Dendritic cell TLR4 induces Th1-type immune response against Cryptosporidium parvum infection

The objective of this study was to investigate the mechanism of Toll-like receptor (TLR4)- mediated dendritic cell (DC) immune against Cryptosporidium parvum infection. C. parvum sporozoites were labeled with 5,6-carboxyfluorescein diacetate succinimidyl ester. Murine bone marrow-derived DCs were isolated, and divided into TLR4 antibody blocking (TAB; infected with 2 × 10⁵ labeled sporozoites and 0.5 μg TLR4 blocking antibody), TLR4 antibody unblocking (TAU; infected with 2 × 10⁵ labeled sporozoites), and blank control (BC; with 1.5 mL Roswell Park Memorial Institute 1640 medium) groups. The adhesion of Cryptosporidium sporozoites to DCs and CD11c⁺ levels were examined by fluorescence microscopy and flow cytometry. Male KM mice were orally injected with C. parvum. The proliferation of T lymphocytes in spleen, expression of cytokines in peripheral blood, and TLR4 distribution features in different organs were further determined by immunohistochemistry. A significantly higher expression of CD11c⁺ and higher C. parvum sporozoite adhesion were found in the TAU group compared with other groups. The expression of CD4⁺CD8^- /CD8⁺CD4^- in the spleen were obviously differences between the TAB and TAU groups. The expression of TLR4, interleukin IL-4, IL-12, IL-18 and IFN-γ improved in the TAU group compared with TAB group. Higher expression of TLR4 was detected in the lymph nodes of mice in the TAU group, with pathological changes in the small intestine. Hence, TLR4 could mediate DCs to recognize C. parvum, inducing Th1 immune reaction to control C. parvum infection.

[Discussion on the indications of internal mammary sentinel lymph node biopsy in breast cancer in the era of precision medicine]

Objective: To determine the clinical benefits of internal mammary sentinel lymph node biopsy (IM-SLNB) acquired by breast cancer patients with clinically positive axillary lymph node (ALN), and further optimize the IM-SLNB indications. Methods: All primary breast cancer patients with clinically positive ALN from February 2014 to September 2017 were prospectively recruited in this study. IM-SLNB was performed under the guidance of the modified injection technique. The success rate and visualization rate of IM-SLNB, metastatic rate of internal mammary sentinel lymph node (IMSLN) and its related factors were analyzed, and the clinical benefits were accessed according to the current guidelines. Results: Among 126 patients, all of 94 patients (74.6%) who showed internal mammary drainage successfully underwent IM-SLNB. The incidence of internal mammary artery bleeding and pleural lesion were 4.3%(4/94) and 9.6%(9/94), respectively. The metastatic rate of IMSLN was 38.3% (36/94), which was significantly associated with the number of positive ALN (P<0.001) and tumor size (P=0.024). The lymph node staging of 94 patients who underwent IM-SLNB was more accurate. Among them, 36 cases with positive IMSLN underwent internal mammary radiotherapy (IMRT), while the other 58 cases with negative IMSLN avoided radiotherapy. Conclusions: IM-SLNB should be routinely performed in patients with positive ALN. IM-SLNB can provide more accurate staging and guide tailored IMRT to benefit more breast cancer patients.

[Efficiency of the Modified Ottawa ankle rules for the differential diagnosis of fracture in acute foot and ankle injury]

Objective: To evaluate the efficiency of modified Ottawa Ankle Rules (OAR) for the differential diagnosis of fractures in acute foot and ankle injuries. Methods: From October 2016 to December 2016, 272cases (135 males and 137 females) of foot and ankle injury in emergency department of Tianjin Hospital were prospective enrolled in the study.The median age was 27.5 years (7-87); left limb 155, right 117 cases; injury time ranged from 0.3 to 24 h (median 4 h). Conventional and modified OAR was applied on physical examination, subsequently radiography performed to determine the occurrence of fractures.The efficiency of the two methods were compared and analyzed. Results: Fractures were found in 100 cases (36.8%), 49 cases of ankle and 51 cases of foot fractures.With the imaging results as the standard, the sensitivity for conventional and modified OAR were 93.0% and 100%, specificity were 9.9% and 8.7%, the positive predictive value were 37.5% and 38.9%, the negative predictive value were 70.8% and 100%, the accuracy were 40.4% and 42.3%, missed diagnosis rate were 7% and 0% respectively.The sensitivity, positive likelihood ratio, positive predictive value, negative predictive value, accuracy, negative likelihood ratio and missed diagnosis ratio were better than in modified OAR compared with Conventional OAR, while the specificity was slightly lower compared to Conventional OAR.The Kappa value of modified OAR was 0.065 (P>0.05), which is better than conventional OAR.Conventional OAR can reduce 6.3% (17/272) X-ray and modified OAR decline 5.5% (15/272). Conclusion: Modified OAR significantly reduces the rate of missed diagnosis of foot fractures, but its specificity is poor. Ultrasound can be assisted to improve the specificity and reduce the number of unnecessary X-rays.

[A childhood-onset rapid-onset dystonia parkinsonism family with ATP1A3 gene mutation and literatures review]

Objective: To explore clinical characteristics, treatment, and prognosis of a family with childhood-onset rapid-onset dystonia parkinsonism (RDP) caused by ATP1A3 gene mutation and review literatures. Method: The clinical data of a RDP child, his brother and mother had been analyzed retrospectively. This family was admitted to Xiangya Hospital in January 2016. DNA samples were analyzed by the next-generation sequencing and confirmed by Sanger sequencing. Related literature from PubMed, Online Mendelian Inheritance in Man (OMIM), CNKI and Wanfang databases to date (up to October 2016) with"Rapid-onset dystonia-parkinsonism""RDP""DYT12" as key words was reviewed. Result: The proband boy was three years and four months old (April 2015) when he had the first attack of the disease. After a febricity, he suddenly acquired acute aphasia and limb movement disorder. Rehabilitation therapy and supportive treatment made his speech gradually recovered but still slurred. However, his abnormal walking posture still existed. Nine months later (January 2016, 4 years and one months old), symptoms including aphasia, dysphagia, and weakness with rostrocaudal gradient reoccured after fever. The disease progressed to the critical condition within 24 hours. He"seizured" four times with tonic spasms of limbs but without loss of consciousness. Family history showed his grandparents were consanguineous marriage. His mother and brother also developed abnormal gait and dysarthria after an infection before primary school age. Their symptoms improved gradually without relapsing. However, they did not recover entirely with mild intellectual disability. His mother had a healthy brother and sister. This proband had no other siblings but the brother. Heterozygous missense mutation p. R756H in ATP1A3 gene was detected in this proband, his mother and his brother. This mutation had been reported pathogenically related to RDP, and it located in highly conserved gene region. Benzodiazepine was used for the proband and his brother, with the proband being improved better although not completely. Meanwhile, benzodiazepine had no significant effect on his mother because of poor compliance. This is the first case report of RDP in China. The mutations of ATP1A3 have been previously reported in 51 patients including 6 large families and 16 other unrelated patients. A total of 14 different mutations in ATP1A3 gene with RDP have been reported to date, including 12 missense mutations, a 3-bp in-frame deletion, and a 3-bp in-frame insertion. The sporadic cases all had the typical clinical phenotypes of RDP, such as the abrupt onset of dysarthria, dysphagia, limb dystonia with bradykinesia, and postural instability. The symptoms of bulbar and arms were much more obvious. It was hard to diagnose RDP in a family because some patients had typical symptoms of RDP, while the others might experience from mild symptoms to no symptoms, which might be related to incomplete penetrance of RDP. Two cases carrying the same mutation as our patients also presented some overlapping phenotypes. Conclusion: The p. R756H heterozygous mutation in ATP1A3 gene is the pathogenic mutation of RDP, analysis of genotype-phenotype correlations of RDP will be very important and meaningful.

[The role of PACAP protein in chronic sinusitis with or without nasal polyps]

Objective:To investigate the expression of PACAP protein in chronic rhinosinusitis without/with nasal polyps and refractory chronic rhinosinusitis.Method: Fifty-three patients with nasal polyps,70 cases with chronic sinusitis, 28 patients with refractory chronic rhinosinusitis and 20 control cases were enrolled for this study. The expression of PACAP protein was detected by immunochemistry.Result: ①PACAP protein were expressed in nasal epithelium，glandular epithelium and goblet cells；②The positive intensity of PACAP was" +", " +++", "－-+",and " ++" in nasal polyps, chronic rhinosinusitis, refractory chronic rhinosinusitis, and control group, respectively.Conclusion:PACAP protein mainly locates in nasal epithelium，glandular epithelium and goblet cells. Reduced expression of PACAP may be related with onset of chronic rhiniosinusitis without/with nasal polyps.

Tuning the structures and electron transport properties of ultrathin Cu nanowires by size and bending stress using DFT and DFTB methods

Electron transport properties of ultrathin Cu nanowires with diameters of 0.2–1.0 nm under different bending stresses are reported, using density functional theory and density-functional-based tight-binding approaches, for application in flexible displays and solar cells.

Consumption of nuts and legumes and risk of stroke: a meta-analysis of prospective cohort studies

BACKGROUND AND AIM

The relationships between dietary nuts and legume intake and risk of stroke are inconsistent. We summarized the evidence by a meta-analysis of prospective cohort studies.

METHODS AND RESULTS

We systematically searched the MEDLINE and EMBASE databases up to 31 January 2014. Random-effects models were used to calculate summary relative risks (SRRs) and 95% confidence intervals (CIs). Between-study heterogeneity was assessed using the Cochran's Q and I(2) statistics. Eight prospective studies with a total of 468,887 subjects and 10,493 stroke events were included in the meta-analysis. Overall, a diet containing greater amounts of legumes may be not associated with a lower risk of stroke (SRR = 0.95, 95% CI: 0.84-1.08; P(heterogeneity) = 0.091, I(2) = 43.2%); however, a diet containing greater amounts of nuts may be associated with a lower risk of stroke (SRR = 0.90, 95% CI: 0.81-0.99; P(heterogeneity) = 0.527, I(2) = 0). Gender significantly modified the effects of nut consumption on stroke risk, and high nut intake was associated with reduced risk of stroke in women (SRR = 0.85, 95% CI: 0.75-0.97) other than in men (SRR = 0.95, 95% CI: 0.82-1.11).

CONCLUSION

The current meta-analysis provides some evidences for the hypothesis that high intake of dietary nut was inversely associated with stroke risk, whereas dietary legumes intake was not associated with stroke risk.

Reovirus as a successful ex vivo purging modality for multiple myeloma

Autologous stem cell rescue (ASCT) following high-dose myeloablative chemotherapy is considered to be a therapeutic option for many multiple myeloma (MM) patients; however relapse post ASCT presents a major challenge. The oncolytic potential of reovirus has been previously demonstrated and is currently undergoing phase I monotherapy clinical trials for MM and phase II/III clinical trials for solid tumors. Here we tested the hypothesis that reovirus can successfully purge MM in a murine model that partially recapitulates human MM. RPMI 8226, MM1S, H929 and U266 human myeloma cell lines were exposed to reovirus and oncolysis was assessed. Apheresis product admixed with MM cells was purged with live reovirus (LV) or dead virus (DV) and purging efficacy was monitored via flow cytometry, reverse transcribed-PCR (RT-PCR) and disease relapse in non obese diabetic/severe combined immune deficient (NOD/SCID) mice. Significant LV purging was seen with MM1S, H929 and U266 and the complete ex vivo purging achieved with RPMI 8226 was confirmed by flow cytometry, RT-PCR and absence of disease relapse in vivo. Mice that received LV-purged autografts exhibited 100% survival in comparison to mice that received DV-purged controls. Reovirus's unique ability to kill MM while sparing hematopoietic stem cells places it as an attractive purging agent for MM during ASCT.

Fabrication of CdZnTe Strip Detectors for Large Area Arrays

A CdZnTe strip detector large area array (∼ 60 cm2 with 36 detectors) with capabilities for high resolution imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. The detector array also has applications in nuclear medical imaging. Two dimensional orthogonal strip detectors with 100 μm pitch have been fabricated and tested. Details for the array design, fabrication and evaluation of the detectors will be presented.

Inhibition of fengycins on the production of fumonisin B1 from Fusarium verticillioides

AIM

To understand the role of fengycins in regulating the fumonisin B1 (FB1)production of Fusarium verticillioides.

METHODS AND RESULTS

The mass ratio of FB1 to mycelia was determined in order to identify the effect of fengycins on FB1 production. It was shown that the amount of FB1 produced by unit mass mycelia decreased to 28% of the control. Results from mycelia resuspension with fengycins also demonstrated that fengycins had a potent impact on FB1 production. Gene expression patterns using quantitative reverse-transcription PCR (RT-PCR) revealed that the transcriptional levels of both FUM1 and FUM8 (coding enzymes for the generation of FB1) were down-regulated with fengycin treatment.

CONCLUSIONS

Fengycins could down-regulate the transcription of some key genes involved in the production of FB1, and impair FB1 synthesis by F. verticillioides.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results further improved our understanding of fengycins as the potential candidates to control FB1 contamination in crops and food.

Reovirus as an experimental therapeutic for brain and leptomeningeal metastases from breast cancer

Brain and leptomeningeal metastases are common in breast cancer patients and our current treatments are ineffective. Reovirus type 3 is a replication competent, naturally occurring virus that usurps the activated Ras-signaling pathway (or an element thereof) of tumor cells and lyses them but leaves normal cells relatively unaffected. In this study we evaluated reovirus as an experimental therapeutic in models of central nervous system (CNS) metastasis from breast cancer. We found all breast cancer cell lines tested were susceptible to reovirus, with > 50% of these cells lysed within 72 h of infection. In vivo neurotoxicity studies showed only mild local inflammation at the injection site and mild communicating hydrocephalus with neither diffuse encephalitis nor behavioral abnormalities at the therapeutically effective dose of reovirus (intracranial) (ie 10(7) plaque-forming units) or one dose level higher. In vivo, a single intratumoral administration of reovirus significantly reduced the size of tumors established from two human breast cancer cell lines and significantly prolonged survival. Intrathecal administration of reovirus also remarkably prolonged survival in an immunocompetent racine model of leptomeningeal metastases. These data suggest that the evaluation of reovirus as an experimental therapeutic for CNS metastases from breast cancer is warranted.

A validated HPLC-ESI-MS method for the determination of loratadine in human plasma and its application to pharmacokinetic studies

A liquid chromatographic-mass spectrometric (LC-MS) assay was developed and validated for the determination of loratadine in human plasma using reversed-phase HPLC combined with electrospray ionization (ESI) mass spectrometry. The analysis involved a simple liquid-liquid extraction. The organic extract was then evaporated and the residue was reconstituted in mobile phase. The reconstituted solution was injected into an HPLC system and was subjected to reverse-phase HPLC on a 5-microm ODS-3 column at a flow-rate of 0.2 ml/min. The mobile phase comprised of acetonitrile-ammonium acetate (pH 4.0; 0.02 M, using formic acid to adjust) using gradient elution. Loratadine was detected in the single ion monitoring (SIM) mode. Standard curves were linear over the concentration range of 0.2-100 ng/ml. The mean predicted concentrations of the quality control (QC) samples deviated by less than 10% from the corresponding nominal values; the intra-assay and inter-assay precision of the assay were within 12% relative standard deviation. The extraction recovery of loratadine was more than 80%. The validated assay was applied to a pharmacokinetic study of loratadine in human plasma following the administration of a single loratadine tablet (40 mg).

A GIS-based prediction and assessment system of off-site accident consequence for Guangdong nuclear power plant

GNARD (Guangdong Nuclear Accident Real-time Decision support system) is a decision support system for off-site emergency management in the event of an accidental release from the nuclear power plants located in Guangdong province, China. The system is capable of calculating wind field, concentrations of radionuclide in environmental media and radiation doses. It can also estimate the size of the area where protective actions should be taken and provide other information about population distribution and emergency facilities available in the area. Furthermore, the system can simulate and evaluate the effectiveness of countermeasures assumed and calculate averted doses by protective actions. All of the results can be shown and analysed on the platform of a geographical information system (GIS).

Reovirus as an oncolytic agent against experimental human malignant gliomas

BACKGROUND

Reovirus is a naturally occurring oncolytic virus that usurps activated Ras-signaling pathways of tumor cells for its replication. Ras pathways are activated in most malignant gliomas via upstream signaling by receptor tyrosine kinases. The purpose of this study was to determine the effectiveness of reovirus as an experimental treatment for malignant gliomas.

METHODS

We investigated whether reovirus would infect and lyse human glioma cell lines in vitro. We also tested the effect of injecting live reovirus in vivo on human gliomas grown subcutaneously or orthotopically (i.e., intracerebrally) in mice. Finally, reovirus was tested ex vivo against low-passage cell lines derived from human glioma specimens. All P values were two-sided.

RESULTS

Reovirus killed 20 (83%) of 24 established malignant glioma cell lines tested. It caused a dramatic and often complete tumor regression in vivo in two subcutaneous (P =.0002 for both U251N and U87) and in two intracerebral (P =.0004 for U251N and P =.0009 for U87) human malignant glioma mouse models. As expected, serious toxic effects were found in these severely immunocompromised hosts. In a less immunocompromised mouse model, a single intratumoral inoculation of live reovirus led to a dramatic prolongation of survival (compared with control mice treated with dead virus; log-rank test, P<.0001 for both U251N and U87 cell lines). The animals treated with live virus also appeared to be healthier and gained body weight (P =.0001). We then tested the ability of reovirus to infect and kill primary cultures of brain tumors removed from patients and found that it killed nine (100%) of nine glioma specimens but none of the cultured meningiomas.

CONCLUSIONS

Reovirus has potent activity against human malignant gliomas in vitro, in vivo, and ex vivo. Oncolysis with reovirus may be a potentially useful treatment for a broad range of human cancers.

Leptin administration improves skeletal muscle insulin responsiveness in diet-induced insulin-resistant rats

In addition to suppressing appetite, leptin may also modulate insulin secretion and action. Leptin was administered here to insulin-resistant rats to determine its effects on secretagogue-stimulated insulin release, whole body glucose disposal, and insulin-stimulated skeletal muscle glucose uptake and transport. Male Wistar rats were fed either a normal (Con) or a high-fat (HF) diet for 3 or 6 mo. HF rats were then treated with either vehicle (HF), leptin (HF-Lep, 10 mg. kg(-1). day(-1) sc), or food restriction (HF-FR) for 12-15 days. Glucose tolerance and skeletal muscle glucose uptake and transport were significantly impaired in HF compared with Con. Whole body glucose tolerance and rates of insulin-stimulated skeletal muscle glucose uptake and transport in HF-Lep were similar to those of Con and greater than those of HF and HF-FR. The insulin secretory response to either glucose or tolbutamide (a pancreatic beta-cell secretagogue) was not significantly diminished in HF-Lep. Total and plasma membrane skeletal muscle GLUT-4 protein concentrations were similar in Con and HF-Lep and greater than those in HF and HF-FR. The findings suggest that chronic leptin administration reversed a high-fat diet-induced insulin-resistant state, without compromising insulin secretion.

Low-dose IGF-I has no selective advantage over insulin in regulating glucose metabolism in hyperglycemic depancreatized dogs

At supraphysiological levels, IGF-I bypasses some forms of insulin resistance and has been proposed as a therapeutic agent in the treatment of diabetes. Unfortunately, side effects of high-dose IGF-I (100-250 microg/kg) have precluded its clinical use. Low-dose IGF-I (40-80 microg/kg), however, shows minimal side effects but has not been systematically evaluated. In our previous study under conditions of declining glucose, low-dose IGF-I infusion was more effective in stimulating glucose utilization, but less effective in suppressing glucose production and lipolysis than low-dose insulin. However, under conditions of hyperglycemia, we could not observe any differential effects between high-dose infusions of IGF-I and insulin. To determine whether the differential effects of IGF-I and insulin are dose-related or related to the prevailing glucose level, 3 h glucose clamps were performed in the same animal model as in the previous studies, i.e. the moderately hyperglycemic (175 mg/dl) insulin-infused depancreatized dog, with additional infusions of low-dose IGF-I (67.8 microg/kg, i.e. 29.1 microg/kg bolus plus 0.215 microg/kg( )per min infusion; n=5) or insulin 49.5 mU/kg (9 mU/kg bolus plus 0.45 mU/kg per min; n=7). As in the previous study under conditions of declining glucose, low-dose IGF-I had significant metabolic effects in vivo, in our model of complete absence of endogenous insulin secretion. Glucose production was similarly suppressed with both IGF-I and insulin, by 54+/-3 and 56+/-2% s.e. (P=NS) respectively. Glucose utilization was stimulated to the same extent (IGF-I 5.2+/-0.2, insulin 5.5+/-0.3 mg/kg per min, P=NS). Glucagon, free fatty acid, glycerol, alanine and beta-hydroxybutyrate, were suppressed, while lactate and pyruvate levels were raised, similarly with IGF-I and insulin. We conclude that: (i) differential effects of IGF-I and insulin may be masked under hyperglycemic conditions, independent of the hormone dose; (ii) low-dose IGF-I has no selective advantage over additional insulin in suppressing glucose production and lipolysis, nor in stimulating glucose utilization during hyperglycemia and subbasal insulin infusion when insulin secretion is absent, as in type 1 diabetes mellitus.

Calorigenic actions of leptin are additive to, but not dependent on, those of thyroid hormones

We examined a possible mechanistic interaction between leptin and thyroid hormones in rats with hypothyroidism induced by thyroidectomy (TX) and propylthiouracil administration. In study 1, the TX rats were treated by vehicle (V, n = 9) or by recombinant murine leptin (L, 0.3 mg. kg(-1). day(-1), n = 9) or were pair-fed (PF, n = 9) against L. In study 2, the TX rats were all given 3, 3'5'-triiodo-L-thyronine (T(3)) replacement (T, 5 microg. kg(-1). day(-1)) to correct hypothyroidism. They were then subdivided into three groups, namely, vehicle (T+V, n = 9), leptin (T+L, n = 10), and pair-feeding (T+PF, n = 9), similar to study 1 except for T(3) (T). Reduced food consumption and weight gain in the TX rats were reversed by T(3) replacement. Leptin suppressed food intake in the TX rats regardless of T(3) replacement. O(2) consumption (VO(2)) and CO(2) production (VCO(2)) were reduced in TX rats (P < 0.05 vs. normal) but were normalized by either T(3) or leptin treatment. T+L additively increased VO(2) and VCO(2) (P < 0.05 vs. TX, T(3), and L). The respiratory exchange ratio was unaltered in TX rats, with and without T(3), but was significantly reduced by L or T+L treatments. These results indicate that the metabolic actions of leptin are not dependent on a normal thyroid status and that the effects of leptin and T(3) on oxidative metabolism are additive.

Leptin reduces body weight gain in neonatal rats

Leptin (OB protein) elicits a neuroendocrine response to starvation and states of nutritional abundance to stabilize the proportion of body fat. Leptin has dramatic effects on food intake and energy expenditure in adult and juvenile rodents. However, whether the neonatal period is associated with the development of an effective leptin feedback system is still not known. In this study, we evaluated the effects of peripherally administered leptin on body weight changes in neonatal rats during the early suckling period (from birth to 10 d). Our results show that daily i.p. injections of leptin (0.3 microg/g and 1.0 microg/g) to neonatal rats led to a significant reduction in weight gain over 10 d compared with the control group (p < 0.01 and p < 0.01, respectively). Concomitant with a reduction in weight gain, retroperitoneal fat pad weight also significantly decreased in the leptin-treated group. Our data indicate that the potential for energy balance regulation by leptin occurs in the first day after birth. In addition, we also observed that 3 d after discontinuing leptin treatment, the body weight as well as the fat pad weight of leptin-treated pups returned to the control level. Our results demonstrate that leptin reduces body weight gain in neonatal rats.

Increased responses of glucagon and glucose production to hypoglycemia with intraperitoneal versus subcutaneous insulin treatment

The study aim was to investigate the effect of the route of insulin treatment on the glucagon and glucose production (GP) responses to hypoglycemia in the diabetic rat. Experiments were performed in 4 groups of rats: (1) streptozotocin (STZ)-induced diabetic, untreated (D, n = 7), (2) diabetic treated with subcutaneous insulin (DSC, n = 8), (3) diabetic treated with intraperitoneal insulin (DIP, n = 6), and (4) normal control (N, n = 10). Slow-release insulin implants were used in DSC and DIP rats for 10 to 14 days (3 U/d). A hyperinsulinemic (120 pmol x kg(-1) x min(-1) insulin)-hypoglycemic (glycemia = 2.5 +/- 0.1 mmol/L) clamp following an isoglycemic basal period was performed in 5-hour fasted rats. Basal plasma glucose was normalized in both DSC and DIP rats; however, in DSC but not DIP rats, glucose normalization required peripheral hyperinsulinemia. Tracer-determined GP, which was elevated in D rats, was completely normalized in DIP but only partially corrected in DSC rats. Basal glucagon levels were similar in all groups. During hypoglycemia, GP was suppressed in D rats (delta, -28.9 +/- 5.0 micromol x kg(-1) x min(-1), moderately increased in DSC rats (delta, 6.1 +/- 5.6, P < .01 v D), but markedly increased in DIP and N rats (delta, 34.5 +/- 4.5 for DIP and 16.8 +/- 2.8 for N; P < .01 vD, P < .05 for DIP v DSC or N). Plasma glucagon increased 6-fold in N (945 +/- 129 pg/mL), only doubled in D (424 +/- 54), and tripled in DSC (588 +/- 83), but increased 5-fold in DIP rats (1,031 +/- 75, P < .05 v D and DSC). We conclude that in STZ-diabetic rats, (1) intraperitoneal but not subcutaneous insulin treatment normalizes basal GP, and (2) intraperitoneal insulin treatment as compared with subcutaneous treatment alleviates peripheral hyperinsulinemia and results in increased glucagon and GP responses to hypoglycemia.

Molecular mechanism for the Shp-2 tyrosine phosphatase function in promoting growth factor stimulation of Erk activity

We have previously shown that activation of extracellular signal-regulated kinase (Erk) by epidermal growth factor (EGF) treatment was significantly decreased in mouse fibroblast cells expressing a mutant Shp-2 molecule lacking 65 amino acids in the SH2-N domain, Shp-2(Delta46-110). To address the molecular mechanism for the positive role of Shp-2 in mediating Erk induction, we evaluated the activation of signaling components upstream of Erk in Shp-2 mutant cells. EGF-stimulated Ras, Raf, and Mek activation was significantly attenuated in Shp-2 mutant cells, suggesting that Shp-2 acts to promote Ras activation or to suppress the down-regulation of activated Ras. Biochemical analyses indicate that upon EGF stimulation, Shp-2 is recruited into a multiprotein complex assembled on the Gab1 docking molecule and that Shp-2 seems to exert its biological function by specifically dephosphorylating an unidentified molecule of 90 kDa in the complex. The mutant Shp-2(Delta46-110) molecule failed to participate in the Gab1-organized complex for dephosphorylation of p90, correlating with a defective activation of the Ras-Raf-Mek-Erk cascade in EGF-treated Shp-2 mutant cells. Evidence is also presented that Shp-2 does not appear to modulate the signal relay from EGF receptor to Ras through the Shc, Grb2, and Sos proteins. These results begin to elucidate the mechanism of Shp-2 function downstream of a receptor tyrosine kinase to promote the activation of the Ras-Erk pathway, with potential therapeutic applications in cancer treatment.

Beta-blockade, but not normoglycemia or hyperinsulinemia, markedly diminishes stress-induced hyperglycemia in diabetic dogs

Stress-induced hyperglycemia can lead to significant deterioration in glycemic control in individuals with diabetes. Previously, we have shown in normal dogs that, after intracerebroventricular (ICV) administration of carbachol (a model of moderate stress), increases in both the metabolic clearance rate (MCR) of glucose and endogenous glucose production (GP) occur. However, in hyperglycemic diabetic dogs subjected to the same stress, the MCR of glucose does not increase and glycemia therefore markedly deteriorates because of stimulation of GP. Our aims were to determine the following: 1) whether insulin-induced acute normalization of glycemia, with or without beta-blockade, would correct glucose clearance and prevent the hyperglycemic effect of stress, and 2) whether hyperinsulinemia per se could correct these abnormalities. Stress was induced by ICV carbachol in 27 experiments in five alloxan-administered diabetic dogs subjected to the following protocols in random order: 1) basal insulin infusion (BI) to restore normoglycemia; 2) basal insulin infusion with beta-blockade (BI+block); 3) normoglycemic-hyperinsulinemic clamp with threefold elevation of insulin above basal (3x BI); and 4) normoglycemic-hyperinsulinemic clamp with fivefold elevation of insulin above basal (5 x BI). The BI+block protocol fully prevented stress-induced hyperglycemia, both by increasing MCR (deltaMCR at peak: 0.72 +/- 0.25 ml x kg(-1) x min(-1) vs. no change in BI, P < 0.05) and by diminishing the stress-induced increment in GP observed in BI (deltaGP at peak: 3.72 +/- 0.09 micromol x kg(-1) x min(-1) for BI+block vs. 14.10 +/- 0.31 micromol x kg(-1) x min(-1) for BI, P < 0.0001). In contrast, 3x BI and 5x BI treatments with normoglycemic-hyperinsulinemic clamps proportionately increased basal MCR at baseline, but paradoxically were not associated with an increase in MCR in response to stress, which induced a twofold increase in GP. Thus, in alloxan-administered diabetic dogs, stress increased GP but not MCR, despite normalization of glycemia with basal or high insulin. In contrast, beta-adrenergic blockade almost completely restored the metabolic response to stress to normal and prevented marked hyperglycemia, both by limiting the rise in GP and by increasing glucose MCR. We conclude that acute normalization of glycemia with basal insulin or hyperinsulinemia does not prevent hyperglycemic effects of stress unless accompanied by beta-blockade, and we speculate that short-term beta-blockade may be a useful treatment modality under some stress conditions in patients with diabetes.

Effects of diabetes and hypertension on myocardial Na+-Ca2+ exchange

Abnormalities in cardiac function have been extensively documented in experimental and clinical diabetes. These aberrations are well known to be exaggerated when hypertension and diabetes co-exist. The objective of the present study was to examine whether alterations in the activity of the myocardial Na+-Ca2+ exchanger (NCX) can account for the deleterious effects of diabetes and (or) hypertension on the heart. To this aim, the following experimental groups were studied: (i) control; (ii) diabetic; (iii) hypertensive; and (iv) hypertensive-diabetic. Wistar rats served as the control group (C) while Wistar rats injected with streptozotocin (STZ, 55 mg/kg) served as the diabetic (D) group. Spontaneously hypertensive (SH) rats were used as the hypertensive group (H) while SH rats injected with STZ served as the hypertensive-diabetic (HD) group. Sarcolemma was isolated from the ventricles of the C, D, H, and HD groups and NCX activity was examined using rapid quenching techniques to study initial rates over a [Ca2+]o range of 10-160 microM. The Vmax of NCX was lower in the D group when compared with the C group (D, 2.96 +/- 0.26 vs. C, 4.0 +/- 0.46 nmol x mgprot(-1) x s(-1), P < 0.05), however combined diabetes and hypertension (HD) did not affect the Vmax of NCX activity (HD, 3.84 +/- 0.88 vs. H, 3.59 +/- 0.24 nmol x mgprot(-1) x s(-1), P > 0.05). However, analysis of the Km values for Ca2+ indicated that both the D and HD groups exhibited a significantly lower Km when compared with their respective control groups (D, 42 +/- 4 vs. C, 56 +/- 4 microM, P < 0.05; HD, 33 +/- 7 vs. H, 51 +/- 8 microM, P < 0.05). Immunoblotting using polyclonal antibodies (against canine cardiac NCX) exhibited the typical banding of 160, 120, and 70 kDa. The 120 kDa band is believed to represent the native exchanger with its post-translational modifications. Examination of the blots revealed a lower intensity of the 120 kDa band in the D group when compared with the C group, however, no significant difference in the HD group was observed. We speculate that the lower Vmax in the D group may be due to a reduced concentration of exchanger protein in the membrane. The absence of this defect in the HD group may be a result of compensatory mechanisms to the overall hemodynamic overload, however, this remains to be determined. The increased affinity for Ca2+ in both the D and HD groups (determined by the lower Km values) is an interesting finding and may be due to changes in sarcolemmal lipid bilayer composition secondary to diabetes-induced hyperlipidemia.

Peripheral gastric leptin modulates brain stem neuronal activity in neonates

Afferent sensory fibers are the primary neuroanatomic link between nutrient-related events in the gastrointestinal tract and the central neural substrates that modulate ingestion. In this study, we evaluated the peripheral gastric effects of leptin (OB protein) on brain stem neuronal activities using an in vitro neonatal rat preparation. We also tested gastric leptin effects as a function of age in neonates. For approximately 33% of the nucleus tractus solitarius units observed, gastric leptin (10 nM) produced a significant activation of 188.2 +/- 8.6% (mean +/- SE) compared with the control level of 100% (P < 0.01). Concentration-dependent leptin effects have also been shown. The remaining neurons (67%) had no significant response to gastric leptin application. Next, we evaluated the peripheral gastric effects of leptin (10 nM) on brain stem unitary activity in three different age groups (1-2 days old, 3-5 days old, and 7-8 days old) of neonatal rats. In the 1- to 2-day-old and the 3- to 5-day-old groups, we observed that response ratios and activity levels were similar. However, there was a significant difference between the 7- to 8-day-old group and the two younger age groups in both the response ratios and the activation levels. The percentage of activation responses increased from approximately 26% in the 1- to 2-day-old and the 4- to 5-day-old age groups to 70% in the 7- to 8-day-old group (P < 0.05). The level of activation increased from 168.3 +/- 2.7% (compared with the control level) in the 1- to 2-day-old and the 4- to 5-day-old age groups to 231.4 +/- 11.9% in the 7- to 8-day-old group (P < 0.01). Our data demonstrate that peripheral gastric leptin modulates brain stem neuronal activity and suggest that gastric leptin has a significantly stronger effect in the 7- to 8-day-old animals than in the younger neonates.

Glucose uptake during centrally induced stress is insulin independent and enhanced by adrenergic blockade

Glucose utilization increases markedly in the normal dog during stress induced by the intracerebroventricular (ICV) injection of carbachol. To determine the extent to which insulin, glucagon, and selective (alpha/beta)-adrenergic activation mediate the increment in glucose metabolic clearance rate (MCR) and glucose production (R(a)), we used five groups of normal mongrel dogs: 1) pancreatic clamp (PC; n = 7) with peripheral somatostatin (0.8 microg x kg(-1) x min(-1)) and intraportal replacement of insulin (1,482 +/- 84 pmol x kg(-1) x min(-1)) and glucagon (0.65 ng x kg(-1) x min(-1)) infusions; 2) PC plus combined alpha (phentolamine)- and beta (propranolol)-blockade (7 and 5 microg x kg(-1) x min(-1), respectively; alpha+beta; n = 5); 3) PC plus alpha-blockade (alpha; n = 6); 4) PC plus beta-blockade (beta; n = 5); and 5) a carbachol control group without PC (Con; n = 10). During ICV carbachol stress (0-120 min), catecholamines, ACTH, and cortisol increased in all groups. Baseline insulin and glucagon levels were maintained in all groups except Con, where glucagon rose 33%, and alpha, where insulin increased slightly but significantly. Stress increased (P < 0.05) plasma glucose in Con, PC, and alpha but decreased it in beta and alpha+beta. The MCR increment was greater (P < 0.05) in beta and alpha+beta than in Con, PC, and alpha. R(a) increased (P < 0.05) in all groups but was attenuated in alpha+beta. Stress-induced lipolysis was abolished in beta (P < 0.05). The marked rise in lactate in Con, PC, and alpha was abolished in alpha+beta and beta. We conclude that the stress-induced increase in MCR is largely independent of changes in insulin, markedly augmented by beta-blockade, and related, at least in part, to inhibition of lipolysis and glycogenolysis, and that R(a) is augmented by glucagon and alpha- and beta-catecholamine effects.

Leptin restores euglycemia and normalizes glucose turnover in insulin-deficient diabetes in the rat

Leptin has been shown to improve insulin sensitivity and glucose metabolism in normoinsulinemic healthy or obese rodents. It has not been determined whether leptin may act independently of insulin in regulating energy metabolism in vivo. The present study was designed to examine the effects of leptin treatment alone on glucose metabolism in insulin-deficient streptozotocin (STZ)-induced diabetic rats. Four groups of STZ-induced diabetic rats were studied: 1) rats treated with recombinant methionine murine leptin subcutaneous infusion with osmotic pumps for 12-14 days (LEP; 4 mg x kg(-1) x day(-1), n = 10); 2) control rats infused with vehicle (phosphate-buffered saline) for 12-14 days (VEH; n = 10); 3) pair-fed control rats given a daily food ration matching that of LEP rats for 12-14 days (PF; n = 8); and 4) rats treated with subcutaneous phloridzin for 4 days (PLZ; 0.4 g/kg twice daily, n = 10). Phloridzin treatment normalizes blood glucose without insulin and was used as a control for the effect of leptin in correcting hyperglycemia. All animals were then studied with a hyperinsulinemic-euglycemic clamp (6 mU x kg(-1) x min(-1). Our study demonstrates that leptin treatment in the insulin-deficient diabetic rats restored euglycemia, minimized body weight loss due to food restriction, substantially improved glucose metabolic rates during the postabsorptive state, and restored insulin sensitivities at the levels of the liver and the peripheral tissues during the glucose clamp. The effects on glucose turnover are largely independent of food restriction and changes in blood glucose concentration, as evidenced by the minimal improvement of insulin action and glucose turnover parameters in the PF and PLZ groups. Our results suggest that the antidiabetic effects of leptin are achieved through both an insulin-independent and an insulin-sensitizing mechanism.

Opposite effects of acute hypoglycemia and acute hyperglycemia on glucose transport and glucose transporters in perfused rat skeletal muscle

This study was undertaken to characterize the effects of glycemia per se (glucose effectiveness) on muscle glucose transport. Isolated rat hindlimbs were perfused in situ for 2 h with perfusate containing either low (2 mmol/l, n = 7), normal (6.5 mmol/l, n = 6), or high (20 mmol/l, n = 6) concentrations of glucose, without insulin, to simulate hypo-, eu-, and hyperglycemic conditions. The effect of varying glucose concentrations on muscle glucose transport was assessed by an ensuing 30-min perfusion with 5.5 mmol/l glucose perfusate without insulin. The 2-h of low glucose perfusion induced significant increases in both muscle glucose clearance (approximately 2.3-fold, P < 0.01) and plasma membrane GLUT4 content (approximately 20%, P < 0.05) relative to normal. In contrast, high glucose perfusion decreased glucose clearance (approximately 1.7-fold, P < 0.01) and plasma membrane GLUT4 content (approximately 20%, P < 0.05). Glucose extraction during the following 30-min perfusion was 2.5-fold greater (P < 0.0001) in the low group and threefold less (P < 0.0001) in the high group, relative to normal. 2-[3H]deoxyglucose-6-phosphate content in both red (soleus) and white (extensor digitorum longus) muscles increased approximately twofold after 2 h of low glucose perfusion (P < 0.0001) and decreased > or =2-fold after high glucose perfusion (P < 0.0001), relative to normal. It is concluded that glycemia regulates glucose transport in skeletal muscle independently of insulin, achieved at least partially via changes in plasma membrane GLUT4. We propose that high glucose levels can acutely downregulate GLUT4 and glucose clearance, thus limiting excessive glucose uptake in muscle. Conversely, low glucose-induced upregulation of muscle glucose clearance and GLUT4 can compensate for reduced glucose availability in the circulation.

Glucagon-like peptide 1 increases insulin sensitivity in depancreatized dogs

To determine whether glucagon-like peptide (GLP)-1 increases insulin sensitivity in addition to stimulating insulin secretion, we studied totally depancreatized dogs to eliminate GLP-1's incretin effect. Somatostatin was infused (0.8 microg x kg(-1) x min(-1)) to inhibit extrapancreatic glucagon in dogs, and basal glucagon was restored by intraportal infusion (0.65 ng x kg(-1) x min(-1)). To simulate the residual intraportal insulin secretion in type 2 diabetes, basal intraportal insulin infusion was given to obtain plasma glucose concentrations of approximately 10 mmol/l. Glucose was clamped at this level for the remainder of the experiment, which included peripheral insulin infusion (high dose, 5.4 pmol x kg(-1) x min(-1), or low dose, 0.75 pmol x kg(-1) x min(-1)) with or without GLP-1(7-36) amide (1.5 pmol x kg(-1) x min(-1)). Glucose production and utilization were measured with 3-[3H]glucose, using radiolabeled glucose infusates. In 12 paired experiments with six dogs at the high insulin dose, GLP-1 infusion resulted in higher glucose requirements than saline (60.9+/-11.0 vs. 43.6+/-8.3 micromol x kg(-1) x min(-1), P< 0.001), because of greater glucose utilization (72.6+/-11.0 vs. 56.8+/-9.7 micromol x kg(-1) x min(-1), P<0.001), whereas the suppression of glucose production was not affected by GLP-1. Free fatty acids (FFAs) were significantly lower with GLP-1 than saline (375.3+/-103.0 vs. 524.4+/-101.1 micromol/l, P<0.01), as was glycerol (77.9+/-17.5 vs. 125.6+/-51.8 micromol/l, P<0.05). GLP-1 receptor gene expression was found using reverse transcriptase-polymerase chain reaction of poly(A)-selected RNA in muscle and adipose tissue, but not in liver. Low levels of GLP-1 receptor gene expression were also found in adipose tissue using Northern blotting. In 10 paired experiments with five dogs at the low insulin dose, GLP-1 infusion did not affect glucose utilization or FFA and glycerol suppression when compared with saline, suggesting that GLP-1's effect on insulin action was dependent on the insulin dose. In conclusion, in depancreatized dogs, GLP-1 potentiates insulin-stimulated glucose utilization, an effect that might be contributed in part by GLP-1 potentiation of insulin's antilipolytic action.

Differential effects of leptin in regulation of tissue glucose utilization in vivo

We have recently shown that leptin enhances systemic insulin sensitivity and whole body glucose utilization in the rat. This study examines our hypothesis that leptin has differential effects in regulating glucose utilization among the tissues, i.e. stimulating glucose utilization in brown adipose tissue (BAT) and skeletal muscle but suppressing glucose utilization in white adipose tissue (WAT) in normal male rats (275-350 g BW). The rats were treated with s.c. infusion of recombinant murine leptin (4 mg/kg x day) or vehicle (V) with Alzet osmotic pumps or with vehicle and pair-feeding (PF) for 7 days. Leptin significantly decreased food intake (leptin, 11.5 +/- 0.4 g/day; V, 16.8 +/- 1.5 g/day; P < 0.05) and body weight (maximum change, 5.0 +/- 0.2%; P < 0.05 vs. V) and lowered plasma triglyceride, insulin, and glucose levels, but raised beta-hydroxybutyrate levels. Glucose utilization by individual tissues was determined with an i.v. bolus of [1-(14)C]2-deoxyglucose (2-DG) after a 90-min hyperinsulinemic (2 mU/kg x min) euglycemic clamp. With leptin treatment, the 2-DG-determined glucose utilization in interscapular BAT was almost 3-fold that in V-treated rats and 70% greater than that in PF rats. In contrast, in the epididymal WAT, glucose utilization was reduced by leptin treatment to only 34% that in V-treated rats and 45% that in PF rats. Leptin increased 2-DG uptake by extensor digitorum longus muscle and soleus muscle compared with that in the V and PF groups. With leptin treatment, the GLUT4 glucose transporter mRNA and protein levels were increased in BAT, but decreased in WAT (both P < 0.05). There was no significant change in GLUT4 mRNA and protein expression in extensor digitorum longus muscle and soleus muscle. Oxygen consumption was significantly increased (32.1 +/- 7.4%) in BAT (139.0 +/- 8.2 nmole O2/30 min x 10(6) cells) of leptin-treated rats vs. that in V control rats (105.3 +/- 6.7 nmole O2/30 min x 10(6) cells). In conclusion, leptin has differential, tissue-specific effects on glucose and oxygen utilization, which contribute to the reduction in whole body adiposity by enhancing energy consumption in BAT and muscle while attenuating energy storage in WAT.

Free fatty acids impair hepatic insulin extraction in vivo

Hyperinsulinemia is a common finding in obesity and results from insulin hypersecretion and impaired hepatic insulin extraction. In vitro studies have shown that free fatty acids (FFAs), which are often elevated in obesity, can impair insulin binding and degradation in isolated rat hepatocytes. To investigate whether FFAs impair hepatic insulin extraction (E(H)) in vivo, either saline (SAL) or 10% Intralipid (0.03 ml x kg(-1) x min(-1)) plus heparin (0.44 U x kg(-1) x min(-1)) (IH) was infused into normal dogs to elevate FFA levels. Insulin was infused intraportally at 18 pmol x kg(-1) x min(-1) for 150 min (period A, high insulin dose), and then at 2.4 pmol x kg(-1) x min(-1) for another 150 min (period B, low insulin dose). After the low portal insulin dose, additional insulin was infused peripherally at 8.4 pmol x kg(-1) x min(-1) for 120 min (period C) to assess the clearance of insulin from the peripheral plasma. In 16 paired experiments, FFA levels were 1,085 +/- 167, 1,491 +/- 240, 1,159 +/- 221 micromol/l (IH) and 221 +/- 44, 329 +/- 72, 176 +/- 44 micromol/l (SAL) in periods A, B, and C, respectively. Peripheral insulin levels were greater with IH (P < 0.001) than with SAL in all periods (1,620 +/- 114, 126 +/- 12, 1,050 +/- 72 pmol/l for IH vs. 1,344 +/- 168, 96 +/- 4.2, 882 +/- 60 pmol/l for SAL). Glucose clearance was impaired by IH in all periods (P < 0.05), whereas glucose production was slightly increased by IH during period B. Peripheral insulin clearance (Cl) and E(H) were calculated from the insulin infusion rate and insulin concentration data in each period by taking into account the nonlinearity of insulin kinetics. Cl was lower (P < 0.01) with IH (9.6 +/- 0.6, 12.0 +/- 0.9, 10.2 +/- 0.6 ml x kg(-1) x min(-1)) than with SAL (11.2 +/- 1, 13.6 +/- 0.7, 11.9 +/- 0.9 ml x kg(-1) x min(-1)) in periods A, B, and C. E(H) was also lower (P < 0.05) with IH (25 +/- 4, 40 +/- 5, 32 +/- 5%) than with SAL (30 +/- 2.8, 47 +/- 3, 38 +/- 3%). We conclude that FFAs can impair hepatic insulin extraction in vivo at high and low insulin levels, an effect that may contribute to the peripheral hyperinsulinemia of obesity.

Increased dependence of glucose production on peripheral insulin in diabetic depancreatized dogs

We have recently found that in nondiabetic dogs and humans, suppression of glucose production (GP) is mediated by both peripheral and hepatic effects of insulin. We have also found that both nonesterified fatty acids (NEFA) and glucagon are important determinants of the peripheral effect of insulin on GP. However, in moderately hyperglycemic depancreatized dogs, suppression of GP appeared to be mediated by peripheral but not hepatic insulin. In this latter study, insulin concentrations were in the high postprandial range (approximately 300 pmol/L) and suppression of GP may have been close to maximum. The aim of the present study was to determine whether GP can be regulated by hepatic insulin in depancreatized dogs at low insulin concentrations in the postabsorptive range. Depancreatized dogs were maintained at moderately hyperglycemic levels (approximately 10 mmol/L) by subbasal insulin infusions. In paired experiments, additional low-dose equimolar insulin infusions (0.75 pmol/kg x min) were administered peripherally (PER, n = 6) or portally (POR, n = 6) during glucose clamps. This resulted in a minimal increase in peripheral insulin levels, which was greater in PER versus POR, 29.0 +/- 3.7 versus 11.7 +/- 2.2 pmol/L. Also, we infused insulin peripherally at half this rate (1/2 PER, n = 6) to match the increase in peripheral insulin levels in POR (1/2 PER, 14.6 +/- 2.2) and thus obtain a selective POR versus 1/2 PER difference in hepatic sinusoidal insulin levels. PER suppressed GP more than POR (45.4% +/- 4.0% v 35.3% +/- 6.8%, P < .001), whereas POR did not suppress GP more than 1/2 PER (35.6% +/- 6.3%). Therefore, suppression of GP was proportional to peripheral rather than hepatic sinusoidal insulin levels, as in our previous study at higher insulin concentrations. In conclusion, during glucose clamps in moderately hyperglycemic depancreatized dogs, (1) suppression of GP was dominated by insulin's peripheral effects not only at postprandial but also postabsorptive insulin levels, and (2) we found no evidence for a hepatic effect of insulin in suppressing GP. We hypothesize that this effect is reduced in the depancreatized dog model of diabetes due to hepatic insulin resistance and/or hyperglycemia.

Intracerebroventricular administration of leptin markedly enhances insulin sensitivity and systemic glucose utilization in conscious rats

This study examines the acute, subacute (overnight), and chronic (7-day) effects of intracerebroventricular (i.c.v.) administration of r-metMuLeptin on insulin sensitivity and systemic glucose turnover in conscious unrestrained rats (body weight, 250 to 300 g). Under postabsorptive conditions, acute i.c.v. leptin ([AL] 10 microg bolus) did not affect tracer (3-(3)H-glucose)-determined glucose production (GP) and utilization (GU) rates during the 2-hour hyperinsulinemic (2 mU x kg(-1) x min(-1)) euglycemic clamp. Chronic i.c.v. leptin ([CL] 10 microg/d for 7 days) administered by osmotic pumps markedly reduced the daily food consumption (P < .05), body weight (P < .05), and postabsorptive basal plasma glucose level (P < .01). During the glucose clamp, GP was markedly suppressed (55%) with CL (P < .001 v vehicle and pair-fed control groups). The insulin-induced increment in GU was significantly greater with CL (23.3 +/- 1.8 mg(-1) x kg(-1) x min(-1)) than with vehicle (16.9 +/- 0.2) and pair-feeding (17.1 +/- 0.6, both P < .001). Subacute i.c.v. leptin ([SL] 10 microg bolus) moderately but insignificantly decreased overnight food consumption (-18%) and body weight (-2.5 +/- 1.5 g). The glucose infusion rate during the final 60 minutes of the glucose clamp was 43% greater than for the vehicle group (P < .0001). SL also significantly increased GU (P < .005) and suppressed GP (P < .05) during the glucose clamp. Thus, we conclude that i.c.v. administered leptin has strong actions on the central nervous system that result in significant increases in insulin sensitivity and systemic GU, and these effects are achieved as early as overnight after leptin administration.

Downregulation of platelet-derived growth factor receptor-beta in Shp-2 mutant fibroblast cell lines

The SH2-containing tyrosine phosphatase Shp-2 appears to function downstream of a variety of growth factor receptors and might play a positive role in cell proliferation. Here we report that expression of the beta subunit of platelet-derived growth factor receptor (PDGFR-beta) was specifically downregulated in mutant fibroblasts lacking a functional Shp-2, while the levels of PDGFR-alpha EGFR and IGFIR were not changed. PDGF-stimulated DNA synthesis and extracellular signal regulated kinase (Erk) activation was severely suppressed in mutant cells. RasGAP, that responds to activation of PDGFR-beta but not PDGFR-alpha, was not phosphorylated on tyrosine in mutant cells upon PDGF-treatment. Northern blot analysis failed to detect PDGFR-beta mRNA in mutant cells. The transcription initiation from the PDGFR-beta gene promoter was not significantly changed, but the half-life of its mRNA was shortened in Shp-2 mutant cells. These observations indicate that Shp-2 not only participates in transmission of signals from growth factor receptors but also plays a specific role in the control of the PDGFR-beta expression. We propose that this is an important mechanism for the positive control of cell proliferation by Shp-2.

The Shp-2 tyrosine phosphatase has opposite effects in mediating the activation of extracellular signal-regulated and c-Jun NH2-terminal mitogen-activated protein kinases

Shp-2 is a widely expressed cytoplasmic tyrosine phosphatase with two SH2 domains. A targeted mutant allele of the Shp-2 gene with a deletion of 65 amino acids in the NH2-terminal SH2 domain was created that leads to embryonic lethality at mid-gestation in homozygous mutant mice. To define the Shp-2 function in cell signaling, we have established mutant fibroblast cell lines, and have examined the effect of the Shp-2 mutation on extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) mitogen-activated protein (MAP) kinase pathways. Insulin-like growth factor (IGF)-I-induced ERK activation was completely abolished, while ERK activity upon platelet-derived growth factor and epidermal growth factor stimulation was significantly reduced and shortened in mutant cells. Stimulation of ERK by phorbol 12-myristate 13-acetate was not affected in mutant cells, but the phorbol 12-myristate 13-acetate-induced ERK activity decayed much faster compared with that in wild-type cells. In contrast, JNK activation upon heat shock was significantly enhanced in Shp-2 mutant cells. Based on these results, we conclude that Shp-2 plays differential positive regulatory roles in various mitogenic signaling pathways leading to ERK activation, and that Shp-2 is a negative effector in JNK activation by cellular stress. This is the first evidence that a tyrosine phosphatase has opposite effects in mediating the activation of ERK and JNK MAP kinases.

Insulin acutely suppresses glucose production by both peripheral and hepatic effects in normal dogs

To determine whether the predominant effect of insulin in suppressing tracer-determined glucose production (Ra) is hepatic or peripheral, we infused insulin peripherally (PER) and portally (POR) at both low (0.75 pmol.kg-1.min-1) and high physiological rates (2.7 pmol.kg-1.min-1) during euglycemic clamps in normal dogs. We also infused insulin peripherally at one-half these rates (1/2 PER) to match the peripheral insulin levels in POR and thus obtain a selective POR vs. 1/2 PER difference in hepatic insulin levels. At the high-rate insulin infusion, peripheral insulin levels were greatest with PER (PER = 212 +/- 10 pM, n = 5; POR = 119 +/- 5 pM, n = 6; 1/2 PER = 122 +/- 5 pM, n = 6). Calculated hepatic insulin levels were greatest with POR (POR = 227 +/- 13 pM, PER = 206 +/- 19 pM, 1/2 PER = 123 +/- 8 pM). High-dose PER yielded a greater suppression of Ra than POR (79 +/- 18 vs. 56 +/- 6%, P < .001). Ra was only suppressed by 45 +/- 6% with 1/2 PER (P < 0.01 vs. POR on 6 paired experiments). Free fatty acid (FFA) was suppressed by 57 +/- 8% with PER and only by 33 +/- 5 and 37 +/- 2% with POR and 1/2 PER, respectively. The low-dose PER and POR yielded an equal Ra suppression (PER = 46 +/- 9%, POR = 43 +/- 4%). Only 1/2 PER was associated with a lower suppression of Ra (36 +/- 8, P < 0.05 vs. POR). FFA showed similar suppression in all three groups (approximately 25%). Using both insulin infusion rates, the percent Ra suppression per unit difference in peripheral insulin was approximately twofold greater than that per unit difference in hepatic insulin. These results suggest that, during euglycemic clamps without somatostatin in normal dogs, Ra suppression is mediated by both peripheral and hepatic effects of insulin and that peripheral insulin, at least at high physiological infusion rates, is more potent than hepatic insulin in suppressing Ra.

Quantitative measurement of islet glucagon response to hypoglycemia by confocal fluorescence imaging in diabetic rats: effects of phlorizin treatment

We have shown that the glucagon irresponsiveness to hypoglycemia in diabetic rats is markedly improved by correction of hyperglycemia independent of insulin. In contrast, normalization of glycemia by insulin did not improve this response. To find out whether these glucagon responses reflect changes in islet glucagon, we directly quantified glucagon area and content in each pancreatic islet by using fluorescent immunostaining and computerized image analysis with confocal laser scanning microscopy (CLSM). The pancreases were analyzed in four groups of rats. 1. Normal controls (NC, n = 4), streptozotocin (65 mg/kg) diabetic rats. 2. Diabetic untreated (DU, n = 4). 3. Diabetic Phlorizin-treated, (0.4 g/kg), twice daily for 4 d (DP, n = 4). 4. Diabetic insulin-treated, using sustained release (2-3 U/d) insulin implant for 5 d (DI, n = 4). Basal plasma glucose was 7.4 +/- 0.3 mM in NC, increased to 14.5 +/- 2.2 mM in DU, which was normalized in DP (5.5 +/- 0.5) and DI (6.7 +/- 0.8). Acute hypoglycemia (H) was induced by i.v. insulin injection. The rats were sacrificed 2 h after insulin injection and the pancreas was removed. By imaging with CLSM, we quantified: 1. Percent of glucagon containing A-cell area/islet area, 2. Fluorescence intensity per islet area, which indicated glucagon content in the islet. 3. Fluorescence intensity per glucagon area indicating glucagon concentration in A-cells. In NC, glucagon containing A cell area was 21 +/- 2% of the islet area, and glucagon intensity and concentration was 11 +/- 1 U and 36 +/- 3.0 U, respectively, in basal (O) state and did not change in (H). In DU, glucagon area increased 183% (O) and 166% (H), and islet glucagon intensity increased by 235% (O) (p < 0.05), but decreased to 135% in H. Glucagon area in DP and DI did not differ significantly from DU. However, hypoglycemia in DP increased glucagon intensity in islet further to 306% of normal control (p < 0.05), suggesting marked increase in glucagon content indicating increased synthesis. In contrast, DI compared to DP showed a decrease in glucagon intensity in islet (46 +/- 3, DP to 22 +/- 2 DI; p < 0.05) in (H) state. Glucagon concentration followed the same pattern as its intensity.

CONCLUSION

1. Increase in islet glucagon content in diabetic rats was associated with increase in glucagon containing A-cell area per islet. 2. Phlorizin-induced insulin independent correction of hyperglycemia increased glucagon content per islet in hypoglycemic state. This, in part, probably contributed to improved glucagon response to hypoglycemia observed earlier 3. Normalization of glycemia with insulin reduced glucagon content of each islet during hypoglycemia. This may explain, in part, unresponsiveness of glucagon to hypoglycemia often observed in insulin-dependent diabetes mellitus (IDDM) with intensive insulin therapy.

Insulin-independent acute restoration of euglycemia normalizes the impaired glucose clearance during exercise in diabetic dogs

At rest and during exercise, chronic hyperglycemia, high free fatty acid (FFA) oxidation, and insulin deficiency in diabetes are well known to impair glucose clearance (metabolic clearance rate [MCR]). The effect of acute restoration of glycemia per se on MCR has been less well characterized. We therefore studied normal and alloxan-diabetic dogs both at rest and during exercise, as diabetic hyperglycemic or after acutely induced euglycemia (<160 min) generated by infusion of either insulin or phlorizin. Glucose uptake was similar under hyperglycemic and normoglycemic conditions both at rest and during exercise, indicating a precise balance between the mass effect of glucose and decreased MCR. Rest and exercise MCR was fourfold lower under conditions of hyperglycemia, but insulin-independent restoration of euglycemia improved basal MCR threefold and normalized MCR during exercise. High FFA turnover did not affect glucose uptake but was correlated with plasma lactate concentrations (r = 0.72, P < 0.001), suggesting that muscle fuel requirements are controlled by glucose oxidation and not uptake. We conclude that in alloxan-diabetic dogs, the impaired MCR may be an adaptive phenomenon because correction of hyperglycemia corrects MCR despite partial insulin deficiency and high FFA turnover. We speculate that constant glucose uptake despite hyperglycemia in diabetes may protect the muscle from excessive exposure to glucose.

Nerve-induced disruption and reformation of beta1-integrin aggregates during development of the neuromuscular junction

The earliest biochemical change detected during synaptogenesis is a local elimination of muscle basal lamina proteins. To explore whether this provides signal(s) that regulate postsynaptic differentiation, we examined the effects of innervation on the distribution of beta1-integrins, which were initially present in scattered aggregates complexed with basal lamina ligands. These beta1-integrin aggregates disappear along paths of nerve contact as their basal lamina ligands are eliminated. New accumulations of these proteins then form during assembly of the postsynaptic apparatus. The new beta1-integrin aggregates at developing synapses form partly via a redistribution of mobile molecules on muscle surface. We thus consider whether (a) the removal of integrins' basal lamina ligands alters their cytoplasmic ligand-interactions, causing the dissociation of integrin clusters, and (b) this receptor modulation helps to transduce local changes in pericellular protease activity into cytoplasmic signals that control postsynaptic differentiation.

A deletion mutation in the SH2-N domain of Shp-2 severely suppresses hematopoietic cell development

Shp-1 and Shp-2 are cytoplasmic protein tyrosine phosphatases that contain two Src homology 2 (SH2) domains. A negative regulatory role of Shp-1 in hematopoiesis has been strongly implicated by the phenotype of motheaten mice with a mutation in the Shp-1 locus, which is characterized by leukocyte hypersensitivity, deregulated mast cell function, and excessive erythropoiesis. A targeted deletion of 65 amino acids in the N-terminal SH2 (SH2-N) domain of Shp-2 leads to an embryonic lethality at midgestation in homozygous mutant mice. To further dissect the Shp-2 function in hematopoietic development, we have isolated homozygous Shp-2 mutant embryonic stem (ES) cells. Significantly reduced hematopoietic activity was observed when the mutant ES cells were allowed to differentiate into embryoid bodies (EBs), compared to the wild-type and heterozygous ES cells. Further analysis of ES cell differentiation in vitro showed that mutation in the Shp-2 locus severely suppressed the development of primitive and definitive erythroid progenitors and completely blocked the production of progenitor cells for granulocytes-macrophages and mast cells. Reverse transcriptase PCR analysis of the mutant EBs revealed reduced expression of several specific marker genes that are induced during blood cell differentiation. Stem cell factor induction of mitogen-activated protein kinase activity was also blocked in Shp-2 mutant cells. Taken together, these results indicate that Shp-2 is an essential component and primarily plays a positive role in signaling pathways that mediate hematopoiesis in mammals. Furthermore, stimulation of its catalytic activity is not sufficient, while interaction via the SH2 domains with the targets or regulators is necessary for its biological functions in cells. The in vitro ES cell differentiation assay can be used as a biological tool in dissecting cytoplasmic signaling pathways.

Direct and indirect effects of insulin in suppressing glucose production in depancreatized dogs: role of glucagon

We have previously shown that during glucose clamps in moderately hyperglycemic depancreatized dogs: 1) peripheral insulin infusion, resulting in greater systemic insulinemia and greater suppression of glucagon than equidose portal infusion, inhibited glucose production (GP) to a greater extent; and 2) portal and half-dose peripheral infusions, resulting in matched peripheral insulinemia and similar suppression of glucagon, inhibited GP equally. These findings are consistent with an indirect effect of insulin in suppressing GP in diabetic dogs, which might be partly mediated by the differential suppression of glucagon. To address this question, we performed the experimental protocols of the previous study under conditions of constant glucagon levels (approximately 550 ng/liter), achieved by a high rate portal glucagon infusion (5 ng/kg.min). As in the previous study (basal glucagon levels, approximately 170 ng/liter), we used depancreatized dogs and assessed GP with HPLC-purified [6(-3)H]glucose. After obtaining constant basal hyperglycemia (approximately 10 mM) with portal infusions of insulin (4.8 +/- 0.5 pmol/kg.min) and glucagon, an additional infusion of insulin was administered for 180 min, either portally (portal; n = 7) or peripherally (peripheral; n = 8) at the same rate (5.4 pmol/kg.min) or at half that rate peripherally (1/2 periph; n = 5). Plasma glucose and glucose specific activities were clamped at basal levels. Systemic insulin levels increased by 215 +/- 16,310 +/- 26, and 184 +/- 15 pM, and estimated hepatic insulin levels increased by 398 +/- 20, 310 +/- 26, and 184 +/- 15 pM with portal, peripheral, and 1/2 periph, respectively. GP was suppressed to the same extent with portal and peripheral (53 +/- 6% and 50 +/- 6%), but less with 1/2 periph (35 +/- 5%). FFA levels were suppressed to a greater extent with peripheral than portal or 1/2 periph, whereas the responses of lactate alanine and glycerol to insulin infusion were similar in the three groups. Thus, in the present report, unlike in our previous study, 1) suppression of GP was proportional to the hepatic insulin levels; and 2) systemic insulin levels did not dominate suppression of GP. We, therefore, conclude that in hyperglycemic depancreatized dogs 1) glucagon, at concentrations seen in poorly controlled diabetes, can unmask a direct effect of hepatic insulin levels on GP; and 2) the suppression of glucagon may play a role in the peripheral effect of exogenously delivered insulin on GP. This is the first in vivo study to show that the main direct effect of insulin on the liver is to counteract the effect of glucagon.

The effect of pioglitazone on hepatic glucose uptake measured with indirect and direct methods in alloxan-induced diabetic dogs

Pioglitazone, a thiazolidinedione derivative, ameliorates hyperglycemia by augmenting peripheral glucose disposal and suppressing hepatic glucose production in diabetic animals. However, the effect of this agent on hepatic glucose uptake has not been explored. To determine this, experiments were conducted in alloxan-induced diabetic dogs with (pioglitazone group, n = 7) or without (control group, n = 5) a 10-day oral treatment with pioglitazone (1 mg x kg(-1) x day(-1)). A euglycemic-hyperinsulinemic (insulin infusion rate 25.2 pmol x kg(-1) x min(-1)) clamp was maintained by adjusting the peripheral glucose infusion rate (GIR). After a 60-min basal period (period I), portal glucose infusion (Pinf, 33.3 micromol x kg(-1) x min(-1)) was administered for 120 min (period II). This was followed by a 60-min recovery period (period III). Arterial insulin levels were kept stable in the supraphysiological range throughout the experiment (1,623 +/- 52, pioglitazone group; 1,712 +/- 52 pmol/l, C group). There was no significant difference in whole-body glucose utilization determined by [3-3H]glucose between the pioglitazone and C groups in period I (68.4 +/- 2.8 vs. 70.1 +/- 2.8 micromol x kg(-1) x min(-1), respectively) and period III (81.2 +/- 5.0 vs. 74.5 +/- 3.3 micromol x kg(-1) x min(-1), respectively). Net hepatic glucose uptake (NHGU) determined by arteriovenous difference method was approximately zero in the basal period (-0.7 +/- 1.1, pioglitazone group; 0.1 +/- 1.2 micromol x kg(-1) x min(-1), C group). In period II, hepatic glucose uptake, determined by the changes in GIR, was significantly higher in the pioglitazone group (6.5 +/- 0.6 micromol x kg(-1) x min(-1)) than in the C group (-0.4 +/- 0.6 micromol x kg(-1) x min(-1), P < 0.001). This observation was also confirmed by NHGU during portal glucose infusion (6.9 +/- 1.4 vs. 2.1 +/- 1.8 micromol x kg(-1) x min(-1), pioglitazone vs. C, respectively; P < 0.025). We conclude that pioglitazone treatment enhances hepatic glucose uptake during portal glucose loading in alloxan-induced diabetic dogs. However, in hyperinsulinemic conditions, pioglitazone does not enhance the already high peripheral glucose uptake.

Proteolytic disruption of laminin-integrin complexes on muscle cells during synapse formation

To explore whether a neural modulation of muscle integrins' extracellular ligand interactions contributes to synapse induction, we compared the distributions of beta1-integrins and basal lamina proteins on Xenopus myotomal myocytes developing in culture. beta1-Integrins formed numerous organized aggregates scattered over the entire muscle surface, with particularly dense accumulations at specialized sites resembling myotendinous and neuromuscular junctions. Integrin aggregates on muscle cells differed from those on surrounding fibroblasts and epithelial cells, both in their lack of response to cross-linking by multivalent ligands and in their consistent association with the cells' own extracellular matrices. Muscle integrin clusters were usually associated with congruent basal lamina accumulations containing laminin and a heparan sulfate proteoglycan (HSPG), sometimes including fibronectin and vitronectin acquired from the surrounding medium. Immediately prior to synaptic differentiation, any existing laminin and HSPG accumulations along the path of cell contact were eliminated, disrupting otherwise stable laminin-integrin complexes. This apparently proteolytic modulation of integrins' extracellular ligand interactions was soon followed by the accumulation of new congruent accumulations of laminin and HSPG in the developing synaptic basal lamina. Combining these results with earlier findings, we consider the possibility that postsynaptic differentiation is induced, at least in part, by the proteolytic disruption of integrin-ligand complexes at sites of nerve-muscle contact.

Glucagon response to hypoglycemia is improved by insulin-independent restoration of normoglycemia in diabetic rats

The aim of this study was to determine whether the impaired glucagon response to insulin-induced hypoglycemia in the diabetic rat can be improved by correction of hyperglycemia independent of insulin. Four groups of age-matched male Sprague-Dawley rats (246 +/- 13 g BW) were studied: 1) normal controls (NC; n = 7); 2) diabetic, untreated (DU; n = 6); 3) diabetic, treated for 5-7 days using sustained release (2-3 U/day) insulin implants (DI; n = 6); and 4) diabetic, treated for 3-4 days with phlorizin (0.4 g/kg), given sc twice daily (DP; n = 7). Diabetes was induced by a single injection of streptozotocin (65 mg/kg). Basal plasma glucose was 7.4 +/- 0.3 mM in NC, but rose to 14.5 +/- 2.2 mM in DU. Basal hyperglycemia was corrected with phlorizin and insulin treatments (5.5 +/- 0.5 and 6.7 +/- 0.8 mM, respectively). NC rats responded to insulin-induced hypoglycemia with a rapid and marked increase in glucagon (peak, 2059 +/- 311 pg/ml). The glucagon response was blunted in DU (635 +/- 180 pg/ml) and was partially improved by prolonged normalization of glycemia in DP (1335 +/- 295 pg/ml; P < 0.05). Plasma somatostatin levels in all diabetic groups were 2- to 3-fold higher in the basal state, but were not different during hypoglycemia, than those in NC rats. Compared to levels in NC rats, diabetes resulted in decreased insulin, but elevated glucagon and somatostatin concentrations in the pancreatic tissue. Treatment with both insulin and phlorizin reversed the changes in the pancreatic content of both glucagon and somatostatin. Pancreatic proglucagon messenger RNA did not show significant differences among the four groups in either state. Insulin treatment in the DI group resulted in a delayed and much smaller increase in the glucagon response (740 +/- 138 pg/ml) to hypoglycemia despite normalization of glycemia. We, therefore, conclude that in streptozotocin-diabetic rats, the impaired glucagon responsiveness to hypoglycemia is significantly improved by insulin-independent correction of hyperglycemia, suggesting the importance of normoglycemia per se in maintaining, at least in part, the glucose sensitivity of pancreatic alpha-cells.

Grap is a novel SH3-SH2-SH3 adaptor protein that couples tyrosine kinases to the Ras pathway

A human cytoplasmic signaling protein has been cloned that possesses the same structural arrangement of SH3-SH2-SH3 domains as Grb2. This protein is designated Grap for Grb2-related adaptor protein. The single 2.3-kilobase (kb) grap transcript was expressed predominantly in thymus and spleen, while the ubiquitously expressed grb2 gene produced two mRNA species of 3.8 and 1.5 kb. Grap and Grb2 consist of 217 amino acids and share 59% amino acid sequence identity, with highest homology in the N-terminal SH3 domain. The GrapSH2 domain interacts with ligand-activated receptors for stem cell factor (c-kit) and erythropoietin (EpoR). Grap also forms a stable complex with the Bcr-Abl oncoprotein via its SH2 domain in K562 cells. Furthermore, Grap is associated with a Ras guanine nucleotide exchange factor mSos1, primarily through its N-terminal SH3 domain. These results show that a family of Grb2-like proteins exist and couple signals from receptor and cytoplasmic tyrosine kinases to the Ras signaling pathway.

A moderate decline in specific activity does not lead to an underestimation of hepatic glucose production during a glucose clamp

We have previously shown that modeling errors lead to underestimation of hepatic glucose production (HGP) during glucose clamps when specific activity (SA) declines markedly. We wished to assess whether the failure to keep SA constant substantially affects calculation of HGP during insulin infusion when glucose requirements to maintain the glucose clamp are moderate. Therefore, 150-minute hyperinsulinemic (5.4 pmol - kg (-1) - min (-1) clamps were performed in depancreatized dogs that were maintained hyperglycemic (approximately 10 mmol/L with either (l) unlabeled glucose infusate (COLD Ginf, n = 5) or (2) labeled glucose infusate (HOT Ginf, n = 6) containing high-performance liquid chromatography (HPLC purified [6-3H]glucose. Insulinemia and glucagonemia were similar between the two groups. Additionally, glucose infusion rates were equivalent with COLD and HOT Ginf, indicating comparable insulin effects on overall glucose metabolism. The SA decreased a maximum of 32% with COLD Ginf, but remained constant with HOT Ginf. HGP was suppressed equally with COLD or HOT Ginf treatments at each time point during the clamp (mean suppression during last hour of clamp, 69% +/- 4% and 69% +/- 5%, P = NS, COLD and HOT Ginf, respectively). We conclude that when glucose requirements are moderate and SA changes slowly, as in the diabetic dog, it is not necessary to keep SA perfectly constant to avoid significant modeling errors when calculating HPG during hyperinsulinemic clamps.

Determinants of glucose turnover in the pathophysiology of diabetes: an in vivo analysis in diabetic dogs

Hyperglycaemia in diabetes results from a combination of increased hepatic glucose production and decreased metabolic clearance of glucose. Our report summarizes recent work conducted in our laboratory to investigate the regulatory factors involved in the control of glucose turnover in diabetes. The action of insulin, both directly and indirectly, in regulating glucose turnover in diabetic dogs is considered. 1) In the depancreatized diabetic dog, peripheral rather than portal insulin levels determine the suppression of hepatic glucose production via indirect mechanisms such as limiting, precursors for gluconeogenesis and/or inhibiting glucagon secretion. 2) The differential effects of insulin and insulin-like growth factor I on glucose turnover may be dependent on a decline in glycaemia since previously observed differential effects on glucose turnover were masked under conditions of clamped hyperglycaemia in the depancreatized dog. 3) In a paradoxical dichotomous fashion, hyperglycaemia both contributes to, and compensates for, defective glucose clearance in diabetes. Acute restoration of euglycaemia significantly improves glucose clearance at rest and normalizes the exercise-induced increment in clearance in alloxan-diabetic dogs. 4) Our model of centrally-induced stress also shows that an increase in glucose utilization and clearance is largely independent of changes in insulin and that the combined effects of catecholamines and glucagon are responsible for increasing glucose production.

Erratic deposition of agrin during the formation of Xenopus neuromuscular junctions in culture

In order to disclose the mechanism that regulate synapse development we compared the distributions of agrin, acetylcholine receptors (AChR) and a basal lamina heparan sulfate proteoglycan (HSPG) in sections and cultures prepared from Xenopus laevis and Ambystoma mexicanum embryos. While agrin, AChR and HSPG may accumulate almost synchronously at synapses in vivo, agrin deposition usually lagged well behind the other synaptic markers during development in culture, and was not detectable at many differentiated junctions. Agrin deposition at nerve-muscle contacts in culture also appeared to require the presence of other synaptic components. A similarly variable deposition occurred on noninnervated myocytes, where agrin again collected near sites of HSPG and AChR accumulation on some cells. Profuse agrin accretion occurred consistently, however, within the extracellular matrices of surrounding epithelial cells derived from both myotomes and neural tubes. In cocultures of Ambystoma neurons and Xenopus myocytes Ambystoma agrin collected at some chimeric neuromuscular junctions, but also accumulated on noninnervated myocytes and in the extracellular matrices of salamander neuroendothelial cells. Based upon these observations we conclude that (a) focal agrin deposition is not required for synaptic differentiation on Xenopus myocytes and (b) agrin may be one of several muscle basal lamina components that stem mainly from the secreted products of nearby epithelial cells.

Importance of substrate changes in the decrease of hepatic glucose cycling during insulin infusion and declining glycemia in the depancreatized dog

We wished to determine whether the elevated glucose cycling (GC) between glucose and glucose-6-phosphate (G<-->G6P) in diabetes can be reversed with acute insulin treatment. In six insulin-deprived, anesthetized, depancreatized dogs, insulin was infused for 6-9 h at a starting dose of 45-150 pmol.kg-1.min-1 to normalize plasma glucose from 23.9 +/- 1.4 to 5.0 +/- 0.4 mmol/l and gradually decreased to and maintained at a basal rate (1.7 +/- 1.0 pmol.kg-1.min-1) during the last 3 h. GC, measured with [2-3H]- and [6-3H]glucose, fell markedly from 15.3 +/- 2.7 and normalized at 1.3 +/- 0.6 mumol.kg-1.min-1 (P < 0.001). This occurred because total hepatic glucose output fell much more (from 41.2 +/- 3.1 to 11.6 +/- 1.2) than did glucose production (from 25.9 +/- 1.9 to 10.3 +/- 1.0 mumol.kg-1.min-1) (both P < 0.01). Freeze-clamped liver biopsies were taken at timed intervals for measurements of hepatic enzymes and substrates. The elevated hepatic hexose-6-phosphate levels decreased with insulin infusion (151 +/- 24 vs. 71 +/- 13 nmol/g, P < 0.01). Maximal activities of glucose-6-phosphatase (G6Pase) (from 17.6 +/- 0.8 to 19.6 +/- 2.6 U/g) and glucokinase (from 1.1 +/- 0.2 to 1.0 +/- 0.2 U/g) did not change. Insulin infusion resulted in a threefold increase (P < 0.05) in the activity of glycogen synthase (active form), but had no effect on hepatic glycogen content.(ABSTRACT TRUNCATED AT 250 WORDS)