corticosteroids Flashcards
Glucocorticoids are produced where?
adrenal gland, adrenal cortex, zona fasiculata
biosynthesis of adrenal steroids
- cholesterol is the common source from which all adrenal steroids are formed **
- cortisol: one pathway of cortisol synthesis involves progesterone, one pathway from 17-hydroxyprogesterone
- aldosterone: from progesterone
- androgens: from 17-hydroxyprogesterone or 17-hydroxypregnenolone
double negative feedback loop regulation of corticosteroid release
- hypothalamus releases CRF
- CRF stimulates anterior pituitary to release ACTH into the bloodstream
- ACTH stimulates the release of cortisol from the adrenal cortex
- high blood levels of cortisol inhibits both (1) hypothalamus release of CRF and (2) ant. pituitary release of ACTH
circadian rhythm
- the result of fluctuating levels of circulating cortisol caused by dbl negative feedback loop regulation
- diurnal peak at about 8am daily, assuming hours of wakefulness from 6a-10p
- affected by travel, sleep patterns, light cycle, exogenous cortisol intake, stress
effect of stress on adrenal steroids
- causes release of catecholamines to maximize utilization of energy
- causes release of glucocorticoids to maximize availability of energy
- catecholamines and glucocorticoids work in concert
mechanism of action of glucocorticoids
- ligand binds to receptor in the interior of the cell (widely distributed in the cytosol)
- ligand/receptor complex moves into the nucleus and binds to DNA where protein production can be activated or inhibited
- influence on DNA transcription of several proteins may take place simultaneously
- this mechanism accounts for the slow onset of action of glucocorticoids
general effects of glucocorticoids (list of 10)
- increases sensitivity to adrinergic drugs
- direct vascular effects (from dyslipidemia and htn)
- anti-inflammatory effects (decreased leukotriene and prostaglandin production, reduced macrophage recruitment); limits the damage associated with spinal cord injury due to inflammation
- inhibits wound healing (inhibits fibrin, inhibits collagen deposition)
- increased bone catabolism / brittle bone syndrome; antagonize effects of vitamin D on calcium absorption
- required for production of surfactant (effect on fetal growth)
- destruction of lymphocytes in lymph nodes
- inhibits mitosis by transformed lymphoblasts
- anabolic in the liver (leads to enlarged liver) / catabolic everywhere else
- anti-insulin effects: increases glucose and fatty acid availability for energy (gluconeogenesis, glycogenesis, lipid breakdown to free fatty acids); overall: increased amino acids, fatty acids, glycerol delivery to liver for glucose/glycogen production
simplified arachidonic acid cascade
- phospholipase A2 causes release of free arachidonic acid from cell membranes (this initial step is blocked by glucocorticoids)
- 2 pathways for metabolism of free arachidonic acid: cyclooxygenase pathway, lipoxygenase pathway
- lipoxygenase pathway: produces leukotrienes
- cyclooxygenase pathway: produces prostaglandins and thromboxane A2 (this pathway blocked by NSAIDS this accounts for anti-inflammatory effects (less prostaglandins) and impaired clotting (less thromboxane A2))
inflammatory mediators
- release is stimulated by prostaglandins
- histamine, serotonin, bradykinin, substance P, lipid mediators
- prostaglandins also cause change in pH of local tissue
lipid mediators (list)
prostaglandins thromboxane A2 HETE leukotrienes platelet activating factor activated complement components lysosomal enzymes autoantibodies cytokines
prostaglandin D2
- cyclooxygenase metabolite
- causes vasodilation, destabilization of basophils, hyperalgesia, *bronchoconstriction
prostaglandin E2
- cyclooxygenase metabolite
- causes vasodilation, increased vascular permeability (swelling), release of calcium from bone, hyperalgesia, *elevated body temp by action on hypothalamus, *maintain renal blood flow and sodium excretion during low flow (inhibiting causes serum hyperkalemia), *protection of GI tract mucosal layer
prostaglandin F2alpha
- cyclooxygenase metabolite
- causes *bronchoconstriction, *dysmennorhea, *uterine contractions, hyperalgesia
prostaglandin I2
- cyclooxygenase metabolite
- causes release of calcium from bone, vasodilation, *inhibits platelet aggregation
thromboxane A2
- cyclooxygenase metabolite
- involved in regulation of platelet function