Exposure to repeated low-level formaldehyde in rats increases basal corticosterone levels and enhances the corticosterone response to subsequent formaldehyde

Abstract

Low-level exposure to volatile organic compounds may produce symptoms in humans reporting multiple chemical sensitivity (MCS) through altered hypothalamic–pituitary–adrenal (HPA) axis functioning. We determined whether repeated formaldehyde (Form) exposure would alter corticosterone (CORT) levels in a rat model of MCS. Male Sprague–Dawley rats were given acute chamber exposures to Air or Form (0.7 or 2.4 ppm), and trunk blood was collected 20 or 60 min later. All groups showed increased CORT levels above naı̈ve basal levels at 20 min and a return to baseline by 60 min, with no differences between treatment groups. The second experiment examined the effect of repeated Form exposure (1 h/day×5 days/week×2 or 4 weeks) on basal CORT levels and after a final challenge. Basal CORT was increased above naı̈ve values after 2 week exposure to Air or 0.7 ppm Form. By 4 week, CORT levels in the Air group returned to naı̈ve values, but remained elevated in the 0.7 ppm Form group. There were no differences in basal CORT levels among either 2.4 ppm exposed groups. After a final Air or Form challenge, the 2 and 4 week Air and 0.7 ppm Form groups had elevated CORT levels similar to their acute response, while the 2 and 4 week 2.4 ppm Form groups had elevated CORT levels compared to their acute response, indicating enhanced reactivity of the HPA axis to subsequent Form. These findings suggest that altered HPA axis functioning occurs after repeated low-level Form exposure, and may have implications for mechanisms mediating MCS in humans.