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Biomedical subjects

W W Fleming

Publications and source records attributed to W W Fleming.

At least 55 records · Page 3Linked to original sources
PubMed1987

Norepinephrine depletion and sensitivity changes in rat heart induced by pretreatment with reserpine.

Depletion of norepinephrine, sensitivity to isoproterenol and sensitivity to tyramine in rat atria were investigated after various doses and schedules of pretreatment of rats with reserpine. Virtually complete depletion of norepinephrine occurred in both right and left atria and ventricles after doses of 1.0 mg/kg/day of reserpine for one or more days of pretreatment. A smaller dose, 0.3 mg/kg/day, produced lesser depletion, and a larger dose, 2.5 mg/kg/day, caused severe central nervous system depression and high mortality. Chronic treatment (5 days or longer) with the 1.0-mg/kg/day dose produced supersensitivity of right atria to the chronotropic, but not inotropic, responses to isoproterenol. Chronic treatment with this dose for 7 days produced inotropic supersensitivity in left atria. Most of the schedules of pretreatment with reserpine depressed the maximum response to tyramine. However, the data indicate that the tyramine-releasable norepinephrine was not a consistent reflection of the total norepinephrine pool, even when depletion was very pronounced. The effects of depletion of cardiac stores of norepinephrine with reserpine in comparison with the effects of cardiac sympathectomy are discussed.

Animals↗
PubMed1987

Characteristics of adaptive supersensitivity in the left atrium of the guinea pig.

Chronic pretreatment of guinea pigs with reserpine (0.1 mg/kg/day for 7 days) induces inotropic supersensitivity in left atria. The sensitivity is increased to isoproterenol, norepinephrine, 5'-guanylylimidodiphosphate and forskolin, and the maximum response is increased to the partial agonist albuterol. These results, coupled with data in the literature, suggest that adaptive supersensitivity in the guinea pig heart is due to a change in one or more of the components of the adenylate cyclase system that is specifically coupled to beta adrenoceptors. The results indicate that the supersensitivity is demonstrable when the concentration-response curves for agonists are determined in isolated whole left atria but not when they are determined in strips cut from left atria. This explains a discrepancy in the literature. It is suggested that cellular changes, possibly in electrolyte distribution, resulting from the additional manipulation of cutting the atria into slices obscure the sensitivity difference between the control and experimental tissues.

Albuterol↗
PubMed1986

Airway epithelium modulates the reactivity of guinea-pig respiratory smooth muscle.

The influence of the epithelium on the reactivity of guinea-pig tracheal smooth muscle in vitro was investigated. Mechanical removal of the epithelium produced contrasting effects on methacholine-, histamine- and K+-induced contractions of tracheal strips. Epithelium removal resulted in 2.1-fold shifts to the left of histamine and methacholine concentration-response curves, and an increase in the maximum response to histamine; the maximum response to methacholine was unaffected. Epithelium removal had little effect on the sensitivity, but decreased the maximum response to K+. The results suggest that inhibitory and excitatory factor(s) are released from epithelial cells, and that these factors modulate the reactivity of the smooth muscle. Indomethacin (1 microM) produced in epithelium-containing preparations qualitatively identical effects on the sensitivity to methacholine and on the maximum response to histamine as removal of the epithelium. However, indomethacin was without effect on the sensitivity to histamine in the presence or absence of the epithelium. Alterations in the production or release of epithelial cell-derived factors may contribute to the airway hyperreactivity observed in respiratory disorders.

Airway Resistance↗
PubMed1986

Epithelium modulates the reactivity of ovalbumin-sensitized guinea-pig airway smooth muscle.

Mechanical removal of the airway epithelium alters the in vitro reactivity of airway smooth muscle. The modulation of reactivity may involve the release of inhibitory and excitatory factors from epithelial cells. Guinea pigs sensitized with ovalbumin have been used as an animal model of airway hyperreactivity. We evaluated the influence of the epithelium on the reactivity of in vitro tracheal smooth muscle from control and ovalbumin-sensitized guinea pigs, and the extent to which the presence of the epithelium affects the contractile response to in vitro challenge with ovalbumin. In both control and ovalbumin-sensitized tissues, epithelium removal increased the sensitivity of the preparations to histamine, methacholine and isoproterenol to a similar extent, i.e., 2- to 2.5-fold. Epithelium removal resulted in an 8.1-fold increase in sensitivity to ovalbumin in sensitized tissues. The epithelium appears not only to modulate the reactivity of the tissues to bronchoactive agents, but it also influences the magnitude of the contractile response following antigen challenge.

Animals↗
PubMed1986

The effect of verapamil is reduced in isolated airway smooth muscle preparations lacking the epithelium.

The effect of epithelium removal on the reactivity of rabbit airway smooth muscle to bronchoactive agents and on the effect of verapamil was studied in vitro using preparations from several levels within the respiratory tree, i.e., trachea, primary (10) and secondary (20) bronchus. Methacholine contracted tissues from all three levels of airway. Histamine contracted strips from 20 bronchus, had an inconsistent action in strips from 10 bronchus and was without effect in tracheal preparations. K+ contracted tissues from the trachea and 10 bronchus, and had a mixed action in 20 bronchial strips. Removal of the epithelial cell layer variably affected the reactivity of the smooth muscle to the three agents studied. In 20 bronchus, epithelium removal potentiated responses to histamine and methacholine. In 10 bronchus, only responses to methacholine were consistently augmented. In tracheal preparations epithelium removal did not alter the reactivity of the tissue to any agent examined. Verapamil (1 microM) attenuated responses to all agents and increased in its potency from tracheal through 10 to 20 bronchial preparations. Following epithelium removal, verapamil was substantially less effective in 20 bronchi, yet its effects were unchanged in the trachea. The results indicate that the epithelial cell layer modulates airway smooth muscle reactivity; this phenomenon is apparently widespread in mammals, the modulatory effect is more prominent in the smaller airways, and the magnitude of the effect of verapamil on airway smooth muscle is, in part, related to the presence of the epithelium.

Animals↗
PubMed1985

Effect of postganglionic denervation and pretreatment with reserpine on alpha-adrenoceptors of the guinea-pig vas deferens.

The radiolabeled alpha-1-adrenoceptor antagonist [3H]WB-4101 was used to determine whether supersensitivity of the guinea pig vas deferens that develops after denervation or reserpine pretreatment is associated with a change in the characteristics of the alpha-1-adrenoceptor. Specific binding of [3H]WB-4101 to membrane fractions of vasa deferentia was saturable and reversible. The dissociation constant (KD) was similar when obtained by equilibrium or kinetic studies. As determined by Scatchard analysis, neither chronic (5 days) pretreatment with reserpine (1.0 mg/kg/day) nor postganglionic denervation (7 days) altered the number or affinity of [3H] WB-4101 binding sites. It is concluded that changes in alpha-1-receptor characteristics are not responsible for postjunctional supersensitivity in this tissue.

Adrenergic alpha-Antagonists↗
PubMed1985

Sensitivity changes in the smooth muscle of the guinea-pig isolated vas deferens after treatment of animals with 6-hydroxydopamine.

Postjunctional supersensitivity of the smooth muscle of the guinea-pig vas deferens induced by denervation, decentralization and treatment of animals with reserpine has been attributed, in part, to a partial membrane depolarization (8-10 mV) resulting from reduced electrogenic Na+,K+-pumping activity. This study was undertaken to characterize sensitivity changes which occur after treatment of animals with 6-hydroxydopamine (100 mg/kg + 250 mg/kg i.v., 1 day apart). Seven days after the second injection, concentration-response curves for isometric contractile responses to norepinephrine, methoxamine, acetylcholine and histamine were shifted 40.6-, 1.7-, 3.6- and 2.7-fold, respectively, to the left of control; however, the sensitivity to KCl was not increased, which contrasts with the results after denervation, decentralization and reserpine treatment. Ouabain (10(-5) M) produced 1.8- and 1.3-fold leftward shifts of the KCl concentration-response curves in tissues from control and 6-hydroxydopamine-treated animals, respectively. The pronounced effect of ouabain in tissues from treated animals may be an indication that 6-hydroxydopamine treatment does not result in as much inhibition of electrogenic Na+,K+-pumping, and resultant membrane depolarization, as other methods which induce supersensitivity of the guinea-pig vas deferens.

Acetylcholine↗
PubMed1985

Surgical sympathectomy of the heart in rodents and its effect on sensitivity to agonists.

A new procedure for sympathetic denervation of the hearts of rats and guinea pigs is described. Bilateral removal of the inferior and medial cervical ganglia results in almost complete loss of catecholamines from atria and ventricles, disappearance of catecholamine-associated histofluorescence from the region of the sinoatrial node and marked depression of the chronotropic concentration-response curve for tyramine in right atria of both species. Seven days after bilateral sympathectomy, the chronotropic concentration-response curve for isoproterenol is shifted to the left by a factor of 3.3 in the rat and 1.7 in guinea-pig right atria. The chronotropic concentration-response curve for histamine was not shifted by sympathectomy in the guinea-pig right atrium. Inasmuch as the rat atrium does not respond to histamine, similar experiments could not be done in the rat. The inotropic concentration-response curve for isoproterenol in electrically driven left atria was not affected by 7 days of sympathectomy in either species. These results indicate that chronic surgical sympathectomy of the heart can be successfully accomplished in the rat and guinea pig. Such sympathectomy induces a postjunctional supersensitivity in guinea-pig right atria which is qualitatively and quantitatively similar to that described previously for chronic treatment with reserpine. Bilateral surgical sympathectomy provides a valuable tool for future investigations of the cellular basis of supersensitivity in the myocardium.

Animals↗
PubMed1984

Sodium-potassium pump sites, as assessed by [3H]-ouabain binding, in aorta and caudal artery of normotensive and spontaneously hypertensive rats.

The results of the present work provide support for the utility of studying [3H]-ouabain binding to in vitro segments of vascular smooth muscle as an indication of the number of Na-K pump sites in blood vessels of rats. Specific binding of [3H]-ouabain to strips of rat abdominal aorta and segments of rat caudal artery was saturable and reversible. Specific [3H]-ouabain binding was displaced by several cardiac glycosides but not by steroid hormones or sodium vanadate. The dissociation constant (KD) of [3H]-ouabain binding, as determined by equilibrium and kinetic studies, was in the range of 50-150 nM in these vessels. Scatchard analysis indicated that the maximum number of [3H]-ouabain-binding sites (Bmax) was 20 and 46 fmol/mg wet weight in the aorta strips and caudal artery, respectively. A comparison of [3H]-ouabain binding in caudal arteries of spontaneously hypertensive rats and of age-matched, genetic controls indicated that neither the affinity for binding nor the maximum number of binding sites was different. This suggests that this genetic form of hypertension is not associated with an alteration in the number of vascular Na-K pump sites.

Animals↗
PubMed1984

Cellular potentials, electrogenic sodium pumping and sensitivity in guinea-pig atria.

Intracellular recording techniques in guinea-pig atrial pacemaker and nonpacemaker cells were used to investigate 1) the role of membrane potential changes in postjunctional supersensitivity, 2) the electrogenicity of the Na+,K+ pump and 3) the role of electrogenic pumping in sensitivity of the atria to agonists. In nonpacemaker cells, ouabain (10(-6) M) had no effect on resting membrane potential (left atria) or maximum diastolic potential (right atria). However, ouabain effectively suppressed the transient hyperpolarization that followed cessation of electrical stimulation. In pacemaker cells, ouabain and chronic treatment with reserpine (0.1 mg/kg/day) produced quite different patterns of changes in intracellular potentials. Chronic treatment with reserpine induced chronotropic supersensitivity to isoproterenol but not to histamine. Ouabain did not alter the chronotropic sensitivity to either agonist. The effects of isoproterenol and histamine on intracellular potentials in pacemaker cells were investigated in the presence and absence of ouabain and in control atria vs. atria from guinea pigs chronically pretreated with reserpine. Analysis of the data indicated that 1) electrophysiological measurements do not provide a discernible explanation for chronotropic supersensitivity, 2) the Na+ pump has the capacity for electrogenic pumping under conditions of Na+ loading, but demonstrates little indication of electrogenicity under basal conditions and 3) chronic treatment with reserpine does suppress the Na+,K+ pump in some areas of the right atrium, but this activity probably does not contribute to chronotropic supersensitivity. Other possible mechanisms of postjunctional supersensitivity in atria are discussed.

Animals↗
PubMed1983

Mobility and function in elastin and collagen.

13C- and 2H-labelled amino acids have been incorporated into elastin and collagen and rotational correlation times of the labelled sites have been derived from an analysis of nuclear magnetic resonance relaxation parameters and line-shapes. The elastin experiments were designed to discriminate between the various models that have been proposed to account for the rubber-like elasticity of elastin. The correlation times of carbonyl carbons of the elastin backbone show that elastin chains are very flexible at the molecular level. In addition, the molecular dynamics and viscoelastic behaviour of elastin are well correlated over a wide range of temperatures and solvents. These results all support the rubber-like network model of elastin structure. The collagen experiments were designed to investigate the intermolecular interactions between molecules in collagen fibres. Correlation times of labelled sites in the collagen backbone and side-chains show that substantial flexibility, especially of the side-chains, takes place in reconstituted (non-cross-linked) collagen fibrils. Therefore, the interactions between side-chains that presumably direct and stabilize the fibrillar assembly take place in fluid domains. The molecular flexibility is not affected by the presence of cross-links but is absent when the collagen is mineralized.

Animals↗
PubMed1982

Effect of reserpine pretreatment on mechanical responsiveness and [125I]Iodohydroxybenzylpindolol binding sites in the guinea-pig right atrium.

The inotropic and chronotropic responses of the guinea-pig right atrium to several pharmacologic agents were measured after acute (0.1 mg/kg/day x 1) and chronic (0.1 mg/kg/day x 7) reserpine administration. A small increase in the sensitivity of the pacemaker to isoproterenol occurred after acute reserpine treatment which was followed by a much greater change in sensitivity to the beta agonist when pretreatment was extended for 7 days. Chronotropic responsiveness to calcium, histamine and pilocarpine was not altered by reserpine pretreatment. The acute administration of reserpine resulted in a slight inotropic supersensitivity of paced right atria to isoproterenol, calcium and histamine. Pretreatment for 7 days produced an additional increase in inotropic sensitivity to isoproterenol but did not affect contractile responses to the other agents. The catecholamine-specific nature of the supersensitivity induced by chronic reserpine treatment suggested that a change in the number and/or affinity of beta adrenergic receptors was involved. The radiolabeled beta adrenoceptor antagonist [125]iodohydroxybenzylpindolol (I-HYP) was used to test this hypothesis. Preliminary experiments revealed the presence of a single class of noninteracting (nH = 0.99), high affinity (Kd = 100 pM) binding sites which exhibited stereospecificity and saturability (47.2 fmol/mg of protein). The agonist potency series for the inhibition of I-HYP binding was identical to the series for mediating mechanical responses. Taken collectively this information suggests that the high affinity I-HYP binding site in the guinea-pig right atrium represents the beta adrenergic receptor. As determined by Scatchard analyses, neither acute (1-day) nor chronic (7-day) low-dose (0.1 mg/kg/day) reserpine administration altered the number or affinity of I-HYP binding sites. It is concluded that changes in beta receptor characteristics are not responsible for reserpine-induced supersensitivity in this tissue.

Aminophylline↗
PubMed1981

The involvement of the sodium-potassium pump in postjunctional supersensitivity of the guinea-pig vas deferens as assessed by [3H]ouabain binding.

Previous evidence has suggested that postjunctional supersensitivity of the guinea-pig vas deferens results, in part, from partial depolarization of the cell membrane. The depolarization is believed to result from a reduction in the activity of the Na-K pump. Indeed, the Na, K+ -adenosine triphosphatase activity of subcellular fractions from supersensitive vas deferens is reduced. In order to determine whether the biochemical alteration seen in subcellular fractions correlate with Na-K pump sites in intact tissues, we have studied the binding of [3H] ouabain to intact vas deferens. [3H]ouabain binds to membrane sites which have the characteristics expected of Na+, K+ - adenosine triphosphatase. Specific binding was saturable and reversible. Scatchard analysis of ouabain-binding in control tissues yielded a single class of binding sites with a dissociation constant (KD) of 156 +/- 7 nM and a maximum number of binding sites (Bmax) of 558.7 +/- 15.6 fmol/mg wet wt. [3H]Ouabain binding was displaceable by several cardiac glycosides and aglycones, but not by steroid hormones or sodium vanadate. Alteration of concentrations of Na+ and K+ markedly affected ouabain binding. Denervation (with 6-hydroxydopamine), decentralization or reserpine treatment for 1 day, which do not produce supersensitivity, did not alter the Bmax, whereas 5 to 7 days after these procedures, when supersensitivity was present, the Bmax was significantly reduced by 20 to 40%. The KD was not changed by any of the treatments. These data provide additional support for the concept that a reduction in the NaK pump sites contributes to postjunctional supersensitivity.

Animals↗
PubMed1980

Effects of sympathetic denervation or chronic reserpine on potassium (42K) and chloride (36Cl) efflux from guinea-pig vas deferens.

Potassium (42K) or chloride (36Cl) efflux curves were determined in guinea-pig vas deferens from control, reserpine-treated animals (1 mg/kg/day i.p. for 5 days), and from animals whose vas deferens had been sympathetically denervated 1 week before. Steady-state 42K turnover in control tissues was 0.0052 +/- 0.0002 min-1; neither reserpine treatment nor sympathetic denervation changed this parameter signicantly. Control 36Cl turnover was 0.058 +/- 0.002 min-1 and it was unaffected by either procedure. Methoxamine (3 x 10(-6) to 10(-4) M) induced dose-related increases in the fractional exchange of 42K and 36Cl. These were of greater magnitude after sympathetic denervation or reserpine treatment. Furtrethonium also produced dose-dependent increases in 42K efflux; its dose-response curve was shifted 2.6-fold to the left of the control curve by reserpine treatment. These results indicate that interruption of adrenergic transmission to the guinea-pig vas deferens is associated with increased changes in membrane permeability to Cl and possibly K in response to drug activation of alpha-adrenergic and cholinegic receptors. It is suggested that the supersensitivity phenomenon observed in the guinea-pig vas deferens after reserpine or sympathetic denervation is, in part, related to improved transduction of drug-receptor interaction into ionic permeability changes.

Animals↗