What does low serum corticosterone, but high plasma ACTH indicate in stressed rats?
Answers
Answer:
Explanation:
Elevated ACTH but low CORT is sometimes seen in rodent models of post-traumatic stress disorder (only in males though, are you using males? There are significant sex differences in the HPA axis response to stress). Diminished CORT release in response to stress could be due to a sensitization (or increase in number) of glucocorticoid receptors (GR) in the pituitary, and if all GR are saturated with ligand, no more suppression of ACTH can occur so that's where you can get high ACTH and low CORT. Due to this, the adrenal glands can become insensitive to ACTH--you can quantify ACTH receptors or just give them an ACTH injection and measure their CORT response to see.
ACTH is made in the corticotroph cells of the anterior pituitary gland, where it is released in bursts into the bloodstream and transported around the body. Like cortisol, levels of adrenocorticotropic hormone are generally high in the morning when we wake up and fall throughout the day (reaching their lowest level during sleep). This is called a diurnal (circadian) rhythm. Once adrenocorticotropic hormone reaches the adrenal glands, it binds on to receptors causing the adrenal glands to secrete more cortisol, resulting in higher levels of cortisol in the blood. It also increases production of the chemical compounds that rat an increase in other hormones such as adrenaline and noradrenaline.