Nocturnal spikes of growth hormone secretion cause the dawn phenomenon in type 1 (insulin-dependent) diabetes mellitus by decreasing hepatic (and extrahepatic) sensitivity to insulin in the absence of insulin waning

Circadian clock, diurnal glucose metabolic rhythm, and dawn phenomenon

The circadian clock provides cue-independent anticipatory signals for diurnal rhythms of baseline glucose levels and glucose tolerance. The central circadian clock is located in the hypothalamic suprachiasmatic nucleus (SCN), which comprises primarily GABAergic neurons. The SCN clock regulates physiological diurnal rhythms of endogenous glucose production (EGP) and hepatic insulin sensitivity through neurohumoral mechanisms. Disruption of the molecular circadian clock is associated with the extended dawn phenomenon (DP) in type 2 diabetes (T2D), referring to hyperglycemia in the early morning without nocturnal hypoglycemia. The DP affects nearly half of patients with diabetes, with poorly defined etiology and a lack of targeted therapy. Here we review neural and secreted factors in physiological diurnal rhythms of glucose metabolism and their pathological implications for the DP.

Patients with Type 1 Diabetes Treated with Insulin Pumps Need Widely Heterogeneous Basal Rate Profiles Ranging from Negligible to Pronounced Diurnal Variability

BACKGROUND

Pump-treated patients with type 1 diabetes have widely differing basal insulin infusion profiles. We analyzed consequences of such heterogeneity for glycemic control under fasting conditions.

METHODS

Data from 339 adult patients with type 1 diabetes on insulin pump therapy undergoing a 24-hour fast (basal rate test) were retrospectively analyzed. Hourly programmed basal insulin infusion rates and plasma glucose concentrations as well as their proportions within, below, or above arbitrarily defined target ranges were assessed for specific periods of the day (eg, 1-7 hours, "dawn" period, 16-19 hours, "dusk" period, reference period 20-1 hours/10-14 hours), by tertiles of a predefined "dawn" index (mean basal insulin infusion rate during the "dawn" divided by the reference periods).

RESULTS

The "dawn" index varied interindividually from 0.7 to 4.4. Basal insulin infusion profiles exhibited substantial differences (P = .011), especially overnight. Despite higher insulin infusion rates at 4 and 6.45 hours, patients with the most pronounced "dawn" phenomenon exhibited higher plasma glucose concentrations at those time points (P < .012). Patients with a marked "dawn" phenomenon exhibited a lower probability for low (<4.4 mmol/L) and a higher probability of high values (>7.2 mmol/L) during the dawn period (all P values <.01).

CONCLUSIONS

We observe substantial interindividual heterogeneity in the "dawn" phenomenon. However, widely different empirically derived basal insulin infusion profiles appear appropriate for individual patients, as indicated by similar plasma glucose concentrations, mainly in the target range, during a 24-hour fasting period.

Prediction of Individual Basal Rate Profiles From Patient Characteristics in Type 1 Diabetes on Insulin Pump Therapy

BACKGROUND

Basal rate profiles in patients with type 1 diabetes on insulin pump therapy are subject to enormous inter-individual heterogeneity. Tools to predict basal rates based on clinical characteristics may facilitate insulin pump therapy.

METHODS

Data from 339 consecutive in-patients with adult type 1 diabetes on insulin pump therapy were collected. Basal rate tests were performed over 24 hours. A mathematical algorithm to predict individual basal rate profiles was generated by relating the individual insulin demand to selected clinical characteristics in an exploratory cohort of 170 patients. The predicted insulin pump profiles were validated in a confirmatory cohort of 169 patients.

FINDINGS

Basal rates (0.27 ± 0.01 IU.d^-1.kg^-1) showed circadian variations with peaks corresponding to the "dawn" and "dusk" phenomena. Age, gender, duration of pump treatment, body-mass-index, HbA_1c, and triacylglycerol concentrations largely predicted the individual basal insulin demand per day (IU/d; exploratory vs prospective cohorts: r² = 0.518, P < .0001). Model-predicted and actual basal insulin rates were not different (exploratory cohort: Δ 0.1 (95% CI -0.9; 1.0 U/d; P = .95; prospective cohort: Δ -0.5 (95% CI -1.5; 0.6 IU/d; P = .46). Similarly, precise predictions were possible for each hour of the day. Actual and predicted "dawn" index correlated significantly in the exploratory but not in the confirmatory cohort.

INTERPRETATION

Clinical characteristics predict 52% of the variation in individual basal rate profiles, including their diurnal fluctuations. The multivariate regression model can be used to initiate or optimize insulin pump treatment in patients with type 1 diabetes.

The dawn phenomenon in type 2 diabetes: its association with glucose excursions and changes after oral glucose-lowering drugs

Background:

We investigated the association between glucose excursions and the dawn phenomenon, and the effects of oral-glucose lowering drugs on the dawn phenomenon in patients with type 2 diabetes (T2D).

Methods:

We conducted a post hoc analysis using data from a previous randomized trial. Patients with T2D on metformin monotherapy were randomized to receive add-on acarbose or glibenclamide for 16 weeks. Ambulatory continuous glucose monitoring (CGM) was conducted before randomization and at the end of the study. Using the CGM data, we assessed glucose excursions as indicated by mean amplitude of glycemic excursions (MAGE). The magnitude of the dawn phenomenon was calculated as the difference between the nocturnal nadir (0:00 to 6:00 a.m.) and prebreakfast glucose level.

Results:

A total of 50 patients with T2D [mean age 53.5 ± 8.2 years, mean glycated hemoglobin (HbA1c) 8.4 ± 1.2%] were analyzed. There was an independent association between MAGE and the dawn phenomenon [β coefficient 0.199, 95% confidence interval (CI) 0.074–0.325, p = 0.003]. HbA1c improved significantly after treatment with acarbose or glibenclamide. However, only treatment with acarbose significantly improved glucose excursions. The dawn phenomenon decreased significantly only in patients treated with acarbose (from 35.9 ± 15.7–28.3 ± 16.5 mg/dl, p = 0.037), but not in those treated with glibenclamide (from 35.9 ± 20.6–34.6 ± 17.0 mg/dl, p = 0.776).

Conclusion:

Glucose excursions were independently associated with the dawn phenomenon in patients with T2D on metformin monotherapy. Both glucose excursions and the dawn phenomenon improved after treatment with acarbose, but not after treatment with glibenclamide.

Regulation of Postabsorptive and Postprandial Glucose Metabolism by Insulin-Dependent and Insulin-Independent Mechanisms: An Integrative Approach

Glucose levels in blood must be constantly maintained within a tight physiological range to sustain anabolism. Insulin regulates glucose homeostasis via its effects on glucose production from the liver and kidneys and glucose disposal in peripheral tissues (mainly skeletal muscle). Blood levels of glucose are regulated simultaneously by insulin-mediated rates of glucose production from the liver (and kidneys) and removal from muscle; adipose tissue is a key partner in this scenario, providing nonesterified fatty acids (NEFA) as an alternative fuel for skeletal muscle and liver when blood glucose levels are depleted. During sleep at night, the gradual development of insulin resistance, due to growth hormone and cortisol surges, ensures that blood glucose levels will be maintained within normal levels by: (a) switching from glucose to NEFA oxidation in muscle; (b) modulating glucose production from the liver/kidneys. After meals, several mechanisms (sequence/composition of meals, gastric emptying/intestinal glucose absorption, gastrointestinal hormones, hyperglycemia mass action effects, insulin/glucagon secretion/action, de novo lipogenesis and glucose disposal) operate in concert for optimal regulation of postprandial glucose fluctuations. The contribution of the liver in postprandial glucose homeostasis is critical. The liver is preferentially used to dispose over 50% of the ingested glucose and restrict the acute increases of glucose and insulin in the bloodstream after meals, thus protecting the circulation and tissues from the adverse effects of marked hyperglycemia and hyperinsulinemia.

Analysis of Prevalence, Magnitude and Timing of the Dawn Phenomenon in Adults and Adolescents With Type 1 Diabetes: Descriptive Analysis of 2 Insulin Pump Trials

OBJECTIVES

To better understand the dawn phenomenon in type 1 diabetes, we sought to determine its prevalence, timing and magnitude in studies specifically designed to assess basal insulin requirements in patients using insulin pumps.

METHODS

Thirty-three participants from 2 sensor-augmented insulin pump studies were analyzed. Twenty participants were obtained from a methodologically ideal semiautomated basal analysis trial in which basal rates were determined from repeated fasting tests (the derivation set) and 13 from an artificial pancreas trial in which duration of fasting was variable (the "confirmation" set). Prevalence was determined for the total cohort and for individual trials using the standard definition of an increase in insulin exceeding 20% and lasting ≥90 minutes. Among cases, time of onset and percent change in the magnitude of basal delivery were determined.

RESULTS

Seventeen participants (52%) experienced the dawn phenomenon (11 of 20 [55%] in the derivation set and 6 of 13 [46%] in the confirmation set). Time of onset was 3 AM (interquartile range [IQR], 3 to 4:15 AM) in the derivation set and 3 AM (IQR, 3 to 4 AM) in the confirmation set. The magnitude of the dawn phenomenon was a 58.1% (IQR, 28.8% to 110.6%) increase in insulin requirements in the derivation set and 65.5% (IQR, 45.6% to 87.4%) in the confirmation set.

CONCLUSIONS

The dawn phenomenon occurs in approximately half of patients with type 1 diabetes; when present, it has predictable timing of onset (generally 3 AM) and a substantial, but highly variable, magnitude. These findings imply that optimization of glycemic control requires clinical emphasis on fasted overnight basal insulin assessment.

Basal rate tests (24-hour fasts) performed in type-1 diabetic subjects with either absolute fasting or snacks containing negligible carbohydrate amounts result in similar glucose profiles: A randomized controlled prospective trial

AIMS

Basal rate tests (24-hour fasting periods) may be necessary to optimize basal insulin replacement in type 1 diabetes. It was the aim of this study to prospectively compare the allowance of negligible carbohydrate snacks vs absolute fasting.

METHODS

A total of 20 patients with type 1 diabetes (age, 48 ± 15 years (9 women, 11 men); BMI, 28.5 ± 4.5 kg/m² ; HbA1c, 8.8% ± 2.0% (73.0 ± 21.9 mmol/mol); insulin dose, 0.69 ± 0.31 IU/kg body weight and per day) participated in 2 basal rate tests lasting 24 hours in random order with unchanged basal insulin replacement. On 1 occasion, negligible carbohydrate snacks (salads and vegetables, up to 5.1 g carbohydrate and 276.3 kJ per portion) were allowed; during the second test subjects were obliged to fast absolutely. Plasma glucose profiles were determined using an exact laboratory method. Hypoglycaemic episodes (plasma glucose < 70 mg/dL) were compared.

RESULTS

Plasma glucose concentrations during fasting periods, with and without negligible carbohydrate snacks, did not differ significantly ( P = .65) and differences were negligible (95% confidence intervals always included a difference of 0 mmol/L). Also, there was no difference in the number of hypoglycaemic plasma glucose values (P = .40) or in compensatory carbohydrate intake. Basal rate testing with negligible carbohydrate snacks was better tolerated (questionnaire, P = .046) and the desire to discontinue the fasting period was significantly reduced (P = .023).

CONCLUSIONS

Allowing negligible carbohydrate snacks results in unchanged plasma glucose profiles during basal rate testing and is better tolerated by patients with type 1 diabetes.

Daily Fasting Blood Glucose Rhythm in Male Mice: A Role of the Circadian Clock in the Liver

Fasting blood glucose (FBG) and hepatic glucose production are regulated according to a circadian rhythm. An early morning increase in FBG levels, which is pronounced among diabetic patients, is known as the dawn phenomenon. Although the intracellular circadian clock generates various molecular rhythms, whether the hepatic clock is involved in FBG rhythm remains unclear. To address this issue, we investigated the effects of phase shift and disruption of the hepatic clock on the FBG rhythm. In both C57BL/6J and diabetic ob/ob mice, FBG exhibited significant daily rhythms with a peak at the beginning of the dark phase. Light-phase restricted feeding altered the phase of FBG rhythm mildly in C57BL/6J mice and greatly in ob/ob mice, in concert with the phase shifts of mRNA expression rhythms of the clock and glucose production-related genes in the liver. Moreover, the rhythmicity of FBG and Glut2 expression was not detected in liver-specific Bmal1-deficient mice. Furthermore, treatment with octreotide suppressed the plasma growth hormone concentration but did not affect the hepatic mRNA expression of the clock genes or the rise in FBG during the latter half of the resting phase in C57BL/6J mice. These results suggest that the hepatic circadian clock plays a critical role in regulating the daily FBG rhythm, including the dawn phenomenon.

The Effectiveness and Risks of Programming an Insulin Pump to Counteract the Dawn Phenomenon in Type 1 Diabetes

OBJECTIVE

Continuous subcutaneous insulin infusion (CSII) programming for an early morning increase in insulin delivery is frequently recommended to counteract the rise in glucose prior to breakfast (dawn phenomenon). However, both the effectiveness and safety of this approach have not been tested in the ambulatory setting. Using continuous glucose monitoring, we investigated the safety and effectiveness of early morning CSII programming for management of the dawn phenomenon in subjects with type 1 diabetes.

METHODS

We conducted a controlled, observational eight-month longitudinal study of type 1 diabetic patients (n=40). Reproducibility of the dawn phenomenon was determined in subjects treated with multiple daily injections of insulin (MDI, n=12) and those on CSII who did not program an early morning increase in insulin delivery (CSII non-programmers, n=8). The effects of early morning CSII programming were determined by comparing rates of the dawn phenomenon and hypoglycemia in CSII non-programmers versus CSII-users who programmed an early morning increase in insulin delivery (CSII programmers, n=20).

RESULTS

The dawn phenomenon occurred in all tested subjects to a variable extent (median rate 56% of nights). CSII programming was not associated with a reduction in the occurrence of the dawn phenomenon (42%) compared to non-programmers (48%) (P=0.47) nor in the magnitude of the dawn phenomenon. Hypoglycemia occurred more frequently in the CSII programmers (37%) compared to non-programmers (18%) (P=0.001).

CONCLUSION

The dawn phenomenon occurs unpredictably; therefore, early morning CSII programming for a fixed increase in early morning insulin delivery is ineffective and may be hazardous to the patient.

Does the dawn phenomenon have clinical relevance in normal pregnancy?

OBJECTIVE

The dawn phenomenon is a transient rise in blood glucose between 4 and 6 am that is attributed to the pulsatile release of pituitary growth hormone (GH). In pregnancy, GH is suppressed by placental GH. Hence, we hypothesize that there is no evidence for the dawn phenomenon in late pregnancy in healthy women.

STUDY DESIGN

Twenty glucose-tolerant women with singleton gestations between 28 weeks and 36 weeks 6 days' gestation were recruited. The women were admitted overnight to the Clinical Research Unit and had continuous glucose monitoring. Insulin and GH were measured at 2-hour intervals from 8 pm to 8 am. GH was grouped into times 1A (8-10 pm), 2A (12-2 am), and 3A (4-8 am) for changes over time. Further analysis was performed with time 1B (8 pm to 2 am) and 2B (4-8 am). Insulin was measured between 4 and 8 am.

RESULTS

Plasma glucose decreased over time (P < .001). There were no significant changes in GH among times 1A, 2A, and 3A (P = .45) or times 1B and 2B (P = .12). Insulin concentrations increased after meals, but there were no changes from 4 am (8.5 ± 1.4 μU/mL) through 8 am (8.6 ± 1.1 μU/mL; P = .98).

CONCLUSION

Glucose and insulin concentrations show no increase from 4-8 am; although there is variability in GH, there is no evidence for the dawn phenomenon in late pregnancy in healthy women.

Dynamic insulin on board: incorporation of circadian insulin sensitivity variation

BACKGROUND

Insulin-on-board (IOB) estimation is used in modern insulin therapy with continuous subcutaneous insulin infusion (CSII) as well as different automatic glucose-regulating strategies (i.e., artificial pancreas products) to prevent insulin stacking that may lead to hypoglycemia. However, most of the IOB calculations are static IOB (sIOB): they are based only on approximated insulin decay and do not take into account diurnal changes in insulin sensitivity.

METHODS

A dynamic IOB (dIOB) that takes into account diurnal insulin sensitivity variation is suggested in this work and used to adjust the sIOB estimations. The dIOB function is used to correct the dosage of insulin boluses in light of this circadian variation.

RESULTS

Basal-bolus as applied by pump users and model predictive control therapy with and without dIOB were evaluated using the University of Virginia/Padova metabolic simulator. Three protocols with four meals of 1 g carbohydrate/kg body weight were evaluated: a nominal scenario and two robustness scenarios, one in which insulin sensitivity was 15% greater than estimated and the other where the lunch is 30% less than announced. In the nominal and robustness scenarios, respectively, the dIOB led to 6% and 24% and 40% less hypoglycemia episodes than approaches without IOB. The new approach was also compared with the sIOB to evaluate the improvements with respect to the previous approach.

CONCLUSIONS

Improved glucose regulation was demonstrated using the dIOB where circadian insulin sensitivity is used to adjust IOB estimation. Use of diurnal variations of insulin sensitivity appears to promote effective and safe insulin therapy using CSII or artificial pancreas. Clinical trials are warranted to determine whether nocturnal hypoglycemia can be reduced using the dIOB approach.

Effect of growth hormone on dawn phenomenon in patients with type 2 diabetes

We aimed to investigate the involvement of growth hormone in dawn phenomenon and insulin sensitivity in patients with type 2 diabetes mellitus (T2DM). On six occasions separated by intervals of at least 3 days, subjects received early evening (16:00 hours) or late night (23:00 hours) pretreatment with subcutaneous injection of normal saline, human growth hormone, or octreotide. Modified euglycemic insulin clamp test was done 16 hours later and variable glucose infusion (M values) was determined. Plasma glucose, serum insulin, insulin-like growth factor-1, non-esterified fatty acids, and metabolic clearance rate of insulin (MCRI) were measured. Early evening application of growth hormone decreased MCRI 16 hours later, suggesting reduction in insulin sensitivity. Exogenous growth hormone injection reduced insulin sensitivity in T2DM patients. Results provide direct evidence for the role of growth hormone in regulating the insulin sensitivity in insulin-resistant patients.

The number of basal rates required to achieve near-normal basal glucose control in pump-treated type 2 diabetes

BACKGROUND

It has been reported that most pump-treated patients with type 2 diabetes require only two or fewer basal rates. Using daily continuous glucose monitoring (CGM)-directed titration, this premise was re-evaluated at near-normal glycemic control.

PATIENTS AND METHODS

Thirty subjects who were insulin-naive (n = 10), on basal insulin (n = 10), or on basal-bolus insulin therapy (n=10) ate a fixed diet. The basal rate was started as a single rate and then adjusted to a basal glucose goal of 70-130 mg/dL. The insulin-to-carbohydrate ratio (ICR) (in g/U) was adjusted to 2-4-h postmeal CGM glucose goal of 80-120% of premeal glucose.

RESULTS

The mean (SE) CGM basal glucose was 99.9 (4.9) mg/dL, and 4.5% (1.4%) of the readings were <70 mg/dL. The mean 2-4-h postmeal glucose was 113.3% (4.8%) of the premeal glucose. Only six subjects (20%) required two basal rates, while the remainder needed only one. The mean (SE) dosing relationships were as follows: total basal dose (TBD) (in U/day) = 0.226(0.018) × weight (in kg); TBD (in U/day) = 0.339(0.012) × total daily dose (TDD) (in U/day); ICR (in g/U) = 126(8)/TBD (in U/day); and ICR (in g/U) = 365(14)/TDD (in U/day).

CONCLUSIONS

This study confirms that one basal rate is adequate for the majority of subjects with type 2 diabetes. The mathematical proportionality between dosing factors closely agrees with those obtained in CGM-titrated pump-treated type 1 diabetes but differs from those derived from clinical studies in which insulin titration was based on infrequent self-monitored plasma glucose testing and while on an unstructured diet.

Insulin doses before and one year after pump start: children have a reversed dawn phenomenon

OBJECTIVE

We aimed to investigate the basal rate and bolus doses in children and adolescents at the start of insulin pump therapy and after 1 year of use.

PATIENTS AND METHODS

Case records from 29 children and adolescents were examined. All pumps were started with rapid-acting insulin (Humalog). Patients were aged 13.1 ± 3.9 years, with a diabetes duration of 5.4 ± 4.1 years at pump start. Sixteen pumps were started for high hemoglobin A1c (HbA1c; >8.8%, 73 mmol/mol) and 13 for other reasons.

RESULTS

Basal rates declined in both groups by 20% at 3 days after pump start. The bolus doses were reduced by 25-30% when the indication was high HbA1c and by 15% in the others. After 1 year, there was a significant difference in the basal rate between age groups. The 3-9-year-old age group had higher basal rates during the late evening (10:00 PM-12:00 AM), while the 15-21-year-old age group had higher basal rates in the early morning (3:00 AM-7:00 AM).

CONCLUSIONS

Insulin doses are reduced considerably when starting with a pump in pediatric practice. Younger children needed higher basal rates late in the evening (reversed dawn phenomenon), while older teenagers seem to need an increase in the morning, which may correspond to a true dawn phenomenon.

Basal rates and circadian profiles in continuous subcutaneous insulin infusion (CSII) differ for preschool children, prepubertal children, adolescents and young adults

OBJECTIVE

Initiation of continuous subcutaneous insulin therapy (CSII) requires an appropriate basal rate profile. Different approaches exist; however, there is a lack of evidence-based recommendations, especially in young children.

STUDY DESIGN

In this large multicenter survey, 5941 CSII patients from the German/Austrian prospective documentation system (DPV) were analyzed. Patients were divided into four age groups: <6 yr (n = 837), 6 to <12 yr (n = 1739), 12 to <18 yr (n = 2985) and 18 to <25 yr (n = 380). Basal insulin requirement and diurnal distribution were evaluated based on the most recent documentation for each patient.

RESULTS

Basal insulin requirement differed significantly between the four age groups (<6: 0.25 ± 0.12; 6 to <12: 0.33 ± 0.12; 12 to <18: 0.43 ± 0.15; 18 to <25: 0.35 ± 0.13 U/kg; p < 0.001). Circadian insulin profiles were markedly different between the younger and older age groups. In addition to age, longer diabetes duration, female gender, higher HbA1c and lower body mass index standard deviation score (BMI-SDS) were related to higher basal insulin requirement per kilogram of body weight.

CONCLUSIONS

Age of the patient is the primary factor that influences both total daily requirement and circadian distribution of basal insulin in CSII. Experience from a large database may therefore facilitate the initiation of pump therapy in pediatric patients.

Clinical experience with insulin glargine in type 1 diabetes

The Diabetes Control and Complications Trial (DCCT) demonstrated the importance of optimal glycemic control achieved through intensive insulin therapy in reducing the microvascular complications associated with type 1 diabetes. However, the DCCT, which was conducted prior to the availability of insulin analogs, also reported a significant increase in severe hypoglycemia with intensive versus conventional therapy. Insulin analogs were developed to aid patients in achieving better diabetes control by providing insulins with optimized pharmacokinetic and pharmacodynamic characteristics. Insulin glargine was the first long-acting insulin analog with a 24-h duration of action, offering once-daily injection, and has now been in clinical use for over 10 years. The authors performed a systematic search of EMBASE, MEDLINE, and Web of Science (Science Citation Index) to determine the efficacy of insulin glargine in type 1 diabetes in basal-bolus insulin regimens. Randomized controlled trials have demonstrated that glycemic control with insulin glargine is at least comparable to that with neutral protamine Hagedorn (NPH) insulin in adults and in children and adolescents, and with continuous subcutaneous insulin infusion in adults. However, these same trials show a significantly lower risk for hypoglycemia with insulin glargine compared with NPH insulin in adults.

Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects

In evolutionary terms, GH and intracellular STAT 5 signaling is a very old regulatory system. Whereas insulin dominates periprandially, GH may be viewed as the primary anabolic hormone during stress and fasting. GH exerts anabolic effects directly and through stimulation of IGF-I, insulin, and free fatty acids (FFA). When subjects are well nourished, the GH-induced stimulation of IGF-I and insulin is important for anabolic storage and growth of lean body mass (LBM), adipose tissue, and glycogen reserves. During fasting and other catabolic states, GH predominantly stimulates the release and oxidation of FFA, which leads to decreased glucose and protein oxidation and preservation of LBM and glycogen stores. The most prominent metabolic effect of GH is a marked increase in lipolysis and FFA levels. In the basal state, the effects of GH on protein metabolism are modest and include increased protein synthesis and decreased breakdown at the whole body level and in muscle together with decreased amino acid degradation/oxidation and decreased hepatic urea formation. During fasting and stress, the effects of GH on protein metabolism become more pronounced; lack of GH during fasting increases protein loss and urea production rates by approximately 50%, with a similar increase in muscle protein breakdown. GH is a counterregulatory hormone that antagonizes the hepatic and peripheral effects of insulin on glucose metabolism via mechanisms involving the concomitant increase in FFA flux and uptake. This ability of GH to induce insulin resistance is significant for the defense against hypoglycemia, for the development of "stress" diabetes during fasting and inflammatory illness, and perhaps for the "Dawn" phenomenon (the increase in insulin requirements in the early morning hours). Adult patients with GH deficiency are insulin resistant-probably related to increased adiposity, reduced LBM, and impaired physical performance-which temporarily worsens when GH treatment is initiated. Conversely, despite increased LBM and decreased fat mass, patients with acromegaly are consistently insulin resistant and become more sensitive after appropriate treatment.

Chronobiology in the endocrine system

Biological signaling occurs in a complex web with participation and interaction of the central nervous system, the autonomous nervous system, the endocrine glands, peripheral endocrine tissues including the intestinal tract and adipose tissue, and the immune system. All of these show an intricate time structure with rhythms and pulsatile variations in multiple frequencies. Circadian (about 24-hour) and circannual (about 1-year) rhythms are kept in step with the cyclic environmental surrounding by the timing and length of the daily light span. Rhythmicity of many endocrine variables is essential for their efficacy and, even in some instances, for the qualitative nature of their effects. Indeed, the continuous administration of certain hormones and their synthetic analogues may show substantially different effects than expected. In the design of drug-delivery systems and treatment schedules involving directly or indirectly the endocrine system, consideration of the human time organization is essential. A large amount of information on the endocrine time structure has accumulated, some of which is discussed in this review.

Effects of recombinant human IGF-I/IGF-binding protein-3 complex on glucose and glycerol metabolism in type 1 diabetes

Recombinant human IGF-I (rhIGF-I) complexed with its natural binding protein IGF-binding protein (IGFBP)-3 (rhIGF-I/IGFBP-3) is a novel formulation that has been shown to improve insulin sensitivity in type 1 diabetes, yet the mechanisms are not clear. We used stable isotopes to investigate the effects of rhIGF-I/IGFBP-3 on glucose and glycerol metabolism in type 1 diabetes. Fifteen subjects (age 13-24 years; 10 males) were studied on three occasions in random order. Each study period lasted for two days, and an injection of either placebo or rhIGF-I/IGFBP-3 (0.1-0.8 mg x kg(-1) x day (-1)) was given subcutaneously at 6:00 p.m. on days 1 and 2. Following the second injection, the subjects were kept euglycemic overnight by a variable rate insulin infusion, followed by a 4-h, two-step (insulin 0.6 and 1.5 mU x kg(-1) x min (-1)) hyperinsulinemic-euglycemic clamp. During the overnight basal steady state, rhIGF-I/IGFBP-3 dose-dependently reduced endogenous glucose production rate (R(a)) (P = 0.004), while peripheral glucose uptake (R(d)) was not different from placebo. The increase in glucose R(d) during hyperinsulinemic clamp was greater following rhIGF-I/IGFBP-3 than placebo, both during the first (P = 0.008) and second step (P = 0.008) of the clamp. No significant differences were found in glycerol R(a), a measure of lipolysis, between rhIGF-I/IGFBP-3 and placebo. In conclusion, rhIGF-I/IGFBP-3 enhances glucose metabolism by controlling both endogenous glucose output and peripheral glucose uptake.

Characteristics of basal insulin requirements by age and gender in Type-1 diabetes patients using insulin pump therapy

Establishment of appropriate basal insulin levels is an essential component of intensive insulin therapy. While the existence of a "dawn phenomenon" is widely recognized, the present study sought to establish whether diurnal basal insulin patterns exist in Type-1 diabetes, and whether these patterns vary by age and gender. Participant data was drawn from 322 Type-1 insulin pump users treated at a private diabetes education practice in suburban Philadelphia. All participants completed a battery of fasting tests designed to match basal insulin levels to endogenous glucose production and insulin sensitivity. Analysis of resultant basal patterns revealed significant differences between juvenile (age < or =20) and adult (age >20) basal insulin patterns. The younger group exhibited a more pronounced and sustained night-time peak; the older group exhibiting a briefer and less pronounced early-morning peak. Lower overall basal insulin requirements were found in the youngest (age < or =10) and oldest (age >60) groups. No noteworthy gender differences were found. Results can serve as a guide for clinicians when initiating and fine-tuning patients who utilize basal/bolus insulin therapy.

The Dawn Phenomenon Revisited: Implications for Diabetes Therapy

OBJECTIVE

To summarize current data on the magnitude, prevalence, variability, pathogenesis, and management of the dawn phenomenon in patients with diabetes mellitus.

METHODS

On the basis of the pertinent available literature and clinical experience, we propose a quantitative definition of the dawn phenomenon, discuss potential pathogenic mechanisms, and suggest management options.

RESULTS

The "dawn phenomenon" is a term used to describe hyperglycemia or an increase in the amount of insulin needed to maintain normoglycemia, occurring in the absence of antecedent hypoglycemia or waning insulin levels, during the early morning hours. To be clinically relevant, the magnitude of the dawn increase in blood glucose level should be more than 10 mg/dL or the increase in insulin requirement should be at least 20% from the overnight nadir. Controversy exists regarding the frequency, reproducibility, and pathogenesis of the dawn phenomenon. Approximately 54% of patients with type 1 diabetes and 55% of patients with type 2 diabetes experience the dawn phenomenon when the foregoing quantitative definition is used. The most likely pathogenic mechanism underlying the dawn phenomenon is growth hormone-mediated impairment of insulin sensitivity at the liver and muscles. The exact biochemical pathways involved are unknown. Therapeutic decisions aimed at correcting fasting hyperglycemia should take into account the variability and magnitude of the dawn phenomenon within individual patients. Successful insulinization appears to minimize the effects of the dawn phenomenon. Currently, no subcutaneous depot preparation of insulin exists that is capable of mimicking the basal insulinsecretion of the healthy pancreas.

CONCLUSION

Increases in the bedtime doses of hypoglycemic agents with nighttime peaks in action may correct early morning hyperglycemia but be associated with undesirable nocturnal hypoglycemia. Targeted continuous subcutaneous insulin infusion programming can facilitate the prevention of early morning hyperglycemia in selected patients.

Basal insulin therapy

The initiation of insulin therapy is a significant event for patients with diabetes and the physicians who care for them. Reluctance to begin insulin is multifactorial, with a major stumbling block being the perceived complexity of insulin. However, this complexity can be easily overcome by separation of insulin administration into its two components: basal and bolus therapy. An understanding of the role of basal insulin in the regulation of glucose and the development of strategies to implement basal insulin therapy can provide a transition that is rational and highly effective in most patients. The strategy also offers a unique approach to diabetes education, which permits a focused and patient-specific correction to glucose abnormalities.

Fasting hyperglycemia: etiology, diagnosis, and treatment

Suboptimal glycemic control in individuals with type 1 and type 2 diabetes mellitus is associated with an increased risk of microvascular and macrovascular complications. Even brief periods of hyperglycemia increase the risk of complications. Fasting hyperglycemia is a phenomenon that has been observed in essentially all individuals with diabetes and may be due to dysregulation of the normal circadian hormonal patterns resulting in increased hepatic glucose output. Controlling hepatic glucose output and disposal is essential for effectively managing fasting hyperglycemia. Fasting hyperglycemia generally can be attributed to inadequate or inappropriate hepatic insulinization or the dawn phenomenon (fasting hyperglycemia occurring in the absence of antecedent hypoglycemia). Less commonly, the Somogyi effect (marked fasting hyperglycemia following antecedent hypoglycemia) can cause fasting hyperglycemia. Accurate diagnosis with overnight home blood glucose monitoring is important in developing an appropriate treatment strategy. Manipulation of the individual's diet or oral agent therapy may be all that is required in some individuals to reduce fasting hyperglycemia. Hepatic glucose output and disposal in the fasting state may be controlled via bedtime administration of either an intermediate-acting insulin such as NPH or a long-acting true basal insulin such as insulin glargine. Attention to fasting hyperglycemia coupled with appropriate individualization of treatment should improve the long-term outcome of individuals with type 1 and type 2 diabetes by reducing the risk of complications. Normalization of the fasting blood glucose, through whatever strategy, minimizes glucotoxicity and insulin resistance, profoundly influences daytime glycemic control, and profoundly reduces the risk of the complications of diabetes.

Nocturnal hypoglycemia: clinical manifestations and therapeutic strategies toward prevention

OBJECTIVE

To review the features of nocturnal hypoglycemia and various preventive strategies.

METHODS

We discuss the physiologic changes, the potential precipitating factors, the immediate and long-term effects, and the currently available options for treatment of nocturnal hypoglycemia in patients with diabetes.

RESULTS

Nocturnal hypoglycemia is common in patients with type 1 diabetes and is usually asymptomatic. Nocturnal hyperinsulinemia frequently occurs with insulin therapy, and although blood glucose levels are often low during sleep, they are seldom measured routinely. Almost 50% of all episodes of severe hypoglycemia occur at night during sleep. Such episodes can cause convulsions and coma and have been implicated as a precipitating factor in cardiac arrhythmias resulting in sudden death--the "dead-in-bed syndrome." Nocturnal hypoglycemia seems to have no immediate detrimental effect on cognitive function; however, on the following day, mood and well-being may be adversely affected. Recurrent exposure to nocturnal hypoglycemia may impair cognitive function; other substantial long-term morbidity includes the development of acquired hypoglycemia syndromes, such as impaired awareness of hypoglycemia, through the putative effect of unsuspected recurrent episodes of nocturnal hypoglycemia.

CONCLUSION

In efforts to decrease the risk of nocturnal hypoglycemic episodes, various strategies can be used to minimize the nocturnal hyperinsulinemia that is associated with many insulin replacement regimens. Regular blood glucose monitoring (particularly at bedtime), the ingestion of appropriate bedtime snacks, and the utilization of short- and long-acting insulin analogues may all help to prevent or minimize the frequency of nocturnal hypoglycemia.

Hepatic glucose metabolism in humans--its role in health and disease

The liver is mainly responsible for maintaining normal concentrations of blood glucose by its ability to store glucose as glycogen and to produce glucose from glycogen breakdown or gluconeogenic precursors. During the last decade, new techniques have made it possible to gain further insight into the turnover of hepatic glucose and glycogen in humans. Hepatic glycogen varies from approximately 200 to approximately 450 mM between overnight fasted and postprandial conditions. Patients with type-1 diabetes (T1DM), type 2 diabetes (T2DM) or partial agenesis of the pancreas exhibit increased endogenous glucose production and synthesize only 25-45% of hepatic glycogen compared with non-diabetic humans. This defect can be partly restored in T1DM by combined long- and short-term optimized treatment with insulin. In T2DM, increased gluconeogenesis was identified as the main cause of elevated glucose production and fasting hyperglycaemia. These patients also exhibit augmented intracellular lipid accumulation which could hint at a link between deranged glucose and lipid metabolism in insulin-resistant states.

Insulin detemir is associated with more predictable glycemic control and reduced risk of hypoglycemia than NPH insulin in patients with type 1 diabetes on a basal-bolus regimen with premeal insulin aspart

OBJECTIVE

Insulin detemir is a soluble basal insulin analog with a unique mechanism of protracted action designed to reduce the variability associated with conventional basal insulins. This trial compared the glycemic control, risk of hypoglycemia, and effect on body weight of insulin detemir and NPH insulin in patients with type 1 diabetes treated with rapid-acting insulin aspart at meals.

RESEARCH DESIGN AND METHODS

This study was a 6-month multinational open parallel-group comparison conducted at 46 centers in five countries and included 448 patients with type 1 diabetes randomized 2:1 to insulin detemir or NPH insulin, respectively.

RESULTS

After 6 months, comparable HbA(1c) levels were found between the two treatment groups. Fasting plasma glucose tended to be lower in patients treated with insulin detemir, but this difference was not statistically significant (-0.76 mmol/l, P = 0.097). Within-subject variation in self-measured fasting blood glucose was lower with insulin detemir than with NPH insulin (SD 3.37 vs. 3.78 mmol/l, P < 0.001). Risk of hypoglycemia was 22% lower with insulin detemir than with NPH insulin (P < 0.05) and 34% lower for nocturnal (2300-0600) hypoglycemia (P < 0.005). Nightly plasma glucose profiles were smoother and more stable with insulin detemir (P = 0.05). Body weight was significantly lower with insulin detemir at the end of the trial (P < 0.001).

CONCLUSIONS

Treatment with insulin detemir resulted in more predictable glycemic control, with smoother plasma glucose profiles than NPH insulin and a significant reduction in the risk of hypoglycemia. The reduction in body weight with insulin detemir is a potential additional advantage. Regimens optimized for insulin detemir may be able to improve glycemic control beyond that possible with NPH insulin.

Continuous subcutaneous insulin infusion at 25 years: evidence base for the expanding use of insulin pump therapy in type 1 diabetes

Continuous subcutaneous insulin infusion (CSII) is used in selected type 1 diabetic subjects to achieve strict blood glucose control. A quarter of a century after its introduction, world-wide use of CSII is increasing. We review the evidence base that justifies this increase, including effectiveness compared with modern intensified insulin injection regimens and concern about possible complications. Review of controlled trials shows that, in most patients, mean blood glucose concentrations and glycated hemoglobin percentages are either slightly lower or similar on CSII versus multiple insulin injections. However, hypoglycemia is markedly less frequent than during intensive injection therapy. Ketoacidosis occurs at the same rate. Nocturnal glycemic control is improved with insulin pumps, and automatic basal rate changes help to minimize a prebreakfast blood glucose increase (the "dawn phenomenon") often seen with injection therapy. Patients with "brittle" diabetes characterized by recurrent ketoacidosis are often not improved by CSII, although there may be exceptions. We argue that explicit clinical indications for CSII are helpful; we suggest the principal indications for health service or health insurance-funded CSII should include frequent, unpredictable hypoglycemia or a marked dawn phenomenon, which persist after attempts to improve control with intensive insulin injection regimens. In any circumstances, candidates for CSII must be motivated, willing and able to undertake pump therapy, and adequately psychologically stable. Some diabetic patients with well-defined clinical problems are likely to benefit substantially from CSII and should not be denied a trial of the treatment. Their number is relatively small, as would therefore be the demand on funds set aside for this purpose.

Frequency of the dawn phenomenon in type 2 diabetes: implications for diabetes therapy

This study was designed to assess the frequency of the dawn phenomenon in patients with type 2 diabetes. A secondary aim was to examine the influence of varying treatment regimens on the frequency of the dawn phenomenon. The dawn phenomenon was defined as a rise in plasma glucose levels of > or = 0.5 mmol/L (10 mg/dL) between 0500 and 0900 h occurring after a growth hormone surge of > or = 5 microg/L. Sixteen subjects (six men, 10 women) with type 2 diabetes were studied overnight on their current mode of therapy in the General Clinical Research Center. Additionally, six of these subjects were restudied in random order after each of the following three therapeutic regimens: (1) 6 weeks of glipizide, (2) 6 weeks of bedtime NPH insulin, and (3) 3 days of intensive insulin therapy with multiple injections of regular insulin followed by assessment during overnight intravenous infusion of insulin. Thus, a total of 34 overnight studies were performed under various treatment conditions to provide an approximate frequency of the dawn phenomenon in type 2 diabetes. Blood was drawn every 30 min between midnight and 0800 h for measurement of glucose, insulin, C-peptide, and growth hormone levels. Additional counterregulatory hormone levels were determined during 24 of the studies, and the integrity of growth hormone secretion in response to insulin-induced hypoglycemia was assessed in 12 of the 16 patients. The subjects were aged 51 +/- 15 years with a body mass index of 31 +/- 5 kg/m(2) and a mean glycosylated hemoglobin of 8.1 +/- 1.2%. The dawn phenomenon occurred in only one of 34 (3%) studies. Moreover, the four different treatment regimens did not affect the frequency of occurrence of the dawn phenomenon. Ten of the 12 patients tested failed to secrete growth hormone in response to insulin-induced hypoglycemia. These data suggest that the dawn phenomenon is unusual in type 2 diabetes. Previously reported high prevalence rates in studies using similar sample size may be attributable to a Biostator-induced artifact. Decisions regarding therapies for type 2 diabetes should not be based on the assumption that the dawn phenomenon routinely causes early morning hyperglycemia.

Intensive diabetes management in pediatric patients

Intensive diabetes management requires frequent home glucose monitoring, multiple daily insulin injections or chronic subcutaneous insulin infusion, and adjustments of insulin doses in response to changes in blood glucose levels, food intake, and exercise. It also requires a periodic review of previous glucose results to recognize patterns of hyper- or hypoglycemia. The goals of intensive management are age dependent. In young children, avoidance of severe hypoglycemia is the major goal. In older children and adolescents, lowering hemoglobin A(1c) becomes an increasingly important goal. In children of all ages, the ability to have a flexible lifestyle and meal plan is often a priority. This article provides a brief overview of the rationale for implementing intensive diabetes management in pediatric patients, and practical guidelines for implementation.

Effects of short-term improvement of insulin treatment and glycemia on hepatic glycogen metabolism in type 1 diabetes

Insufficiently treated type 1 diabetic patients exhibit inappropriate postprandial hyperglycemia and reduction in liver glycogen stores. To examine the effect of acute improvement of metabolic control on hepatic glycogen metabolism, lean young type 1 diabetic (HbA1c 8.8 +/- 0.3%) and matched nondiabetic subjects (HbA1c 5.4 +/- 0.1%) were studied during the course of a day with three isocaloric mixed meals. Hepatic glycogen concentrations were determined noninvasively using in vivo 13C nuclear magnetic resonance spectroscopy. Rates of net glycogen synthesis and breakdown were calculated from linear regression of the glycogen concentration time curves from 7:30-10:30 P.M. and from 10:30 P.M. to 8:00 A.M., respectively. The mean plasma glucose concentration was approximately 2.4-fold higher in diabetic than in nondiabetic subjects (13.6 +/- 0.4 vs. 5.8 +/- 0.1 mmol/l, P < 0.001). Rates of net glycogen synthesis and net glycogen breakdown were reduced by approximately 74% (0.11 +/- 0.02 vs. 0.43 +/- 0.04 mmol/l liver/min, P < 0.001) and by approximately 47% (0.10 +/- 0.01 vs. 0.19 +/- 0.01 mmol/l liver/min, P < 0.001) in diabetic patients, respectively. During short-term (24-h) intensified insulin treatment, the mean plasma glucose level was not different between diabetic and nondiabetic subjects (6.4 +/- 0.1 mmol/l). Net glycogen synthesis and breakdown increased by approximately 92% (0.23 +/- 0.04 mmol/l liver/min, P = 0.017) and by approximately 40% (0.14 approximately 0.01 mmol/l liver/min, P = 0.011), respectively. In conclusion, poorly controlled type 1 diabetic patients present with marked reduction in both hepatic glycogen synthesis and breakdown. Both defects in glycogen metabolism are improved but not normalized by short-term restoration of insulinemia and glycemia.

Individualized low-dose growth hormone (GH) treatment in GH-deficient adults with childhood-onset disease: metabolic effects during fasting and hypoglycemia

Growth hormone (GH) has insulin-antagonistic effects, and GH secretion is augmented during fasting and hypoglycemia. In the present study, 10 patients aged 21 to 28 years with childhood-onset GH deficiency (GHD) were studied during a 24-hour fast and a hypoglycemic glucose clamp before and after 9 months of GH replacement. During the 24-hour fast, blood glucose, serum insulin, and serum free fatty acid (FFA) levels were measured. In the hypoglycemic clamp, the counterregulatory hormones (plasma catecholamines, serum glucagon, and serum cortisol), serum insulin-like growth factor (IGF) binding protein-1 (IGFBP-1), serum FFA, and glucose uptake were measured. The GH dose was adjusted to the response of serum IGF-I, and the median GH dose was 0.14 IU/kg/wk (range, 0.08 to 0.19). At the end of the study, serum IGF-I levels were normalized in all but one patient, in whom serum IGF-I was above the normal range. Nine months of GH treatment did not cause any significant changes in the blood glucose level, insulin to glucose ratio, or serum FFA level during the 24-hour fast, and none of the patients experienced hypoglycemia either before or after GH treatment. However, GH therapy resulted in increased insulin resistance during hypoglycemia, without changes in the counterregulatory hormonal responses, serum IGFBP-1, or serum FFA.

Bedtime uncooked cornstarch supplement prevents nocturnal hypoglycaemia in intensively treated type 1 diabetes subjects

OBJECTIVES

The present study tests two interrelated hypotheses: (1) that bedtime ingestion of uncooked cornstarch exerts a lower and delayed nocturnal blood glucose peak compared with a conventional snack; (2) that bedtime carbohydrate supplement, administered as uncooked cornstarch, prevents nocturnal hypoglycaemia without altering metabolic control in intensively treated type 1 diabetes (IDDM) patients.

DESIGN AND SUBJECTS

The above hypotheses were tested separately (1) by pooling and analysing data from two overnight studies of comparable groups of patients with non-insulin dependent diabetes mellitus (NIDDM) (14 and 10 patients, respectively), and (2) by a double-blind, randomized 4-week cross-over study in 12 intensively treated IDDM patients.

SETTING

Sahlgrenska University Hospital, Göteborg. Sweden.

INTERVENTIONS

(1) Ingestion of uncooked cornstarch and wholemeal bread (0.6 g of carbohydrates kg-1 body weight) and carbohydrate-free placebo at 22.00 h. (2) Intake of uncooked cornstarch (0.3 g kg-1 body weight) and carbohydrate-free placebo at 23.00 h.

MAIN OUTCOME MEASURES

(1) Nocturnal glucose and insulin levels; (2) frequency of self-estimated hypoglycaemia (blood glucose [BG] levels < 3.0 mmol L-1) at 03.00 h, HbA1c and fasting lipids.

RESULTS

Bedtime uncooked cornstarch ingestion led to a lower (2.9 +/- 0.5 vs. 5.2 +/- 0.6 mM, P = 0.01) and delayed (4.3 +/- 0.6 vs. 2.0 +/- 0.0 h, P < 0.01) BG peak, compared with a conventional snack, in NIDDM patients. Four weeks of bedtime uncooked cornstarch supplement, as compared with placebo, led to a 70% reduction in the frequency of self-estimated hypoglycaemia at 03.00 h (P < 0.05), without affecting HbA1c or fasting lipids in IDDM patients.

CONCLUSIONS

Uncooked cornstarch, ingested at bedtime, mimicked the nocturnal glucose utilization profile following insulin replacement, with a peak in blood glucose after 4 h. In IDDM patients, bedtime uncooked cornstarch supplement diminished the number of self-estimated hypoglycaemic episodes, without adversely affecting HbA1c and lipid levels. Hence, bedtime uncooked cornstarch ingestion may be feasible to prevent a mid-nocturnal glycaemic decline following insulin replacement in IDDM and, based on the nocturnal blood glucose profile, may also be preferable compared with conventional snacks.

Effects of low-dose recombinant human insulin-like growth factor-I on insulin sensitivity, growth hormone and glucagon levels in young adults with insulin-dependent diabetes mellitus

Despite recent interest in the therapeutic potential of recombinant human insulin-like growth factor-I (rhIGF-I) in the treatment of diabetes mellitus, its mechanism of action is still not defined. We have studied the effects of low-dose bolus subcutaneous rhIGF-I (40 microg/kg and 20 microg/kg) on insulin sensitivity, growth hormone (GH) and glucagon levels in seven young adults with insulin-dependent diabetes mellitus (IDDM) using a randomized double-blind placebo-controlled crossover study design. Each was subjected to a euglycemic clamp (5 mmol/L) protocol consisting of a variable-rate insulin infusion clamp (6:00 PM to 8:00 AM) followed by a two-dose hyperinsulinemic clamp (insulin infusion of 0.75 mU x kg(-1) x min(-1) from 8 to 10 AM and 1.5 mU x kg(-1) x min(-1) from 10 AM to 12 noon) incorporating [6,6 2H2]glucose tracer for determination of glucose production/utilization rates. Following rhIGF-I administration, the serum IGF-I level (mean +/- SEM) increased (40 microg/kg, 655 +/- 90 ng/mL, P < .001; 20 microg/kg, 472 +/- 67 ng/mL, P < .001; placebo, 258 +/- 51 ng/mL). Dose-related reductions in insulin were observed during the period of steady-state euglycemia (1 AM to 8 AM) (40 microg/kg, 48 +/- 5 pmol/L, P = .01; 20 microg/kg, 58 +/- 8 pmol/L, P = .03; placebo, 72 +/- 8 pmol/L). The mean overnight GH level (40 microg/kg, 9.1 +/- 1.4 mU/L, P = .04; 20 microg/kg, 9.6 +/- 2.0 mU/L, P = .12; placebo, 11.3 +/- 1.7 mU/L) and GH pulse amplitude (40 microg/kg, 18.8 +/- 2.9 mU/L, P = .04; 20 microg/kg, 17.0 +/- 3.4 mU/L, P > .05; placebo, 23.0 +/- 3.7 mU/L) were also reduced. No differences in glucagon, IGF binding protein-1 (IGFBP-1), acetoacetate, or beta-hydroxybutyrate levels were found. During the hyperinsulinemic clamp conditions, no differences in glucose utilization were noted, whereas hepatic glucose production was reduced by rhIGF-I 40 microg/kg (P = .05). Our data demonstrate that in subjects with IDDM, low-dose subcutaneous rhIGF-I leads to a dose-dependent reduction in the insulin level for euglycemia overnight that parallels the decrease in overnight GH levels, but glucagon and IGFBP-1 levels remain unchanged. The decreases in hepatic glucose production during the hyperinsulinemic clamp study observed the following day are likely related to GH suppression, although a direct effect by rhIGF-I cannot be entirely discounted.

Different effects of octreotide by continuous night infusion at increasing rate or by evening injections at different times on morning hyperglycemia and growth hormone levels in insulin-dependent diabetic patients

The effect of octreotide on morning hyperglycemia and GH levels was evaluated in eight insulin-dependent diabetic patients. Octreotide (50 mcg) was administered through subcutaneous injections at different hours (20:00, 22:00 and 24:00 h) or through continuous subcutaneous night infusion from midnight to 08:00 at increasing rate between 03:00 and 08:00 h. After octreotide injection at midnight we noticed a sharp decrease of both glycemia (p < 0.005) and GH (p < 0.05) at 04:00 h, but not at 08:00 h. Only the night continuous infusion at increasing rate was able to reduce glycemia and GH at 04:00 and at 08:00 h (p < 0.001 and p < 0.01 respectively). The injections of octreotide at 20:00 and 22:00 h lowered GH values at 24:00 h (p < 0.01 and p < 0.05 vs insulin alone) but did not show any significant effect on blood glucose levels and GH at 04:00 and 08:00 h. In conclusion, only the continuous subcutaneous night infusion of octreotide at increasing rate during the last hours of the night was able to reduce simultaneously morning hyperglycemia and GH levels in insulin-dependent diabetic patients, whereas evening subcutaneous injections at different times did not show any appreciable effect.

Blood glucose control on Sunday in IDDM patients: intensified conventional insulin therapy versus continuous subcutaneous insulin infusion

We have assessed the capacity of continuous subcutaneous insulin infusion (CSII) to maintain good blood glucose metabolic control on Sundays, when waking is delayed, with reference to intensified conventional insulin therapy by multiple daily injections (MDI). The study lasted 3 weeks, including 3 week-ends. A total of 20 IDDM patients were selected for metabolic control: ten were treated by CSII and ten by MDI. Blood glucose was determined at least three times a day (fasting on waking, pre-lunch and pre-dinner). The times of blood glucose determinations and their values were recorded in a memory reflectance meter. Waking, the first blood glucose measurement and the first insulin injection (MDI) or bolus (CSII) were about 1 h later on Sundays than on a weekday (44 +/- 4 min in MDI group, P < 0.04; and 59 +/- 7 min in CSII group, P < 0.02). The times of the pre-lunch and pre-dinner blood glucose determinations were not significantly different. The mean waking and pre-lunch blood glucose values of the MDI group were higher on Sundays (11.5 +/- 3.8 and 9.7 +/- 4.5 mmol/l) than on weekdays (8.7 +/- 2.3 and 7.1 +/- 2.5 mmol/1)(P < 0.01). The pre-prandial blood glucose levels of the CSII group on Sundays and weekdays were not statistically different at any time. Changes in the waking time and the subsequent delay in the first insulin bolus on Sunday may alter blood glucose control in patients on MDI, but CSII allows such changes without any glycemic side effects.

Insulin-like growth factor-I and diabetes. A review

Although diabetes is a heterogeneous condition, IGF-I has been shown to improve glycaemic control and reduce insulin requirements in both IDDM and NIDDM. In IDDM, the therapeutic rationale for IGF-I is as a replacement therapy "topping up" low circulating IGF-I levels. There is now convincing evidence that this is associated with a reduction in GH secretion resulting in an improvement in insulin sensitivity and glycaemic control. The mechanism may simply be reduced GH-secretion, but pre- and post-receptor effects on insulin sensitivity are also likely. It is not clear what effect IGF-I treatment has on IGF binding proteins, but with the restoration of a more normal GH/IGF-I axis they are likely to be restored to normal concentrations which may in turn have a direct effect on glucose metabolism. In NIDDM, the mechanism of action of IGF-I remains unclear. At high doses, IGF-I may mimic insulin, but at levels resulting in unacceptable "acromegalic" IGF-I levels and side-effects. The most exciting data concerning IGF-I is with a low dose where IGF-I improves insulin sensitivity by an unknown mechanism. This may be mediated via the IGF-I receptor, by cross-reactivity with the insulin receptor, or by activation of hybrid receptors. The exact mechanism and interaction remains to be elucidated. In severe insulin-resistant states, IGF-I-treatment appears to be effective, and may be the only realistic therapeutic measure in the near future, and warrants further investigation. Detailed genetic characterization of these syndromes following treatment with IGF-I may also help to characterize the mechanism of action of IGF-I and its interactions with the insulin receptor. Thus, IGF-I appears to have a future as a therapeutic agent in treating diabetes, but long-term studies addressing safety and short-term studies addressing mechanisms are essential. With only a few pharmaceutical companies having the capability to produce IGF-I for scientific and therapeutic investigation, it is important that short-term marketing strategy does not prevent the proper exploration of this exciting peptide hormone as a therapeutic agent for all types of diabetes.

Recombinant human insulin-like growth factor-I abolishes changes in insulin requirements consequent upon growth hormone pulsatility in young adults with type I diabetes mellitus

To investigate whether recombinant human insulin-like growth factor-I (rhIGF-I) has direct effects on the insulin requirement to maintain euglycemia independent of the growth hormone (GH) level, nine subjects with insulin-dependent diabetes mellitus ([IDDM] seven females; median (range) age, duration of diabetes, and hemoglobin A1C [HbA1C], 16.9 (12.5 to 21.9) years, 11.8 (4.6 to 16.8) years, and 9.8% (7.9% to 14.1%), respectively) underwent two euglycemic studies (6:00 PM to 8:00 AM) after double-blind subcutaneous administration of rhIGF-I/placebo (40 microg/kg). Octreotide infusion (300 ng/kg/h) suppressed endogenous GH, and three identical discrete GH pulses were infused on both nights. Variable-rate insulin infusion maintained euglycemia. Samples were taken every 15 minutes (glucose and GH), 30 minutes (insulin and intermediate metabolites), and 60 minutes (IGF-I and nonesterified fatty acids [NEFA]). Variables were analyzed during the steady-state period of euglycemia (4:00 to 8:00 AM). Data are expressed as the mean +/- SEM. The insulin infusion rate and free-insulin level were both significantly reduced after rhIGF-I administration (0.13 +/- 0.03 v placebo 0.23 +/- 0.05 mU/kg/min, P = .04, and 8.4 +/- 1.3 v placebo 12.1 +/- 1.4 mU/L, P = .03, respectively). GH pulse-related changes in the insulin requirement observed after placebo were not present after rhIGF-I. Glucagon levels were equally suppressed on both nights. Insulin clearance was not altered after rhIGF-I administration. NEFA and ketone levels also were not different on the 2 nights. In conclusion, in adolescents and young adults with diabetes, rhIGF-I administration directly affected insulin requirements independent of GH levels, but had no effect on fatty acid or ketone levels. This difference is related to the abolition of changes in the insulin requirement after GH pulses, and would suggest a complex interaction between GH and IGF-I on insulin action.

Characterization of the insulin-antagonistic effect of growth hormone in insulin-dependent diabetes mellitus

To characterize its insulin-antagonistic effect, growth hormone (GH) was infused at variable rates (24, 12 or 6 mU kg-1 min-1) for 1 h in 7 IDDM patients. Saline infusion was used as control (C) and all patients participated in all studies. The effect of insulin was measured with the euglycaemic clamp technique for 6 h combined with d-(3-3H)-glucose to evaluate glucose turnover. The insulin levels during the clamps were similar in all studies (23 +/- 3 mU l-1). The infusions produced peak GH levels of (24 rate = 24) 157 +/- 11, (12 rate = 12) 76 +/- 7, and (6 rate = 6) 45 +/- 8 mU l-1 (mean +/- SEM). The insulin-antagonistic effect of GH on glucose uptake was seen after 2 h and was at a maximum 4 to 5 h after the start of the GH infusion (difference in glucose infusion rate between C and 24 was 1.7 +/- 0.4 mg kg-1 min-1, p < 0.01). The resistance was due to a less pronounced effect of insulin to both inhibit rate of appearance and to stimulate rate of disappearance. Infusion of GH at 12 mU kg-1 min-1 induced a less pronounced insulin resistance both with regards to maximal effect (glucose infusion rate C - GH 1.4 +/- 0.5 mg kg-1 min-1, p < 0.05) and duration (3 h). At 6 mU kg-1 min-1, a clear GH-induced insulin-antagonistic effect was only seen during the third hour of the clamp (glucose infusion rate C-GH 1.3 +/- 0.5 mg kg-1 min-1, p < 0.05). GH infusion impaired the effect of insulin to lower both the levels of free fatty acids (NEFA) and glycerol between 2 and 5 h after the start of the infusion (NEFA, C:110 +/- 29, 24:303 +/- 95, p < 0.05: glycerol, C:32 +/- 4, 24:50 +/- 7 mumol l-1, p < 0.05). The present study therefore demonstrates that the insulin-antagonistic effect of GH in IDDM is related to the plasma levels both with regard to duration and response. The results also indicate that GH impairs the effect of insulin on lipolysis in IDDM after physiological peaks.

The effects of repeated daily recombinant human insulin-like growth factor I administration in adolescents with type 1 diabetes

Reduced insulin-like growth factor bioactivity has been linked to poor metabolic control and growth hormone hypersecretion in adolescents with Type 1 diabetes. The safety and efficacy of recombinant human insulin-like growth factor I administered subcutaneously in a dose of 40 micrograms kg-1 for 28 days was studied in a group of 6 adolescent male subjects with Type 1 diabetes (aged 13.6-19.4 years, puberty stage 3-5). After a 4-week run-in period (week -4 day 0) recombinant human insulin-like growth factor I was administered for 4 weeks (day 0 to week +4) before a run-out of a further 4 weeks duration (week +4 to +8). HbA1c levels were measured throughout the study and overnight profiles were undertaken to study levels of insulin-like growth factor 1, insulin-like growth factor binding protein-3, and growth hormone concentrations (week -1, day 0, and week +4). The injections were well tolerated and hypoglycaemia was not problematic at any stage of the study. Recombinant insulin-like growth factor I administration appeared to lead to a sustained increase in insulin-like growth factor I levels (week -1; 198 +/- 16 ng ml-1, week +4; 422 +/- 18 ng ml-1, mean +/- SEM; p = 0.03). Insulin-like growth factor binding protein-3 concentrations (n = 6) increased in 5 subjects (week -1; 4.5 +/- 0.3 micrograms ml-1, week +4; 5.1 +/- 0.4 micrograms ml-1) and mean overnight growth hormone decreased (week -1; 14.0 +/- 3.1 mUI-1, week +4; 7.6 +/- 1.7 mUI-1) during the period of study but these differences were not statistically significant. HbA1c levels fell significantly at the time of rhIGF-I administration (day 0; 10.4 +/- 1.9% vs week +4; 9.4 +/- 1.9%; p = 0.03) despite a reduction in subcutaneous isophane insulin dose from 0.50 +/- 0.02 U kg-1 to 0.41 +/- 0.02 U kg-1 (p = 0.03). There was no significant change in biochemical and haematological indices, glomerular filtration rate or urinary albumin excretion. The restoration of IGF-I levels in adolescents with Type 1 diabetes may have a beneficial impact on glycaemic control.

Insulin-like growth factors (IGFs) and IGF-I treatment in the adolescent with insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) during adolescence is associated with complex derangements of the growth hormone (GH)/insulin-like growth factor (IGF) axis. Despite GH hypersecretion, IGF-I levels and IGF bioactivity are reduced. The diabetogenic effects of GH are well established, and GH hypersecretion has been implicated in the deterioration in glycemic control during adolescence and in the development of microangiopathy. Insulin deficiency or reduced portal delivery of insulin plays a central role in the development of these abnormalities, and although continuous subcutaneous insulin delivery may improve plasma IGF-I levels, it does not necessarily suppress GH levels. Recombinant IGF-I has been proposed as an adjunct to conventional insulin therapy, as restoring circulating IGF-I levels might lead to GH suppression. Placebo-controlled studies have shown a consistent reduction in GH secretion and related improvements in insulin sensitivity following a single subcutaneous IGF-I injection (40 micrograms/kg). Repeated daily subcutaneous IGF-I administration for 1 month resulted in a sustained increase in IGF-I levels, as well as a reduction in GH secretion and insulin requirements. There was no increase in hypoglycemia or other adverse effects. Recombinant IGF-I used in conjunction with insulin may therefore provide an additional approach to the management of IDDM during adolescence, allowing correction of abnormalities in the GH/IGF axis and leading to improved control and, hence, reduced risk of long-term complications. However, this hypothesis needs to be rigorously tested in long-term placebo-controlled studies.

The effects of recombinant insulin-like growth factor I administration on growth hormone levels and insulin requirements in adolescents with type 1 (insulin-dependent) diabetes mellitus

Type 1 (insulin-dependent) diabetes mellitus in adolescence is associated with reduced levels of insulin-like growth factor I, elevated growth hormone concentrations and insulin resistance. In order to determine whether restoring insulin-like growth factor I levels to normal might lead to a reduction in growth hormone levels and insulin requirements, we undertook a double-blind placebo controlled study of a single s.c. dose of recombinant insulin-like growth factor I (40 micrograms/kg body weight) in nine late pubertal subjects with Type 1 diabetes. After administration of placebo or insulin-like growth factor I at 18.00 hours, a variable rate insulin infusion was used to maintain euglycaemia overnight. Plasma insulin-like growth factor I, growth hormone, free insulin, and intermediate metabolite concentrations were monitored throughout the study. Recombinant insulin-like growth factor I led to a rise in plasma concentrations which reached a peak at 5.5 h (413.1 +/- 28.2 ng/ml, mean +/- SEM). Mean growth hormone levels between 20.00 and 08.00 hours were significantly reduced after recombinant insulin-like growth factor I (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; p = 0.01), as were the insulin requirements for euglycaemia (0.25 +/- 0.02 compared with 0.31 +/- 0.04 mU.kg-1.min-1; p = 0.03). Plasma free insulin levels were lower after recombinant insulin-like growth factor I administration (31.9 +/- 2.7 compared with 67.9 +/- 16.0 mU/l; p = 0.001) but no significant differences in ketone or lactate levels were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cigarette smoking and of a transdermal nicotine delivery system on glucoregulation in type 2 diabetes mellitus

The effect of nicotine absorbed transdermally from a patch (TNS) and from cigarette smoking on insulin secretion and action in Type 2 diabetes has been compared. Twelve Type 2 diabetic smoking patients, aged 51 y, with diabetes for 9 y, treated either with diet and/or oral hypoglycaemic agents, were studied on three occasions, according to a double-blind, placebo-controlled, cross-over design. The subjects were investigated 12 h after their last cigarette or application of one patch of TNS 30 cm2 or TNS placebo, or whilst smoking their usual cigarette. Insulin secretion was assessed by a glucagon (1 mg IV) stimulation test. On a second occasion, insulin action was assessed by a hyperglycaemic-hyperinsulinaemic clamp, the spontaneous hyperglycaemia of the fasting state (8.61 mmol.l-1) being maintained during a 4 h insulin infusion (at 0.1 mU.kg-1.min-1 for the initial 2 h, and 1 mU.kg-1.min-1 during the last 2 h). TNS and the cigarette did not affect endogenous insulin secretion as compared to placebo. During the initial 2 h of the clamp study, plasma insulin increased from 88 to 155 pmol.l-1, hepatic glucose production (3-3H-glucose) was less suppressed after TNS (4.31 mumol.kg-1.min-1) than after placebo (2.5 mumol.kg-1.min-1), but was more suppressed than after cigarette smoking (5.61 mumol.kg-1.min-1). In the last 2 h of the clamp (plasma insulin 646 pmol.l-1), glucose utilization was less stimulated after TNS (36.1 mumol.kg-1.min-1) vs placebo (39.8 mumol.kg-1.min-1), but more than after cigarette smoking (33.6 mumol.kg-1.min-1), primarily because of a decrease in glucose storage.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of cancer cachexia and abnormal glucose metabolism in humans with cancer

In 1919, glucose intolerance became the earliest recognized metabolic abnormality in cancer patients. Prior to the development of severe malnutrition, colon, gastric, sarcoma, endometrial, prostate, localized head, neck, and lung cancer patients had many of the metabolic abnormalities of type II (noninsulin dependent) diabetes mellitus. These metabolic abnormalities include glucose intolerance, an increase in both hepatic glucose production (HGP) and glucose recycling, and insulin resistance. In a study of over 600 cancer patients, a diabetic pattern of glucose tolerance test was noted in over one-third of the patients. An increased rate of HGP, commonly seen in diabetics, has been noted in almost all types of cancer patients studied to date. Etiology of the increased glucose production in the cancer patient is not known, but abnormalities in the counter regulatory hormones, especially growth hormone, may contribute to the development of abnormal glucose metabolism. A second possible stimulus for the increase in HGP could be the glucose needs of the tumor. Abnormally high glucose utilization rates in small amounts of tumor tissue have recently been described. This suggests that small tumors may have large needs for glucose calories. An increase in anaerobic glycolysis in the tumor tissue can increase lactate production in the tumor-bearing human, thus supplying substrate to the liver to increase glucose production rates. In this paper, the nature of abnormal glucose metabolism in cancer patients is described.