Hypoglycemic peripheral neuropathy in association with insulinoma: implication of glucopenia rather than hyperinsulinism. Case report and literature review

A syndrome of peripheral polyneuropathy associated with islet cell tumors and hypoglycemia has been reported in 28 patients. Despite varying features in these patients, the clinical characteristics of this syndrome are remarkably similar. These consist of the development of a sensorimotor neuropathy during a protracted course of recurrent severe hypoglycemia, related to underlying insulinoma. Cerebral symptoms dominate the clinical picture and a predominantly or entirely motor, distal and symmetric, peripheral neuropathy ensures. Upper limb involvement is more frequent, accompanied by severe weakness and distal wasting, usually without fasciculations. Painful distal paresthesias without objective sensory loss are characteristic. Direct relationship to a single hypoglycemic insult is often absent. This report describes the clinical features and laboratory investigation of a new case with this condition, reviews the literature and discusses the syndrome with special regard to the etiology.

Gastrointestinal/pancreatic hormone concentrations in the portal venous system of nine patients with organic hyperinsulinism

Percutaneous transhepatic sampling of blood in the portal venous system (TPVS) was used to; (1) localize hormone secreting tumors and help in differentiating tumors from diffuse disease (nesideoblastosis and hyperplasia with adenomata) in 9 patients with fasting hypoglycemia and hyperinsulinism, and (2) study the concentration an distribution of the immunoreactive peptides: insulin (IRI), gastrin (IG), glucagon (IRG), pancreatic polypeptide (hPP), and somatostatin (SRIF-LI), in the venous drainage of the uninvolved portion of the pancreas and GI tract. Localized elevations of IRI (64-920 microunits/ml) predicted tumor localization in 6 patients with single tumors that were not demonstrable angiographically. In one patient with nesideoblastosis and another with islet cell hyperplasia with adenoma, elevated IRI concentrations at multiple locations suggested a diffuse or multicentric process. Elevations of SRIF-LI in the same region as IRI elevations in one patient and of IRG in another patient suggested that these tumor produced two hormones. Some problems in the interpretation of portal venous insulin concentrations are discussed. The locations of maximum portal venous system plasma concentrations and portal-arterial gradients (mean +/- SE pg/ml) in five patients with small single insulinomas were: IG, gastrocolic trunk (126 +/- 27, 46 +/- 22); IRG, proximal splenic vein (130 +/- 30, 47 +/- 13) and gastrocolic trunk (131 +/- 23, 60 +/- 13); hPP, portal vein (164 +/- 48, 49 +/- 22); SRIF-LI, superior mesenteric vein (186 +/- 50, 57 +/- 20) and gastrocolic trunk (178 +/- 59, 55 +/- 21). It is concluded; (1) TPVS can be used successfully to localize single insulin-secreting tumors of the pancreas and to help distinguish them from diffuse disease but problems in such differentiation do occur, (2) circulating SRIF-LI and IRG are derived from both the pancreas and the gut, IG predominantly from the proximal gut and hPP from the head of the pancreas, and (3) The data provide new information for the interpretation of portal insulin concentrations in patients with organic hyperinsulinism and of hormone concentrations for localization of peptide-producing tumors of the pancreas other than insulinomas.

The metabolic effects of chronic hyperglucagonaemia

A subject with a benign glucagonoma was studied before and after complete resection of his pancreatic tumour. Studies were undertaken pre- and post-operatively to determine the effects of chronic hyperglucagonaemia on glucose tolerance and glucose kinetics both in the fasting state and during physiological insulin infusions, employing the [3H]-3-glucose technique. In addition the plasma cyclic AMP response to an acute infusion of glucagon was studied pre- and post-operatively. The basal immunoreactive glucagon levels pre- and post-operatively were 10492 +/- 1296 and 149 +/- 15 pg/ml respectively. Pre- and post-operative oral glucose tolerance tests did not differ but were abnormal. Pre-operatively basal hepatic glucose production was normal and it was suppressed rapidly by the low dose insulin infusion, despite continuing hyperglucagonaemia. The metabolic clearance rate of glucose was slightly reduced. There was no plasma cyclic AMP response to a glucagon infusion, suggesting down-regulation of the glucagon receptor by the chronic hyperglucagonaemia. Post-operatively the hepatic glucose production and clearance rate of glucose fell, whereas the plasma cyclic AMP responses to the glucagon infusion reverted to a normal pattern. It is concluded that chronic hyperglucagonaemia is not a major factor in the development of the glucose intolerance, but it may lead to down-regulation of the biological action of glucagon.

hCG and hCG subunits as tumour markers in patients with endocrine pancreatic tumours and carcinoids

Serum levels of hCG, hCG-alpha- and hCG-beta-subunits were measured in 29 patients with APUD-tumours, 16 patients with endocrine pancreatic tumours (EPT) and 13 patients with carcinoids. Twenty out of 29 patients (69%) had elevated level of hCG and its subunits. Among patients with EPT, 11 out of 16 (69%) had raised levels of these peptides. Three patients with benign tumours had normal concentrations, thus giving a frequency of 85% in the group of malignant EPT. In patients with carcinoids 9 out of 13 (69%) had elevated serum levels of at least one of the components. A discordance in secretion pattern between the two types of APUD-tumours was noticed. Only one patient, a case with a carcinoid had raised levels of the complete hCG molecule. The levels of hCG-alpha were elevated in 23% of the patients with malignant EPT and 69% of the patients with carcinoids while the corresponding frequencies of raised hCG-beta levels were 69% and 8%, respectively. Three out of 4 patients with so-called non-functioning islet cell tumours had raised levels of the subunits. These results indicate that hCG subunits are valuable tumour markers in both of these APUD-tumours, and that malignant EPT predominantly secrete hCG-beta- and carcinoids hCG-alpha-subunits.

Excessive circulating large molecular weight immunoreactive glucagon components in subjects with the idiopathic postprandial syndrome

The glucagon RIA measures several molecular components in human plasma. Clinical disorders have been described associated with abnormal elevations of certain of these components. This report documents another clinical disorder, the idiopathic postprandial syndrome, which also appears associated with excessive circulating large molecular weight immunoreactive glucagon (IRG) components. During studies of glucose homeostasis in subjects with apparent idiopathic postabsorptive hypoglycemia, 80 subjects were evaluated using oral glucose tolerance tests; 18 subjects were found to have clinical and laboratory findings consistent with the disorder, and of these, 3 had markedly elevated basal total plasma IRG levels. Plasma IRG responses in the subjects after oral glucose or mixed meals were variable. Physical characterization of the excessive large molecular weight IRG components revealed molecular weight estimates of 300,000 and 345,000 daltons in 2 subjects and of more than 200,000 daltons in the third subject. The origin and chemical nature of this material is uncertain. None of these subjects had evidence for a glucagonoma, as supported by the virtual absence of detectable levels of native (3500-dalton) glucagon after gel filtration. Since the origin of the idiopathic postprandial syndrome as well as the origin and chemical nature of large molecular weight IRG components are unknown, the association of these two findings remains unclear but is clinically important in the differential diagnosis of the glucagonoma syndrome.

Insulin and glucagon in rats with islet cell tumors induced by small doses of streptozotocin

Plasma insulin and glucagon responses to oral glucose loading were examined in rats with islet cell tumors induced by a single intravenous injection of streptozotocin (30 or 40 mg/kg body weight). Twenty-four macroscopic and six microscopic tumors occurred in 21 rats. In 15 of 21 tumor-bearing rats, there was exaggerated insulin release in response to oral glucose. Plasma glucose levels did not rise with the oral glucose load and were comparable to those seen in normal animals. Hence these rats are described as having "responsive tumors." In six rats with "nonresponsive tumors" there was no insulin response and the plasma glucose levels rose. No significant differences in plasma levels were observed between the two groups. Nonresponsive tumors as well as responsive tumors contained a significant amount of extractable insulin (17.68 +/- 8.60 and 35.07 +/- 10.05 mg/g wet weight, respectively) and detectable amounts of immunoreactive glucagon (1.47 +/- 0.61 and 2.24 +/- 0.67 micrograms/g wet weight, respectively). These results suggest that a small dose of streptozotocin produces two types of islet cell tumors. One is insulin producing and insulin secreting whereas the other is insulin producing but not insulin secreting.

[Vasoactive intestinal polypeptide in digestive processes in the Verner Morrison syndrome]

Some physiological digestive processes thought to be under the control of VIP-ergic neurones are presented. The etiological role of the Vasoactive Intestinal Polypeptide in the Verner Morrison syndrome is discussed.

Nesidioblastosis associated with insulin-mediated hypoglycemia in an adult

Nesidioblastosis, the process of differentiation of pancreatic islets from ductular epithelium, is a well-described cause of insulin-mediated hypoglycemia in neonates and infants, but not in adults. A 58-yr-old woman with characteristic clinical features of fasting hypoglycemia had inappropriately elevated plasma immunoreactive insulin levels during symptomatic episodes of fasting hypoglycemia. Angiography, palpation at laparotomy, and resection of the distal three-quarters of the pancreas provided no evidence of a tumor. Pathologic examination of the resected pancreas revealed the findings of nesidioblastosis, i.e., budding of islets from the wall of ductules, and also increased number and size of islets and abnormal shape and location of islets. An entire spectrum of islet cell abnormalities including nesidioblastosis can cause insulin-mediated hypoglycemia in adults, as it does in neonates and infants.

Pathogenesis of hypoglycemia in insulinoma patients: suppression of hepatic glucose production by insulin

To determine the mechanism by which hyperinsulinemia causes hypoglycemia in insulinoma patients, rates of glucose production and utilization, and circulating levels of insulin, glucagon, alanine, lactate, and glycerol were measured in 6 insulinoma patients during development of fasting hypoglycemia and in 8 normal volunteers studied over an identical interval. Initially, insulinoma patients had a greater plasma insulin (42 +/- 9 versus 15 +/- 1 microunits/ml) and glucagon levels (214 +/- 31 versus 158 +/- 21 pg/ml) than normal subjects, P less than 0.05, but their plasma glucose levels (81 +/- 4 mg/dl) and rates of glucose production and utilization (1.71 +/- 0.08 and 1.74 +/- 0.08 mg/kg . min, respectively) were not significantly different from those of normal subjects (93 +/- 2 mg/dl, 1.93 +/- 0.11, and 1.92 +/- 0.13 mg/kg . min, respectively). During a subsequent 8-h fast, glucose production and glucose utilization decreased in both groups, but more markedly in insulinoma patients. Since glucose utilization exceeded glucose production to a greater extent in insulinoma patients than in normal subjects, plasma glucose decreased to 44 +/- 3 mg/dl in insulinoma patients, but only to 84 +/- 1 mg/dl in normal subjects (P less than 0.001). Glucose utilization in insulinoma patients never exceeded that of normal subjects. These results demonstrate that fasting hypoglycemia in the insulinoma patients is usually due to suppression of glucose production rather than to acceleration of glucose utilization, as is widely thought. A direct effect of insulin on the liver is probably responsible, since circulating levels of gluconeogenic precursors are normal and since plasma glucagon increases during development of hypoglycemia in insulinoma patients.

Elevated serum prolactin level in the Zollinger-Ellison syndrome

To estimate the prevalence of prolactinoma in the Zollinger-Ellison syndrome (ZES), serum prolactin (PRL) levels were measured by radioimmunoassay in 36 patients with ZES. Eight patients had elevated PRL levels; however, in one patient the finding was attributed to primary hypothyroidism rather than a prolactinoma. The seven other patients were believed to have previously undiagnosed prolactinomas on the basis of elevated serum PRL levels; the presence of pituitary tumors were confirmed in four by demonstration of sella turcica erosions or enlargement. Serial determinations over three to six years showed a tendency for serum PRL levels to increase modestly in four of six patients. Thus far, two patients have undergone transsphenoidal tumor resections with good results. This study suggests that the prevalence of prolactinoma in patients with ZES is substantial (10% for those with isolated ZES and 54% for those with ZES with multiple endocrine neoplasia, type 1, syndrome), and that early diagnosis is possible with measurement of serum PRL levels. Since levels of PRL tend to increase and clinically significant pituitary tumors can develop, determinations of serial serum PRL levels are recommended for all patients with ZES.

Lack of effect of calcium infusion on blood glucose and plasma insulin levels in patients with insulinoma

In vitro calcium plays a fundamental role in regulating insulin secretion. On the other hand, the influence of calcium excess on insulin release in vivo is not clearly defined. Recently, calcium infusion has been proposed as a provocative test for the diagnosis of insulin-secreting tumors. A 2-h infusion of calcium gluconate was performed (4 mg/kg . h) in six patients with islet cell adenoma. As a result, mean calcium plasma levels increased from 9.6 +/- 0.4 to 11.6 +/- 0.8 mg/100 ml. During calcium infusion, blood glucose and plasma insulin concentrations remained unchanged. These observations suggest that calcium fails to stimulate basal insulin secretion even in cases of organic hyperinsulinism. They show that calcium infusion is not helpful as a provocative test in the diagnosis of insulinoma.

Radioimmunoassay of extracted glucagon compared with three non-extraction assays

Radioimmunoassay of glucagon was performed with three different antisera, i.e. E7, 30K and 4305, all directed against the carboxyl-terminal region of glucagon and thus avoiding co-determination of glucagon-like polypeptides from the gut. Plasma samples from five healthy people subjected to various A-cell stimulation and suppression tests were used and immunoreactive glucagon assessed with the three antisera. Aliquots from all plasma samples were also extracted with acetone and glucagon re-assessed with antiserum E7. Even though all four baseline glucagon concentrations obtained were different, the glucagon profiles were comparable after superimposing the baselines. The differences in baseline concentrations of immunoreactive glucagon seem due to the interference of "big plasma glucagon", a still unidentified factor in the E7 and 30K assays that can be precipitated by acetone. Since acetone extraction yielded the lowest baselines without altering the glucagon profiles, it is suggested that the baseline glucagon concentrations of acetone-extracted plasma reflect the physiological level of the biologically active hormone. Using antiserum E7, our own antiserum, the normal range of glucagon values in acetone-extracted plasma samples from 22 healthy, fasting people of both sexes was 42 +/- 16 ng/l (mean +/- 2 S.D.). These values agree well with those obtained by other assay techniques.

Dimethyltriazenoimidazole carboxamide therapy of islet cell carcinoma of the pancreas

Four patients with metastatic glucagonoma and one patient with metastatic diarrheogenic islet cell carcinoma of the pancreas were treated with dimethyltriazenoimidazole carboxamide (DTIC), 250 mg/M2 daily for five days repeated every four weeks. All patients responded clinically and chemically in one or more ways by a reduction in plasma glucagon levels, improved glucose tolerance, decreased measureable tumor, weight gain, and resolution of necrolytic migratory erythema and diarrhea. This experience and other cases from the literature call for the investigation of DTIC as the initial therapy in metastatic islet cell carcinoma of the pancreas and as being of possible benefit in other tumors of neuroendocrine origin.

Effect of propranolol on glucose-induced insulin response in rats with insulinomas

This paper describes an inhibitory effect of propranolol on insulin secretion in rats with pancreatic islet cell tumors which have been induced by streptozotocin (65 mg/kg body weight) and nicotinamide (500 mg/kg). Following glucose ingestion (3 g/kg), propranolol (4 mg/kg) was injected into the tumor-bearing rats. Plasma insulin decreased paradoxically despite an increase in blood glucoses. In contrast, propranolol did not suppress insulin secretion in normal rats. The drug was found to have no effect on glucagon secretion in either experimental or control animals during glucose load. This may suggest that the experimentally induced insulinoma in hypersensitive to propranolol for inhibiting insulin secretion.

Pathophysiology of gastrointestinal hormones. Implications for paediatrics

Gastrointestinal hormones (GI hormones) have received growing interest in endocrinology, gastroenterology and neuroendocrinology. Because of new methodological techniques, they can be measured in plasma and therefore be related to different pathophysiological conditions. In childhood, our present knowledge is as yet limited to the physiological rôle of gastrin at different ages and in some diseases (gastrinoma; Verner-Morrison syndrome) caused by humoral dysfunction. The present review relates the clinical important GI hormones to chemically classified families. The diagnostic value of determining endogenous hormone concentration in plasma and the validity of function tests carried out by administration of exogenous hormones are pointed out. Particular emphasis is given to the trophic action of GI hormones in the development and function of the gastrointestinal tract during childhood. More speculatively, GI hormones are involved in the complex function of the central nervous system, thus making food intake a trophotropic action in a broader sense.

Are elevated pancreatic polypeptide levels in patients with insulinoma secondary to hypoglycaemia?

In 13 patients with insulinoma, human pancreatic polypeptide (hPP) was measured under basal conditions, after a mixed meal, and during a fast of up to 72 h. Significant negative correlatons between hPP and plasma-glucose levels were found both under basal conditions and during fasting. Patients with insulinoma and basal plasma-glucose values above 60 mg/dl had hPP values similar to those in control subjects, whereas insulinoma patients with plasma-glucose values under 60 mg/dl had significantly higher hPP values (323 versus 115 pg/ml). The mean hPP response to a mixed meal was similar in patients with insulinoma and in control subjects. hPP values during symptomatic hypoglycaemia were higher in insulinoma patients than controls fasted for comparable times (751 versus 171 pg/ml). Under conditions of euglycaemia, hPP is not a reliable marker for insulinoma.