Insulin and glucagon secretion in swimming mice: effects of autonomic receptor antagonism

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

The role of LIM and SH3 protein-1 in bladder cancer metastasis

The LIM and SH3 protein-1 (LASP-1) is a multi-domain protein that is involved in several malignant cancers. The role of LASP-1 in malignant phenotypes including high invasive properties and unrestricted cell proliferation, remain to be elucidated. The present study reported the association of LASP-1 expression with bladder cancer malignancy and its role in cancer cell invasion and proliferation. The immunohistochemical analysis of the expression status of LASP-1 in radical cystectomy specimens from invasive bladder cancer patients revealed that the LASP-1-positive patients demonstrated a decreased survival rate compared with the LASP-1-negative patients. The expression level of LASP-1 was increased in invasive bladder cancer cell lines compared with the non-invasive bladder cancer cell lines. Invasive cancer cells form invadopodia, the filamentous actin-based membrane protrusions that are essential in cancer cell invasion. Knockdown of LASP-1 reduced the ability to form invadopodia, resulting in decreased invasive capacity of the LASP-1 knockdown cells. In addition, knockdown of LASP-1 reduced cell proliferation. These results suggest that LASP-1 is important in invadopodia formation and cell proliferation of bladder cancer cells, promoting the malignant properties and resulting in poor-prognosis.

Knock-in Luciferase Reporter Mice for In Vivo Monitoring of CREB Activity

The cAMP response element binding protein (CREB) is induced during fasting in the liver, where it stimulates transcription of rate-limiting gluconeogenic genes to maintain metabolic homeostasis. Adenoviral and transgenic CREB reporters have been used to monitor hepatic CREB activity non-invasively using bioluminescence reporter imaging. However, adenoviral vectors and randomly inserted transgenes have several limitations. To overcome disadvantages of the currently used strategies, we created a ROSA26 knock-in CREB reporter mouse line (ROSA26-CRE-luc). cAMP-inducing ligands stimulate the reporter in primary hepatocytes and myocytes from ROSA26-CRE-luc animals. In vivo, these animals exhibit little hepatic CREB activity in the ad libitum fed state but robust induction after fasting. Strikingly, CREB was markedly stimulated in liver, but not in skeletal muscle, after overnight voluntary wheel-running exercise, uncovering differential regulation of CREB in these tissues under catabolic states. The ROSA26-CRE-luc mouse line is a useful resource to study dynamics of CREB activity longitudinally in vivo and can be used as a source of primary cells for analysis of CREB regulatory pathways ex vivo.

Intermittent hypoxia-induced glucose intolerance is abolished by α-adrenergic blockade or adrenal medullectomy

Obstructive sleep apnea causes intermittent hypoxia (IH) during sleep and is associated with dysregulation of glucose metabolism. We developed a novel model of clinically realistic IH in mice to test the hypothesis that IH causes hyperglycemia, glucose intolerance, and insulin resistance via activation of the sympathetic nervous system. Mice were exposed to acute hypoxia of graded severity (21, 14, 10, and 7% O2) or to IH of graded frequency [oxygen desaturation index (ODI) of 0, 15, 30, or 60, SpO2 nadir 80%] for 30 min to measure levels of glucose fatty acids, glycerol, insulin, and lactate. Glucose tolerance tests and insulin tolerance tests were then performed under each hypoxia condition. Next, we examined these outcomes in mice that were administered phentolamine (α-adrenergic blockade) or propranolol (β-adrenergic blockade) or that underwent adrenal medullectomy before IH exposure. In all experiments, mice were maintained in a thermoneutral environment. Sustained and IH induced hyperglycemia, glucose intolerance, and insulin resistance in a dose-dependent fashion. Only severe hypoxia (7% O2) increased lactate, and only frequent IH (ODI 60) increased plasma fatty acids. Phentolamine or adrenal medullectomy both prevented IH-induced hyperglycemia and glucose intolerance. IH inhibited glucose-stimulated insulin secretion, and phentolamine prevented the inhibition. Propranolol had no effect on glucose metabolism but abolished IH-induced lipolysis. IH-induced insulin resistance was not affected by any intervention. Acutely hypoxia causes hyperglycemia, glucose intolerance, and insulin resistance in a dose-dependent manner. During IH, circulating catecholamines act upon α-adrenoreceptors to cause hyperglycemia and glucose intolerance.

Energy homeostasis targets chromosomal reconfiguration of the human GH1 locus

Levels of pituitary growth hormone (GH), a metabolic homeostatic factor with strong lipolytic activity, are decreased in obese individuals. GH declines prior to the onset of weight gain in response to excess caloric intake and hyperinsulinemia; however, the mechanism by which GH is reduced is not clear. We used transgenic mice expressing the human GH (hGH) gene, GH1, to assess the effect of high caloric intake on expression as well as the local chromosome structure of the intact GH1 locus. Animals exposed to 3 days of high caloric intake exhibited hyperinsulinemia without hyperglycemia and a decrease in both hGH synthesis and secretion, but no difference in endogenous production of murine GH. Efficient GH1 expression requires a long-range intrachromosomal interaction between remote enhancer sequences and the proximal promoter region through "looping" of intervening chromatin. High caloric intake disrupted this interaction and decreased both histone H3/H4 hyperacetylation and RNA polymerase II occupancy at the GH1 promoter. Incorporation of physical activity muted the effects of excess caloric intake on insulin levels, GH1 promoter hyperacetylation, chromosomal architecture, and expression. These results indicate that energy homeostasis alters postnatal hGH synthesis through dynamic changes in the 3-dimensional chromatin structure of the GH1 locus, including structures required for cell type specificity during development.

Choline, CDP-choline or phosphocholine increases plasma glucagon in rats: involvement of the peripheral autonomic nervous system

The present study was designed to test the effects of choline, cytidine-5'-diphosphocholine (CDP-choline) and phosphocholine on plasma glucagon concentrations in rats. Intraperitoneal (i.p.) injection of 200-600 micromol/kg of choline, CDP-choline or phosphocholine produced a dose-dependent increase in plasma glucagon and choline concentrations. Pretreatment with hexamethonium (15 mg/kg; i.p.), a peripherally-acting ganglionic nicotinic acetylcholine receptor antagonist, entirely blocked the increases in plasma glucagon by 600 micromol/kg of choline, CDP-choline or phosphocholine. The increases in plasma glucagon by these choline compounds was reduced significantly (P<0.01) by about 25% by pretreatment with atropine methylnitrate (2 mg/kg), a peripherally-acting muscarinic acetylcholine receptor antagonist. Blockade of central acetylcholine receptors did not alter the increase in plasma glucagon induced by i.p. choline (600 micromol/kg). While alpha(2)-adrenoceptor blockade or bilateral adrenalectomy attenuated the increase in plasma glucagon evoked by choline compounds, blockade of alpha(1)- or beta-adrenoceptors or chemical sympathectomy failed to alter this increase. Intracerebroventricular (i.c.v.) choline (1.5 micromol) administration also increased plasma glucagon; the effect was blocked by central pretreatment with a neuronal type nicotinic acetylcholine receptor antagonist, mecamylamine (50 microg; i.c.v.) or the neuronal choline uptake inhibitor, hemicholinium-3 (20 microg; i.c.v.). These data show that choline, CDP-choline or phosphocholine increases plasma glucagon concentrations by increasing peripheral nicotinic and muscarinic cholinergic neurotransmissions. Central choline also increases plasma glucagon by augmenting central nicotinic cholinergic neurotransmission by acting presynaptically. Stimulation of adrenal medullary catecholamine release and subsequent activation of alpha(2)-adrenoceptors are mainly involved in the increase in plasma glucagon induced by choline, CDP-choline or phosphocholine.

Insulin secretion and glucose kinetics during exercise with and without pharmacological alpha(1)- and alpha(2)-receptor blockade

The mechanism behind exercise-induced decreases in plasma insulin concentrations was examined in eight healthy young men. In addition, the influence of specific alpha(1)- and alpha(2)-adrenoceptor blockade on glucose kinetics during exercise was studied. To test the hypothesis that exercise-induced decreases in insulin secretion are mediated via alpha(2)-adrenoceptors, all subjects exercised for 60 min on separate occasions under four conditions: with and without alpha(1)-receptor blockade (1 mg prazosin) and with and without or alpha(2)-receptor blockade (15 mg yohimbine). Glucose kinetics were measured using [3-(3)H]glucose. During exercise with alpha(2)-receptor blockade, the insulin concentration initially increased (first 20 min) then decreased, whereas it continually decreased in the corresponding control experiment. The C-peptide concentration did not change during exercise with alpha(2)-receptor blockade but decreased in the control experiment. During exercise with alpha(1)-receptor blockade and corresponding control experiments, insulin and C-peptide levels always decreased. With alpha(1)-receptor blockade, the glucose concentration increased (first 30 min) and then decreased, whereas it slightly decreased in all other experiments. In addition, with alpha(1)-receptor blockade, the glucose rate of appearance (Ra) increased rapidly (because of higher catecholamine concentrations in alpha(1)-receptor blockade versus control) and the glucose rate of disappearance (Rd) was higher compared with control. During exercise with alpha(2)-receptor blockade, the Ra and Rd were always lower compared with control. Therefore, we conclude that exercise-induced decreases in insulin secretion are mediated via alpha(2)-adrenoceptors and that blockade of alpha(1)- and alpha(2)-adrenoceptors during exercise elicits opposite responses in glucose Ra and Rd.

Possible evidence for endogenous production of a novel galanin-like peptide

Galanin mRNA and peptide are not detectable in normal islets. We studied the effect of galanin antagonists on insulin secretion in the rat beta cell line, RIN5AH, and in perifused rat islets. In RIN cell membranes galanin and its antagonists showed high affinity for 125I-galanin binding sites [Kd: (galanin) 0.03+/-0.01; Ki for galanin antagonists: (C7) 0.12+/- 0.02, (M35) 0.21+/-0.04, and (M40) 0.22+/-0.03 nM, mean+/- SEM, n = 4]. Galanin (1 microM) inhibited glucose-induced insulin release in islets (control 21.2+/-1.5 vs. galanin 4.5+/-0.2 fmol/islet per min, P < 0.001, n = 6) and RIN5AH cells (control 0.26+/-0.01 vs. galanin 0.15+/-0.02 pmol/10(6) cells per h, P < 0.001, n = 9). In RIN5AH cells, all antagonists blocked the inhibitory effects of galanin and stimulated insulin release in the absence of galanin. C7 and M40 (1 microM) alone significantly stimulated glucose-induced insulin secretion. Purified porcine galanin antibody (GAb) enhanced glucose-induced insulin release from islets (control 100+/- 16.3% vs. GAb 806.1+/-10.4%, P < 0.001, n = 6), and RIN5AH cells (control 100+/-9.6% vs. GAb 149+/-6.8%, P < 0. 01, n = 6). Western blotting of dexamethasone-treated islet extracts using GAb showed a specific band of similar molecular weight to porcine galanin not detected using a rat specific galanin antibody. One possible explanation for these results is the presence of an endogenous galanin-like peptide.

Metabolic and hormonal responses to adrenoceptor antagonists in 48-hour-starved exercising rats

The influence of 48 hours of starvation on sympathoadrenal regulation of nutrient utilization was investigated in rats. To assess the role of alpha- and beta-adrenoceptors, rats were studied during alpha- and beta-blockade. Energy metabolism was measured using indirect calorimetry before, during, and after moderate swimming exercise (approximately 60% maximal O2 consumption [VO2max]). Additionally, blood samples were taken for determination of nutrient and hormone concentrations. In 48-hour-starved rats, under baseline conditions, there was a reduction in energy expenditure (EE) accompanied by a shift toward fat oxidation (fat-ox) in comparison to fed rats. Exercise-induced responses in EE, fat-ox, and carbohydrate oxidation (CHO-ox) did not differ from those in fed rats. In starved rats, a stronger response to exercise of the sympathoadrenal system was observed. In comparison to control 48-hour-starved rats, blockade of alpha- and beta-adrenoceptors led to a reduction in the exercise-induced increase in EE and fat-ox. The rate of CHO-ox was slightly reduced after blockade of either adrenoceptor type. Alpha-blockade prevented the exercise-induced increase in blood glucose. Plasma free fatty acid (FFA) was not affected. Blood lactate, plasma insulin, norepinephrine (NOR), and epinephrine (EPI) were increased after alpha-blockade. Due to beta-blockade, exercise-induced increases in glucose and FFA were prevented. Blood glucose even declined below the baseline value. EPI showed an exaggerated increase, and NOR showed a smaller increase. Results obtained in starved rats support the idea that alpha-adrenoceptor blockade-induced changes in energy metabolism are the result of a diminished oxygen supply due to diminished circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic and hormonal responses to adrenoceptor antagonists in exercising rats

alpha- and beta-adrenoceptors play a key role in the regulation of nutrient supply to working muscles during exercise. To assess their influence in the regulation of substrate utilization, rats were studied during alpha- or beta-adrenoceptor blockade. Energy metabolism was studied by means of indirect calorimetry before, during, and after moderate swimming exercise. Blood samples were taken for the determination of nutrient and hormone concentrations. In addition, central venous blood samples were withdrawn for determination of blood gases, pH, and total hemoglobin concentration (c/Hb). alpha- and beta-adrenoceptor blockade decreased the rates of energy expenditure (EE) and fat oxidation (fat-ox) during and after swimming in comparison to swimming without adrenoceptor blockade. The oxidation of carbohydrates (CHO-ox) was increased in both cases. alpha-Blockade prevented the exercise-induced increase in blood glucose, plasma free fatty acids (FFA) were not affected, and plasma insulin, norepinephrine (NOR), epinephrine (EPI), and lactate were markedly increased. beta-adrenoceptor blockade prevented the exercise-induced increases in blood glucose and FFA. EPI increased slightly more than and NOR less than in the control experiment. The exercise-induced decrease in insulin was more pronounced after beta-blockade. alpha-Blockade caused a less pronounced decrease in venous oxygen saturation (SO2) and tension (PO2) than in the control experiment. The exercise-induced increase in carbon dioxide tension (PCO2) was almost absent. After beta-blockade, venous SO2 and PO2 decreased more and PCO2 increased more than in the control experiment. It is concluded that both alpha and beta-blockade restrict the rate of EE during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of galanin to stress-induced impairment of insulin secretion in swimming mice

This study examines the potential role of the neuropeptide, galanin, in stress-induced inhibition of insulin secretion in swimming mice. Firstly, the pancreatic and adrenal content of galanin-like immunoreactivity was determined in mice after swimming stress. It was found that pancreatic content was significantly lower in stressed mice than in resting controls, both after 2 (P less than 0.05) and 6 (P less than 0.025) minutes of swimming, suggesting partial release of pancreatic galanin during stress. In contrast, the adrenal content of galanin-like immunoreactivity did not change during the swimming stress. Gel filtration of tissue extracts indicated that (1) mouse pancreas contains two forms of galanin-like immunoreactivity; one co-eluting with synthetic porcine galanin (centered on Kav of 0.70) and another with a larger molecular weight (centered on Kav of 0.30), and (2) mouse adrenal contains a small void volume-peak and a larger peak of immunoreactivity, the latter co-eluting with synthetic galanin. Secondly, the effects of swimming stress on plasma glucose and insulin levels were compared in mice that received high titre rabbit anti-galanin serum with those in mice receiving normal rabbit serum. In normal rabbit serum-pretreated swimming mice, glucose-induced insulin levels were only 50% of resting controls (P less than 0.01). Immunoneutralization of galanin with specific antiserum abolished this swimming stress-induced inhibition of glucose-stimulated insulin levels. This was accompanied by a modestly enhanced rate of glucose disappearance. These findings suggest that pancreatic galanin is released during swimming stress in mice and that endogenous galanin makes a major contribution to stress-induced impairment of insulin secretion.