title: Enhanced hemeoxygenase activity in the rostral ventrolateral medulla mediates exaggerated hemin-evoked hypotension in the spontaneously hypertensive rat.
abstract: In anesthetized normotensive rats, activation of brainstem hemeoxygenase (HO) elicits sympathoinhibition and hypotension. Accordingly, we tested the hypothesis that attenuated basal or induced HO activity in the rostral ventrolateral medulla (RVLM) contributes to hypertension in the spontaneously hypertensive rat (SHR). We measured basal RVLM HO expression and catalytic activity and investigated the effects of intra-RVLM HO activation (hemin) or selective HO isoform 1 (HO-1) inhibition [zinc protoporphyrin IX (ZnPPIX)] on mean arterial pressure (MAP), heart rate, and RVLM neuronal norepinephrine (NE) level (index of sympathetic activity) in conscious SHRs and Wistar Kyoto rats. Basal RVLM HO catalytic activity (bilirubin level) and HO-1 expression were significantly higher in the SHR. These neurochemical findings were corroborated by the significantly greater decreases (hemin) and increases (ZnPPIX) in RVLM NE and MAP in the SHR. By contrast, HO-independent CO release in the RVLM (CO-releasing molecule 3) elicited similar MAP reductions in both rat strains. Furthermore, pretreatment with ZnPPIX or the selective neuronal nitric-oxide synthase (nNOS) inhibitor N-propyl-l-arginine abrogated the neurochemical (RVLM cGMP) and hypotensive responses caused by hemin. In addition to demonstrating, for the first time, higher basal RVLM HO catalytic activity and HO-1 expression in the SHR, the findings suggest: 1) the exaggerated hypotension elicited by intra-RVLM HO activation in the SHR is nNOS-dependent, and 2) in the SHR, the enhanced RVLM HO-nNOS signaling compensates for the reduced expression/activity of the downstream target, soluble guanylyl cyclase. Together, the findings suggest a protective role for the RVLM HO-nNOS pathway against further increases in MAP in the SHR.
authors.affiliation: Department of Pharmacology and Toxicology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, USA.
authors.forename: Noha N
authors.initials: NN
authors.lastname: Nassar
authors.forename: Guichu
authors.initials: G
authors.lastname: Li
authors.forename: Aurel L
authors.initials: AL
authors.lastname: Strat
authors.forename: Abdel A
authors.initials: AA
authors.lastname: Abdel-Rahman
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D015153:Blotting, Western; D002248:Carbon Monoxide / Q000378:metabolism; D002404:Catheterization; D006152:Cyclic GMP / Q000378:metabolism; D006162:Guanylate Cyclase / Q000378:metabolism; D006339:Heart Rate / Q000187:drug effects; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D006427:Hemin / Q000494:pharmacology*; D007022:Hypotension / Q000139:chemically induced* / Q000503:physiopathology*; D007267:Injections; D008297:Male; D008526:Medulla Oblongata / Q000201:enzymology*; D009569:Nitric Oxide / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D009942:Organometallic Compounds / Q000494:pharmacology; D011524:Protoporphyrins / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY
chemical_list: D009942:Organometallic Compounds; D011524:Protoporphyrins; C476530:tricarbonylchloro(glycinato)ruthenium(II); C017803:zinc protoporphyrin; D009569:Nitric Oxide; D006427:Hemin; D002248:Carbon Monoxide; D052248:Nitric Oxide Synthase Type I; D006419:Heme Oxygenase (Decyclizing); D006162:Guanylate Cyclase; D006152:Cyclic GMP; D009638:Norepinephrine