Effect of stress on the production of O2 in alveolar macrophages

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Abstract

Alveolar macrophages (AM) of male rats (200–250 g), stressed or not, were evaluated with relationship to superoxide production (SP). Plasma levels of corticosterone were measured. The control group showed larger SP than the stressed group in all intervals of time. Exposure in vitro of AM to a synthetic glucocorticoid for 40 min (the same time of restraint stress) inhibits SP. Therefore, it seems under stress situations there is an increase of plasma levels of corticosterone and a decrease of SP in AM after stimulation with PMA. O2 is a potent microbicide and its reduction could cause the loss of microbicidal activity of AM.

Introduction

Over the past several years, a substantial body of evidence has emerged supporting the hypothesis that stress situations are associated with altered immune function (Dantzer, 1991). Stressors can provoke an imbalance in the immune response, a phenomenon that suggests neuroimmunological modulation and a relationship between the immunological, nervous and endocrine systems (Blalock et al., 1985, Dardenne and Savino, 1996). Receptors for molecules such as neurotransmitters and several neuropeptides that are implicated in stress reactions and anxiety are present in the membranes of distinct populations of immune cells (Blalock et al., 1985, Dantzer, 1991).

Recent progress in immunology has emphasized the critical role of the macrophages in the immune system (IS), as homeostasis regulators or as effector cells in infections, in tumors and in wounds (Celada and Nathan, 1994). The respiratory tract is continually exposed to organisms or particles that are contained in the inhaled air. The lungs defend themselves from eventual harmful effects of microparticles and microorganisms through phagocytosis, which is accomplished by the alveolar macrophages (AM) (Sibille and Reynolds, 1990).

Macrophages as well as granulocytes and neutrophils produce large amounts of oxidants such as superoxide ion (O2) (Babior, 1997). The O2 anion is produced when an electron reduces oxygen. O2 is produced by the action of the enzyme NADPH oxidase, which is linked to cellular membranes (Chanock et al., 1994). These oxidizing agents participate in the pathogenesis of several neoplastic diseases due to their ability to cause genomic mutations and their capacity to oxidize lipoproteins. However, these properties of oxidizing agents are also essential for the defense of the host against microorganisms (Johnston and Newman, 1977, Babior, 1997). An oxidizing agent not only kills bacteria and fungi, but also attacks tumoral cells and parasites (Weissmann et al., 1980).

The role of superoxide liberation by the macrophages in the defense against pathogenic agents is well known. However, studies are still necessary concerning the liberation of oxidizing agents by AM and their eventual alteration during stress. The aims of this work were both to determine in in vitro cell culture systems the kinetics of superoxide production (SP) by AM activated with PMA and to study the eventual effects of stress.

Section snippets

Animals and stress procedure

All the manipulations were performed in male Wistar rats, weighing 200–250 g at the time of the experiment. The animals were kept under controlled conditions (ad libitum access to water and food, 12-h light–dark cycle and 20±1°C room temperature) during at least 1 week before any experimental manipulation. Rats were subjected to restraint stress by keeping them immobilized in glass cylinders (6 cm diameter×17 cm long) during 40 min. Immediately after, the materials collection for the study was

Corticosterone level in the plasma and effect of the stress

The plasma levels of corticosterone (5.0±0.5 μg/100 ml) in control animals were slightly higher than those usually observed under basal conditions. Some degree of stress might have occurred during the experiment with the control group. However, the corticosterone level in the plasma of the stressed animals was significantly (P<0.001) higher when compared to that of the control animals after 40 min of stress (Fig. 1).

Time course of superoxide production by the alveolar macrophages

The analysis of SP was started immediately before the stimulation of the

Discussion

In vitro cell culture systems were utilized to establish the kinetics of SP by AM activated with PMA and to study SP in AM from stressed animal. The kinetics of SP was determined in cells stimulated during 24 h to find the best interval of time of stimulation of the macrophages. In this study, there was a progressive increase of SP reaching the maximum 6 h after PMA stimulation. SP then decreased continuously to levels approximately 50% of the maximum at 24 h. The SP in AM culture of stressed

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