonomic neuropathy. The response in the controls and patients without autonomic neuropathy was characteristic and consistent, with tachycardia maximal at around the 15th beat and relative bradycardia maximal at around the 30th beat. The diabetics with autonomic neuropathy, however, showed a flat response. In three controls the response was abolished with intravenous atropine but not with propranolol, showing that it is mediated through the vagus. A simplified test using routine ECGs and measuring the R-R interval at beats 15 and 30 with a ruler is easily performed as an outpatient procedure and may be used as a measure of autonomic function in diabetes.     

Defective blood glucose counter-regulation in diabetics is a selective form of autonomic neuropathy.

Administration of a low-dose insulin infusion to normal subjects results in a mild drop in blood glucose concentration (1.1 mmol/1 (20 mg/100 ml)) and the resetting of the basal glucose at the lower concentration. Clinical hypoglycaemia does not develop, and there is a significant release of glucagon, growth hormone, and cortisol. A similar infusion in insulin-requiring diabetics results in hypoglycaemia accompanied by a release of growth hormone and cortisol but no significant release of glucagon. Subsequently giving arginine to these patients results in a significant release of glucagon, indicating that the alpha cell is intact and can respond to local, direct stimulation. In one patient the defect in glucagon response to impending hypoglycaemia developed after two years'' insulin treatment. This type of dissociated response'' of the alpha cell has been reported in animals after denervation of the pancreas, and insulin-requiring diabetics may develop a selective form of autonomic neuropathy affecting the vagal control of glucagon release.     

Impaired glucagon response to sympathetic nerve stimulation in the BB diabetic rat: effect of early sympathetic islet neuropathy

We investigated the functional impact of a recently described islet-specific loss of sympathetic nerves that occurs soon after the autoimmune destruction of beta-cells in the BB diabetic rat (35). We found that the portal venous (PV) glucagon response to sympathetic nerve stimulation (SNS) was markedly impaired in newly diabetic BB rats (BB D). We next found a normal glucagon response to intravenous epinephrine in BB D, eliminating the possibility of a generalized secretory defect of the BB D alpha-cell as the mediator of the impaired glucagon response to SNS. We then sought to determine whether the glucagon impairment to SNS in BB D was due solely to their loss of islet sympathetic nerve terminals or whether other effects of autoimmune diabetes contributed. We therefore reproduced, in nondiabetic Wistar rats, an islet nerve terminal loss similar to that in BB D with systemic administration of the sympathetic neurotoxin 6-hydroxydopamine. The impairment of the glucagon response to SNS in these chemically denervated, nondiabetic rats was similar to that in the spontaneously denervated BB D. We conclude that the early sympathetic islet neuropathy of BB D causes a functional defect of the sympathetic pathway to the alpha-cell that can, by itself, account for the impaired glucagon response to postganglionic SNS.     

Ventilatory response to exercise in diabetic subjects with autonomic neuropathy

Tantucci, C., P. Bottini, M. L. Dottorini, E. Puxeddu, G. Casucci, L. Scionti, and C. A. Sorbini. Ventilatory response toexercise in diabetic subjects with autonomic neuropathy.J. Appl. Physiol. 81(5):1978-1986, 1996.We have used diabetic autonomic neuropathy as amodel of chronic pulmonary denervation to study the ventilatoryresponse to incremental exercise in 20 diabetic subjects, 10 with(Dan+) and 10 without (Dan) autonomic dysfunction, and in 10 normal control subjects. Although both Dan+ and Dan subjectsachieved lower O₂ consumption andCO₂ production(CO₂) thancontrol subjects at peak of exercise, they attained similar values ofeither minute ventilation(E) oradjusted ventilation (E/maximalvoluntary ventilation). The increment of respiratory rate withincreasing adjusted ventilation was much higher in Dan+ than inDan and control subjects (P < 0.05). The slope of the linearE/CO₂relationship was 0.032 ± 0.002, 0.027 ± 0.001 (P < 0.05), and 0.025 ± 0.001 (P < 0.001) ml/min inDan+, Dan, and control subjects, respectively. Bothneuromuscular and ventilatory outputs in relation to increasingCO₂ were progressivelyhigher in Dan+ than in Dan and control subjects. At peak ofexercise, end-tidal PCO₂ was muchlower in Dan+ (35.9 ± 1.6 Torr) than in Dan (42.1 ± 1.7 Torr; P < 0.02) and control (42.1 ± 0.9 Torr; P < 0.005) subjects.We conclude that pulmonary autonomic denervation affects ventilatoryresponse to stressful exercise by excessively increasing respiratoryrate and alveolar ventilation. Reduced neural inhibitory modulationfrom sympathetic pulmonary afferents and/or increasedchemosensitivity may be responsible for the higher inspiratoryoutput.

     

Detection of unrecognised nocturnal hypoglycaemia in insulin-treated diabetics.

Cortisol to creatinine ratios in overnight urine samples, urinary glucose excretion, and plasma glucose concentrations were determined in 43 diabetic inpatients. All initially had normal cortisol to creatinine ratios (less than 55 x 10(-6)) and were initially treated by increasing their long-acting insulin component. Nine patients in whom this ratio became raised then had their long-acting insulin component reduced until their fasting plasma glucose concentration was 4-7 mol/l (72-126 mg/100 ml). The 34 patients who had never had a raised ratio were treated by increasing their long-acting insulin component until their fasting plasma glucose concentration was in the range 4-7 mmol/l. All the raised cortisol to creatinine ratios were clearly separate from the other values. A mean reduction in total insulin dose of 23% and in long-acting insulin dose of 53% was achieved, abolishing presumptive nocturnal hypoglycaemia by reducing the ratio to normal and dramatically improving diabetic control. Although there was no definite evidence that the patients who had raised cortisol to creatinine ratios had suffered from nocturnal hypoglycemia, these results strongly support the view that a raised ratio indicates an otherwise unrecognised episode of this condition.     

Diabetic autonomic neuropathy and iritis: an association suggesting an immunological cause.

Of 47 insulin requiring diabetics aged 21-40 years with autonomic neuropathy (heart rate variability less than 10), 14 had previously developed iritis. In all except two cases the iritis preceded the autonomic symptoms. The autonomic neuropathy was very severe, 10 patients having two or more characteristic symptoms. Ten of the patients with iritis were women. The association of iritis (itself an immune disorder) with severe symptomatic autonomic neuropathy raises the possibility of an underlying immunological basis for autonomic neuropathy.     

Decreased response of epinephrine and norepinephrine to insulin-induced hypoglycemia in diabetic autonomic neuropathy

The responses of epinephrine, norepinephrine and other counter-regulatory hormones to insulin-induced hypoglycemia were investigated in 5 diabetics who showed signs of autonomic neuropathy, in 7 age-matched diabetics without autonomic neuropathy and in 7 healthy subjects. The presence of autonomic neuropathy was evaluated by decreased beat-to-beat variation in heat rates during hyperventilation or orthostatic hypotension. Catecholamines were determined by a totally automated plasma catecholamine analyzing system using a two-column system of high performance liquid chromatography. Plasma epinephrine and norepinephrine responses to hypoglycemia in diabetics with autonomic neuropathy were significantly lower than those in diabetics without autonomic neuropathy. Plasma glucagon response in diabetics was apparently attenuated compared to normal controls and there was no significant difference in glucagon response between the two patient groups. Other counter-regulatory hormone responses did not differ among the three groups. The data demonstrate that the responses of plasma epinephrine and norepinephrine to insulin-induced hypoglycemia are impaired in diabetics with autonomic neuropathy.     

Preparation of pancreatic mRNA: cell-free translation of an insulin-immunoreactive polypeptide.

Total nucleic acid extraction and selection of poly A-containing molecules yield preparative quantities of undegraded mRNA from adult and fetal pancreas. Using a stringent immunoassay, this mRNA is found to direct the synthesis of an immunoreactive insulin polypeptide in the wheat germ translation system. On sodium dodecyl sulfate polyacrylamide gels, this polypeptide (12,000-13,000 daltons) is larger than proinsulin (9,000 daltons).     

Effect of exercise on the pancreatic polypeptide response to food in man

Modest elevations in pancreatic polypeptide (PP) have been observed during exercise while fasting. To determine whether the PP response to a meal is similarly affected by exercise, seven healthy subjects were studied on two occasions. First, the postprandial PP response was determined during rest and then compared to a meal which was subsequently followed by a 45 min period of moderate exercise. Postprandial exercise significantly (P less than 0.01) enhanced the plasma PP response to peak levels of 182 +/- 22 pM versus 85 +/- 22 pM at rest. Concomitantly the plasma glucose fell to a nadir of 84 +/- 4 mg/dl which was significantly (P less than 0.01) below the rest level of 129 +/- 8 mg/dl. Although the rise in PP paralleled the fall in glucose, there was little relationship (r = 0.27) between the incremental changes in these two parameters. Thus, exercise is a natural setting which augments the plasma PP response to a meal. The mechanism may be related to the enhanced cholinergic vagal activity associated with the attendant fall in glycemia.     

Pupillary signs in diabetic autonomic neuropathy.

Pupillary function was investigated in 36 insulin-dependent diabetics and 36 controls matched for age and sex. About half of the diabetics had evidence of peripheral somatic or autonomic neuropathy, or both. The diabetic patients had abnormally small pupil diameters in the dark and less fluctuation in pupil size (hippus) during continuous illumination than the controls. They also had reduced reflex responses to light flashes of an intensity adjusted for individual retinal sensitivities. The pupillary findings were compared with results of five tests of cardiovascular function and five tests of peripheral sensory and motor nerve function. Almost all the patients with autonomic neuropathy had pupillary signs, which we therefore conclude are a common manifestation of diabetic autonomic neuropathy.     

Blood pressure response to standing in the diagnosis of autonomic neuropathy: the EURODIAB IDDM Complications Study

Autonomic neuropathy is associated with poor prognosis. Cardiovascular reflexes are essential for the diagnosis of autonomic nerve dysfunction. Blood pressure response to standing is the most simple test for the evaluation of sympathetic integrity, however it is still discussed which diagnostic criteria of abnormal response should be considered as optimal. The EURODIAB IDDM Complications Study involved the examination of randomly selected Type 1 diabetic patients from 31 centres in 16 European counties. Data from 3007 patients were available for the present evaluation. Two tests of autonomic function (response of heart rate /R-R ratio/ and blood pressure from lying to standing) just as the frequency of feeling faint on standing up were assessed. R-R ratio was abnormal in 24% of patients. According to different diagnostic criteria of abnormal BP response to standing (>30 mmHg, >20 mmHg, and >10 mmHg fall in systolic BP), the frequency of abnormal results was 5.9%, 18% and 32%, respectively (p < 0.001). The frequency of feeling faint on standing was 18%, thus, it was identical with the prevalence of abnormal blood pressure response to standing when >20 mmHg fall in systolic blood pressure was considered as abnormal. Feeling faint on standing correlated significantly with both autonomic test results (p < 0.001). A fall >20 mmHg in systolic blood pressure after standing up seems to be the most reliable criterion for the assessment of orthostatic hypotension in the diagnosis of autonomic neuropathy in patients with Type 1 diabetes mellitus.