Hypothalamic-pituitary-adrenal axis activity in the inbred Brown Norway and Fischer 344 rat strains

We have examined the basal and the stress-induced secretion of corticosterone in relation to the expression of adrenal steroid receptors in the pituitary, hypothalamus and hippocampus of the inbred Brown Norway and Fischer 344 rat strains. Our data indicated that plasma transcortin and integrated plasma corticosterone levels were significantly higher in Fischer 344 compared to Brown Norway rats. Fischer 344 hypersecrete corticosterone during the dark phase of the diurnal cycle and during the phase of recovery following a 20 min period of restraint stress compared to Brown Norway rats. This hypersecretion of corticosterone was negatively correlated with the size of the adrenal gland but might be related to the higher density of mineralocorticoid receptors in the hippocampus of Fischer 344 rats.