A comparison of the effects of repeated stressor exposures and corticosterone injections on plasma cholesterol, thyroid hormones and corticosterone levels in rats.

Persistently elevated serum cholesterol (CHOL) levels have been observed in rats given repeated stressor exposures and fed a normal laboratory diet. To determine the relative contribution of persistent hormone changes in the hypothalamic-pituitary-adrenal (HPAA) and thyroid axes to persistent stress-induced CHOL elevations, the present experiment assessed the contribution of persistently elevated corticosterone (CORT) from both endogenous and exogenous sources. Groups of rats were exposed for 7 days to stress sessions (7DS; 40, 2mA tailshocks given over 2 h each day), CORT injections (CI; 10 mg/l ml vehicle/day) or vehicle injections (VI; sesame oil), or served as noninjected, undisturbed controls (CON). In addition, another group of rats were adrenalectomized (ADX). Basal blood samples were drawn for CORT determination on the 1st, 4th, 7th, and 8th experimental days. The blood samples from the 8th day, 22 h after the last stress session or injection were also assayed for CHOL, T3 and T4. The basal CORT levels of both 7DS and CI rats were elevated on the 4th and 7th experimental days. Contrary to expectations, 7 daily exposures to the stress regimen did not persistently alter plasma CORT, CHOL, T3 or T4 levels. The CI rats did exhibit elevated CORT on the 8th experimental day which was accompanied by elevated CHOL levels and suppressed T4 levels. However, elevated CHOL levels were also found in ADX rats and these elevations were accompanied by suppressed T3 levels. These data suggest that persistent CORT elevations are not necessary for persistent plasma CHOL elevations after stressor exposure, but further research is necessary to clarify the role of the HPAA and thyroid axes in stress-induced plasma CHOL elevations.