Biomedical subjects

M A Permutt

Publications and source records attributed to M A Permutt.

At least 127 records · Page 7Linked to original sources

PubMed1987

Linkage analysis of the human insulin receptor gene and maturity onset diabetes of the young.

The cloning of the insulin receptor cDNA has permitted the definition of restriction fragment length polymorphisms at that locus. These polymorphisms were used to study the role of the insulin receptor in four pedigrees with maturity onset diabetes of the young through linkage analyses. When each pedigree was individually analysed, no linkage was demonstrated in the two larger pedigrees, implying that an insulin receptor defect was not responsible for the predisposition to diabetes in these pedigrees. One of these pedigrees was known to be hypoinsulinaemic, while insulin levels were unavailable in the second pedigree. In the two smaller pedigrees, however, a single haplotype cosegregated with diabetes. One of these pedigrees is known to be hyperinsulinaemic. The small size of the pedigrees which demonstrated cosegregation precluded statistical proof of linkage. Nonetheless, the presence of an uncommon insertional polymorphism which cosegregated with diabetes in both pedigrees was improbable and suggested that this insertion could be responsible for diabetes in these families. This study thus may be additional evidence for heterogeneity in maturity onset diabetes of the young. For the two larger pedigrees, the insulin gene and HLA region have already been eliminated as genetic markers. This study provides data which eliminate a third candidate gene in these two pedigrees.

Diabetes Mellitus, Type 2↗

PubMed1987

Genetic susceptibility to diabetes in inbred strains of mice: measurements of proinsulin mRNA and response to dexamethasone.

The insulin resistance produced by the recessive db mutation has led to more severe diabetes in C57BL/KsJ mice relative to that in C57BL/6J mice, suggesting genetic differences between the two strains affecting insulin production or insulin action. To assess these parameters blood glucose, serum insulin, pancreatic insulin, and proinsulin mRNA were measured in both normal and diabetic (db/db) KsJ and 6J strains. The mice were compared at 5 weeks of age, prior to the development of insulin lack known to occur with age in KsJ db/db mice. As a further provocation to insulin production, another group of the normal and db/db mice were given dexamethasone for 4 days. In normal mice there were no strain differences in blood glucose, serum insulin, pancreatic insulin, or proinsulin mRNA. Dexamethasone, presumably by augmenting insulin resistance, induced increases in serum insulin and proinsulin mRNA to the same extent in KsJ and 6J mice. In db/db mice, while blood glucose, serum insulin, and proinsulin mRNA were considerably higher than in normal mice, there were no strain differences observed. After dexamethasone the db/db mice exhibited strain differences which included higher blood glucose and higher serum insulin levels in KsJ mice. These findings were compatible with greater insulin resistance in KsJ than in 6J db/db mice. While dexamethasone treatment increased serum insulin in KsJ db/db mice, there was no augmentation of proinsulin mRNA in either strain, suggesting a limit to the insulin synthesis. Analysis of serum insulin/glucose and proinsulin mRNA/glucose ratios demonstrated a dexamethasone-induced increase in serum insulin/glucose in normal and diabetic mice of both strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Quantitative analysis of pancreatic proinsulin mRNA in genetically diabetic (db/db) mice.

C57BL/KsJ db/db mice develop hyperphagic obesity and nonketotic diabetes similar to non-insulin-dependent diabetes mellitus in humans. Initially the mice demonstrate an abundant beta-cell mass and hyperinsulinemia, which is followed by apparent beta-cell loss. As an index of insulin synthesis, this study assesses pancreatic proinsulin mRNA, measured by dot hybridization to cloned cDNA, during the development of diabetes in the mice. Changes in proinsulin mRNA from 5 to 13 wk of age are compared with serum insulin, pancreatic insulin content, and blood glucose. In control (+/db) mice, total proinsulin mRNA and pancreatic insulin content increased with age. Both changes were proportional to an increase in body weight. Obesity, hyperglycemia, and hyperinsulinemia were evident in diabetic (db/db) mice at 5 wk of age. Although pancreatic insulin content was comparable to that in the +/db controls at 5 wk, a fourfold relative elevation of proinsulin mRNA was observed. Despite an increase in body weight, proinsulin mRNA concentration and total proinsulin mRNA fell to levels similar to those of the control mice at 10 and 13 wk, associated with a loss of hyperinsulinemia, a mild decrease in pancreatic insulin content, and a marked increased in fasting blood glucose. A separate group of db/db mice was pair fed with the +/db controls from 4 to 13 wk. These diet-restricted diabetic mice were heavier than control mice and gained weight with age, but they weighed less than the unrestricted mice at all ages. Compared with the unrestricted db/db mice, a more modest fasting hyperglycemia was apparent, and a persistent hyperinsulinemia was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Multiple restriction fragment length polymorphisms at the insulin receptor locus: a highly informative marker for linkage analysis.

Although resistance to insulin action is a well-studied phenomenon in non-insulin-dependent diabetes and certain genetic syndromes, the role of inherited defects of the insulin receptor in these disorders is unknown. To facilitate the evaluation of that role, restriction fragment length polymorphisms (RFLPs) were identified using various portions of the insulin receptor cDNA to examine digested DNA from American Blacks, Pima Indians, and Caucasians. Five RFLPs were identified in Caucasians. Two of these were detected with a single 1.3-kilobase probe in Rsa I digests with minor allele frequencies of 0.48 and 0.23. An additional RFLP was noted with Bgl II and two more RFLPs with Sac I using a different 1.6-kilobase probe, with minor allele frequencies of 0.17 for Bgl II and 0.12 for both Sac I RFLPs. All RFLPs except for the second Sac I RFLP were present in American Blacks, while only the Rsa I RFLPs were present in Pima Indians. Pairwise analysis showed random association between all sites except for the Bgl II and second Rsa I sites, where the disequilibrium statistic, delta, was -0.70 (different from 0 at P less than 0.001). No association of any RFLP was noted with non-insulin-dependent diabetes in a small population. These studies show that this is a highly informative locus that should be important for mapping of chromosome 19p and for linkage studies.

Black People↗

PubMed1986

Evidence for increased recombination near the human insulin gene: implication for disease association studies.

Haplotypes for four new restriction site polymorphisms (detected by Rsa I, Taq I, HincII, and Sac I) and a previously identified DNA length polymorphism (5' FP), all at the insulin locus, have been studied in U.S. Blacks, African Blacks, Caucasians, and Pima Indians. Black populations are polymorphic for all five markers, whereas the other groups are polymorphic for Rsa I, Taq I, and 5' FP only. The data suggest that approximately equal to 1 in 550 base pairs is variant in this region. The polymorphisms, even though located within 20 kilobases, display low levels of nonrandom association. Population genetic analysis suggests that recombination within this 20-kilobase segment occurs 24 times more frequently than expected if crossing-over occurred uniformly throughout the human genome. These findings suggest that population associations between DNA polymorphisms and disease susceptibility genes near the insulin gene or structural mutations in the insulin gene will be weak. Thus, population studies would probably require large sample sizes to detect associations. However, the low levels of nonrandom association increase the information content of the locus for linkage studies, which is the best alternative for discovering disease susceptibility genes.

Black People↗

PubMed1986

Identical transcription initiation sites for proinsulin messenger ribonucleic acid in three insulin-expressing tissues.

Proinsulin mRNA was analyzed by RNA blot hybridization from four insulin-expressing tissues of the rat, including adult and fetal pancreas, yolk sac, and an insulinoma cell line (RIN 5F). The proinsulin mRNA transcripts from the insulinoma cell line and fetal pancreatic tissue were estimated to be, respectively, 100 and 50 bases larger than the transcript from adult pancreas. Yolk sac proinsulin mRNA comigrated with the fetal transcript. While glucose is an important regulator of proinsulin mRNA in the adult, there is a marked increase in the concentrations of proinsulin mRNA and insulin in the developing rat, although plasma glucose levels are quite low. Expression of proinsulin mRNA independent of glucose levels is also found in insulinoma tissue. In addition, there is a second TATA sequence upstream of the putative start site in rat insulin II gene, and the transcription initiation site(s) has not been mapped in all of these tissues. These observations suggested that alternative transcription initiation sites may place the genes under different promoter control during development. To map the 5' end of the gene, primer extension was performed using a synthetic oligonucleotide primer complementary to the first 20 bases of the coding portion of the rat insulin I gene. The extended products of the proinsulin mRNAs from adult insulinoma cell line and fetal pancreas were identical and consistent in size with those predicted if transcription occurs at the putative start site. The 3' ends of the proinsulin mRNA transcripts were evaluated by ribonuclease H digestion, and it was shown that the noted size differences could be accounted for by different lengths of 3'-polyadenylation. Northern blot analysis of proinsulin mRNA from animals treated under conditions where mRNA varied from low to high levels failed to show any modulation of polyadenylation. The role of polyadenylation of proinsulin mRNA in the physiological regulation of insulin biosynthesis, if any, is currently unknown.

Animals↗

PubMed1985

The genetics of type I and type II diabetes: analysis by recombinant DNA methodology.

Susceptibility to IDDM is linked to the HLA-D locus on the short arm of chromosome 6, a region believed to be involved in the process of communication between cells which determines immune responses. Presumably an HLA molecule encoded by this region, unable to present a particular antigenic pathogen to the immune system, is inherited. The HLA-DR locus is quite complex, however. The gene which codes for this defective molecule may be identified by a combination of use of monoclonal antibodies and cloned gene probes which specifically hybridize to various portions of this region. Investigators are searching for HLA-DR4 containing chromosomes in IDDM which show similar patterns of restriction enzyme polymorphism. Hopefully, complete structural analysis of these related sequences will provide information about the mechanisms which confer susceptibility to develop IDDM. A strong genetic component is involved in NIDDM evidenced by a high concordance in monozygotic twins. Nevertheless, there is much evidence of genetic heterogeneity. At the present time no clear cut genetic marker has been defined. The human insulin gene has been cloned and by Southern blot hybridization analysis of peripheral leukocyte DNA, the insulin gene locus is being evaluated as a possible contributor to the genetic defect. Population studies at the present time have not identified any particular polymorphic insulin allele associated with NIDDM. Population studies are complicated by heterogeneity of NIDDM, racial and ethnic differences, and heterogeneity of insulin alleles. Linkage analysis in family studies will provide an alternative approach to population studies to determine what role if any the insulin gene plays in the genetic component of this disease. Because NIDDM is heterogeneous and perhaps polygenic in nature, these linkage analyses in families with NIDDM can be extended to other genes when they are cloned such as that coding for the insulin receptor. The familial aggregation of diabetes has long been noted (see ref. 1 for review). In relatives of diabetics, the prevalence ranges from 10-30%, while it is variously estimated to be between 0.1-3% in the general population. But familial aggregation of a trait may be caused either by genetic or environmental factors. One approach to dissecting the contribution of these factors is the study of concordance in twins. Pyke and associates observed that overall identical twins always show a higher concordance rate than dizygotic twins, irrespective of their age of diagnosis. Furthermore, they noted that identical twins of younger onset are often discordant for diabetes while identical twins of older onset are usually concordant.(ABSTRACT TRUNCATED AT 400 WORDS)

Alleles↗

PubMed1985

Evaluation of rat insulin messenger RNA in pancreatic and extrapancreatic tissues.

The purpose of these studies was to determine whether insulin detected immunochemically in extrapancreatic tissues of the adult rat is synthesized in situ by quantitating mRNA in these tissues. A blot hybridization assay was utilized with cloned 32P-proinsulin cDNA. The lower limit of detection was estimated to be 3pg. Proinsulin mRNA concentration was found to be 1000-1500 micrograms in isolated pancreatic islets and was easily detected in total pancreatic RNA at 10-15 pg/micrograms. Proinsulin mRNA was quantitated in rat insulinoma cells adapted to culture at levels 1:50 those in normal islets. Samples of RNA (20-50 micrograms) enriched about 50-fold for mRNA sequences by repeated oligo-deoxythymidylate chromatography were assayed. No insulin mRNA was detected in 50 micrograms samples of RNA from brain or in 20 micrograms samples from subsections of brain or other extrapancreatic tissues. RNA samples were undegraded as assessed by ability to stimulate protein synthesis in a cell-free system. Proinsulin mRNA from pancreas as added to brain homogenates and recovered intact. Brain RNA samples with insulin mRNA levels 1:1000 that of pancreas would be predicted to have 50-75 pg proinsulin mRNA/50 micrograms sample assayed if present. Because none was found, brain must have a concentration less than 1:6,000 that of pancreas. These findings suggest that immunoassayable insulin detected in extrapancreatic tissues of the adult rat is synthesized by the pancreas.

Animals↗

PubMed1985

Modulation of proinsulin messenger RNA after partial pancreatectomy in rats. Relationships to glucose homeostasis.

These studies of partial pancreatectomy assess pancreatic proinsulin messenger RNA (mRNA) levels as an index of in vivo insulin biosynthesis, and show relationships to glucose homeostasis. Rats were subjected to sham operation, 50% pancreatectomy (Px), or 90% Px, and were examined after 1, 3, or 14 wk. Proinsulin mRNA was measured by dot hybridization to complementary DNA. After 50% Px there was a nearly complete adaptation of proinsulin mRNA. After 90% Px a marked increase of proinsulin mRNA occurred, but it was insufficient and it was not maintained with time. The deficit in insulin production is related to development of hyperglycemia. Sham-operated controls showed no worsening of fasting or fed blood glucose or of intraperitoneal glucose tolerance within the period of observation. Total proinsulin mRNA and pancreatic insulin content rose in proportion to body weight. 50% Px produced no change from controls in body weight or blood glucose. The concentration of proinsulin mRNA in the 50% pancreatic remnant paralleled that of controls after 1 and 3 wk, but then increased after 14 wk, such that total proinsulin mRNA approached control levels. This adaptive response was reflected by changes in serum insulin, but not by pancreatic insulin content, which was only 30% of control after 14 wk. Intraperitoneal glucose tolerance was impaired mildly, and did not worsen with time after pancreatectomy. 90% Px led to elevated fed blood glucose and reduced serum insulin after 3 wk, and fasting hyperglycemia was seen after 14 wk. Proinsulin mRNA concentration in the 10% pancreatic remnant showed an adaptive increase after 1 and 3 wk, such that total proinsulin mRNA reached 40% of control. After 14 wk, however, remnant proinsulin mRNA concentration was no longer increased; total proinsulin mRNA and pancreatic insulin content were severely reduced. Intraperitoneal glucose tolerance was impaired more dramatically than with the 50% Px animals, and worsened with time after operation. These observations indicate ability to increase proinsulin mRNA levels as an adaptation to pancreatectomy. Insufficiency of this adaptation is associated with the development of hyperglycemia, and the loss of this adaptation correlates with a worsening of glucose tolerance.

Age Factors↗

PubMed1985

New polymorphisms at the insulin locus increase its usefulness as a genetic marker.

Polymorphic sites adjacent to known genes can be used to examine the segregation of a disease relative to that gene in families, or to map the gene of interest relative to other loci. The polymorphic region 5' to the human insulin gene (5' FP) permits such analysis, but the three size classes previously identified are insufficient for many studies. More alleles are identified with restriction enzymes that generate small fragments (Pvu II). Nonetheless, sufficient polymorphism for informative family analyses is often not present. To facilitate such analyses, we searched for other polymorphisms in over 20 KB of DNA at the insulin locus in Pima Indians, American Blacks, and Caucasians. The previously described allelic variant at a Pst I site in the 3'-untranslated portion of the gene was not polymorphic in any race. An upstream Hinc II site (-62 BP) was present in only 48% of Black alleles, but was not polymorphic in Pima Indians or Caucasians. New polymorphisms were found at a Taq I site (-11,000 BP) and a Rsa I site (-13,000 BP). The Taq I site was present in 89% of Black alleles, 87% of Pima Indian alleles, and 84% of Caucasian alleles. In contrast, the Rsa I site was present in 60% of Black and Caucasian alleles, but in only 47% of Pima Indian alleles. The Hinc II, Rsa I, and Taq I sites show no obvious linkage with each other or the 5' FP. A fourth polymorphism, previously identified with Sac I, was found to be the creation of a new Sac I site at +2500 BP in 10% of Black alleles.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗

PubMed1985

Insulin gene analysis in a family with maturity-onset diabetes of the young.

The insulin gene locus has been studied in a large kindred with maturity-onset diabetes of the young (MODY) characterized by hypoinsulinemia. DNA was isolated from peripheral leukocytes of 42 family members and 5 spouses. A highly polymorphic region in the 5'-flanking portion of the human insulin gene provided an opportunity for linkage analysis. The presence of three different length polymorphisms of + 1600 base pairs (bp), - 50 bp, and - 150 bp different from the common size allele allowed haplotype assignment of insulin alleles. The hypothesis of linkage was tested by calculating the log of the ratio of the likelihood of the hypothesis of linkage to that of the hypothesis of nonlinkage (LOD score) at a given recombination distance between the insulin polymorphism and the diabetes locus. At a recombination frequency of 0.0, the LOD score was - 14.50 and, therefore, the hypothesis of tight linkage can be strongly rejected. This report is the third study of the relationship between the insulin locus and MODY; however, it is the first report in which a formal linkage analysis indicates with a high degree of probability no linkage between the insulin locus and hypoinsulinemia in a family. Because MODY is a heterogeneous disorder, it may be that different genotypes result in a composite phenotype. The lack of linkage between an insulin allele and MODY in a total of four families studied, however, suggests that the insulin locus is probably not a marker for the MODY phenotype. These results do not exclude the possibility that the insulin locus may be involved in the etiology of other forms of NIDDM.

Adolescent↗

PubMed1985

Impaired insulin biosynthetic capacity in a rat model for non-insulin-dependent diabetes. Studies with dexamethasone.

These studies of a rat model for non-insulin-dependent diabetes mellitus (NIDDM) were performed to determine whether hyperglycemia occurs when capacity to synthesize insulin is exceeded. The neonatal streptozocin (STZ)-treated rat has acute hyperglycemia with marked destruction of pancreatic beta-cells, followed by gradual regeneration to 50-70% normal beta-cell number. At age 4 wk, fed serum glucose concentration is only mildly elevated relative to controls. With age, the rats become progressively hyperglycemic, and by 12 wk they have marked impairment of glucose-stimulated insulin release. In these studies, dexamethasone (0.125 mg/kg/day for 4 days) was administered to control and to STZ-treated animals to produce insulin resistance. The relationship between insulin biosynthesis and serum glucose concentrations was assessed. In control rats, response to dexamethasone was similar at both 4 and 12 wk. Serum glucose levels and pancreatic insulin concentration remained unchanged. Both insulin biosynthetic rates (as measured by 3H-leucine incorporation into proinsulin) and proinsulin mRNA levels increased twofold. STZ-treated rats at age 4 wk demonstrated mild hyperglycemia. Dexamethasone injection resulted in an increase in insulin biosynthesis and proinsulin mRNA in these animals, while serum glucose did not increase. STZ-treated rats at 12 wk showed more profound hyperglycemia (serum glucose 315 +/- 38 mg/dl versus control, 187 +/- 12 mg/dl). A marked rise in serum glucose (to 519 +/- 42 mg/dl) was observed after 4 days of dexamethasone injection. Pancreatic insulin content became severely depleted relative to saline-injected, STZ-treated animals, and there was no response of levels of proinsulin mRNA.

Animals↗

PubMed1985

Islet beta-cell function and polymorphism in the 5'-flanking region of the human insulin gene.

The present study investigates the possible relationship between human beta-cell secretory capacity and polymorphism in the 5'-flanking region of the human insulin gene. The glucose potentiation slope was measured in normal and non-insulin-dependent diabetic subjects (NIDDM). This slope, as reported previously (Ward, W. K., et al., Am. J. Physiol. 1984; 246:E405-11), is an index of the ability of hyperglycemia to potentiate the insulin response to arginine and as such is a measure of beta-cell responsiveness to glucose. Restriction enzyme analysis using a human insulin gene probe was performed on leukocyte DNA isolated from the same individuals. We conclude that a 1.6 kb polymorphism in the 5'-flanking region of the human insulin gene in both normal and NIDDM subjects has no association with insulin secretory responses as defined here by the glucose potentiation slope.

Adult↗

PubMed1985

Lack of association of the polymorphic locus in the 5'-flanking region of the human insulin gene and diabetes in American blacks.

A polymorphic region 5' to the human insulin gene has been associated with diabetes in earlier studies. This polymorphic region is composed of tandem repeats that fall into 3 general size classes, designated class 1 (600 base pairs), class 2 (1300 base pairs), and class 3 (2500 base pairs). Frequencies of these classes of alleles vary among racial groups. American Blacks have been underrepresented in published studies of insulin gene polymorphism and diabetes. We undertook a cooperative study between two centers (San Francisco and St. Louis) to determine geno-types at the insulin locus in 313 unrelated American Blacks (132 nondiabetic, 27 with IDDM, and 154 with NIDDM). In both centers, nondiabetic individuals were younger and leaner than NIDDM patients. Allelic and genotypic frequencies at the insulin locus were not different between the two centers. Class 1 alleles represented 60% of all alleles, class 2 alleles 11%, and class 3 29%. No class of insulin allele was associated with NIDDM in this study. Subdivision of the study population by obesity, family history, or age at diagnosis failed to detect a subgroup for which the insulin allele was associated with NIDDM. Only 27 IDDM individuals were studied, and no significant association of class 1 alleles with this group was noted. However, examination of more IDDM individuals is required before a definitive statement can be made. Fasting serum triglyceride levels were determined retrospectively in 50 NIDDM individuals. No differences in triglyceride levels among genotypes were noted. The frequency of class 3 alleles in 13 hypertriglyceridemic NIDDM subjects was not different from that of the whole group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Hyperproinsulinemia in a family with a proposed defect in conversion is linked to the insulin gene.

Two previously described pedigrees with familial hyperproinsulinemia have elevated proinsulin conversion intermediates resulting from amino acid substitutions in the proinsulin molecule. In contrast, a third family with elevated levels of an apparently normal proinsulin molecule may have a defect in the converting process. To determine if the defect in this family lies in the insulin gene region, we used restriction fragment length polymorphisms adjacent to the insulin gene to examine cosegregation with hyperproinsulinemia. We demonstrate linkage of hyperproinsulinemia and the insulin gene in this family with a LOD score of 1.8, suggesting that the defect lies in or near the insulin gene. This method has wide applicability in determining whether hyperproinsulinemia or hyperinsulinemia is the result of defects at the insulin gene, and should permit the detection of new defects at or near this locus.

Alleles↗

PubMed1985

Glucose regulated insulin biosynthesis in isolated rat pancreatic islets is accompanied by changes in proinsulin mRNA.

Isolated rat pancreatic islets were incubated in high (28 mM) or low (2.8 mM) glucose for 0, 1 or 4 hr and insulin biosynthesis and messenger RNA quantified. During the 4 hr course of the experiments the fraction of protein synthesised specifically into proinsulin increased in the presence of high vs low glucose (14.3 +/- 3.7 vs 0.8 +/- 0.5%, p less than 0.01). The relative amount of proinsulin mRNA was found to be about 5-fold higher in islets incubated in high glucose at 4 hr as determined by RNA blot hybridization. Total translatable islet mRNA was unaffected by glucose in the medium. These data extend observations of changes in proinsulin mRNA in rats in vivo during fasting and glucose injection, and suggest a direct effect of glucose on islets. These data further demonstrate that glucose modulates selectively the level of proinsulin mRNA during incubation of isolated pancreatic islets and that changes in the level of proinsulin mRNA play an important role in regulation of insulin biosynthesis.

Animals↗

PubMed1984

An in vivo analysis of pancreatic protein and insulin biosynthesis in a rat model for non-insulin-dependent diabetes.

The purpose of these experiments was to estimate insulin biosynthesis in vivo in a rat model for non-insulin-dependent diabetes. Insulin biosynthesis rates were determined in 4-wk-old animals that had been injected with 90 mg/kg of streptozotocin 2 d postpartum. Control and diabetic animals did not differ in body weight or fasting plasma glucose. Fed plasma glucose was significantly elevated (186 +/- 13 micrograms/dl vs. 139 +/- 7 mg/dl, P less than 0.05) and pancreatic insulin content was reduced (41 +/- 2 micrograms/g vs. 63 +/- 8 micrograms/g, P less than 0.05) in the diabetic rats. Insulin biosynthesis was estimated in vivo by measuring and comparing [3H]leucine incorporation into proinsulin with that into total pancreatic protein 45 min after injection. Insulin biosynthesis was 0.391 +/- 0.07% of pancreas protein synthesized in control rats and 0.188 +/- 0.015% (P less than 0.05) in diabetic rats. In animals of the same age, the fractional and absolute rate of pancreatic protein synthesis were determined. Total pancreatic protein synthesis was not reduced in streptozotocin treated animals (185.5 +/- 14.1%/d vs. 158.6 +/- 14.9%/d, NS) but was markedly reduced in control rats after a 48-h fast (to 70.8 +/- 5.5%/d, P less than 0.01). Because total pancreatic protein synthesis was not decreased in the diabetic rats, the decrease in the fraction of radiolabel incorporated into insulin seems to represent an absolute decrease in the rate of insulin biosynthesis in this animal model for diabetes. Through RNA blot hybridization with 32P-labeled cloned rat insulin complementary DNA, proinsulin messenger RNA (mRNA) was estimated as the rate of insulin biosynthesis in control and diabetic animals. There was a 61% reduction in proinsulin mRNA at 4 wk and an 85% reduction at 7 wk (P less than 0.001) in the diabetic animals. After streptozotocin injection in neonatal rats, there is marked beta-cell damage and hyperglycemia. Beta-cell regeneration occurs with return to normoglycemia, but with age hyperglycemia develops. The reduction in insulin synthesis and proinsulin mRNA seemed disproportionate with the more modest reduction in beta-cell number. The importance of these observations is that, in this animal model, diabetes is associated with a limited ability to regenerate beta-cell mass and to synthesize insulin. The relationship between the defect in glucose-stimulated insulin release and impaired insulin biosynthesis has yet to be determined.

Animals↗

PubMed1984

Polymorphism in the 5' flanking region of the human insulin gene. Relationships with noninsulin-dependent diabetes mellitus, glucose and insulin concentrations, and diabetes treatment in the Pima Indians.

Variations in DNA sequences flanking the insulin gene were studied in relation to noninsulin-dependent diabetes mellitus (NIDDM) in 87 unrelated Pima Indians at least 35 yr of age. DNA was isolated from nuclei of peripheral blood leukocytes and digested with restriction endonucleases. Less variation in this region was found in Pima Indians than in other racial groups previously studied. Only two classes of alleles (classes 1 and 3) were found, and there was virtually no variation within classes. At least one class 3 allele was found in 47% of the 38 nondiabetic subjects and in 37% of the 49 with NIDDM (odds ratio = 0.65, P = 0.4, 95% confidence interval for the odds ratio = 0.25 to 1.67). Homozygosity for class 3 alleles, however, was found only in diabetics. There were no differences according to genotype in obesity, fasting or postload glucose or insulin concentrations, or in the relationships between insulin and glucose concentrations. 61% (11/18) of the diabetics with a class 3 allele were receiving drug treatment for diabetes compared with only 26% (8/31) of diabetics without a class 3 allele (P = 0.03). The insulin gene polymorphism probably plays no important role in the genesis of NIDDM in Pima Indians, nor does it influence the glucose or insulin concentrations or their relationship to each other, but the class 3 allele, especially when homozygous in this population, may influence the severity of the disease as indicated by need for drug treatment.

Adult↗