Impact of acute exposure to air pollution on the cardiorespiratory performance of military firemen.

The objective of the present study was to determine the impact of acute short-term exposure to air pollution on the cardiorespiratory performance of military firemen living and working in the city of Guarujá, São Paulo, Brazil. Twenty-five healthy non-smoking firemen aged 24 to 45 years had about 1 h of exposure to low and high levels of air pollution. The tests consisted of two phases: phase A, in Bertioga, a town with low levels of air pollution, and phase B, in Cubatão, a polluted town, with a 7-day interval between phases. The volunteers remained in the cities (Bertioga/Cubatão) only for the time required to perform the tests. Cumulative load 10 +/- 2 min-long exertion tests were performed on a treadmill, consisting of a 2-min stage at a load of 7 km/h, followed by increasing exertion of 1 km h-1 min-1 until the maximum individual limit. There were statistically significant differences (P < 0.05) in anaerobic threshold (AT) between Cubatão (35.04 +/- 4.91 mL kg-1 min-1) and Bertioga (36.98 +/- 5.62 mL kg-1 min-1; P = 0.01), in the heart rate at AT (AT HR; Cubatão 152.08 +/- 14.86 bpm, Bertioga 157.44 +/- 13.64 bpm; P = 0.001), and in percent maximal oxygen consumption at AT (AT%VO2max; Cubatão 64.56 +/- 6.55%, Bertioga 67.40 +/- 5.35%; P = 0.03). However, there were no differences in VO2max, maximal heart rate or velocity at AT (ATvel) observed in firemen between towns. The acute exposure to pollutants in Cubatão, SP, caused a significant reduction in the performance at submaximal levels of physical exertion.

Impact of acute exposure to air pollution on the cardiorespiratory performance of military firemen

The objective of the present study was to determine the impact of acute short-term exposure to air pollution on the cardiorespiratory performance of military fireman living and working in the city of Guarujá, São Paulo, Brazil. Twenty-five healthy non-smoking firemen aged 24 to 45 years had about 1 h of exposure to low and high levels of air pollution. The tests consisted of two phases: phase A, in Bertioga, a town with low levels of air pollution, and phase B, in Cubatão, a polluted town, with a 7-day interval between phases. The volunteers remained in the cities (Bertioga/Cubatão) only for the time required to perform the tests. Cumulative load 10 ± 2 min-long exertion tests were performed on a treadmill, consisting of a 2-min stage at a load of 7 km/h, followed by increasing exertion of 1 km h-1 min-1 until the maximum individual limit. There were statistically significant differences (P < 0.05) in anaerobic threshold (AT) between Cubatão (35.04 ± 4.91 mL kg-1 min-1) and Bertioga (36.98 ± 5.62 mL kg-1 min-1; P = 0.01), in the heart rate at AT (AT HR; Cubatão 152.08 ± 14.86 bpm, Bertioga 157.44 ± 13.64 bpm; P = 0.001), and in percent maximal oxygen consumption at AT (AT percentVO2max; Cubatão 64.56 ± 6.55 percent, Bertioga 67.40 ± 5.35 percent; P = 0.03). However, there were no differences in VO2max, maximal heart rate or velocity at AT (ATvel) observed in firemen between towns. The acute exposure to pollutants in Cubatão, SP, caused a significant reduction in the performance at submaximal levels of physical exertion.

In vitro cytotoxicity of the LDE: daunorubicin complex in acute myelogenous leukemia blast cells.

Acute myelogenous leukemia (AML) blast cells show high-affinity degradation of low-density lipoprotein (LDL), suggesting an increased expression of cellular LDL receptors. LDE is a lipid microemulsion easily synthesized in vitro which is known to mimic the metabolic pathway of LDL. We used LDE as a carrier for daunorubicin and assayed the cytotoxicity of the complex using AML blast cells since RT-PCR analysis showed that AML cells express LDL receptor mRNA. The LDE:daunorubicin complex killed 46.7% of blast cells and 20.2% of normal bone marrow cells (P<0.001; Student t-test). Moreover, this complex destroyed AML blast cells as efficiently as free daunorubicin. Thus, LDE might be a suitable carrier of chemotherapeutic agents targeting these drugs to neoplastic cells and protecting normal tissues.

In vitro cytotoxicity of the LDE-daunorubicin complex in acute myelogenous leukemia blast cells

Acute myelogenous leukemia (AML) blast cells show high-affinity degradation of low-density lipoprotein (LDL), suggesting an increased expression of cellular LDL receptors. LDE is a lipid microemulsion easily synthesized in vitro which is known to mimic the metabolic pathway of LDL. We used LDE as a carrier for daunorubicin and assayed the cytotoxicity of the complex using AML blast cells since RT-PCR analysis showed that AML cells express LDL receptor mRNA. The LDE:daunorubicin complex killed 46.7 percent of blast cells and 20.2 percent of normal bone marrow cells (P<0.001; Student t-test). Moreover, this complex destroyed AML blast cells as efficiently as free daunorubicin. Thus, LDE might be a suitable carrier of chemotherapeutic agents targeting these drugs to neoplastic cells and protecting normal tissues

Delta-aminolevulinic acid-induced lipid peroxidation in rat kidney and liver is attenuated by melatonin: an in vitro and in vivo study.

Acute intermittent porphyria (AIP) is a genetically inherited disease characterized by a partial block in liver heme biosynthesis and by increased urinary excretion of the delta-aminolevulinic acid (ALA). Recently, it has been proposed that the toxic effects of ALA are related to the generation of free radicals. In the present study the in vitro and in vivo effect of melatonin, a recently described antioxidative agent, on ALA-induced lipid peroxidation in rat liver and kidney was determined. The concentration of malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA) was assayed as an index of induced membrane oxidative damage. In vitro melatonin protected, in a concentration-dependent manner, against ALA-induced lipid peroxidation in liver and kidney homogenates. In in vivo experiments as well, it was demonstrated that ALA (40 mg/kg)-induced lipid peroxidation in liver and kidney was reduced by acute melatonin (10 mg/kg) treatment. The results support the involvement of free radicals in ALA toxicity and show that in vitro and in vivo melatonin confers protection against this toxicity, likely due to the antioxidative capability of the indole.

Melatonin protects against lipid peroxidation induced by delta-aminolevulinic acid in rat cerebellum, cortex and hippocampus.

The in vitro and in vivo effect of melatonin on delta-aminolevulinic acid-induced lipid peroxidation in rat cerebellum, cortex and hippocampus was determined. The concentration of malonaldehyde and 4-hydroxyalkenals was assayed as an index of induced membrane oxidative damage. The rise in malonaldehyde+4-hydroxyalkenals concentrations induced by delta-aminolevulinic acid in cerebellar homogenates was concentration-dependent (P < 0.001) and also time-dependent in cerebellar, cortical and hippocampal homogenates (P < 0.01). In vitro melatonin and vitamin E protected, in a concentration-dependent manner, against delta-aminolevulinic acid-induced lipid peroxidation in cortical, cerebellar and hippocampal homogenates. In in vivo experiments it was demonstrated that delta-aminolevulinic acid-induced lipid peroxidation (40 mg/kg) in cerebellum and hippocampus was reduced by acute melatonin (10 mg/kg) treatment (P < 0.05). The results show that both in vitro and in vivo melatonin confers protection against delta-aminolevulinic acid-induced oxidative toxicity in brain regions. The findings suggest that melatonin may be useful in reducing neural damage in individuals suffering from acute intermittent porphyria.

Melatonin in relation to cellular antioxidative defense mechanisms.

Melatonin's actions in organisms are more widespread than originally envisaged. Over three decades ago, the changing pattern of nocturnal melatonin production was found to be the signal for the annual cycle of reproduction in photoperiodic species. Since then, melatonin's actions also have been linked to circadian rhythms, immune function, sleep, retinal physiology and endocrine functions in general. In recent years, however, the sphere of influence of melatonin was further expanded when the indole was found to be an effective free radical scavenger and antioxidant. Free radicals are toxic molecules, many being derived from oxygen, which are persistently produced and incessantly attack and damage molecules within cells; most frequently this damage is measured as peroxidized lipid products, carbonyl proteins, and DNA breakage or fragmentation. Collectively, the process of free radical damage to molecules is referred to as oxidative stress. Melatonin reduces oxidative stress by several means. Thus, the indole is an effective scavenger of both the highly toxic hydroxyl radical, produced by the 3 electron reduction of oxygen, and the peroxyl radical, which is generated during the oxidation of unsaturated lipids and which is sufficiently toxic to propagate lipid peroxidation. Additionally, melatonin may stimulate some important antioxidative enzymes, i.e., superoxide dismutase, glutathione peroxidase and glutathione reductase. In in vivo tests, melatonin in pharmacological doses has been found effective in reducing macromolecular damage that is a consequence of a variety of toxic agents, xenobiotics and experimental paradigms which induce free radical generation. In these studies, melatonin was found to significantly inhibit oxidative damage that is a consequence of paraquat toxicity, potassium cyanide administration, lipopolysaccharide treatment, kainic acid injection, carcinogen administration, carbon tetrachloride poisoning, etc., as well as reducing the oxidation of macromolecules that occurs during strenuous exercise or ischemia-reperfusion. In experimental models which are used to study neurodegenerative changes associated with Alzheimer's and Parkinson disease, melatonin was found to be effective in reducing neuronal damage. Its lack of toxicity and the ease with which melatonin crosses morphophysiological barriers and enters subcellular compartments are essential features of this antioxidant. Thus far, most frequently pharmacological levels of melatonin have been used to combat oxygen toxicity. The role of physiological levels of melatonin, which are known to decrease with age, is being investigated as to their importance in the total antioxidative defense capacity of the organism.

Melatonin modulation of presynaptic nicotinic acetylcholine receptors in the rat vas deferens.

Melatonin, the pineal hormone produced during the dark phase of the light-dark cycle, modulates neuronal acetylcholine receptors located presynaptically on the sympathetic nerve terminals of the rat vas deferens. The pD2 values for nicotine were significantly higher at night (4.20 +/- 0.01) than in the afternoon (3.80 +/- 0.07). Exogenous melatonin shifted the concentration-response curves for nicotine to the left, mimicking the effect of darkness. Melatonin modifies both the displacement and the saturation curves of [3H](-)nicotine binding. In membranes from animals killed at 15:00 h, the binding of [3H](-)nicotine (5-6 nM) was first potentiated and then inhibited by sequential concentrations of (-)nicotine. Higher concentrations of [3H](-)nicotine (50-60 nM) were displaced by all concentrations of nonlabeled ligand. However, when membranes from tissues exposed to melatonin (exogenous or endogenous) were tested, the lower [3H](-)nicotine concentration was displaced progressively by increasing concentrations of nonlabeled ligand. Equilibrium binding studies show a single class of high-affinity nicotinic binding sites with an apparent Kd value of 16 nM and an average maximal number of binding sites of 66 fmol mg-1 protein when animals were killed at the afternoon. Melatonin, although it did not change the properties of high-affinity binding sites, induced the appearance of a second population of lower apparent affinity (Kd = 36.7 nM; Bmax = 185.4 fmol/mg). Melatonin does not modify the functional response and the displacement of [3H](-)nicotine by dimethylphenylpiperazinium. The data suggest that nicotinic neuronal acetylcholine receptors stimulated by dimethylphenylpiperazinium do not change between the light and dark phases. Rather, the higher sensitivity to nicotine in prostatic portions incubated with exogenous melatonin, and in organs from animals killed at night, after the rise of endogenous melatonin, is probably due to the appearance of low-affinity neuronal nicotinic ACh binding sites.

Modulation of sympathetic neurotransmission by melatonin.

Melatonin is of considerable interest for its regulatory influence on a variety of physiological processes including biological rhythms and neuroendocrine functions. We showed that melatonin potentiates sympathetic neurotransmission in the prostatic portion of the rat vas deferens, by increasing contractions in response to noradrenaline and ATP released by acetylcholine stimulation of presynaptic nicotinic receptors. Melatonin in vitro (100 pg/ml; for 4 h) increased the maximal acetylcholine-induced contraction only when the hypogastric ganglion was present, and this effect was blocked by cycloheximide (100 micrograms/ml). Melatonin also modulated the sympathetic trophic influence on smooth muscle, since it reduced [35S]methionine incorporation into the vas deferens in the hypogastric ganglion-vas deferens preparation. Thus, it is suggested that the regulation of protein synthesis might be one of the mechanisms whereby melatonin modulates endogenous rhythms and synchronizes them to the environmental light cycle.

Age-related changes in melatonin modulation of sympathetic neurotransmission.

An age-related reduction in the maximal acetylcholine (ACh)-induced contraction in the prostatic portion of rat vas deferens during the day was observed. This contraction is due to the release of norepinephrine and adenosine triphosphate from sympathetic nerve terminals. Male Wistar rats (4 and 24 months-old) were housed on a light/dark cycle (12:00 h/12:00 h, lights on at 6:00). The diurnal variation of ACh-induced contraction was determined on animals sacrificed every 3 h during the day. Aging reduced the maximal contraction and shortened the length of the nocturnal response. In both young and old rats, the response to ACh increased at 21:00, but it remained elevated until 12:00 in young rats and until 24:00 in old rats. Both nocturnal administration of melatonin for 2 consecutive days (9 mg/kg/day, s.c.) and melatonin incubation (100 pg/ml, 4 h) of the vas deferens from old rats sacrificed at 15:00 h significantly potentiated the ACh-induced contraction. However, this potentiation was smaller than that observed in young rats. The results presented here show the loss of maximal contractile response to ACh with age and a qualitative change in the rhythm characteristics of this phenomenon. Moreover, the age-related decrease in the ACh-induced contraction in the prostatic portion of the rat vas deferens is dependent not only on a reduction in the plasma nocturnal increase of melatonin concentration but also on a lower responsiveness of short sympathetic neurons to melatonin.

2-[125I]iodomelatonin binding sites in the rat vas deferens.

To further understand the mechanism by which melatonin potentiates noradrenergic transmission in the rat vas deferens, we localized and partially characterized 2-[125I]-iodomelatonin-binding sites in tissue sections of the rat vas deferens using quantitative autoradiography. High-affinity 2-[125I]-iodomelatonin-binding sites were localized around the lumen of the prostatic portion, but not in the epididymal portion of the rat vas deferens. The binding of 2-[125I]-iodomelatonin to sections of the prostatic portion was stable, reversible and saturable. Saturation studies revealed a single class of high-affinity binding sites with a dissociation constant (Kd) of 104.2 +/- 23.7 pM (n = 4) and a binding capacity (Bmax) of 2.07 +/- 0.19 fmol/mg of protein (n = 4). These results suggest that melatonin may regulate sympathetic neurotransmission through activation of specific melatonin receptors in the prostatic portion of the rat vas deferens.

Presynaptic modulation by melatonin of the nicotine-induced calcium-dependent release of norepinephrine from rat vas deferens.

This study demonstrates that melatonin potentiates the nicotine-induced calcium-dependent release of [3H]-norepinephrine from the rat vas deferens. Slices of the prostatic portion of the rat vas deferens were labelled in vitro with [3H]-norepinephrine and superfused with physiological solution. Nicotine (1 mM, 4 min) induced a calcium-dependent release of norepinephrine during the first (N1 = 1.43 +/- 0.16%) and the second (N2 = 1.11 +/- 0.2%, n = 22) nicotine stimulations. The ratio N2/N1 between two consecutive periods of nicotine stimulations was: 0.84 +/- 0.09 (n = 22). Melatonin (10-300 nM) did not modify the spontaneous release of [3H]-norepinephrine but potentiated in a concentration-dependent manner the calcium-dependent release. The competitive melatonin receptor antagonist luzindole did not modify the calcium-dependent release of [3H]-norepinephrine when added alone but completely antagonized the potentiation of release elicited by melatonin, suggesting interaction at the level of a melatonin receptor. We conclude that melatonin potentiates the nicotine-evoked release of [3H]-norepinephrine in the rat vas deferens through activation of melatonin presynaptic heteroreceptors on noradrenergic nerves involved in a positive feedback mechanism. This mechanism may mediate the increase in sympathetic neurotransmission observed with melatonin in the vas deferens. We cannot exclude, however, an effect of melatonin on cellular proteins and enzymes associated with the exocytotic process, which directly or indirectly may lead to the facilitation of release.

Diurnal variation of the rat vas deferens contraction induced by stimulation of presynaptic nicotinic receptors and pineal function.

A rhythmic variation of maximal contraction induced by acetylcholine in the prostatic portion of rat vas deferens was tested. This contraction is due to the release of norepinephrine and ATP from sympathetic nerve terminals. Male Wistar rats (4 months old) were housed on a light/dark cycle (12 hr/12 hr, lights on at 6:00 A.M.). The diurnal variation of acetylcholine-induced contraction was determined on animals sacrificed every 3 hr during the day. The maximal contractile response shows a circadian (24:00 hr) and an ultradian (12:20 hr) rhythm. Otherwise, the sensitivity to acetylcholine (pD2 values) and the maximal contraction or pD2 values to norepinephrine, ATP and K+ did not change throughout the day. The blocking effect of hexamethonium on the contraction induced by field stimulation was higher at 9:00 P.M. than at 3:00 P.M., indicating a diurnal variation of the effect of endogenous released acetylcholine. When melatonin released by the pineal gland is suppressed by constant illumination or superior cervical ganglionectomy, the circadian rhythm was abolished and the period of the ultradian rhythm changed to 6:30 hr. The acetylcholine-induced contraction of vasa deferentia from animals sacrificed at 3:00 P.M. and incubated "in vitro" with melatonin (100 pg/ml) increased reaching nocturnal values. In conclusion, it seems that a functional pineal gland, most probably through the synthesis and release of melatonin, is necessary for expression (circadian) and modulation (ultradian) of the rhythmicity in the maximal acetylcholine-induced contraction in the prostatic portion of the rat vas deferens.

Presynaptic nicotinic receptors involved in release of noradrenaline and ATP from the prostatic portion of the rat vas deferens.

A differential response to cholinomimetic agonists in epididymal and prostatic portions of rat vas deferens was characterized. The prostatic portion was less sensitive to acetylcholine and carbachol than the epididymal portion. The contraction induced by cholinomimetic agonists was inhibited in the epididymal portion by atropine (1.0-3.0 nM) and in the prostatic portion by hexamethonium (0.1 mM). The contractile response of the prostatic portion to exogenous acetylcholine was not inhibited by textrodotoxin (1.0 microM) but was attenuated by reserpine treatment (10 mg.kg-1 i.p. 24 h) and by prazosin or alpha, beta-methylene ATP. A combination of an alpha-1-adrenoceptor antagonist (prazosin) and P2 purinoceptor desensitization with alpha, beta-methylene ATP abolished the contractile response of the prostatic portion. The contraction induced by repetitive field stimulation of the prostatic portion was attenuated by hexamethonium whereas the response to a single stimulus was not modified. The data suggest that cholinomimetic drugs activate both nicotinic receptors located in nerve terminals of the prostatic portion and muscarinic receptors located in the smooth muscle cells of the epididymal portion, and that stimulation of nicotinic receptors induces the release of noradrenaline and ATP.

[Thrombolysis in acute myocardial infarction. Streptokinase or r-TPA?]. / Trombólise no infarto agudo do miocárdio. Estreptoquinase ou r-TPA?

PURPOSE: To compare the results of intravenous thrombolytic therapy with streptokinase (SK), with those of the recombinant human tissue-type plasminogen activator (r-TPA), in acute myocardial infarction (AMI). MATERIAL AND METHODS: One hundred patients with AMI of less than 6 hours duration were randomized in two groups: 50 patients were allocated to 1.200.000 IU of SK (Group SK) and 50 patients received 100 mg of r-TPA over 180 minutes. The two groups were similar respecting age, sex, location and previous infarction. The angiographic study was performed 48 h after the thrombolytic therapy. RESULTS: In the angiographic study, 85% of the Group SK vs 66% of Group r-TPA had patient infarct-related vessel (p = 0.025). Reocclusion was 6.6% in Group SK vs 19% in Group r-TPA and hospital mortality was similar in the two groups. CONCLUSION: In the late angiographic evaluation (48 h), the frequency of coronary patency was found to be higher after intravenous SK than after intravenous r-TPA.

[Coronary angioplasty in elderly patients. A therapeutic option]. / Angioplastia coronariana em pacientes idosos. Uma opçáo terapêutica.

Of 304 consecutive percutaneous transluminal coronary angioplasties (PTCA) performed between March 86 and March 88, 61 patients were 65 years or older. The indications for PTCA were: stable angina, unstable angina and acute myocardial infarction with suitable anatomy. In elderly patients, the female sex, and the calcific deposits, were more frequent than in the younger group (p less than 0.0001). Primary success was achieved in 82%, vs 88% in patients younger than 65 years; complications and mortality were also statistically irrelevant between the two groups. Late clinical follow-up ranging from 3 to 36 months (mean 10) showed that symptomatic improvement was achieved in 86% of elderly patients in whom PTCA was successful (vs 80% in the younger group). These data support the safety and clinical effectiveness of PTCA in elderly symptomatic patients with suitable anatomy.