Strain differences in hypothalamic pituitary adrenocortical axis function and adipogenic effects of corticosterone in rats.

Our aim was to explore the nutritional consequences of functional variations in the hypothalamic-pituitary-adrenocortical (HPA) axis in rats. We first aimed to compare the HPA axis activity and reactivity to stress between Fischer 344 (F344) and LOU/C (LOU) strains that differ in food behavior and metabolism. When compared with F344 rats, LOU rats showed lower corticosterone (Cort) levels across the circadian cycle and after restraint stress. Then, we compared the effects of adrenalectomized (ADX) and Cort substitution after ADX on food intake, body weight gain, body composition, and biochemical parameters related to metabolism and HPA axis function between 1) the F344 rat strain, a model of HPA axis hyperactivity and hyperreactivity to stress, and characterized by a large fat mass; 2) the LOU strain, shown to exhibit hypoactive/hyporeactive HPA axis, reduced fat mass, and resistance to diet-induced obesity; and 3) the Lewis (LEW) strain, a third condition of fat deposition (high) related to HPA axis function (low activity/reactivity). The F344 and LEW strains exhibited classical responses to ADX and Cort. On the contrary, LOU rats showed an apparent insensitivity to ADX. Despite the highest effects of Cort related to glucocorticoid receptor (on thymus weight, corticotropin-releasing factor, or corticosteroid-binding globulin), the LOU strain was insensitive to Cort effects on body weight, liver, and abdominal fat mass. These characteristics could be involved in the leanness, insensitivity to diet-induced obesity, and healthy aging in LOU. Our study shows the relevance of comparing the F344, LOU, and LEW strains to cover the complexity of interactions between metabolism and HPA axis function.