Hypersecretion of truncated glucagon-like peptide-1 and gastric inhibitory polypeptide in obese patients

Postprandial insulin secretion is modulated by both neural and humoral gastrointestinal insulinotropic factors in addition to the absorbed nutrient. To investigate the involvement of the potent insulinotropic hormones gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1) in the postprandial hyperinsulinaemia of obesity, we examined the changes in plasma levels of GIP and tGLP-1 by an oral glucose tolerance test (OGTT) in nine normal subjects (controls), nine obese subjects without glucose intolerance (Group A), and six obese mild diabetic patients (Group B). Following the OGTT, plasma GIP levels in Group B were increased more markedly than those in the other two groups. Plasma levels of tGLP-1 were estimated by the difference between the values measured with the N-terminal directed antiserum (GLP-1NT) and those with the C-terminal directed antiserum (GLP-1 CT). Plasma levels of GLP-1 NT were increased in Group B, but decreased in the other two groups. Plasma GLP-1 CT levels were increased in all groups with the highest response in Group B. These results suggest that the combined augmentation of plasma GIP and tGLP-1 responses were involved in the delayed and considerable increases in plasma insulin after glucose ingestion in obese diabetic patients. Since tGLP-1 is suppressed in the hyperglycaemic hyperinsulinaemic state in normal subjects, the augmented tGLP-1 response appears to be characteristic of obese Type 2 diabetes.

The third IGF-II promoter specifies transcription of three transcripts out of five in human placenta

Insulin-like growth factor-II (IGF-II) mRNA exists as multiple transcript size classes, such as 6.0, 5.3, 4.9, 3.2, and 2.2 kb mRNAs in various human tissues. Three different promoters, 2 different polyadenylation sites, and alternative splicing are involved in producing these multiple transcripts. Initiation of transcription at the 3 different promoters results in multiple mRNAs which contain identical coding regions but different 5'-untranslated regions (5'-UTRs). The first promoter is thought to direct expression of 5.3 kb mRNA in adult human liver. The second promoter region directs expression of 6.0, 3.2, and 2.2 kb mRNAs in human fetal tissues and several adult nonliver tissues. The third promoter specifies transcription of a 4.9 kb mRNA in various tissues. We isolated and sequenced a cDNA clone (pIGF-II-1-70) from a human placental cDNA library, which contains the IGF-II coding region and the 5'-UTR associated with the third promoter. By using a 5'-UTR-specific probe from the clone, we found that this third 5'-UTR is contained in the IGF-II mRNA of 2.2 kb and is absent in the 3.2 kb IGF-II mRNA. We also found an 0.9 kb transcript expressed in placenta, which hybridized strongly to the third 5'-UTR specific probe but not to IGF-II coding region probes. This finding might indicate the existence of an mRNA encoding an IGF-II-associated peptide.

Sepsis inhibits insulin-stimulated glucose transport in isolated rat adipocytes

To assess the mechanism of insulin resistance in sepsis, we investigated insulin receptor binding and glucose uptake in isolated rat epididymal adipocytes. Male Sprague-Dawley (SD) rats weighing 200-220 g were submitted to cecal ligation under chloral hydrate anesthesia, followed by double punctures with 18-G needle into the ligated portion to produce peritonitis. Age-matched SD rats without operation were used as the controls. After starvation for 16 h, blood samples were taken from the inferior vena cava for bacterial culture and assayed for plasma glucose and IRI levels, and then adipocytes were isolated from the dissected epididymal fat tissues. Plasma levels of both glucose and IRI in septic rats were higher than those in the controls. The [125I]-insulin binding rate of the adipocytes in septic rats was similar to that of the controls. However, [3H]-2-deoxy-D-glucose uptake by adipocytes was markedly decreased in the septic group (approximately 45% of the control group at the plateau). In conclusion, this study suggests that insulin resistance in the septic state results, at least partly, from impairment in the post-binding level of the insulin receptor.

Differences in glucagon-like peptide-1 and GIP responses following sucrose ingestion

To investigate the mechanism of oral carbohydrate-stimulated secretion of the two most potent incretin candidates, gastric inhibitory polypeptide (GIP) and truncated glucagon-like peptide-1 (tGLP-1), we studied the changes in the plasma levels of these peptides in five healthy men after sucrose ingestion with or without pretreatment with an alpha-D-glucosidase inhibitor (AO-128). After sucrose ingestion, plasma levels of GIP peaked at 15 min and remained high up to 120 min. Plasma levels of GLP-1 NT measured with antiserum R1043 (N-terminal specific) tended to decrease gradually and those of GLP-1 CT measured with antiserum R2337 (C-terminal specific) increased. Therefore, estimated plasma levels of tGLP-1 increased markedly within 30 min, then declined slightly over the next 60 min. After treatment with AO-128 (0.6 mg/day) for 1 week, increases in plasma glucose and insulin levels were attenuated and the increase in plasma GIP levels was diminished, while the increase in tGLP-1 levels was sustained much longer. It is concluded that GIP secretion is stimulated by glucose absorption and tGLP-1 secretion by the presence of sucrose in the gut.

Unique 3'-untranslated sequence of insulin-like growth factor-I isolated from human placenta

A cDNA clone of 525 bp corresponding to the 3'-untranslated region of insulin-like growth factor-I was isolated from a human placenta library. The sequence of this clone extended 200 nucleotides downstream from the previously reported 3'-end of IGF-IA cDNA, indicating the existence of IGF-IA transcripts having an even larger 3'-untranslated region. By using this clone for RNA transfer blot hybridization, it was shown that this longer 3'-untranslated region is included in the 7.5- and 5.0-kb transcripts, but not in the 1.1- and 0.9-kb transcripts. It is also apparent that transcripts bearing the extended 3'-untranslated sequence are highly expressed in human placenta.

Expression of the insulin-like and platelet-derived growth factor genes in human uterine tissues

The human uterus repeatedly exhibits cyclic biochemical and cytological changes during the reproductive period of life. These changes are the result of a well-characterized endocrine network involving the hypothalamus, pituitary, and ovary. The exact nature of the mechanism(s) by which the sex steroids act on the uterus remains to be elucidated. Possible local mediators of hormonal action on the uterus include polypeptide growth factors. Using the method of RNA transfer blot hybridization, we have analyzed tissue samples from the cycling human endometrium and tissue samples of human myometrium and myometrial benign tumor (leiomyoma) for the presence of platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF) RNA. All the uterine tissues examined possessed RNA for PDGF-B chain and IGF-I and -II. Two transcripts were observed for PDGF-B chain, four were observed for IGF-I, and eight were observed for IGF-II. Overall, the relative abundance of PDGF-B chain RNA was consistent in all of the uterine tissues examined. In contrast, IGF RNA relative abundance varied. IGF-I RNA was highest in late proliferative stage endometrium, and IGF-II RNA was highest in early proliferative stage endometrium. Both IGF-I and IGF-II RNAs were greater in amount of leiomyoma than in myometrium. The increased IGF-I RNA in late proliferative-stage human endometrium correlates with the known elevation of estradiol secretion by the ovary and the increased concentration of uterine estradiol receptors during this stage of the menstrual cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of experimental hepatic artery embolization with lipiodol and gelatin sponge on liver tissue]

The effect of hepatic artery embolization with Lipiodol (Lp) and Gelatin sponge particles (GSP) on liver tissue was evaluated in 17 dogs embolized with GSP, 12 dogs with Lp and 19 dogs with Lp + GSP. Survival rate and extent of liver damage were used as evaluation criteria. None of the dogs with GSP died during the 4 week period, two exhibited small liver infarctions. Of the dogs with 0.2 to 5 ml/kg Lp, two dogs with 4 ml/kg or 5 ml/kg Lp died of cardiac failure. Gross liver examination did not show any liver infarction. Eight of the 19 dogs with Lp + GSP died of liver failure. Gross examination of the surviving dogs demonstrated infarction in 9 of the 11 livers with 100% incidence in those with 0.2 ml/kg or 0.5 ml/kg Lp. Liver infarction increased in size with the increase of Lp volume. In combination with Lp + GSP, the Lp volume should be less than 0.1 ml/kg.

Insulin-like growth factor-I messenger ribonucleic acid in the developing human placenta and in term placenta of diabetics

Fetal growth and development are dependent upon the growth and development of the placenta. Control of placental growth and development is little understood. Immunoreactive insulin-like growth factor-I and -II (IGF-I and IGF-II) have been shown to be released by human placental tissue and human placental membranes have been observed to contain specific receptors for these growth factors. Furthermore, we have demonstrated the presence of IGF-II mRNA transcripts in the developing human placenta and at gestational term in placentae of diabetics. Thus, the IGFs may have a regulatory role in the growth and development of the placenta via autocrine and/or paracrine mechanism(s) of action. In this report we demonstrate the presence of four differing size species of placental poly(A)+ RNA which specifically hybridize to an IGF-I probe originally isolated from an adult human liver cDNA library and localize IGF-I and IGF-II mRNA to syncytiotrophoblasts and fibroblasts, respectively, of the placenta by in situ hybridization. The major transcript is 7500 bases in size and the remaining three transcripts are 5000, 1100, and 900 bases in length with no apparent changes from these sizes throughout gestation and at term in diabetics. Quantification by densitometry of placental IGF-I mRNA detected by dot blot hybridization indicated that first and second trimester placentae each express more IGF-I mRNA relative to that expressed in placenta at term. These results suggest that there are developmental changes in the relative amount of IGF-I mRNA expressed in the human placenta. IGF-I is, therefore, most likely important early in gestation as a placental growth factor. This time period is critical for fetal development and growth, when embryonic induction, organogenesis, and rapid cell proliferation occur.

Isolation of an insulin-like growth factor II cDNA with a unique 5' untranslated region from human placenta

Human insulin-like growth factor II (IGF-II) cDNA from a placental library was isolated and sequenced. The 5' untranslated region (5'-UTR) sequence of this cDNA differs completely from that of adult human liver and has considerable base sequence identity to the same region of an IGF-II cDNA of a rat liver cell line, BRL-3A. Human placental poly(A)+ RNA was probed with either the 5'-UTR of the isolated human placental IGF-II cDNA or the 5'-UTR of the IGF-II cDNA obtained from adult human liver. No transcripts were detected by using the 5'-UTR of the adult liver IGF-II as the probe. In contrast, three transcripts of 6.0, 3.2, and 2.2 kilobases were detected by using the 5'-UTR of the placental IGF-II cDNA as the probe or the probe from the coding sequence. A fourth IGF-II transcript of 4.9 kilobases presumably containing a 5'-UTR consisting of a base sequence dissimilar to that of either IGF-II 5'-UTR was apparent. Therefore, IGF-II transcripts detected may be products of alternative splicing as their 5'-UTR sequence is contained within the human IGF-II gene or they may be a consequence of alternative promoter utilization in placenta.

DNA methylation and the regulation of aldolase B gene expression

DNA methylation was studied as a potential factor for the regulation of tissue-specific and developmentally specific expression of the rat aldolase B gene. We examined cytosine methylation in the HpaII and HhaI recognition sequences in the aldolase B gene in aldolase expressing and nonexpressing tissues and cells. Out of the 15 methyl-sensitive restriction sites examined, the sites in the 3'-half and 3'-flanking regions were found to be heavily methylated in all the tissues or cells, regardless of the level of aldolase B gene expression. However, the methylation pattern in the region immediately upstream and in the 5'-half of the gene exhibited tissue-specificity: the site located about 0.13 kb upstream of the cap site (just next to the CCAAT box), and the sites in the first intron (intron 1) were heavily methylated in nonexpressing cells and tissues (ascites hepatoma AH130 and brain), whereas those in an expressing tissue (liver) were considerably less methylated. These results suggest that cytosine methylation at the specific sites in the 5'-flanking and 5'-half regions of the gene is associated with repression of the gene activity. However, the gene is still substantially methylated in the fetal liver on day 16 of gestation, when it is in a committed state for rapid activation in the period immediately afterwards (Numazaki et al. (1984) Eur. J. Biochem. 152, 165-170). This suggests that demethylation of the methylated cytosine residues in the specific gene region is not necessarily required before activation of the gene during development, but it may occur along with or after the activation.

[Rat aldolase isozyme gene: structure and expression in the liver during both fetal development and chemical carcinogenesis]

Changes in the gene expression of aldolase A and B isozymes in rat liver during both fetal development and chemical carcinogenesis were analyzed using cDNA probes. The structure of the rat aldolase B gene was also determined, and was discussed in relation to its expression.

Nucleotide sequence of rat liver aldolase B messenger RNA

The nucleotide sequence of messenger RNA encoding rat liver aldolase B has been determined by sequence analysis using recombinant cDNAs cloned in bacterial plasmids. The sequence contains part of the 5'-untranslatable region (68 nucleotides), the entire coding region (1092 nucleotides), and the complete 3'-untranslatable region (387 nucleotides), excluding the poly(A) tail. A potential ribosomal-binding site is located about 30 nucleotides upstream from the initiation codon. The amino acid sequence of rat liver aldolase B is composed of 364 amino acids and has 70% homology with rabbit muscle aldolase A.

Changes of aldolase A and B messenger RNA levels in rat liver during azo-dye-induced hepatocarcinogenesis

The expression of aldolase A and B mRNAs during azo-dye-induced carcinogenesis in rat liver was examined. After feeding the dye for 18 weeks, the level of aldolase A mRNA increased to about 11 times that in a normal liver, with the concomitant decrease of aldolase B mRNA level to about 25% of that in a normal liver. These changes did not occur progressively during the carcinogenesis, but occurred as an additional phase after 4 week-feeding of the azo-dye. At this stage, the levels of aldolase A and B mRNAs were about 7 times and 45% of that in a normal liver, respectively. This biphasic pattern in the aldolase isozyme expression in the azo-dye-fed rat liver is discussed together with the kinetic data of the enzyme activity.