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A number of disease states, including type 2 diabetes (T2D), are associated with an increased risk of pulmonary infection. Glucagon-like peptide-1 (GLP-1) receptor agonists are used to treat T2D and exert anti-inflammatory actions through a single, well-defined GLP-1 receptor (GLP-1R). Although highly expressed in the lung, little is known about the role of the GLP-1R in the context of pulmonary inflammation. Here we examined the consequences of gain or loss of GLP-1R activity in infectious and noninfectious lung inflammation. We studied wild-type mice treated with a GLP-1R agonist, and Glp1r–/– mice, in the setting of bleomycin-induced noninfectious lung injury and influenza virus infection. Loss of the GLP-1R attenuated the severity of bleomycin-induced lung injury, whereas activation of GLP-1R signaling increased pulmonary inflammation via the sympathetic nervous system. In contrast, GLP-1R agonism reduced the pathogen load in mice with experimental influenza virus infection in association with increased expression of intracellular interferon-inducible GTPases. Notably, the GLP-1 receptor agonist liraglutide improved the survival rate after influenza virus infection. Our results reveal context-dependent roles for the GLP-1 system in the response to lung injury. Notably, the therapeutic response of GLP-1R agonism in the setting of experimental influenza virus infection may have relevance for ongoing studies of GLP-1R agonism in people with T2D susceptible to viral lung injury.

G protein-coupled receptor 119 (GPR119) was originally identified as a β-cell receptor. However, GPR119 activation also promotes incretin secretion and enhances peptide YY action. We examined whether GPR119-dependent control of glucose homeostasis requires preservation of peptidergic pathways in vivo. Insulin secretion was assessed directly in islets, and glucoregulation was examined in wild-type (WT), single incretin receptor (IR) and dual IR knockout (DIRKO) mice. Experimental endpoints included plasma glucose, insulin, glucagon, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide YY. Gastric emptying was assessed in WT, Glp1r−/−, DIRKO, Glp2r−/−, and GPR119−/− mice treated with the GPR119 agonist AR231453. AR231453 stimulated insulin secretion from WT and DIRKO islets in a glucose-dependent manner, improved glucose homeostasis, and augmented plasma levels of GLP-1, GIP, and insulin in WT and Gipr−/−mice. In contrast, although AR231453 increased levels of GLP-1, GIP, and insulin, it failed to lower glucose in Glp1r−/− and DIRKO mice. Furthermore, AR231453 did not improve ip glucose tolerance and had no effect on insulin action in WT and DIRKO mice. Acute GPR119 activation with AR231453 inhibited gastric emptying in Glp1r−/−, DIRKO, Glp2r−/−, and in WT mice independent of the Y2 receptor (Y2R); however, AR231453 did not control gastric emptying in GPR119−/− mice. Our findings demonstrate that GPR119 activation directly stimulates insulin secretion from islets in vitro, yet requires intact IR signaling and enteral glucose exposure for optimal control of glucose tolerance in vivo. In contrast, AR231453 inhibits gastric emptying independent of incretin, Y2R, or Glp2 receptors through GPR119-dependent pathways. Hence, GPR119 engages multiple complementary pathways for control of glucose homeostasis.

Background: In Europeans and populations of European origin, several groups have recently identified novel type 2 diabetes susceptibility genes, including FTO, SLC30A8, HHEX, CDKAL1, CDKN2B, and IGF2BP2, none of which were in the list of functional candidates. Objective and Design: The aim of this study was to replicate in a Japanese population previously identified associations of single nucleotide polymorphisms (SNPs) within 10 candidate loci with type 2 diabetes using a relatively large sample size: 1921 subjects with type 2 diabetes and 1622 normal controls. Results: A total of 15 SNPs were genotyped. Eight SNPs in five loci were found to be associated with type 2 diabetes: rs3802177 [odds ratio (OR) = 1.16 (95% confidence interval (CI) 1.05–1.27); P = 4.5 × 10−3] in SLC30A8; rs1111875 [OR = 1.27 (95% CI 1.14–1.40); P = 1.4 × 10−5] and rs7923837 [OR = 1.27 (95% CI 1.13–1.43); P = 1.0 × 10−4] in HHEX; rs10811661 [OR = 1.27 (95% CI 1.15–1.40); P = 1.9 × 10−6] in CDKN2B; rs4402960 [OR = 1.23 (95% CI 1.11–1.36); P = 8.1 × 10−5] and rs1470579 [OR = 1.18 (95% CI 1.07–1.31); P = 8.3 × 10−4] in IGF2BP2; and rs7754840 [OR = 1.28 (95% CI 1.17–1.41); P = 4.5 × 10−7] and rs7756992 [OR = 1.27 (95% CI 1.15–1.40); P = 9.8 × 10−7] in CDKAL1. The first and second strongest associations were found at variants in CDKAL1 and CDKN2B, both of which are involved in the regenerative capacity of pancreatic β-cells. Conclusion: Some of these variants represent common type 2 diabetes-susceptibility genes in both Japanese and Europeans.

Gastrointestinal hormones including gastric inhibitory polypeptide (GIP), glucagon-like peptide (GLP)-1, and GLP-2 are secreted immediately after meal ingestion, and GIP and GLP-2 have been shown to regulate bone turnover. We hypothesize that endogenous GLP-1 may also be important for control of skeletal homeostasis. We investigated the role of GLP-1 in the regulation of bone metabolism using GLP-1 receptor knockout (Glp-1r(-/-)) mice. A combination of bone density and histomorphometry, osteoclast activation studies, biochemical analysis of calcium and PTH, and RNA analysis was used to characterize bone and mineral homeostasis in Glp-1r(-/-) and Glp-1r(+/+) littermate controls. Glp-1r(-/-) mice have cortical osteopenia and bone fragility by bone densitometry as well as increased osteoclastic numbers and bone resorption activity by bone histomorphometry. Although GLP-1 had no direct effect on osteoclasts and osteoblasts, Glp-1r(-/-) mice exhibited higher levels of urinary deoxypyridinoline, a marker of bone resorption, and reduced levels of calcitonin mRNA transcripts in the thyroid. Moreover, calcitonin treatment effectively suppressed urinary levels of deoxypyridinoline in Glp-1r(-/-), mice and the GLP-1 receptor agonist exendin-4 increased calcitonin gene expression in the thyroid of wild-type mice. These findings establish an essential role for endogenous GLP-1 receptor signaling in the control of bone resorption, likely through a calcitonin-dependent pathway.

Several polymorphisms of genes involved in autonomic nervous system (ANS) function have been reported to affect metabolic regulation. We have investigated the association of an alpha(2B)-adrenergic receptor (alpha(2B)AR) three-amino acid deletion polymorphism with ANS activity in young healthy subjects by means of electrocardiogram R-R interval power spectral analysis. Three hundred eighty-one young healthy Japanese males (mean +/- SE, 20.6 +/- 0.1 yr) were studied. One hundred sixty-eight (44.1%) were homozygotes of Long allele (Long/Long), 162 (42.5%) were heterozygotes (Long/Short), and 51 (13.4%) were homozygotes of Short allele (Short/Short). The allele frequency of Short allele was 0.35. No significant differences were observed in any of the characteristics investigated: body mass index, plasma glucose, plasma insulin, or family history of diabetes and obesity. In R-R spectral analysis of heart rate variability, carriers of Short/Short had significantly greater low frequency and very low frequency than Long/Long, as well as a higher sympathetic nervous system index. These findings suggest that the alpha(2B)AR deletion polymorphism might result in metabolic disorder by altering ANS function.

The 112/121 haplotype combination defined by the UCSNP-43, -19, and -63 alleles in the calpain-10 gene is associated with type 2 diabetes in Mexican Americans. To determine whether this genetic variation constitutes risk of type 2 diabetes in Japanese, we investigated its frequency in 177 patients with type 2 diabetes and 172 controls. Though this variation occurs in Japanese more frequently than in Mexican Americans, there is no significant difference in frequency between diabetic (29.9%) and control (31.9%) subjects. We also screened all exons and the putative promoter of the calpain-10 gene for mutations in 96 of the genotyped patients, resulting in the identification of 7 coding variants, including 3 missense mutations and 5 nucleotide alterations in the promoter. However, their frequencies all are similar in patients and controls, suggesting that these genetic variations are not a major factor in the occurrence of type 2 diabetes in Japanese, although they could yet be associated with various phenotypes of the disease.

A brief exposure to elevated glucose augments the insulin secretory response of islets to subsequent stimulation. The site of this priming effect of glucose in the mechanism of the regulation of insulin secretion is not completely known, however. Insulin release triggered by a depolarizing concentration of K+ in the presence of basal glucose is markedly enhanced in primed rat islets. To clarify the role of priming on Ca(2+) and ATP efficacy in the exocytotic apparatus, islets were electrically permeabilized to vary the intracellular Ca(2+) and ATP concentrations according to the extracellular medium, and insulin release was evaluated. Ca(2+) and ATP efficacy in Ca(2+)- and ATP-dependent insulin secretion was not affected by priming, and alteration of the intracellular Ca(2+) concentration after depolarization cannot account for the phenomenon. There was no difference in ATP content before depolarization between nonprimed and primed islets. Moreover, the decline in ATP level after depolarization with basal glucose was observed in both primed and nonprimed islets. However, a reduced decline in ATP level in the early phase was observed in primed islets. In addition, oligomycin, a mitochondrial metabolism inhibitor, abolished the difference in ATP level between primed and nonprimed islets, suggesting that mitochondrial ATP production may be linked to the phenomenon.

The effect of 1α,25-dihydroxylumisterol3 (1α,25(OH)2lumisterol3) on insulin release from rat pancreatic β-cells was measured to investigate the nongenomic action of vitamin D via the putative membrane vitamin D receptor (mVDR). 1α,25(OH)2lumisterol3, a specific agonist of mVDR, dose-dependently augmented 16.7 mm glucose-induced insulin release from rat pancreatic islets and increased the intracellular Ca2+ concentration ([Ca2+]i), though not increasing Ca2+ efficacy in the exocytotic system. These effects were completely abolished by an antagonist of mVDR, 1β,25-dihydroxyvitamin D3 (1β,25(OH)2D3), or by a blocker of voltage-dependent Ca2+ channels, nitrendipine. Moreover, both [Ca2+]i elevation, caused by membrane depolarization, and sufficient intracellular glucose metabolism are required for the expression of these effects. 1α,25(OH)2lumisterol3, therefore, has a rapid insulinotropic effect, through nongenomic signal transduction via mVDR, that would be dependent on the augmentation of Ca2+ influx throu...

The β3-adrenergic receptor plays a significant role in the control of lipolysis and thermogenesis in brown adipose tissue through autonomic nervous system (ANS) activity. As the Trp64Arg polymorphism of the β3-adrenergic receptor gene might affect ANS activity, we investigated the association of the polymorphism with ANS activity. The prevalence of the polymorphism was determined in 204 subjects. Ten normal homozygous, 10 heterozygous, and 1 variant homozygous subjects were examined for ANS activity during supine rest and standing by electrocardiogram R-R interval power spectral analysis. Subjects with the variant did not differ from subjects without the variant in body mass index, plasma glucose, plasma insulin, or family history of diabetes or obesity. The total power of heterozygotes at supine rest was lower than that of normal subjects (1124.6 ± 191.6 vs. 3029.8 ± 758.8 ms2; mean ± se). With a postural change to standing, the parasympathetic and sympathetic nervous system activity indexes of heterozyg...

Pimobendan is a new class of inotropic drug that augments Ca2+ sensitivity and inhibits phosphodiesterase (PDE) activity in cardiomyocytes. To examine the insulinotropic effect of pimobendan in pancreatic beta-cells, which have an intracellular signaling mechanism similar to that of cardiomyocytes, we measured insulin release from rat isolated islets of Langerhans. Pimobendan augmented glucose-induced insulin release in a dose-dependent manner, but did not increase cAMP content in pancreatic islets, indicating that the PDE inhibitory effects may not be important in beta-cells. This agent increased the intracellular Ca2+ concentration ([Ca2+]i) in the presence of 30 mM K+, 16.7 mM glucose, and 200 microM diazoxide, but failed to enhance the 30 mM K+-evoked [Ca2+]i rise in the presence of 3.3 mM glucose. Insulin release evoked by 30 mM K+ in 3.3 mM glucose was augmented. Then, the direct effects of pimobendan on the Ca2+-sensitive exocytotic apparatus were examined using electrically permeabilized islets in which [Ca2+]i can be manipulated. Pimobendan (50 microM) significantly augmented insulin release at 0.32 microM Ca2+, and a lower threshold for Ca2+-induced insulin release was apparent in pimobendan-treated islets. Moreover, 1 microM KN93 (Ca2+/calmodulin-dependent protein kinase II inhibitor) significantly suppressed this augmentation. Pimobendan, therefore, enhances insulin release by directly sensitizing the intracellular Ca2+-sensitive exocytotic mechanism distal to the [Ca2+]i rise. In addition, Ca2+/calmodulin-dependent protein kinase II activation may at least in part be involved in this Ca2+ sensitization for exocytosis of insulin secretory granules.

Dihydropyridine-sensitive voltage-dependent calcium channels (VDCC) play a crucial role in insulin secretion. We recently have cloned a human alpha 1-subunit of the VDCC expressed in pancreatic beta-cells, designated CACN4. In this study we have isolated complementary DNAs encoding two forms of rat CACN4 (rCACN4A and rCACN4B) from a rat insulinoma RINm5F complementary DNA library. Rat CACN4A is a protein of 2203 amino acids and is the rat homolog of human CACN4, whereas rCACN4B lacks 535 amino acids in the carboxyl-terminal region, probably due to alternative splicing. We have found two additional variations, one in the intracellular loop between repeats I and II and the other in the extracellular region between the third and fourth segments of repeat IV. Reverse transcriptase-polymerase chain reaction analysis of rat pancreatic islet messenger RNA reveals that these variants are present in pancreatic islets. In addition, whole-cell voltage-clamp recordings of Chinese hamster ovary cells stably expressing the alpha 1-subunit (rCACN4A or rCACN4B) with or without the calcium channel beta 2-subunit show that coexpression of rCACN4A with the beta 2-subunit or rCACN4B with the beta 2-subunit elicits L-type VDCC currents, whereas expression of the alpha 1-subunit alone does not, indicating that CACN4 can associate functionally with the beta 2-subunit and that the beta-subunit is essential for functional expression of CACN4. These results suggest that there are various subtypes of CACN4 expressed in pancreatic beta-cells, and that both rCACN4A and rCACN4B can function as VDCC. Furthermore, the present study suggests that the expression of the beta-subunit as well as the alpha 1-subunit may participate in the regulation of insulin secretion.

We previously reported the cloning of two distinct somatostatin receptor (SSTR) subtypes, SSTR1 and SSTR2. Although both SSTR1 and SSTR2 bound somatostatin specifically and with high affinity, neither was coupled to adenylyl cyclase, a major cellular effector of somatostatin's actions. Here we report the cloning and functional characterization of a third member of the SSTR family. Human SSTR3 is a protein of 418 amino acids and has 45% and 46% identity with human SSTR1 and SSTR2, respectively. RNA blotting studies showed that SSTR3 mRNA could be readily detected in brain and pancreatic islets. The pharmacological properties of human SSTR3 were characterized by transiently expressing the human SSTR3 gene in COS-1 cells. Membranes from cells expressing human SSTR3 bound the somatostatin agonist [125I]CGP 23996 specifically and with high affinity, with a rank order of potency of somatostatin-28 = CGP 23996somatostatin-14SMS-201-995. Studies using cells transiently coexpressing the human dopamine D1 receptor and human SSTR3 showed that somatostatin was able to inhibit dopamine-stimulated cAMP formation in a dose-dependent manner, indicating that SSTR3 was functionally coupled to adenylyl cyclase. These results indicate that the diverse biological effects of somatostatin are mediated by a family of receptor with distinct, but overlapping, tissue distributions, unique pharmacological properties, and potentially different functions.

Gastric inhibitory polypeptide (GIP) is a 42-amino-acid hormone which may have a role in the regulation of insulin secretion. The characterization of cDNA clones encoding this hormone indicates that it is derived by proteolytic processing of a 153-amino-acid precursor. The human gene coding for the human GIP precursor spans approximately 10 kilobase pairs and consists of six exons. Similar to genes encoding other members of the glucagon superfamily, each exon appears to encode a distinct region of the GIP precursor or its mRNA. The promoter region of the human GIP gene contains potential binding sites for a number of transcriptional factors including Sp 1, AP-1, and AP-2. The human GIP gene has been assigned to chromosome 17q21.3----q22.

The effect of intravenous xylitol infusions on plasma glucagon and insulin responses to intravenous arginine infusions (30 g for 45 min) or arginine "pulses" (4 g for 2 min) was studied in normal subjects. Intravenous infusion of arginine caused biphasic increases in plasma glucagon and insulin in all subjects studied. The increase in plasma glucagon induced by arginine infusion was significantly reduced by xylitol infusions started at 45 min before arginine infusion, irrespective of virtually unchanged blood glucose levels. Plasma insulin response to arginine was exaggerated by xylitol infusion. Repeated arginine pulses given at 30 min intervals evoked uniphasic and almost identical rises of plasma insulin and glucagon with each pulse. Intravenous xylitol infusions significantly blunted plasma glucagon responses and augumented the plasma insulin response to arginine pulses, despite only slight elevations of plasma glucose. These results suggest that xylitol has an inhibitory effect on both basal and arginine-stimulated glucagon secretion, while it enhances insulin secretion.

Effects of various gastrointestinal peptides on gastric somatostatin release from the isolated perfused rat stomach were studied. After isolation of the stomach in a fasted rat by the method of Lefebvre and preperfusion with 4.6% dextran-Krebs-Ringer bicarbonate buffer containing 5.5 mm glucose, each peptide was infused into the left gastric artery at a constant rate for 15 min. Secretin and bombesin caused a significant increase of gastric somatostatin release in a dose-related manner (10−8−10−6 m). Gastric somatostatin release was also stimulated after the administration of pentagastrin (10−8−10−6 m). In contrast, both methionine-enkephalin and substance P decreased gastric somatostatin release in a dose-related manner (10−8−10−6 m), whereas neurotensin (10−8−10−6 m) failed to change it significantly. The present results suggest that these various gastrointestinal peptides may regulate gastric somatostatin secretion. (Endocrinology 106: 145, 1980)

Plasma insulin and glucagon responses to l-arginine were compared in normal subjects and patients with hyper- and hypothyroidism. Hyperthyroid patients were characterized by low plasma insulin response and almost normal plasma glucagon response, whereas hypothyroid patients showed high insulin and glucagon responses. The impaired insulin response to l-arginine in the case of hyperthyroidism was significantly improved after thyroid function was normalized by treatment.

To investigate the role of glucose and arginine in short term regulation of preproinsulin mRNA (ppImRNA) levels, the rat pancreas was perfused in the presence of glucose and/or arginine, and changes in ppImRNA levels in the pancreas were compared with the amount of insulin released during the per fusion. Perfusion of the pancreas with high glucose and arginine induced a significant increase in ppImRNA levels within 2 h, whereas perfusion with low glucose and arginine or high glucose alone had no significant effect during this period. The insulin release induced by perfusion of high glucose combined with arginine was 2 times greater than that induced by high glucose alone or low glucose with arginine. In conclusion, insulin gene transcription can be evoked during a short period in response to an extremely large secretory demand for insulin. (Endocrinology 124: 707–711,1989)

In order to elucidate the relationship between the release of gastric inhibitory polypeptide (GIP) and insulin, we compared plasma GIP and insulin concentration responses to meal ingestion in normal subjects and patients with various surgical modifications of the food pathway. Nine patients with Billroth I partial gastrectomy (BI), 7 patients with Billroth II partial gastrectomy (BII), and 6 patients with total gastrectomy (TG) were tested. In BI patients the increase in blood glucose was similar to that in normal subjects, but the response was significantly greater in BII and TG patients. In TG patients blood glucose rose significantly higher in response to a standard meal than in all other groups. In BI patients the mean peak GIP level after meal ingestion was significantly higher than in normal subjects. In BII and TG patients an extremely exaggerated GIP response after the meal was observed. The insulin response to feeding was increased only in the BII and TG patients. Since the insulin response was enhanced only when both the glucose and GIP responses were magnified, we conclude that endogenous GIP is a glucose-dependent insulinotropic factor. In addition, from the fact that meal-stimulated GIP release is most marked in patients with total gastrectomy, we conclude that the direct contact of food with the GIP-producing cells is a strong mechanical or chemical stimulus for GIP release.

Fasting plasma gastrin levels measured by radioimmunoassay were found to be elevated in patients with hyperthyroidism. The intravenous injection of arginine caused an increase of plasma gastrin in hyperthyroid patients as in normal subjects. The elevated gastrin level in patients with hyperthyroidism was significantly lowered after the thyroid function was normalized by treatment.