Independent roles of beta-adrenergic and glucocorticoid receptors in systemic and pulmonary effects of ozone

Abstract

Background: The release of catecholamines is preceded by glucocorticoids during a stress response. We have shown that ozone-induced pulmonary responses are mediated through the activation of stress hormone receptors.

Objective: To examine the interdependence of beta-adrenergic (βAR) and glucocorticoid receptors (GRs), we inhibited βAR while inducing GR or inhibited GR while inducing βAR and examined ozone-induced stress response.

Methods: Twelve-week-old male Wistar-Kyoto rats were pretreated daily with saline or propranolol (PROP; βAR-antagonist; 10 mg/kg-i.p.; starting 7-d prior to exposure) followed-by saline or dexamethasone (DEX) sulfate (GR-agonist; 0.02 mg/kg-i.p.; starting 1-d prior to exposure) and exposed to air or 0.8 ppm ozone (4 h/d × 2-d). In a second experiment, rats were similarly pretreated with corn-oil or mifepristone (MIFE; GR-antagonist, 30 mg/kg-s.c.) followed by saline or clenbuterol (CLEN; β₂AR-agonist; 0.02 mg/kg-i.p.) and exposed.

Results: DEX and PROP + DEX decreased adrenal, spleen and thymus weights in all rats. DEX and MIFE decreased and increased corticosterone, respectively. Ozone-induced pulmonary protein leakage, inflammation and IL-6 increases were inhibited by PROP or PROP + DEX and exacerbated by CLEN or CLEN + MIFE. DEX and ozone-induced while MIFE reversed lymphopenia (MIFE > CLEN + MIFE). DEX exacerbated while PROP, MIFE, or CLEN + MIFE inhibited ozone-induced hyperglycemia and glucose intolerance. Ozone inhibited glucose-mediated insulin release.

Conclusions: In summary, 1) activating βAR, even with GR inhibition, exacerbated and inhibiting βAR, even with GR activation, attenuated ozone-induced pulmonary effects; and 2) activating GR exacerbated ozone systemic effects, but with βAR inhibition, this exacerbation was less remarkable. These data suggest the independent roles of βAR in pulmonary and dependent roles of βAR and GR in systemic effects of ozone.

Keywords:

• Stress response
• glucocorticoid receptors
• beta adrenergic receptors
• ozone
• lung injury
• metabolic response

Acknowledgments

The authors thank Drs. Aimen Farraj and Ian Gilmour of the US EPA and Dr. Samir Kelada of the University of North Carolina, Chapel Hill for their critical review of the manuscript. We acknowledge the help of Mr. Allen Ledbetter of the US EPA for performing ozone inhalation exposures and Ms. Judy Richards of the US EPA for performing clinical assays.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported in part by Fulbright [Becas Chile, CONICYT; IIE-15120279] to ARH and EPA-UNC Cooperative Training Agreement [CR-83578501] to ARH.