A single exposure to eucalyptus smoke sensitizes rats to the postprandial cardiovascular effects of a high carbohydrate oral load

Abstract

Objective

Previous studies have shown that air pollution exposure primes the body to heightened responses to everyday stressors of the cardiovascular system. The purpose of this study was to examine the utility of postprandial responses to a high carbohydrate oral load, a cardiometabolic stressor long used to predict cardiovascular risk, in assessing the impacts of exposure to eucalyptus smoke (ES), a contributor to wildland fire air pollution in the Western coast of the United States.

Materials and methods

Three-month-old male Sprague Dawley rats were exposed once (1 h) to filtered air (FA) or ES (700 µg/m³ fine particulate matter), generated by burning eucalyptus in a tube furnace. Rats were then fasted for six hours the following morning, and subsequently administered an oral gavage of either water or a HC suspension (70 kcal% from carbohydrate), mimicking a HC meal. Two hours post gavage, cardiovascular ultrasound, cardiac pressure–volume (PV), and baroreceptor sensitivity assessments were made, and pulmonary and systemic markers assessed.

Results

ES inhalation alone increased serum interleukin (IL)-4 and nasal airway levels of gamma glutamyl transferase. HC gavage alone increased blood glucose, blood pressure, and serum IL-6 and IL-13 compared to water vehicle. By contrast, only ES-exposed and HC-challenged animals had increased PV loop measures of cardiac output, ejection fraction %, dP/dt_max, dP/dt_min, and stroke work compared to ES exposure alone and/or HC challenge alone.

Discussion and conclusions

Exposure to a model wildfire air pollution source modifies cardiovascular responses to HC challenge, suggesting air pollution sensitizes the body to systemic triggers.

Keywords:

• Air pollution
• wildland fires
• eucalyptus smoke
• inhalation
• cardiovascular
• postprandial
• high carbohydrate meal

Acknowledgments

The authors would like to thank Dr. Michael Stewart of the U.S. EPA for his thorough review of this manuscript prior to submission.

Disclosure statement

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

This manuscript has been reviewed by the Center for Public Health and Environmental Assessment, United States Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

Data availability statement

All data (i.e. individual values used to generate means and standard deviations presented in the tables and figures reported in this manuscript) will be made available on the U.S. E.P.A. public data repository located at https://catalog.data.gov/harvest/epa-sciencehub.

Additional information

Funding

This work was supported by the intramural research program of the Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC. WKM was supported by a pre-doctoral traineeship (National Research Service Award T32 ES007126).