Repeated saline injections reduce the pulmonary allergic inflammatory response in rats by inducing short-term stress

Asthma is characterized by pulmonary cell infiltration and hyper-responsiveness of the airways. Short-term stress reduces airway inflammation. Thus, in the present study, we examined the effects of short-term stress induced by repeated treatment with saline injections on the pulmonary allergic inflammatory response in rats.

Adult male rats were divided into three groups: Naïve group (non-sensitized, challenged, or treated rats), Control group (rats sensitized with ovalbumin (OVA) to induce lung inflammation), and Saline group (rats treated for five days with saline before OVA sensitization). Inhalation challenges were performed one week after the booster with aerosolized OVA. On day 18, the effect of saline injections on total and differential leukocytes in bronchoalveolar lavage (BAL), femoral marrow lavage (FML), and blood was evaluated. The percentage of mucus, serum corticosterone, collagen, cytokines in lung explants, and norepinephrine levels were also measured.

OVA sensitization increased the circulating leukocytes and their migration to the lung, decreasing the bone marrow leukocytes. The repeated saline injections prevented this migration by decreasing the number of leukocytes in BAL and blood in the control group. Cytokine Interleukin-4 (IL-4) was higher in the control group than in the naive and saline groups; cytokines Interleukin-6 (IL-6), Interleukin-10 (IL-10), and tumor necrosis factor-alpha (TNFα) were higher in the control and saline groups than in the naïve group; Interferon gamma (IFNγ) was higher in the saline group than in the naive and control groups; norepinephrine increased in animals sensitized with OVA and was higher only in the saline group relative to the naïve group.

These results suggest that short-term stress could contribute to the anti-allergic airway inflammation effects of a given treatment.