Adrenal Steroid Receptors: Interactions with Brain Neuropeptide Systems in Relation to Nutrient Intake and Metabolism

Abstract

The glucocorticoid, corticosterone (CORT), is believed to have an important function in modulating nutrient ingestion and metabolism. Recent evidence described in this review suggests that the effects of this adrenal hormone are mediated through two steroid receptor subtypes, the type I mineralocorticoid receptor and the type II glucocorticoid receptor. These receptors, which have different affinities for CORT, respond to different levels of circulating hormone. They mediate distinct effects of the steroid, which can be distinguished by the specific nutrient ingested and by the particular period of the circadian cycle.Under normal physiological conditions, the type I receptor is tonically activated, either by low basal levels of circulating CORT (0.5-2 pg%) normally available across the circadian cycle or possibly by the mineralocorticoid aldosterone. This type I activation is required for the maintenance of fat ingestion and fat deposition that occurs during most meals of the feeding cycle. In contrast, the type II receptor is phasically activated by moderate levels of CORT (2-1 0 pg%) normally reached during the circadian peak. Activation of this receptor is required for the natural surge in carbohydrate ingestion and metabolism that is essential at the onset of the active feeding cycle when the body's glycogen stores are at their nadir, and gluconeogenesis is needed to maintain blood glucose levels. This receptor is also activated during periods of increased energy requirements, such as, after exercise and food restriction, when CORT levels rise further ( > 10 pg%) and when its catabolic effects on fat and protein stores predominate to provide additional substrates for glucose homeostasis. These functions of CORT on fat and carbohydrate balance are mediated, in part, by type I and type II receptors located within the hypothalamic paraventricular nucleus, which is known to have key functions in controlling nutrient intake and metabolism, as well as circulating CORT levels. Moreover, the type II receptors within this nucleus, in addition to the arcuate nucleus, may interact positively with the peptide, neuropeptide Y, and the catecholamine, norepinephrine, both of which act to enhance natural carbohydrate feeding and CORT release at the onset of the natural feeding cycle.Thus, under normal conditions, endogenous CORT has a primary function in controlling nutrient ingestion and metabolism over the natural circadian cycle, through the coordinated action of the type I and type II steroid receptor systems. Through this action, CORT has impact on total caloric intake and body weight gain over the long term. Moreover, under conditions of obesity, diabetes and food restriction, steroid receptor function is greatly disturbed in association with chronic high circulating levels of CORT and abnormal glucose homeostasis. These disturbances in steroid action, along with dysfunction in brain neurochemical processes, very possibly contribute to the maintenance of hyperphagia and body weight gain in obese and diabetic ...

The arcuate NPY, POMC, and CART expressions responding to food deprivation are exaggerated in young female rats that experienced neonatal maternal separation

“…mRNA expressions of NPY, proopiomelanocortin (POMC) and cocaine-amphetamine regulated transcript (CART) in the arcuate nucleus responding to food deprivation were examined together with the plasma levels of leptin and corticosterone. Circulating leptin decreases (Schwartz et al, 1995;Ahima et al, 1996;Makimura et al, 2003) and corticosterone increases (Timofeeva et al, 2002;Makimura et al, 2003;Jahng et al, 2005) during food deprivation, and these stress-responding hormones are known to be involved in the arcuate expression of feeding peptides (Tempel and Leibowitz, 1994;Ahima et al, 1996;Zakrzewska et al, 1999;Schwartz et al, 2000;Swart et al, 2002;Makimura et al, 2003).…”

Sustained hyperphagia in adolescent rats that experienced neonatal maternal separation

“…[5][6][7][8] Glucocorticoids, stress hormones released by activation of the HPA axis, are known to be involved in the regulation of energy balance, 9,10 and some of the central effects of glucocorticoids are believed to be mediated by hypothalamic neuropeptides. 11,12 It has been reported that experiences of repeated MS during pre-weaning period increase the hypothalamic level of neuropeptide Y (NPY) in rats later in life. 13,14 NPY, a potent orexic peptide, stimulates feeding.…”

Contribution of several candidate gene polymorphisms in the determination of adiposity changes: results from the Québec Family Study

“…LEP and LEPR are known to modulate food intake and energy balance 16 and are responsible for some rare monogenic forms of obesity. 3 When activated, GCCR exerts orexigenic 17 and antithermogenic effects. 18,19 The peripheral sympathetic nervous system is a major player in the regulation of energy balance and the physiological responses to adrenaline and noradrenaline are exerted through the adrenergic receptors a and b.…”