Correction: Sundaram et al. Effects of Intermediate Frequency (150 kHz) Electromagnetic Radiation on the Vital Organs of Female Sprague Dawley Rats. Biology 2023, 12, 310

In the original publication [...].

Grading Acanthosis Nigricans Using a Smartphone and Color Analysis: A Novel Noninvasive Method to Screen for Impaired Glucose Tolerance and Type 2 Diabetes

Objective

The objective of this study was to develop ANcam, a novel method for identifying acanthosis nigricans (AN) using a smartphone camera and computer-aided color analysis for noninvasive screening of people with impaired glucose tolerance (IGT).

Research Design and Methods

Adult and juvenile participants with or without diagnosed type 2 diabetes were recruited in Trinidad and Tobago. After obtaining informed consent, participants' history, demographics, anthropometrics, and A1C were collected and recorded. Three subject matter experts independently graded pictures of the posterior neck and upper back using the ANcam smartphone application and Burke methods. A correlation matrix investigated 25 color channels for association with hyperpigmentation, and the diagnostic thresholds were determined with a receiver operating characteristic curve analysis.

Results

For the 227 participants with captured images and A1C values, the cyan/magenta/yellow/black (CMYK) model color channel CMYK_K was best correlated with IGT at an A1C cutoff of 5.7% (39 mmol/mol) (R = 0.45, P <0.001). With high predictive accuracy (area under the curve = 0.854), the cutoff of 7.67 CMYK_K units was chosen, with a sensitivity of 81.1% and a specificity of 70.3%. ANcam had low interrater variance (F = 1.99, P = 0.137) compared with Burke grading (F = 105.71, P <0.001). ANcam detected hyperpigmentation on the neck at double the self-reported frequency. Elevated BMI was 2.9 (95% CI 1.9-4.3) times more likely, elevated blood pressure was 1.7 (95% CI 1.2-2.4) times more likely, and greater waist-to-hip ratio was 2.3 (95% CI 1.4-3.6) times more likely with AN present.

Conclusion

ANcam offers a sensitive, reproducible, and user-friendly IGT screening tool to any smartphone user that performs well with most skin tones and lighting conditions.

Effects of Intermediate Frequency (150 kHz) Electromagnetic Radiation on the Vital Organs of Female Sprague Dawley Rats

Exposure to electromagnetic radiation (EMR) from intermediate frequency sources has increased exponentially in recent years. The consequences of this exposure on biological systems are prompting scientists to study the effects on human health. This current study aimed to determine the effects of intermediate frequency (150 kHz) EMR exposure on the vital organs of female Sprague Dawley rats. The EMR group (n = 10 animals) was exposed to a frequency of 150 kHz with an intensity of 65 ± 15 μW/cm2 for two months. The control group (n = 10 animals) was exposed to an intensity of 35 ± 15 nW/cm2. Haematological, histochemical, gross, and histopathological profiles of all major organs of all animals were then performed using standard procedures. All major organs generally showed no significant detectable effects in either the control or EMR groups. However, gross and histopathological examinations revealed the effects of EMR on the liver and lungs, which showed inflammatory changes without significant biochemical/haematological manifestations. In addition, a significant increase in serum sodium level and a decrease in serum urea level were also observed in the EMR group. It can be concluded that the current frequency and duration of exposure trigger the changes in the liver and lungs but are not sufficient to cause clinical and functional manifestations. Therefore, a long-term exposure study might be helpful to determine the effects of 150 kHz IF EMR on these organs.

A cross-sectional study to determine the prevalence of obesity and other risk factors for type 2 diabetes among school children in Trinidad, West Indies

BACKGROUND

Our previous work has shown that type 2 diabetes mellitus is a problem in the school-aged population of Trinidad, West Indies. The current study evaluated the prevalence in this population of selected risk factors for diabetes, viz: obesity, family history of diabetes and acanthosis nigricans.

OBJECTIVE

To assess the prevalence of the following risk factors for type 2 diabetes (T2DM) in school children in Trinidad: obesity, family history of diabetes in first- or second-degree relatives and the presence of acanthosis nigricans (AN).

METHODS

A cross-sectional survey was performed among school children aged 7-18 years from September 2009 to June 2010. A convenience sample was selected from a random sample of 32 schools drawn from all educational districts. A self-administered questionnaire was employed to record family history, gender and ethnicity. AN was assessed and scored clinically at the neck and obesity was measured by anthropometry and bio-impedance.

RESULTS

There were 2130 participants in the study. Fifteen per cent were obese and 17% were overweight. Primary school children had a higher prevalence of obesity (22·9% vs 11·0%) and overweight (20·0% vs 15·6%) than secondary school children (P<0·05). A greater proportion of males than females had combined overweight/obesity as measured by BMI for age (35·8 vs 29·4%, P<0·05). The overall prevalence of AN was 43·4%. However, just over 18% of all school children have a degree of AN greater than grade 2, which clinically is readily recognisable. Females displayed this physical sign more commonly than males (P<0·05). The prevalences of a family history of diabetes in first- and second-degrees relatives were 11·0% and 1·1%, respectively. Forty-three per cent had one risk factor for diabetes, 23·1% had two and 2·9% had three.

CONCLUSION

Risk factors for T2DM are very common among school children in Trinidad. More than 40% had at least one risk factor. Strategies aimed at reducing risk factors for T2DM, especially obesity, among Trinidadian school children are urgently warranted.

Monitoring of International Diabetes Federation-recommended Clinical Diabetes Indicators in a Public Health Centre in Southwest Trinidad

OBJECTIVES

To examine availability of International Diabetes Federation (IDF)-recommended diabetes indicators in the medical charts of patients in active care at a public health centre in southwest Trinidad and Tobago, and to determine clinical status of the patient population according to Caribbean Health Research Council/Pan American Health Organization (CHRC/PAHO) guidelines for disease control.

METHODS

Data were extracted from the medical records of consecutive patients with diagnosed diabetes who presented for routine care at the health centre over a seven-month period. The three most recent dates and results for the following clinical indicators were extracted: glycated haemoglobin (HbA1c), blood pressure, lipid panel, random blood sugar and weight.

RESULTS

Data were extracted from 486 patient medical records (91% of patients who presented for care). The majority of records, 366 (76%), had one of three recommended IDF indicators of HbA1c, blood pressure or low-density lipoprotein (LDL) in the past year, 58 (12%) had two, 55 (11%) had three and seven (1%) had no indicators recorded. Random blood sugar and blood pressure were recorded in 93% of records, while only 20% had an HbA1c reported in the past year. The vast majority of patients did not meet guidelines for control of blood sugar, blood pressure or cholesterol. Due to a non-standardized HbA1c assay, rate of controlled HbA1c, based on CHRC/PAHO clinical guidelines, could not be determined.

CONCLUSIONS

Although availability of indicators suggests an increase from prior audits reported in the literature, current reporting patterns challenge optimal patient management and future systematic evaluation of trends in diabetes care and outcomes.

Association of the KCNJ11 variant E23K with type 2 diabetes in Indo-Trinidadians

OBJECTIVE

To examine the effect of genetic variation in KCNJ11 on the risk of Type 2 diabetes mellitus in Trinidadians.

METHODS

The coding and bordering intron-exon regions of the KCNJ11 gene were sequenced in 168 diabetic and 61 non-diabetic subjects who historically were thought to be of South Asian Indian ancestry as well as 66 diabetic and 59 non-diabetic subjects of African ancestry. Allele and haplotype frequency differences were calculated between cases and controls and linkage equilibrium was assessed across the KCNJ11 region.

RESULTS

We identified novel missense mutations in both subject groups including A94P and R369C in a diabetic Indo-Trinidadian subject, S113G in a non-diabetic Indo-Trinidadian subject, and S118L in a diabetic Afro-Trinidadian subject. It is unknown if these mutations are pathogenic as other family members were not available for study. Additionally, the common variant E23K was associated with Type 2 diabetes in the Indo-Trinidadian group (OR = 1.797 [1.148-2.814], p = 0.0098).

CONCLUSIONS

Rare variants in KCNJ11 are segregating in the Indo- and Afro-Trinidadian populations and further studies are needed to determine their contribution, if any, to the overall prevalence of diabetes in these groups. Common variants such as E23K may increase the risk in the Indo-Trinidadian population.

Prevalence of the metabolic syndrome in patients with diabetes mellitus

BACKGROUND

Metabolic syndrome (MetS) is a vascular risk factor with prevalence in the general population of 17-25%.

AIM

To determine the prevalence of MetS in patients with diabetes mellitus (DM).

METHODS

A total of 200 patients [18% type 1 (T1DM), 82% type 2 (T2DM)] attending for annual review were studied. Standard blood tests were requested. Blood pressure and waist circumference were measured. Adult Treatment Panel III (ATP III) criteria for diagnosis of MetS were applied.

RESULTS

A total of 122 (61%) patients had MetS. More patients with T2DM (69.5%) than TIDM (22.2%) had MetS. Despite treatment of DM (100%), hypertension (69.5%) and dyslipidaemia (48.3%), 114 patients (57%) still met the criteria for MetS at time of study.

CONCLUSIONS

Most T2DM patients have MetS but it is uncommon in T1DM. Despite treatment, almost half of patients still met the criteria for MetS. Aggressive treatment of MetS components is required to reduce cardiovascular risk in DM.

Insulin promoter factor-1 mutations and diabetes in Trinidad: identification of a novel diabetes-associated mutation (E224K) in an Indo-Trinidadian family

This study investigated the prevalence of insulin promoter factor-1(IPF-1) mutations in familial early-onset diabetes mellitus in Trinidad. We screened 264 unrelated subjects with type 2 diabetes diagnosed before 40 yr of age and a family history of diabetes for mutations in the minimal promoter and coding region of the IPF-1 gene (IPF1). This study population included 169 patients of East Indian descent (Indo-Trinidadians), 66 of African descent (Afro-Trinidadians), and 29 of mixed ancestry. We identified five IPF1 variants, including one new missense mutation E224K, the previously described diabetes-associated duplication P242 P243dupP, two silent mutations in the codons for Leu54 (c.162G>A) and Ala256 (c.768C>A), and a substitution in the 5'-untranslated region (c.-18C>T). The E224K mutation was found in two unrelated diabetic Indo-Trinidadians and 0 of 60 controls. It was present on the same haplotype in both patients suggesting a founder effect. The E224K mutation cosegregated with early-onset diabetes or impaired glucose tolerance in a large family, suggestive of the type 4 form of maturity-onset diabetes of the young rather than type 2 diabetes. Functional studies of E224K showed reduced transactivation activity. IPF1 mutations leading to synthesis of a mutant protein may contribute to the development of familial early-onset diabetes/maturity-onset diabetes of the young in Indo-Trinidadians.

Early-onset Type II diabetes mellitus in Italian families due to mutations in the genes encoding hepatic nuclear factor 1 alpha and glucokinase

AIMS/HYPOTHESIS

Maturity-onset-diabetes of the young (MODY) is caused by mutations in at least five different genes. Our aim was to determine the prevalence of the most common MODY genes in Italian families with early-onset Type II (non-insulin-dependent) diabetes mellitus.

METHODS

We screened 28 Italian early-onset Type II diabetic families (diagnosis < 35 years) for mutations in the hepatic nuclear factor-4 alpha, (MODY1), glucokinase (MODY2) and hepatic nuclear factor-1 alpha (MODY3). Both strands of exons, flanking introns and minimal promoter regions of the above-mentioned genes were amplified using polymerase chain reaction and were sequenced directly.

RESULTS

We identified four different mutations, three of which are not described, (W113X, G42P43fsCC --> A, H514R) and four new polymorphisms (G184G, T513T, IVS3-nt47delG, IVS1- nt53C --> G) in the hepatic nuclear factor-1 alpha gene, two new potential mutations (G44S, IVS4nt + 7C --> T) and three new polymorphisms (promoter-nt84C --> G, IVS9 + nt8C --> T, IVS9 + nt49G --> A) in the glucokinase gene, and a new polymorphism (IVS1c-nt11T --> G) in the hepatic nuclear factor-4 alpha gene.

CONCLUSION/INTERPRETATION

Mutations in the hepatic nuclear factor-1 alpha and glucokinase are associated with Type II diabetes in 14 % and 7 % of Italian families, respectively. Our findings provide an impetus for screening Italian MODY and early-non Type II diabetic families for mutations in the above mentioned genes to identify relatives at risk who could benefit from primary prevention care. [

Molecular genetics of diabetes mellitus in Chinese subjects: identification of mutations in glucokinase and hepatocyte nuclear factor-1alpha genes in patients with early-onset type 2 diabetes mellitus/MODY

AIMS

To examine the prevalence of identified MODY-related genes in Chinese subjects with early onset Type 2 diabetes mellitus and a positive family history of diabetes and to look for possible associations between the gene mutations and the development of diabetes.

METHODS

Ninety-two unrelated Chinese subjects with diabetes diagnosed before the age of 40 years who had a positive family history of diabetes were screened for mutations in hepatocyte nuclear factors (HNF-1alpha and HNF-4alpha) and glucokinase genes by direct sequencing. The family members of patients with mutations and 100 healthy controls were also examined.

RESULTS

Mutations in the HNF-1alpha and the glucokinase genes were found in 5% and 3% of the diabetic subjects, respectively but no mutations were found in the coding region of the HNF-4alpha gene. Three mutations found in the glucokinase gene were novel missense mutations (I110T, A119D and G385V). The mutations in the HNF-1alpha gene were also new and included four missense mutations (G20R, R203H, S432C, I618M) and one splice acceptor site mutation (IVS2nt-1G-->A). Patients with mutations in these genes were clinically heterogeneous with respect to phenotype and basal pancreatic beta cell function.

CONCLUSIONS

Genetic factors such as mutations in the HNF-1alpha and glucokinase genes may be important in the development of diabetes in Chinese people, especially when the disease is of early onset.

Basal insulin hypersecretion in insulin-resistant Zucker diabetic and Zucker fatty rats: role of enhanced fuel metabolism

The biochemical mechanisms responsible for basal hyperinsulinemia in insulin-resistant states have not been fully defined. We therefore studied pancreatic beta-cell function in vitro to characterize the relative importance of fuel metabolism or secretion via a constitutive pathway in the maintenance of high basal insulin secretion in Zucker diabetic fatty (ZDF) and Zucker fatty (ZF) rats. Insulin secretion from ZF (10+/-1.8 v 5+/-0.6 pmol/ng DNA/h) and ZDF (30+/-4 v 7+/-0.8 pmol/ng DNA/h) islets at 2.8 mmol/L glucose was two to four times greater than secretion from islets of lean littermate control rats. In response to a decreasing glucose concentration (from 12 to 0 mmol/L), a paradoxical increase in insulin secretion was observed in perfused ZDF rat pancreas. Insulin secretion at 2.8 mmol/L glucose was suppressed approximately 70% to 80% in islets from ZDF and ZF rats following exposure to diazoxide, a K+-adenosine triphosphate (K(ATP)) channel opener that inhibits membrane depolarization, or rotenone and oligomycin, agents that inhibit ATP production, or by incubation at 23 degrees C. Inhibition of glycolysis with mannoheptulose, 2-deoxyglucose, and iodoacetate or fatty acid oxidation with a carnitine palmitoyltransferase I inhibitor also significantly inhibited basal insulin secretion in islets of ZDF and ZF rats but not their lean littermates. Furthermore, the glycolytic flux at 2.8 mmol/L glucose was significantly higher in ZDF islets versus ZDF lean littermate (ZLC) islets (2.2+/-0.1 v 3.7+/-0.3 pmol/ng DNA/2 h, P < .01) and was suppressed by mannoheptulose. In ZDF and ZF islets, high basal insulin secretion was maintained despite a 50% reduction in the rate of proinsulin/insulin biosynthesis at 2.8 mmol/L glucose. The rate of proinsulin to insulin conversion and the ratio of proinsulin to insulin secretion by islets of ZDF rats were similar to the values in the lean littermates. Thus, basal hypersecretion in these two insulin-resistant models appears to be related to enhanced fuel metabolism rather than the contribution of a constitutive pathway of secretion.

Adaptation to hyperglycemia enhances insulin secretion in glucokinase mutant mice

The present study was undertaken to test the hypothesis that exposure to high glucose concentrations enhances insulin secretion in pancreatic islets from glucokinase-deficient mice. Insulin secretion and intracellular calcium ([Ca2+]i) were measured as the glucose concentration was increased from 2 to 26 mmol/l in islets from heterozygous glucokinase (GK)-deficient mice (GK+/-) and their wild-type littermates (GK+/+). Results obtained in islets incubated in 11.6 or 30 mmol/l glucose for 48-96 h were compared. GK+/- islets that had been incubated in 30 mmol/l glucose showed improved although not normal insulin secretory and [Ca2+]i responses to the standard glucose challenge as well as an enhanced ability to sense small amplitude glucose oscillations. These effects were associated with increased glucokinase activity and protein. In contrast, exposure of GK+/+ islets to 30 mmol/l glucose increased their basal insulin secretion but reduced their incremental secretory responses to glucose and their ability to detect small amplitude glucose oscillations. Thus exposure of GK+/- islets to 30 mmol/l glucose for 48-96 h enhanced their ability to sense and respond to a glucose stimulus, whereas similar exposure of GK+/+ islets induced evidence of beta-cell dysfunction. These findings provide a mechanistic framework for understanding why glucokinase diabetes results in mild hyperglycemia that tends not to increase over time. In addition, the absence of one allele of the glucokinase gene appears to protect against glucose-induced beta-cell dysfunction (glucose toxicity).

A missense mutation, Val62Ala, in the glucokinase gene in a Norwegian family with maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a form of diabetes mellitus characterized by autosomal dominant inheritance, onset usually before 25 y of age and a primary defect in glucose-stimulated insulin secretion. It is a heterogeneous disorder both with respect to aetiology and clinical features. Mutations in the genes encoding the glycolytic enzyme glucokinase, the liver-enriched transcription factors, hepatocyte nuclear factor-1alpha (HNF-1alpha), HNF-1beta and HNF-4alpha, and the transcription factor, insulin promoter factor-1 (IPF-1) have all been associated with MODY. Here, we report a family, Norway-2 (N2), characterized by the presence of a mild, complication-free form of diabetes with autosomal dominant inheritance. Sequencing of the glucokinase gene in the proband revealed a T-to-C mutation in codon 62 which resulted in a valine-to-alanine substitution, designated Va162Ala (V62A). The V62A mutation, which has not been previously reported, cosegregated with diabetes in the N2 family. The results presented here indicate that the glucokinase form of MODY occurs in Norway. Moreover, screening the glucokinase gene for mutations in other families with clinical features similar to those of the N2 family could lead to improved treatment for patients with this form of diabetes.

Deletion and site-directed mutagenesis of the ATP-binding motif (P-loop) in the bifunctional murine ATP-sulfurylase/adenosine 5'-phosphosulfate kinase enzyme

The P-loop is a common motif found in ATP- and GTP-binding proteins. The recently cloned murine ATP-sulfurylase/adenosine 5'-phosphosulfate (APS) kinase contains a P-loop (residues 59-66) in the APS kinase portion of the bifunctional protein. A series of enzymatic assays covering the multiplicity of functions of this unique protein (reverse ATP-sulfurylase, APS kinase, and an overall assay) were used to determine the effect of deleting or altering specific residues constituting this motif. In addition to the full-length cDNA construct (1MSK), two deletion mutants that progressively shortened the N terminus by 34 amino acids (2MSK) and 70 amino acids (3MSK) were designed to examine the effects of translation initiation before (2MSK) and after (3MSK) the P-loop. The 2MSK protein possessed sulfurylase and kinase activity equivalent to the full-length construct, but 3MSK exhibited no kinase activity and reduced sulfurylase activity. In light of the evident importance of this motif, a number of site-directed mutants were designed to investigate the contribution of key residues. Mutation of a highly conserved lysine in the P-loop to alanine (K65A) or arginine (K65R) or the following threonine (T66A) to alanine ablated APS kinase activity while leaving ATP-sulfurylase activity intact. Three mutations (G59A, G62A, and G64A) addressed the role of the conserved glycines as follows: G64A showed diminished APS kinase activity only, whereas G62A had no effect on either activity. G59A caused a significant decrease in ATP-sulfurylase activity without effect on APS kinase activity. A series of highly conserved flanking cysteines (Cys-53, Cys-77, and Cys-83) were mutated to alanine, but none of these mutations showed any effect on either enzyme activity.

[Non-insulin dependent diabetes in children and adolescents]

Maturity-onset diabetes of the young (MODY) is a clinically and genetically heterogenous disorder characterized by autosomal dominant inheritance with onset usually before 25 years of age, and a primary defect in glucose-stimulated insulin secretion. Genetic analyses have shown that mutations in at least five different genes can cause MODY. These are the genes encoding the glycolytic enzyme glucokinase, three liver-enriched transcription factors, hepatocyte nuclear factor (HNF)-1 alpha, HNF-1 beta and HNF-4 alpha, and the gene encoding the transcription factor, insulin promoter factor-1 (IPF-1). Patients with MODY3 run a considerable risk of developing diabetic eye disease. MODY2, related to glucokinase deficiency, is a relatively benign disorder which does not usually require insulin. Experiences with the three other MODY forms have so far been restricted to very few families. We present the first Norwegian family with MODY2. Furthermore, a previously published Norwegian family is shown to be MODY3. Subjects who fulfil the criteria of MODY can, by genetic testing, gain information important for prognosis and perhaps also for therapy.

Maturity-onset diabetes of the young due to a mutation in the hepatocyte nuclear factor-4 alpha binding site in the promoter of the hepatocyte nuclear factor-1 alpha gene

Recent studies have shown that mutations in the transcription factor hepatocyte nuclear factor (HNF)-1 alpha are the cause of one form of maturity-onset diabetes of the young (MODY3). These studies have identified mutations in the mRNA and protein coding regions of this gene that result in the synthesis of an abnormal mRNA or protein. Here, we report an Italian family in which an A-->C substitution at nucleotide-58 of the promoter region of the HNF-1 alpha gene cosegregates with MODY. This mutation is located in a highly conserved region of the promoter and disrupts the binding site for the transcription factor HNF-4 alpha, mutations in the gene encoding HNF-4 alpha being another cause of MODY (MODY1). This result demonstrates that decreased levels of HNF-1 alpha per se can cause MODY. Moreover, it indicates that both the promoter and coding regions of the HNF-1 alpha gene should be screened for mutations in subjects thought to have MODY because of mutations in this gene.

Hepatic function in a family with a nonsense mutation (R154X) in the hepatocyte nuclear factor-4alpha/MODY1 gene

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous monogenic disorder characterized by autosomal dominant inheritance, onset usually before 25 yr of age, and abnormal pancreatic beta-cell function. Mutations in the hepatocyte nuclear factor(HNF)-4alpha/MODY1, glucokinase/MODY2, and HNF-1alpha/MODY3 genes can cause this form of diabetes. In contrast to the glucokinase and HNF-1alpha genes, mutations in the HNF-4alpha gene are a relatively uncommon cause of MODY, and our understanding of the MODY1 form of diabetes is based on studies of only a single family, the R-W pedigree. Here we report the identification of a second family with MODY1 and the first in which there has been a detailed characterization of hepatic function. The affected members of this family, Dresden-11, have inherited a nonsense mutation, R154X, in the HNF-4alpha gene, and are predicted to have reduced levels of this transcription factor in the tissues in which it is expressed, including pancreatic islets, liver, kidney, and intestine. Subjects with the R154X mutation exhibited a diminished insulin secretory response to oral glucose. HNF-4alpha plays a central role in tissue-specific regulation of gene expression in the liver, including the control of synthesis of proteins involved in cholesterol and lipoprotein metabolism and the coagulation cascade. Subjects with the R154X mutation, however, showed no abnormalities in lipid metabolism or coagulation except for a paradoxical 3.3-fold increase in serum lipoprotein(a) levels, nor was there any evidence of renal dysfunction in these subjects. The results suggest that MODY1 is primarily a disorder of beta-cell function.

Changes in pancreatic islet glucokinase and hexokinase activities with increasing age, obesity, and the onset of diabetes

We examined changes in high- and low-Km glucose phosphorylating activity in pancreatic islet extracts from the prediabetic Zucker diabetic fatty (ZDF) rat between 5-6 weeks and 12 weeks of age (after the onset of diabetes). Comparisons were made between the activity observed in the ZDF rat and that seen in the ZDF lean control (ZLC) rat and the obese nondiabetic Zucker fatty (ZF) rat. At 5-6 weeks of age, insulin resistant ZDF and ZF rats were hyperinsulinemic, compared with the ZLC rat, but had normal plasma glucose levels. Kinetic parameters (Vmax and Km for glucose) of hexokinase (HK) and Km of glucokinase (GCK) did not differ between groups. Islet GCK activity for ZDF and ZF rats was 1.7-fold greater than in ZLC rats (P < 0.02 and P < 0.001, respectively). By 12 weeks of age, hypersecretion of insulin at 5.0 mmol/l glucose was observed in perifused islets from both obese groups relative to the ZLC rat. Islets from ZDF rats failed to increase insulin secretion in response to increased glucose concentration. Group differences in the kinetic parameters for GCK or in the Km values for HK were not significant. Islet HK activity for ZDF and ZF rats was 1.9-fold (P < 0.05) and 1.7-fold (P < 0.05) greater, respectively, than for ZLC rats. Compared with the 5- to 6-week-old animals, HK activity increased 3.1-fold (P < 0.001), 2.5-fold (P < 0.002), and 2.0-fold (P < 0.05) for ZDF, ZF, and ZLC rats, respectively. Differences in GCK activity between 5- to 6- and 12-week-old rats were not significant for any of the groups. We conclude: 1) increased islet glucose phosphorylating activity is present in insulin resistant and hyperinsulinemic ZF and ZDF rats, relative to the ZLC rat; 2) at 12 weeks of age, hyperinsulinemic ZDF and ZF rats demonstrated significant increases in HK activity, compared with lean controls; and 3) deficiency in GCK activity does not explain failure of diabetic ZDF islets to respond to glucose, since differences between diabetic ZDF and nondiabetic ZF rats were not statistically significant. Increases in pancreatic islet phosphorylating activity seem to be important in maintaining basal hyperinsulinemia in insulin-resistant animals, but do not appear to play a role in the progression to glucose intolerance and diabetes.

Starvation reduces pyruvate dehydrogenase phosphate phosphatase activity in rat kidney

Pyruvate dehydrogenase complex (PDC) from rat kidney or pig heart previously inactivated by phosphorylation (PDHP) was activated in vitro by PDHP phosphatase from kidneys of starved or fed rats. Starvation for 48 h of the rats from which the PDC was prepared led to a decrease in the rate of activation of PDC at early time periods (< 2 min), particularly at submaximal concentrations of Mg2+. Using intact permeable kidney mitochondria incubated for 15 sec, it was found that starvation of rats more than doubled the Mg2+ concentration at which the half maximal increment of PDC activity (PDCa) was observed. Reduction of PDHP phosphatase activity due to starvation was also apparent when phosphatase was separated from PDC and recombined with PDC from the same or different animals. Intraperitoneal injection of insulin and glucose 1 h before sacrifice of starved rats prevented the reduction of PDHP phosphatase activity whether or not protein synthesis was inhibited. The effect of insulin in restoration of PDHP phosphatase activity of starved rats was not mimicked by 5-methylpyrazole 3-carboxylic acid, an inhibitor of lipolysis. When renal PDHP phosphatase was incubated with pig heart PDC in the presence of 10 mM Mg2+ and 0.1 mM Ca2+ the increment in PDCa, in 1 min was 30% of fully activated PDC activity (PDCt) observed after 15 min. Removal of divalent cations did not affect the increment in 1 min but prevented further increments. Conversely okadaic acid diminished 1 min increment but did not disturb PDCt. It is suggested that the different behaviour of renal PDC from fed and starved animals may partly be due to different divalent cation independent PDHP phosphatase activity.