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Pharm Session #15

Eicosanoids

QuestionAnswer
PGE1 (alprostadil) relaxes smooth muscle; used as injection for men w/ erectile dysfunction or (in newborns) to maintain patent ductus arteriosus before cardiac surgery
Misoprostol (stable PGE2-analog) can be given orally to prevent gastric ulcers, or to "ripen" cervix before delivery (or as an abortifacient, w/ mefipristone, and antiprogestational agent, better known as RU486)
PGE2 and PGF2alpha both used in obstetrics to induce labor
Latanoprost 1 of several stable PGF2alpha analogs used in opthalmology for open-angle glaucoma
Prostacyclin (PGI2, epoprostenol) used in treatment of pulmonary HTN
Lipoxygenase name for family of enzymes that abstract a hydrogen from allylic carbon in PUFAs, producing hydroperoxyeicoatatrenoic acids (HPETEs) from arachidonate; rapidly converted to hydroxy-derivatives (HETEs) & leukotrienes (LT4s, from arachidonate)
COX-1 constitutive enzyme in most cells, involved in "housekeeping functions" (e.g. gastroprotection) in intact organism
COX-2 inducible enzyme, involved more in inflammation, CA, & thrombosis
Celecoxib COX-2 inhibitor developed to avoid much impact on COX-1
Both cyclooxygenase enzymes convert arachidonate to: cyclic endoperoxides, 1st PGG2, reduced to PGH2 =serves as substrate for other enzymes in specific cells that convert it to: TXA2 (@ least initially), PGE2 or PGF2alpha, PGD2, or prostacyclin (PGI2, @ least initially); quickly metabolized to inactive pdts
Eicosanoids comprise large family of oxygenated PUFAs; short 1/2-lives (0-60s)
Arachidonate 20:4omega6; most impt (& most abundant) of precursor FAs that become eicosanoids; 1st released from membr. lipids by phospholipase A (PLA): cytosolic PLA2, secretory PLA2, or Ca2+-independent PLA2 or (less well-reg'd) phospholipase C or diglyceride lipase
After release, arachidonate can be oxygenated by 1 of 4 separate pathways: 1. Cyclooxygenase (COX) 2. Lipoxygenase (LOX) 3. P450 epoxygenase 4. Isoprostane pathway *many factors influence which pathway's activated, incl. dietary source of the precursor PUFAs
Lipoxygenase end-products most impt of these biologically = the 5-HPETEs, which later become LTA4 (epoxide), then LTB4 & (if reacted w/ glutathione), LTC4, LTD4, & LTE4 (the "peptidoleukotrienes"); potent bronchoconstrictors in allergic asthma & anaphylaxis
Epoxygenase products dihydroxyeicosatrienoic acids (DHETs) can briefly lower BP (esp. in coronary circulation); in endothelial cells, can be incorporated into phospholipids, from which they can then be released, causing vasodilation
Isoprostanes enantiomers of prostaglandins formed by peroxidation and epimerization of the resulting peroxides; vasoconstrict renal & other vascular beds; NOT affected by COX-inhibitors
Describe eicosanoid receptors all eicosanoids act close to their site of formation (autocrine/paracrine hormones); they interact w/ large variety of cell surface receptors via specific G-proteins
Created by: aostromecki