(1/4955) Hierarchy of ventricular pacemakers.
To characterize the pattern of pacemaker dominance in the ventricular specialized conduction system (VSCS), escape ventricular pacemakers were localized and quantified in vivo and in virto, in normal hearts and in hearts 24 hours after myocardial infarction. Excape pacemaker foci were localized in vivo during vagally induced atrial arrest by means of electrograms recorded from the His bundle and proximal bundle branches and standard electrocardiographic limb leads. The VSCS was isolated using a modified Elizari preparation or preparations of each bundle branch. Peacemakers were located by extra- and intracellular recordings. Escape pacemaker foci in vivo were always in the proximal conduction system, usually the left bundle branch. The rate was 43+/-11 (mean+/-SD) beats/min. After beta-adrenergic blockade, the mean rate fell to 31+/-10 beats/min, but there were no shifts in pacemaker location. In the infarcted hearts, pacemakers were located in the peripheral left bundle branch. The mean rate was 146+/-20 beats/min. In isolated normal preparations, the dominant pacemakers usually were in the His bundle, firing at a mean rate of 43+/-10 beats/min. The rates of pacemakers diminished with distal progression. In infarcted hearts, the pacemakers invariably were in the infarct zone. The mean firing rates were not influenced by beta-adrenergic blockade. The results indicate that the dominant pacemakers are normally in the very proximal VSCS, but after myocardial infarction pacemaker dominance is shifted into the infarct. Distribution of pacemaker dominance is independent of sympathetic influence. (+info)
(2/4955) Allyl-containing sulfides in garlic increase uncoupling protein content in brown adipose tissue, and noradrenaline and adrenaline secretion in rats.
The effects of garlic supplementation on triglyceride metabolism were investigated by measurements of the degree of thermogenesis in interscapular brown adipose tissue (IBAT), and noradrenaline and adrenaline secretion in rats fed two types of dietary fat. In Experiment 1, rats were given isoenergetic high-fat diets containing either shortening or lard with or without garlic powder supplementation (8 g/kg of diet). After 28 d feeding, body weight, plasma triglyceride levels and the weights of perirenal adipose tissue and epididymal fat pad were significantly lower in rats fed diets supplemented with garlic powder than in those fed diets without garlic powder. The content of mitochondrial protein and uncoupling protein (UCP) in IBAT, and urinary noradrenaline and adrenaline excretion were significantly greater in rats fed a lard diet with garlic powder than in those fed the same diet without garlic. Other than adrenaline secretion, differences due to garlic were significant in rats fed shortening, also. In Experiment 2, the effects of various allyl-containing sulfides present in garlic on noradrenaline and adrenaline secretion were evaluated. Administration of diallyldisulfide, diallyltrisulfide and alliin, organosulfur compounds present in garlic, significantly increased plasma noradrenaline and adrenaline concentrations, whereas the administration of disulfides without allyl residues, diallylmonosulfide and S-allyl-L-cysteine did not increase adrenaline secretion. These results suggest that in rats, allyl-containing sulfides in garlic enhance thermogenesis by increasing UCP content in IBAT, and noradrenaline and adrenaline secretion. (+info)
(3/4955) Further studies on the mechanism of adrenaline-induced lipolysis in lipid micelles.
Lipase [EC 22.214.171.124] depleted lipid micelles, in which lipolysis was not elicited by adrenaline, were prepared from lipid micelles. When these lipase-depleted lipid micelles incubated with adipose tissue extract containing lipase activity, adrenaline-induced lipolysis was restored to almost the same level as that of native lipid micelles. Adrenaline-induced lipolysis was not restored when the lipase-depleted lipid micelles were homogenized or sonicated. Various tissue extracts from kidney, lung, liver, and pancreas, and post-heparin plasma, which contained lipase activity, restored adrenaline-induced lipolysis in lipase-depleted lipid micelles. (+info)
(4/4955) Lipolytic action of cholera toxin on fat cells. Re-examination of the concept implicating GM1 ganglioside as the native membrane receptor.
The possible role of galactosyl-N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide (GM1) ganglioside in the lipolytic activity of cholera toxin on isolated fat cells has been examined. Analyses of the ganglioside content and composition of intact fat cells, their membranous ghosts, and the total particulate fraction of these cells indicate that N-acetylneuraminylgalactosylglucosylceramide (GM3) represents the major ganglioside, with substantial amounts of N-acetylgalactosaminyl-[N-acetylneuraminyl]-galactosylglucosylceramide (GM2) and smaller amounts of other higher homologues also present. Native GM1 was not detected in any of these preparations. Examination of the relative capacities of various exogenously added radiolabeled sphingolipids to bind to the cells indicated that GM2 and glucosylsphingosine were accumulated by the cells to extents comparable to GM1. Galactosylsphingosine and sulfatide also exhibited significant, although lesser, binding affinities for the cells. The adipocytes appeared to nonspecifically bind exogenously added GM1; saturation of binding sites for GM1 could not be observed up to the highest concentration tested (2 X 10(-4) M), wherein about 7 X 10(9) molecules were associated with the cells. Essentially all of this exogenously added GM1 was found bound to the plasma membrane "ghost" fraction. Investigation of the biological responses of the cells confirmed their sensitivities to both cholera toxin and epinephrine-stimulated lipolysis, as well as the lag period displayed during the toxin's action. While we could confirm that the toxin's lipolytic activity can be enhanced by prior treatment of the fat cells with GM1, several of the observed characteristics of this phenomenon differ from earlier reported findings. Accordingly, added GM1 was able to enhance only the subsequent rate, but not the extent, of toxin-stimulated glycerol release (lipolysis) from the cells. We also were unable to confirm the ability of GM1 to enhance the toxin's activity at either saturating or at low toxin concentrations. The limited ability of added GM1 to enhance the toxin's activity appeared in a unique bell-shaped dose-response manner. The inability of high levels of GM1 to stimulate a dose of toxin that was ineffective on native cells suggests that the earlier reported ability of crude brain gangliosides to accomplish this was due to some component other than GM1 in the crude extract. While several glycosphingolipids and some other carbohydrate-containing substances that were tested lacked the ability to mimic the enhancing effect of GM1, 4-methylumbelliferyl-beta-D-galactoside exhibited an effect similar to, although less pronounced than, that of GM1. The findings in these studies are unable to lend support to the earlier hypothesis that (a) GM1 is cholera toxin's naturally occurring membrane receptor on native fat cells, and (b) the ability of exogenously added GM1 to enhance the toxin's lipolytic activity represents the specific creation of additional natural receptors on adipocytes... (+info)
(5/4955) Adrenoreceptors of the guinea-pig urinary bladder.
1 Adrenaline, noradrenaline and isoprenaline (5 mug/ml) did not affect the resting tone of the isolated urinary bladder of the guinea-pig. 2 The catecholamines (1-2 mug/ml) inhibited neuronally evoked contractions at various stimulation frequencies; the inhibition was maximum at 2 Hz and minimum at 50 Hz. Isoprenaline produced maximum inhibition. 3 Propranolol (0.5 mug/ml) completely blocked the catecholamine-induced inhibition at all the frequencies employed. The concentration-response curves of isoprenaline at 2, 10 and 50 Hz were characteristically shifted by propranolol (50 ng/ml). Phenoxybenzamine (0.2 mug/ml) was totally ineffective. 4 In some experiments adrenaline significantly raised the tone of the bladder exposed to propranolol; this effect could be blocked by phenoxybenzamine. 5 Acetylcholine-induced bladder contractions were inhibited by adrenaline (2 mug/ml); the inhibition was completely blocked by propranolol (0.5 mug/ml). 6 The results indicate the presence of an inhibitory beta-adrenoceptor and suggest the possibility of an excitatory alpha-adrenoceptor in guinea-pig urinary bladder. (+info)
(6/4955) A possible mode of cardiovascular actions of dopamine in dogs.
A possible mode of cardiovascular actions of dopamine was studied using ephedrine. In the dog pretreated with repeated administrations of ephedrine (total dose, 40 or 80 mg/kg, i.v.) or with combined administrations of ephedrine (total dose, 90 mg/kg, s.c. and i.v.) and reserpine (2 mg/kg, s.c., 24 hr previously), pressor responses to dopamine were eliminated and reversed to depressor responses whereas depressor responses to dopamine were potentiated. Positive chronotropic effects of dopamine were almost eliminated. Pressor and positive chronotropic effects of tyramine were almost abolished. Sympathomimetic effect of noradrenaline and adrenaline were potentiated while those of isoprenaline were inhibited. In the heart-lung preparation of ephedrine-treated dogs (total dose, 40 mg/kg, i.v.), cardiac stimulating effects of dopamine and tyramine were strongly depressed, and those of noradrenaline, adrenaline and isoprenaline were reduced to some extent. In the open-chest dogs, after pretreatment of cocaine (4 mg/kg, i.v.), pressor, positive inotropic and chronotropic effects of noradrenaline were potentiated, whilst those of tyramine were inhibited. Those of dopamine were not visibly altered, but depressor, negative chronotropic and inotropic effects of dopamine appeared at small doses. In the ephedrine-pretreated dogs, these sympathomimetic effects of dopamine and tyramine after cocaine were strongly depressed and those of noradrenaline were inhibited to a certain degree. The results obtained with ephedrine suggest that dopamine differs from other catecholamines and tyramine in the mode of cardiovascular actions. (+info)
(7/4955) alpha-adrenergic stimulation mediates glucose uptake through phosphatidylinositol 3-kinase in rat heart.
We examined whether insulin and catecholamines share common pathways for their stimulating effects on glucose uptake. We perfused isolated working rat hearts with Krebs-Henseleit buffer containing [2-3H]glucose (5 mmol/L, 0.05 microCi/mL) and sodium oleate (0.4 mmol/L). In the absence or presence of the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (3 micromol/L), we added insulin (1 mU/mL), epinephrine (1 micromol/L), phenylephrine (100 micromol/L) plus propranolol (10 micromol/L, selective alpha-adrenergic stimulation), or isoproterenol (1 micromol/L) plus phentolamine (10 micromol/L, selective beta-adrenergic stimulation) to the perfusate. Cardiac power was found to be stable in all groups (between 8.07+/-0.68 and 10.7+/-0. 88 mW) and increased (25% to 47%) with addition of epinephrine, but not with selective alpha- and beta-adrenergic stimulation. Insulin and epinephrine, as well as selective alpha- and beta-receptor stimulation, increased glucose uptake (the following values are in micromol/[min. g dry weight]: basal, 1.19+/-0.13; insulin, 3.89+/-0.36; epinephrine, 3.46+/-0.27; alpha-stimulation, 4.08+/-0.40; and beta-stimulation, 3.72+/-0.34). Wortmannin completely inhibited insulin-stimulated and selective alpha-stimulated glucose uptake, but it did not affect the epinephrine-stimulated or selective beta-stimulated glucose uptake. Sequential addition of insulin and epinephrine or insulin and alpha-selective stimulation showed additive effects on glucose uptake in both cases. Wortmannin further blocked the effects of insulin on glycogen synthesis. We conclude that alpha-adrenergic stimulation mediates glucose uptake in rat heart through a PI3-K-dependent pathway. However, the additive effects of alpha-adrenergic stimulation and insulin suggest 2 different isoforms of PI3-K, compartmentation of PI3-K, potentiation, or inhibition by wortmannin of another intermediate of the alpha-adrenergic signaling cascade. The stimulating effects of both the alpha- and the beta-adrenergic pathways on glucose uptake are independent of changes in cardiac performance. (+info)
(8/4955) Lactate kinetics at rest and during exercise in lambs with aortopulmonary shunts.
In a previous study [G. C. M. Beaufort-Krol, J. Takens, M. C. Molenkamp, G. B. Smid, J. J. Meuzelaar, W. G. Zijlstra, and J. R. G. Kuipers. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H1503-H1512, 1998], a lower systemic O2 supply was found in lambs with aortopulmonary left-to-right shunts. To determine whether the lower systemic O2 supply results in increased anaerobic metabolism, we used [1-13C]lactate to investigate lactate kinetics in eight 7-wk-old lambs with shunts and eight control lambs, at rest and during moderate exercise [treadmill; 50% of peak O2 consumption (VO2)]. The mean left-to-right shunt fraction in the shunt lambs was 55 +/- 3% of pulmonary blood flow. Arterial lactate concentrations and the rate of appearance (Ra) and disappearance (Rd) of lactate were similar in shunt and control lambs, both at rest (lactate: 1, 201 +/- 76 vs. 1,214 +/- 151 micromol/l; Ra = Rd: 12.97 +/- 1.71 vs. 12.55 +/- 1.25 micromol. min-1. kg-1) and during a similar relative workload. We found a positive correlation between Ra and systemic blood flow, O2 supply, and VO2 in both groups of lambs. In conclusion, shunt lambs have similar lactate kinetics as do control lambs, both at rest and during moderate exercise at a similar fraction of their peak VO2, despite a lower systemic O2 supply. (+info)