Counterregulatory hormonal responses to hypoglycaemia in type 1 (insulin-dependent) diabetes: evidence for diminished hypothalamic-pituitary hormonal secretion

Prolactin effects on the pathogenesis of diabetes mellitus

BACKGROUND

Prolactin (PRL) is a pituitary hormone promoting lactation in response to the suckling reflex. Beyond its well-known effects, novel tissue-specific and metabolic functions of PRL are emerging.

AIMS

To dissect PRL as a critical mediator of whole-body gluco-insulinemic sensitivity.

METHODS

PubMed-based search with the following terms 'prolactin', 'glucose metabolism', 'type 2 diabetes mellitus', 'type 1 diabetes mellitus', 'gestational diabetes mellitus' was performed.

DISCUSSION

The identification of the PRL-glucose metabolism network poses the basis for unprecedented avenues of research in the pathogenesis of diabetes mellitus type 1 or 2, as well as of gestational diabetes. In this regard, it is of timely relevance to define properly the homeostatic PRL serum levels since glucose metabolism could be influenced by the circulating amount of the hormone.

RESULTS

This review underscores the basic mechanisms of regulation of pancreatic β-cell functions by PRL and provides a revision of articles which have investigated the connection between PRL unbalancing and diabetes mellitus. Future studies are needed to elucidate the burden and the role of PRL in the regulation of glucose metabolism and determine the specific PRL threshold that may impact the management of diabetes.

CONCLUSION

A careful evaluation and context-driven interpretation of PRL levels (e.g., pregnancy, PRL-secreting pituitary adenomas, drug-related hyper- and hypoprolactinemia) could be critical for the correct screening and management of glucometabolic disorders, such as type 1 or 2 as well as gestational diabetes mellitus.

Modulatory role of prolactin in type 1 diabetes

Objectives

Patients with type 1 diabetes mellitus have been reported to have elevated prolactin levels and a possible relationship between prolactin levels and the development of the disease has been proposed. However, some studies show that prolactin mediates beneficial functions in beta cells. Therefore, we review information on the roles of prolactin in type 1 diabetes mellitus.

Content

Here we summarize the functions of prolactin in the immune system and in pancreatic beta cells, in addition, we describe studies related to PRL levels, its regulation and alterations of secretion in patients with type 1 diabetes mellitus.

Summary

Studies in murine models have shown that prolactin protects beta cells from apoptosis, stimulates their proliferation and promotes pancreatic islet revascularization. In addition, some studies in patients with type 1 diabetes mellitus have shown that elevated prolactin levels correlate with better disease control.

Outlook

Prolactin treatment appears to be a promising strategy to improve beta-cell vascularization and proliferation in transplantation and immunotherapies.

Enhanced carbohydrate craving in patients with poorly controlled Type 2 diabetes mellitus

AIMS

Although hyperphagia is a common manifestation of diabetes mellitus, data on food craving in patients with diabetes are limited. This study compared food craving in patients with Type 2 diabetes mellitus and a control group without diabetes.

METHODS

A total of 210 subjects (105 with Type 2 diabetes and 105 age-, sex- and BMI-matched control subjects) participated in two food craving surveys. The surveys were as follows: the General Food Cravings Questionnaire--Trait, which assesses the general trait of food craving; and the Food Cravings Questionnaire--State, which assesses the state of food craving or current desire for high-carbohydrate or high-fat foods in response to pictures of food. Follow-up Food Cravings Questionnaire--State surveys were administered approximately 3 months later to the subjects with diabetes. Survey results were analysed to assess relationships between food craving and glycaemic control.

RESULTS

The General Food Cravings Questionnaire--Trait scores in the group with Type 2 diabetes and the control group were not significantly different. The group with Type 2 diabetes had higher carbohydrate craving scores, but lower fat craving scores, than the control group. Carbohydrate craving scores in subjects with diabetes were positively correlated with HbA(1c). In follow-up surveys, carbohydrate craving scores declined in patients with improved glycaemic control.

CONCLUSIONS

The surveys showed that patients with Type 2 diabetes had higher carbohydrate cravings and lower fat cravings than the age-, sex- and BMI-matched control group. Carbohydrate craving in patients with diabetes was associated with poor glycaemic control.

Somatostatin receptor type 2 antagonism improves glucagon and corticosterone counterregulatory responses to hypoglycemia in streptozotocin-induced diabetic rats

Diminished responsiveness to hypoglycemia contributes to defective counterregulation in diabetes. Pancreatic and/or circulating somatostatin are elevated in diabetes, which may inhibit counterregulatory hormone release during hypoglycemia. Thus, a selective somatostatin receptor type 2 antagonist (SSTR2a) should improve hormone counterregulation to hypoglycemia. Nondiabetic (N) and streptozotocin-induced diabetic (D) rats underwent 4-h infusion of saline or SSTR2a with insulin-induced hypoglycemia clamped at 2.5 ± 0.5 mmol/L. To evaluate the effect of the SSTR2a in the absence of hypoglycemia, rats underwent a 4-h infusion of saline (Ctrl:N, Ctrl:D) or SSTR2a (Ctrl:D+SSTR2a) only. The attenuated glucagon response to hypoglycemia in D (P < 0.0002) was fully restored by SSTR2a (P < 0.0001). Furthermore, the attenuated corticosterone response in D (P < 0.002) was also enhanced by SSTR2a (P < 0.05). In the absence of hypoglycemia, SSTR2a did not alter basal blood glucose levels. D exhibited 62% more pancreatic somatostatin than N after hypoglycemia. In N rats, SSTR2a did not augment the glucagon or corticosterone response to hypoglycemia. Thus, somatostatin may contribute to impaired glucagon responsiveness to hypoglycemia in diabetes. We demonstrate that SSTR2 antagonism enhances hypoglycemia-stimulated glucagon and corticosterone release in D but not in N rats. SSTR2 antagonism does not affect basal glycemia in D rats.

The impact of blood glucose levels on stimulated adrenocorticotropin hormone and growth hormone release in healthy subjects

OBJECTIVE

In studies investigating the influence of glucose levels on the pituitary function the methods used have been variable and mainly focused on the change in function as a reaction to unphysiological low or high blood glucose levels. In the present study the impact of physiological and elevated blood glucose levels on adrenocorticotropin hormone (ACTH) and growth hormone release are investigated.

DESIGN

The euglycaemic and hyperglycaemic clamp techniques were used to reach stable levels of 4, 8 and 12 mmol/l blood glucose levels. After a stabilization phase of 2 h, a corticotropin releasing hormone (CRH) or a growth hormone releasing hormone (GHRH) stimulation test was performed.

SUBJECTS

Seven and eight healthy male volunteers, belonging to two groups, participated in this study.

MEASUREMENTS

The area under the curve (AUC), peak values and time to peak of ACTH, cortisol and growth hormone were calculated to evaluate the response to the CRH and GHRH stimulation test.

RESULTS

The peak values of ACTH, cortisol and growth hormone seemed to be the highest during the 4 mmol/l clamp sessions, compared with the 8 and 12 mmol/l clamps, although the differences were not statistically significant when analysed for every subject individually. The AUC and time to peak measurements were comparable during the three clamp procedures.

CONCLUSION

The pituitary reaction on CRH and GHRH was not significantly changed by various blood glucose levels.

Food cravings during acute hypoglycaemia in adults with Type 1 diabetes

BACKGROUND

Food craving is defined as an intense desire to eat a specific foodstuff. It may be distinguished from the sensation of hunger, which is relieved by nonspecific foodstuffs. No controlled studies have examined the effects of hypoglycaemia on food cravings. Thus, the aim of this study was to examine change in cravings for eight specified food types during euglycaemia and insulin-induced hypoglycaemia.

METHODS

Thirteen adults with Type 1 diabetes attended two experimental sessions where acute hypoglycaemia was induced with either insulin aspart or human soluble insulin. Food cravings were assessed, using a questionnaire, at baseline and at the onset of the autonomic reaction to hypoglycaemia ("R").

RESULTS

The mean arterialised blood glucose concentration at baseline was 6.0+/-0.3 mmol l(-1) and at R was 1.9+/-0.4 mmol l(-1) (P<.01). Fifteen percent of subjects reported having a craving for food during euglycaemia. The prevalence increased to 65% during hypoglycaemia (P<.01). Cravings for seven of the eight food types increased during hypoglycaemia, but the greatest effect sizes (>1.0 standard deviations) were observed for three food types that had a high carbohydrate content.

CONCLUSIONS

In people with Type 1 diabetes, acute hypoglycaemia produces a highly reliable generalised increase in cravings for food, particularly foodstuffs with a high content of carbohydrate. The mechanisms behind this response remain to be elicited.

Glucose counterregulation in Type 2 diabetes mellitus

Glucose counterregulatory failure and hypoglycaemia unawareness frequently complicate treatment of Type 1 diabetes mellitus, especially when aiming for intensive metabolic control. Since tight metabolic control reduces microvascular long-term complications in Type 2 diabetes mellitus, the integrity of glucose counterregulation in Type 2 diabetic patients is important. Using a Medline search, we identified 12 studies in which counterregulatory responses to insulin-induced hypoglycaemia were compared between Type 2 diabetic patients and appropriate controls. A review of these studies showed that some patients with Type 2 diabetes mellitus develop mild counterregulatory dysfunction and reduced awareness of insulin-induced hypoglycaemia. Some studies suggested an association between counterregulatory impairment and intensity of metabolic control. We speculate that the relatively low frequency of (severe) hypoglycaemic events in Type 2 diabetes may explain why glucose counterregulation remains unaffected in most patients. We hypothesize that residual beta-cell reserve and insulin resistance provide protection against severe hypoglycaemia and limit impaired counterregulation. Diabet. Med. 18, 519-527 (2001)

Growth hormone response to the insulin tolerance and clonidine tests in type 1 diabetes

The insulin tolerance test (ITT) is regarded the gold standard for assessing growth hormone (GH) release in adult patients with suspected GH deficiency. Some of these patients also have diabetes mellitus. There are contradictory reports regarding the GH response to ITT in type 1 diabetic patients with varying degrees of metabolic control. This is also true for the clonidine test. We studied ten patients with uncomplicated type 1 diabetes mellitus during periods of poor and improved metabolic control and compared them with ten healthy control subjects. The GH secretion was assessed by an ITT with an insulin infusion of 2.5 mU/kg/min and an intravenous clonidine test. The GH response to ITT was similar during poor and improved metabolic control (mean +/- SEM) (AUC 2327 +/- 616 vs. 2649 +/- 508 microg/l x min) and did not differ from the response in control subjects (AUC 2587 +/- 343 microg/1 x min). The clonidine test induced a significantly greater GH response during poor than during improved metabolic control in the diabetic patients (AUC 2598 +/- 492 vs. 1508 +/- 368 microg/l x min, p < 0.05); this response was greater than in the control subjects (670 +/- 226 x microg/l x min, p < 0.005 vs. improved metabolic control). Thus, the GH response to ITT is similar in diabetic patients with varying degrees of metabolic control and healthy subjects, while the GH response to the clonidine test is higher in the type 1 diabetic patients than in healthy controls.

Prolactin and beta-endorphin responses to hypoglycemia are reduced in well-controlled insulin-dependent diabetes mellitus

Several pituitary hormones, including corticotropin (ACTH), growth hormone (GH), prolactin, and beta-endorphin (but not thyrotropin, follicle-stimulating hormone, or luteinizing hormone), are released in response to hypoglycemia in normal subjects. In patients with insulin-dependent diabetes mellitus (IDDM), the degree of glycemic control is known to alter ACTH and GH responses to hypoglycemia. The current study was performed to examine the effect of glycemic control on prolactin and beta-endorphin responses to hypoglycemia in subjects with IDDM. We performed 3-hour stopped hypoglycemic-hyperinsulinemic clamp studies (12 pmol/kg/min) during which plasma glucose was decreased from 5.0 mmol/L to 2.2 mmol/L in steps of 0.6 mmol/L every 30 minutes in 20 subjects with uncomplicated IDDM (12 males and eight females; age, 26 +/- 2 years; IDDM duration, 10 +/- 1 years; body mass index, 23.6 +/- 0.6 kg/m2) and 10 healthy subjects (five males and five females aged 30 +/- 1 years). The 10 diabetic subjects in good glycemic control (mean hemoglobin A1 [HbA1], 7.5% +/- 0.3%; normal range, 5.4% to 7.4%) were compared with the 10 poorly controlled patients (mean HbA1, 12.6% +/- 0.5%; P < .001 v well-controlled diabetic group). During hypoglycemia, prolactin levels in the well-controlled diabetic group did not change (7 +/- 1 microgram/L at plasma glucose 5.0 mmol/L to 9 +/- 2 micrograms/L at plasma glucose 2.2 mmol/L), whereas prolactin levels increased markedly in the poorly controlled diabetic group (7 +/- 2 micrograms/L to 44 +/- 17 micrograms/L) and healthy volunteers (12 +/- 2 micrograms/L to 60 +/- 19 micrograms/L, P < .05 between IDDM groups). The plasma glucose threshold required for stimulation of prolactin secretion was 2.2 +/- 0.1 mmol/L in well-controlled IDDM, 3.0 +/- 0.4 mmol/L in poorly controlled IDDM, and 2.4 +/- 0.1 mmol/L in healthy subjects (P < .05 between IDDM groups). Responses in males and females were similar. The increase in beta-endorphin levels was also attenuated in well-controlled IDDM patients (4 +/- 1 pmol/L at plasma glucose 5.0 mmol/L to 11 +/- 4 pmol/L at plasma glucose 2.2 mmol/L) versus poorly controlled IDDM patients (5 +/- 1 pmol/L to 26 +/- 7 pmol/L) and healthy subjects (8 +/- 1 pmol/L to 56 +/- 13 pmol/L). The plasma glucose threshold required for stimulation of beta-endorphin release was again lower in well-controlled IDDM versus poorly controlled IDDM patients (2.2 +/- 0.1 v 3.0 +/- 0.3 mmol/L) and healthy subjects (2.5 +/- 0.4 mmol/L, P < .05 between IDDM groups). In conclusion, prolactin and beta-endorphin responses to a standardized hypoglycemic stimulus (plasma glucose, 2.2 mmol/L) are reduced and plasma glucose levels required to stimulate release of prolactin and beta-endorphin are lower in well-controlled IDDM compared with poorly controlled IDDM and healthy subjects. Thus, stress hormones not previously considered to have a primary role in plasma glucose recovery from hypoglycemia are affected by glycemic control, suggesting a more generalized alteration of hypothalamic-pituitary responses to hypoglycemia in IDDM patients with strict glycemic control.

Monitoring set-up for selection of parameters for detection of hypoglycaemia in diabetic patients

Recurrent severe hypoglycaemia is often an unsolved problem in diabetic patients under intensified insulin treatment. As no reliable long-term stable blood glucose sensor has yet been developed, registration of other body function changes could help to detect severe hypoglycaemia. A measuring system is described, capable on the one hand of recording EEG, heart rate, peripheral pulse, skin temperature, respiratory movements, skin impedance and arterial blood pressure, and capable of registering plasma glucose, counter-regulatory hormones, symptoms and cognitive performance under experimental conditions during hypoglycaemia, on the other. In a clinical study involving both insulin-induced hypoglycaemia in healthy subjects and insulin-dependent diabetic patients, the practical value and the character of changes of the recorded parameters are investigated. Currently insensitivity to hypoglycaemia, impracticability, complexity or susceptibility to artefacts make use of most parameters unsuitable for hypoglycaemia prevention. It is believed, however, that future efforts could result in indirect registration of hypoglycaemia, including a qualified combination of different parameters, individual adaptation in accordance with particular responses of individual patients, together with new measuring and sensor techniques.

Increase in plasma beta endorphins precedes vasodepressor syncope

BACKGROUND

Endogenous opioids have a tonic inhibitory effect on sympathetic tone and have been implicated in the pathophysiology of vasodepressor syncope. Plasma beta endorphin concentrations increase after vasodepressor syncope induced by exercise or by fasting.

AIMS

To take frequent samples for plasma beta endorphin estimation during tilt testing, and to determine whether plasma beta endorphin increased before the start of syncope.

PATIENTS

24 patients undergoing tilt testing for investigation of unexplained syncope.

SETTING

Tertiary referral centre.

METHODS

Blood samples were obtained during 70 degrees head up tilt testing. Plasma beta endorphin concentrations were estimated by radioimmunoassay (mean(SD) pmol/l).

RESULTS

Patients with a positive test showed a rise in beta endorphin concentrations before syncope (baseline 4.4(1.5) v start of syncope 8.5(3.1), p < 0.002). In contrast, patients with a negative test showed no change in beta endorphin concentrations (baseline 3.4(1.0) v end of test 4.5(2.3), NS). After syncope all patients showed a large secondary increase in beta endorphins (32.3(18.6)).

CONCLUSION

An increase in plasma beta endorphins precedes vasodepressor syncope. This finding supports a pathophysiological role for endogenous opioids.

The effect of a ventral medial hypothalamic lesion on the insulin-induced hypotensive response in normal rats

The cardiovascular responses to insulin-induced hypoglycemia were studied in normal and ventral medial hypothalamic (VMH)-lesioned rats. The goal of this study was to investigate the role of the VMH in mediating the insulin-induced decreases in cardiovascular tone. Male Wistar rats were anesthetized with urethane/chloralose. Following the induction of anesthesia, the trachea, femoral artery, and femoral vein were cannulated. The femoral artery was attached to a pressure transducer for cardiovascular monitoring. The cardiovascular activity was recorded using a Modular Instruments Micro 5000 signal processing system. The mean arterial pressure and pulse pressures and heart rate were evaluated. In control studies, a stable plasma glucose and blood pressure were obtained with urethane/chloralose anesthesia for the duration of the experiments. Insulin (2.0 or 5.0 U/kg) significantly decreased the plasma glucose as well as the blood pressure. In VMH-lesioned rats, the lesions were accomplished by radiofrequency, and the cardiovascular response to insulin-induced hypoglycemia was investigated 1 or 6 weeks later. There was no difference in the cardiovascular response to insulin-induced hypoglycemia between the low or high insulin dose after 1 week in VMH-lesioned animals. The low dose after 6 weeks in VMH-lesioned animals did not produce a change in the mean arterial pressure response compared with controls. The pulse pressure was higher than in the sham-lesioned animals, and the plasma glucose response was greater.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in plasma beta endorphins precedes vasodepressor syncope

BACKGROUND

Endogenous opioids have a tonic inhibitory effect on sympathetic tone and have been implicated in the pathophysiology of vasodepressor syncope. Plasma beta endorphin concentrations increase after vasodepressor syncope induced by exercise or by fasting.

AIMS

To take frequent samples for plasma beta endorphin estimation during tilt testing, and to determine whether plasma beta endorphin increased before the start of syncope.

PATIENTS

24 patients undergoing tilt testing for investigation of unexplained syncope.

SETTING

Tertiary referral centre.

METHODS

Blood samples were obtained during 70 degrees head up tilt testing. Plasma beta endorphin concentrations were estimated by radioimmunoassay (mean(SD) pmol/l).

RESULTS

Patients with a positive test showed a rise in beta endorphin concentrations before syncope baseline 4.4(1.5) v start of syncope 8.5(3.1), p < 0.002). In contrast, patients with a negative test showed no change in beta endorphin concentrations (baseline 3.4(1.0) v end of test 4.5(2.3), NS). After syncope all patients showed a large secondary increase in beta endorphins (32.3(18.6)).

CONCLUSION

An increase in plasma beta endorphins precedes vasodepressor syncope. This finding supports a pathophysiological role for endogenous opioids.

Physiological, symptomatic and hormonal responses to acute hypoglycaemia in type 1 diabetic patients with autonomic neuropathy

The effects of peripheral autonomic neuropathy on the symptomatic, physiological, and hormonal responses to acute insulin-induced hypoglycaemia were studied in two groups of patients with Type 1 diabetes, matched for age, duration of diabetes, and prevailing glycaemic control. A group of eight patients who gave a history of normal awareness of hypoglycaemia and had normal cardiovascular autonomic function tests were compared to a group of six patients who had symptoms of autonomic dysfunction and gross abnormalities of cardiovascular autonomic function tests. An additional two patients with autonomic neuropathy who also had hypoglycaemia unawareness were studied. Acute hypoglycaemia was induced by intravenous infusion of insulin (2.5 mU kg-1 min-1) and the onset of the acute autonomic reaction (R) was identified objectively by the sudden rise in heart rate and onset of sweating. Cognitive function and hypoglycaemia symptom scores were estimated serially, and plasma counterregulatory hormones were measured. Acute autonomic activation was observed to occur in all subjects in response to hypoglycaemia and commenced at similar venous plasma glucose concentrations in both groups (neuropathic patients: 1.6 +/- 0.2 mmol l-1 vs non-neuropathic patients 1.6 +/- 0.2 mmol l-1, p = 0.9,). In the neuropathic patients plasma adrenaline responses were significantly lower at all time points from time R until time R + 30 min (MANOVA for repeated measures, F = 19.4, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Reversibility of unawareness of hypoglycemia in patients with insulinomas

BACKGROUND

A lack of appropriate autonomic warning symptoms before the development of neuroglycopenia occurs frequently in patients with diabetes mellitus. The pathogenesis of this phenomenon is unclear, but it is associated with intensive insulin therapy, prolonged duration of diabetes, frequent episodes of hypoglycemia, and impaired glucose counterregulation. Recently, it has been proposed that repeated episodes of hypoglycemia may themselves induce the phenomenon.

METHODS

To test this hypothesis and to determine whether the phenomenon is reversible, we assessed autonomic and neuroglycopenic symptoms, counterregulatory hormonal responses, and cognitive function during stepped hypoglycemic-clamp studies in 6 patients with insulinomas before and approximately six months after curative surgery and in 14 normal subjects matched for age, weight, and sex.

RESULTS

Before surgery, the patients with insulinomas had lower scores than the normal subjects for autonomic symptoms (mean [+/- SD], 3.5 +/- 0.8 vs. 9.6 +/- 4.5) and neuroglycopenic symptoms (2.8 +/- 1.5 vs. 8.9 +/- 5.3). The patients also had impaired counterregulatory hormonal responses (their plasma epinephrine, norepinephrine, glucagon, growth hormone, and cortisol responses before surgery were 187 +/- 227 pg per milliliter [1.03 +/- 1.25 nmol per liter], 223 +/- 85 pg per milliliter [1.32 +/- 0.50 nmol per liter], 86 +/- 21 ng per liter, 7.4 +/- 5.2 micrograms per liter, and 12.1 +/- 1.5 micrograms per deciliter [334 +/- 41 nmol per liter], respectively, as compared with 842 +/- 439 pg per milliliter [4.63 +/- 2.41 nmol per liter], 519 +/- 150 pg per milliliter [3.07 +/- 0.89 nmol per liter], 201 +/- 58 ng per liter, 25.3 +/- 13.7 micrograms per liter, and 26.3 +/- 1.2 micrograms per deciliter [726 +/- 33 nmol per liter] in the normal subjects) and less deterioration in cognitive function than the normal subjects during hypoglycemia (sum of z scores for seven tests of cognitive function, 1.7 +/- 1.9 vs. 8.9 +/- 3.5) (P < 0.02 for all comparisons). Surgical cure reversed all these abnormalities (P not significant for all comparisons with the normal subjects).

CONCLUSIONS

Hypoglycemia itself can induce unawareness of the autonomic and neuroglycopenic symptoms of hypoglycemia and decrease the counterregulatory hormonal responses to hypoglycemia.

An analysis of the glucagon response to hypoglycaemia in patients with type 1 diabetes and in healthy subjects

The study aimed to analyse the glucagon response during hypoglycaemia in relation to gender, level of hypoglycaemia, and hyperinsulinaemia as well as its relation to other counterregulatory hormones in patients with Type 1 diabetes and in nondiabetic subjects. Mild hypoglycaemia was induced by an i.v. insulin infusion (244 pmol kg-1h-1) for 180 min in 43 Type 1 diabetic patients and 22 nondiabetic subjects. Venous blood glucose, plasma free insulin, glucagon, adrenaline, noradrenaline, growth hormone, and cortisol were measured every 15-30 min. The hormonal responses during hypoglycaemia were evaluated from the incremental areas under their respective curves. There was a linear correlation between the glucagon response and the decremental area of blood glucose (p < 0.005), but the slope of the regression line in the diabetic group was less steep than in the controls (p < 0.5), and, in spite of the deeper hypoglycaemia in the diabetic groups, their glucagon response was diminished (p < 0.05). Plasma, adrenaline, growth hormone and cortisol all increased during hypoglycaemia. The glucagon response correlated with the responses of growth hormone and cortisol in both groups, while it was positively correlated with the adrenaline response (p < 0.001) and inversely with the plasma insulin (p < 0.001) only in the diabetic patients. Although the insulin infusion rate was identical, the female diabetic patients had a lower metabolic clearance rate of insulin as compared with the males (p < 0.05). There was no statistical difference in the counterregulatory hormone responses between males and females in neither of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproducibility of glycaemic thresholds for activation of counterregulatory hormones and hypoglycaemic symptoms in healthy subjects

Nine healthy subjects were studied on two separate occasions, at least two weeks apart, using the glucose clamp technique to produce a gradual hypoglycaemia. Glucose thresholds for neuroendocrine and symptom responses varied up to 1.5 mmol/l between subjects. There was a significant correlation between individual glucose thresholds on day 1 and 2 for adrenaline (p = 0.0008), growth hormone (p = 0.007) and pancreatic polypeptide (p = 0.02), and for autonomic (p = 0.018) and neuroglycopoenic (p = 0.023) symptoms, whereas no significant correlations were found for glucagon and cortisol. The mean intra-individual differences in glucose thresholds between day 1 and 2 were 0.22 mmol/l for the hormones and 0.25 mmol/l for the symptoms. We conclude that healthy subjects differ in hypoglycaemic thresholds, and that the difference reflects individual variation.

Pancreatic and pituitary hormonal responses to insulin-induced hypoglycaemia during muscarinic cholinergic blockade in man

To investigate the role of muscarinic cholinergic mechanisms in mediating the pancreatic and pituitary hormonal responses to hypoglycaemia, six normal subjects were studied during acute insulin-induced hypoglycaemia under control conditions, and during blockade with intravenous atropine. During atropine blockade the response of pancreatic polypeptide was suppressed while the maximum response of plasma glucagon was significantly higher. The increment in plasma vasopressin was also increased significantly during cholinergic blockade. During blockade with atropine the responses of plasma prolactin was reduced, with a slight but significant reduction in the growth hormone response, and although a similar maximum response of plasma ACTH was achieved, this rise was delayed. These results implicate involvement of a cholinergic muscarinic inhibitory and stimulatory mechanisms in regulating the responses of pancreatic and pituitary hormones to hypoglycaemia.

Hypoglycaemia unawareness in type 1 diabetes: a lower plasma glucose is required to stimulate sympatho-adrenal activation

To investigate the relationship between awareness of symptoms and the autonomic reaction of hypoglycaemia, acute hypoglycaemia was induced with intravenous insulin (2.5 mU kg-1 min-1) in diabetic and non-diabetic subjects, all of whom had normal cardiovascular autonomic function tests. Three groups were studied: (1) nine patients with Type 1 diabetes with loss of awareness of hypoglycaemia; (2) eight patients who had normal awareness of hypoglycemia, matched for duration of diabetes and blood glucose control; (3) eleven non-diabetic volunteers. The onset of the acute autonomic reaction was identified objectively by the sudden and rapid responses of heart rate and sweating. Cognitive function and hypoglycaemia symptom scores were estimated serially. Acute autonomic activation was observed to occur in all subjects in response to hypoglycaemia. In the 'unaware' diabetic patients, onset of the reaction occurred at a significantly lower plasma glucose (1.0 +/- 0.1 mmol l-1) than in the 'aware' diabetic patients (1.6 +/- 0.2 mmol l-1) (p less than 0.05) or in the non-diabetic control group (1.4 +/- 0.1 mmol l-1) (p less than 0.05). Obvious neuroglycopenia was observed only in the 'unaware' diabetic group and developed when plasma glucose had declined to approximately 1.4 +/- 0.1 mmol l-1, and thus preceded the reaction (p less than 0.02 vs the autonomic threshold). The maximal rise in plasma adrenaline was of similar magnitude in all three groups but a lower plasma glucose was required to stimulate this hormonal response in the 'unaware' patients, in whom the plasma adrenaline concentration was lower at the time of the reaction. Thus, the plasma glucose at which activation of the autonomic reaction was observed was lower in the diabetic patients with unawareness of hypoglycaemia.

Unawareness of hypoglycaemia in insulin-treated diabetic patients: prevalence and relationship to autonomic neuropathy

Three-hundred and two insulin-treated diabetic patients were questioned about hypoglycaemia using a structured questionnaire interview. Two-hundred and twenty-six patients (75%) had normal symptomatic awareness, 48 (16%) had partial awareness, 21 (7%) had absent awareness of hypoglycaemia, and 7 (2%) denied ever experiencing hypoglycaemia. Patients with complete loss of awareness of hypoglycaemia had diabetes of longer duration; none had a HbA1 concentration within the non-diabetic range. Loss of awareness of hypoglycaemia was associated with an increased incidence of severe hypoglycaemia, 19 (91%) of the patients with absent awareness, and 33 (69%) with partial awareness of hypoglycaemia experiencing severe hypoglycaemia over 1 year compared with only 41 (18%) of patients with normal awareness of hypoglycaemia (p less than 0.001). Cardiovascular autonomic function tests were performed in 226 (75% of the whole group). Of the patients who had diabetes for more than 15 years, 54% (n = 39) with normal awareness of hypoglycaemia, compared with 59% (n = 10) with absent awareness of hypoglycaemia, had evidence of cardiovascular autonomic impairment (NS). Seven (41%) of the 17 patients with absent awareness of hypoglycaemia and diabetes of greater than 15 years duration had no evidence of autonomic dysfunction. Loss of hypoglycaemia awareness is a common problem in patients with insulin-treated diabetes of long duration, is associated with an increased incidence of severe hypoglycaemia, but is not invariably associated with abnormal cardiovascular autonomic function tests.