Biomedical subjects

Z Q Shi

Publications and source records attributed to Z Q Shi.

At least 19 recordsLinked to original sources

PubMed2004

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.

Animals↗

PubMed2004

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).

Adolescent↗

PubMed2003

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).

China↗

PubMed2001

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.

Animals↗

PubMed2001

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.

3-O-Methylglucose↗

PubMed2001

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.

3-Hydroxybutyric Acid↗

PubMed2000

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.

Animals↗

PubMed2000

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.

Animals↗

PubMed2000

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.

Animals↗

PubMed2000

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.

Animals↗

PubMed2000

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.

Animals↗

PubMed2000

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.

Adrenergic beta-Antagonists↗

PubMed1999

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.

Alanine↗

PubMed1999

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.

Aging↗

PubMed1999

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.

Adrenergic Agents↗

PubMed1999

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.

3-Hydroxybutyric Acid↗

PubMed1999

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.

Animals↗

PubMed1999

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.

Adipose Tissue↗