title: Cerebrovasodilatory contribution of endogenous carbon monoxide during seizures in newborn pigs.
abstract: Carbon monoxide (CO) and the excitatory amino acid glutamate both dilate cerebral arterioles in newborn pigs. The key enzyme in CO synthesis is heme oxygenase, which is highly expressed in neurons with glutamatergic receptor activity as well as cerebral microvessels. During seizures the extracellular level of glutamate is increased, which results in excessive depolarization of neurons. We hypothesized that CO is a mediator of excitatory amino acid-induced dilation of the cerebral microvasculature during seizures. Three groups of piglets were examined: 1) i.v. normal saline (sham control), 2) topical chromium mesoporphyrin (Cr-MP, 15 x 10(-6) M), and 3) i.v. tin-protoporphyrin (Sn-PP, 4 mg/kg). Synthetic metalloporphyrins (Cr-MP and Sn-PP) are heme oxygenase inhibitors, thereby reducing CO synthesis. Implanted closed cranial windows were used to monitor changes in pial arteriolar diameters. Seizures were induced by administration of i.v. bicuculline. Changes in pial arteriolar diameters were monitored during 30 min of status epilepticus. The percent increase in pial arteriolar dilation in the saline group during seizures was 68 +/- 3%. In the metalloporphyrin groups, the pial arteriolar dilation was markedly reduced (35 +/- 3% and 13 +/- 1%, for Cr-MP and Sn-PP, respectively; p < 0.05, compared with the saline group). We conclude that metalloporphyrins by inhibition of heme oxygenase and prevention of CO synthesis attenuate pial arteriolar dilation during seizures. Therefore, CO appears to be involved in cerebral vasodilation caused by glutamatergic seizures.
authors.affiliation: Laboratory for Research in Neonatal Physiology, Departments of Pediatrics, The University of Tennessee Health Sciences Center, Memphis, Tennessee 38163, USA. mpourcyrous@utmem.edu
authors.forename: Massroor
authors.initials: M
authors.lastname: Pourcyrous
authors.forename: Henrietta S
authors.initials: HS
authors.lastname: Bada
authors.forename: Helena
authors.initials: H
authors.lastname: Parfenova
authors.forename: Michael L
authors.initials: ML
authors.lastname: Daley
authors.forename: Sheldon B
authors.initials: SB
authors.lastname: Korones
authors.forename: Charles W
authors.initials: CW
authors.lastname: Leffler
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001160:Arterioles / Q000503:physiopathology; D001640:Bicuculline / Q000633:toxicity; D002248:Carbon Monoxide / Q000378:metabolism*; D002536:Cerebral Arteries / Q000503:physiopathology*; D002560:Cerebrovascular Circulation; D003292:Convulsants / Q000633:toxicity; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018756:GABA Antagonists / Q000633:toxicity; D005971:Glutamates / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008652:Mesoporphyrins / Q000494:pharmacology; D008665:Metalloporphyrins / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D009474:Neurons / Q000201:enzymology; D010841:Pia Mater / Q000098:blood supply; D011524:Protoporphyrins / Q000494:pharmacology; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology*; D013226:Status Epilepticus / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D013552:Swine; D014664:Vasodilation / Q000502:physiology*
chemical_list: D003292:Convulsants; D004791:Enzyme Inhibitors; D018756:GABA Antagonists; D005971:Glutamates; D008652:Mesoporphyrins; D008665:Metalloporphyrins; D009419:Nerve Tissue Proteins; D011524:Protoporphyrins; C427471:chromium mesoporphyrin; D006418:Heme; D002248:Carbon Monoxide; C032628:tin protoporphyrin IX; D000242:Cyclic AMP; D006419:Heme Oxygenase (Decyclizing); D006152:Cyclic GMP; D001640:Bicuculline