Biomedical subjects
Publications and source records attributed to R W Fuller.
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We have investigated the effect of the manipulation of intracellular cyclic adenosine monophosphate (cyclic AMP) and the stimulation of adenosine receptors on the function of human alveolar macrophages in vitro. Human alveolar macrophages harvested by bronchoalveolar lavage were stimulated by opsonised zymosan 1 mg/ml in the presence of N6,2'0-dibutyryladenosine 3':5' cyclic monophosphate (dibutyryl cyclic AMP) 5 x 10(-6) to 5 x 10(-3) M,8-bromoadenosine 3':5'-cyclic monophosphate (8-bromo cyclic AMP) 5 x 10(-6) to 5 x 10(-3) M, 5'-(N-ethylcarboxamido)-adenosine (NECA) 10(-7) to 10(-4) M, adenosine 10(-7) to 10(-4) M, theophylline 5 x 10(-6) to 5 x 10(-3) M and enprofylline 5 x 10(-8) to 5 x 10(-4) M. The subsequent release of thromboxane B2 (TXB2) and N-acetyl-beta-D-glucosaminidase (NAG) activity was monitored. In addition, the release of TXB2 and NAG from zymosan stimulated human monocytes incubated in the presence of NECA 10(-7) to 10(-4) M was measured. The TXB2 release from alveolar macrophages were inhibited by dibutyryl cyclic AMP and 8-bromo cyclic AMP and to a lesser extent by NECA, theophylline and enprofylline. However, adenosine had no effect. None of the agents studied altered NAG release. In addition, monocytes showed greater sensitivity to the inhibitory effects of 5-N-ethylcarboxamido adenosine than alveolar macrophages. In conclusion, the alveolar macrophage was inhibited by stable analogues of cyclic AMP and xanthines at supratherapeutic concentrations but have no functional excitatory adenosine receptors and only a residual inhibitory adenosine receptor function compared to the precursor monocyte.
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p-Chloroamphetamine (PCA) is a useful pharmacologic tool for selectively increasing brain serotonin function acutely by release of serotonin into the synaptic cleft. PCA produces behavioral, neurochemical and neuroendocrine effects believed due to serotonin release after doses in the range of 0.5-5 mg/kg. At higher doses and at longer times, PCA causes depletion of brain serotonin. The mechanisms of this depletion are not well understood but require the serotonin uptake carrier. Antagonism of PCA-induced depletion of brain serotonin is a useful means of assessing the ability of a compound to block the serotonin uptake carrier on brain serotonin neurons. PCA can also be used as a neurotoxic agent to deplete brain serotonin in functional studies, apparently by destroying some serotonergic nerve terminals. Used in this way, PCA has an advantage over 5,6- and 5,7-dihydroxytryptamines in being effective by systemic injection, and it affects brain serotonergic projections with a different neuroanatomic specificity than the dihydroxytryptamines.
MPTP-3-ol injected s.c. once daily for 4 days resulted in a dose-dependent depletion of striatal dopamine and cortical norepinephrine one week after the last dose. MPTP-3-ol was approximately one-fourth as potent as MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in causing these effects. MPTP-3-ol was oxidized by monoamine oxidase in mouse brain in vitro and resulted in MPP+ (1-methyl-4-phenylpyridinium) formation in brain in vivo, both at about one-fourth the rates with MPTP. The in vitro metabolism of MPTP-3-ol was inhibited by deprenyl, a selective inhibitor of monoamine oxidase type B, and deprenyl pretreatment also blocked the depletion of striatal dopamine and cortical norepinephrine in vivo. Pretreatment with EXP 561, an inhibitor of catecholamine uptake, also prevented the dopamine- and norepinephrine-depleting effects of MPTP-3-ol. Thus, substitution of a hydroxy group on the 3-position of MPTP retains its neurotoxic potential toward catecholamine neurons but reduces potency by decreasing the rate of oxidation via monoamine oxidase type B.
The administration of amphetamine to rats pretreated with iprindole to inhibit the metabolism of amphetamine results in a long-lasting depletion of striatal dopamine and its metabolites, DOPAC and HVA. Pretreatment with MK801, a noncompetitive antagonist of the NMDA (N-methyl-D-aspartate) subclass of excitatory amino acid receptors, antagonized the depletion of striatal dopamine, DOPAC and HVA 3 days after a single dose of amphetamine in iprindole-treated rats. MK801 pretreatment was effective up to 4 hours but not at 8 or 24 hours in preventing amphetamine effects on striatal dopamine, DOPAC and HVA.
Fluoxetine injected i.p. into rats at a dose of 10 mg/kg rapidly increased serotonin concentration in microdialysis fluid from the striatum by at least 4-fold, an increase that was maintained throughout the 3 hr observation period. Dopamine concentration in the microdialysis fluid did not change. The concentration of the two dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, was not changed in the microdialysis fluid, whereas the concentration of the serotonin metabolite, 5-hydroxyindoleacetic acid, was significantly decreased after fluoxetine injection. The increased extracellular concentration of serotonin no doubt resulted from inhibition of the serotonin uptake carrier by fluoxetine, and the lack of change in dopamine is evidence for the specificity of action of this uptake inhibitor.
Norfluoxetine, the N-desmethyl metabolite of fluoxetine, has been reported to resemble fluoxetine in being a potent and selective inhibitor of the serotonin uptake carrier. The enantiomers of norfluoxetine have now been compared as serotonin uptake inhibitors in vivo, based on their antagonism of p-chloroamphetamine-induced depletion of serotonin in brain and their lowering of concentrations of the metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA) in brain. In rats, S-norfluoxetine (ED50 3.8 mg/kg) was more potent than R-norfluoxetine (ED50 > 20 mg/kg) in blocking the depletion of serotonin by p-chloroamphetamine after intraperitoneal administration. The S enantiomer decreased concentrations of 5-HIAA in whole brain after doses of 2.5-20 mg/kg, whereas the R enantiomer did not. The concentrations of both enantiomers in brain increased in proportion to dose and the R enantiomer disappeared from the brain at a slightly slower rate than the S enantiomer. The relative inability of the R enantiomer to block the uptake of serotonin was therefore not a result of smaller concentrations of drug in the brain. In mice, S-norfluoxetine was also more potent than R-norfluoxetine in blocking depletion of serotonin by p-chloroamphetamine (ED50 values 0.82 and 8.3 mg/kg, respectively). Thus, in contrast to the relatively similar potencies of the enantiomers of fluoxetine in blocking the uptake of serotonin, the enantiomers of norfluoxetine have markedly different potencies as inhibitors of the uptake of serotonin.
LY274614, 3SR,4aRS,6SR,8aRS-6-[phosphonomethyl]decahydr oisoquinoline-3- carboxylic acid, has been described as a potent antagonist of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Here its ability to antagonize the prolonged depletion of dopamine in the striatum by amphetamine in iprindole-treated rats is reported. A single 18.4 mg/kg (i.p.) dose of (+/-)-amphetamine hemisulfate, given to rats pretreated with iprindole, resulted in persistent depletion of dopamine in the striatum 1 week later. This prolonged depletion of dopamine in the striatum was antagonized by dizocilpine (MK-801, a non-competitive antagonist of NMDA receptors) or by LY274614 (a competitive antagonist of NMDA receptors). The protective effect of LY274614 was dose-dependent, being maximum at 10-40 mgkg (i.p.). A 10 mg/kg dose of LY274614 was effective in antagonizing the depletion of dopamine in the striatum, when given as long as 8 hr prior to amphetamine but not when given 24 hr prior to amphetamine. Depletion of dopamine in the striatum was also antagonized when LY274614 was given after the injection of amphetamine; LY274614 protected when given up to 4 hr after but not when given 8 or 24 hr after amphetamine. The prolonged depletion of dopamine in the striatum in mice, given multiple injections of methamphetamine, was also antagonized dose-dependently and completely by LY274614. The data strengthen the evidence that the neurotoxic effect of amphetamine and related compounds toward nigrostriatal dopamine neurons involves NMDA receptors and that LY274614 is an NMDA receptor antagonist with long-lasting in vivo effects in rats.
Salmeterol (SM) is a novel beta 2-adrenoceptor agonist with a duration of action in excess of 12 hours. Evidence from in vitro studies has also demonstrated that, unlike the short-acting beta 2-agonists, such as salbutamol (SB), it may have some anti-inflammatory properties. With a randomized, double-blind, crossover design, we have compared the inhibitory effects of SM (50 micrograms) and SB (200 micrograms) delivered by metered-dose inhaler on allergen-induced bronchoconstriction, changes in airway reactivity, and urinary leukotriene (LT) E4 excretion in 12 atopic subjects with mild asthma. The immediate bronchoconstriction to allergen was significantly reduced by both beta 2-agonists (p less than 0.005), when reduction was expressed either in terms of maximum fall in FEV1 at 15 minutes after allergen (percent fall in FEV1, mean +/- SEM: 6.2 +/- 4.9, SM; 5.7 +/- 2.5, SB; 40.4 +/- 6.3, placebo) or the area under the FEV1 time curve (AUC) for the first 120 minutes after allergen. Four hours after challenge, results in the SB-treated and placebo-treated groups were not significantly different and demonstrated a small persistent bronchoconstriction compared to bronchodilatation in the SM-treated group (percent fall in FEV1, respectively, 9.3 +/- 3.7, 14.3 +/- 7.1, and -6.3 +/- 2.7; p less than 0.005, SM versus SB; p less than 0.02, SM versus placebo). Expressed in terms of AUC, only SM significantly reduced bronchoconstriction in the period 120 to 240 minutes after allergen (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
3-Chloro-alpha-phenylpyrazinemethanol (3-CPM) inhibited monoamine oxidase (MAO) types A and B in vivo in mouse brain, heart and liver. The inhibition was dose-dependent at doses of 0.3-32 mg/kg i.p. and occurred within 1 h after the compound was injected. 3-CPM was a very weak inhibitor of mouse brain mitochondrial MAO activity in vitro, even when preincubated with the enzyme; MAO-A was inhibited only about 50% at a high concentration of 3-CPM (1 mM), and MAO-B was inhibited even less. After a 10 mg/kg i.p. dose of 3-CPM in mice, both MAO-A and MAO-B were inhibited at day 1, but activity had largely recovered within a few days in brain, liver and heart. 3-CPM at doses of 1, 3, 10 and 32 mg/kg i.p. caused dose-dependent antagonism of the depletion of striatal dopamine and of cortical norepinephrine by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 3-CPM is therefore a potent inhibitor of MAO-A and of MAO-B in mice in vivo despite its weak effect on the enzyme in vitro. A metabolite of the drug may be involved in the in vivo effects.
Antihistamines have been reported to have antitussive actions in allergic rhinitis which may be due to an effect of the drug on the cough reflex. We have studied the effect on induced cough in normal volunteers. Ten volunteers inhaled capsaicin at concentrations between 0.78 and 200 microM, in increasing dose order, until they coughed more than five times. The challenge was performed three times before and three times each at 2 and 4 h after 120 mg terfenadine or matched placebo tablet in a double-blind, randomized, cross-over study. Neither affected the capsaicin cough challenge. Thus, any antitussive effect of terfenadine is more likely to be via an indirect mechanism such as inhibition of released histamine rather than on the cough reflex itself.
Fluoxetine selectively inhibits serotonin uptake in vitro and in vivo and thus enhances serotonergic function, leading to a decrease in food intake beginning with the first dose and a decrease in body weight or in weight gain after multiple doses of fluoxetine. Fluoxetine and other drugs that increase serotonergic function decrease food intake with characteristics that make them attractive for use in weight reduction. In rats, for instance, fluoxetine and other serotonergic drugs suppress stress-induced eating, suppress carbohydrate consumption selectively, and suppress insulin-induced hyperphagia. Fluoxetine and other serotonergic drugs do not cause amphetamine-like behavioral stimulation in animals and have no known abuse or addiction liability. In obese yellow mice and in normal mice, as in rats, fluoxetine causes a sustained decrease in food intake and body weight. The pharmacologic effects of fluoxetine in animals suggest its potential use in weight-reduction programs in obese humans.
The airway macrophage has the characteristics required of the conducting cell in asthma. First, the airway macrophage is the most numerous cell within the airway lumen. Second, it can be activated by antigen and virus infections to release both spasmogens and chemotactic cytokines. Thus the common triggers to asthma are capable of activating the airway macrophage. Third, the response of the airway macrophage to therapeutic agents used in asthma bears a close similarity to the profile of disease modification with drugs in asthma, that is, they are inhibited by glucocorticosteroids but not beta 2-adrenoceptor agonists.
A randomised placebo-controlled cross-over group study was conducted to ascertain the occurrence and duration of xerostomia induced by 240 micrograms (high dose) and 120 micrograms (low dose) of ipratropium bromide (IPB) delivered by metered dose inhaler (MDI) into the mouth in normal subjects. Salivary output was higher with both doses of IPB than with placebo though the differences were not statistically significant. IPB was less palatable than placebo as indicated on visual analogue scale (VAS) and the taste of the drug may have caused a reflex increase in salivary output from the major salivary glands which would have masked any possible local effect of the drug on the smaller submucosal glands of the mouth. IPB delivered into the oral cavity by MDI is therefore not a suitable treatment for hypersalivation.
The effect of a single, high dose of aspirin has been assessed against low chloride cough challenge. The drug does not affect the cough response, suggesting that airway prostaglandin generation is not responsible for the tussive activity of low chloride solution.
The effects of nebulized diuretics on citric acid-induced cough and airway obstruction in guinea pigs and capsaicin-induced cough and increase in airway resistance in humans have been studied. Half-maximum inhibition of cough in the guinea pig was produced by 1.3 mM furosemide and 0.25 mM hydrochlorothiazide. Cough was inhibited by 78 +/- 9% by 3 mM furosemide (P less than 0.05) and 89 +/- 11% by 3 mM hydrochlorothiazide (P less than 0.01). At the same time, airway obstruction was inhibited by 50 +/- 9% (P less than 0.001) and 42 +/- 15% (P less than 0.05), respectively. Nebulized furosemide (3 mM) was without effect on the airway obstruction produced by inhaled histamine or acetylcholine in the guinea pigs. Intravenously administered furosemide (270 nmol/kg) did not affect citric acid-induced responses. In humans, aerosolized furosemide (9 mM) and hydrochlorothiazide (3.4 mM) reduced the percent increase in respiratory resistance from 22.1 +/- 3.7 and 15.6 +/- 3.4 to 10.5 +/- 4.9 and 9.4 +/- 3.3%, respectively (P less than 0.05), but were without effect on cough due to capsaicin. Thus both furosemide and hydrochlorothiazide inhibited airway obstruction in the guinea pig and reduced the capsaicin-induced increase in airway resistance in humans. However, whereas coughing was inhibited in the guinea pig, neither drug affected cough in humans. This difference in the action of the loop diuretic and thiazide, which interact differently with Na(+)-K(+)-Cl-transport within the airway mucosa, on the cough and airflow obstruction in guinea pig and humans supports the view that different sensory limbs are involved in these reflexes.(ABSTRACT TRUNCATED AT 250 WORDS)