title: Hypothermia enhances contractility in cerebral arteries of newborn lambs.
abstract: Hypothermia is the major factor influencing autoregulatory properties of the cerebral circulation in human infants undergoing hypothermic cardiopulmonary bypass. The present investigation evaluated the effect of decreased temperature on the contractility of isolated middle cerebral arteries obtained from newborn lambs. Reducing bath temperature from 37 to 21 degrees C caused a temperature-dependent increase in contractile tension, achieving 1.32 +/- 0.09 g above resting tension (0.75 g). Pretreatment with nonselective (alpha 1 and alpha 2) alpha-adrenoceptor antagonist, phentolamine (10(-5) M), with an inhibitor of nitric oxide synthase, NG-nitro-L-arginine methyl ester hydrochloride (10(-4) M), and with a cyclooxygenase inhibitor, indomethacin (10(-5) M), did not affect the contractile response to a decrease in bath temperature from 37 to 21 degrees C. Furthermore, cerebral arteries were responsive to both norepinephrine (constriction) and sodium nitroprusside (relaxation) and the sensitivity of cerebral arteries to the sympathetic neurotransmitter norepinephrine appears to be enhanced at low temperatures. We postulate that direct cerebral vasoconstriction and enhanced adrenergic contractility may be responsible for increased cerebrovascular resistance during and after hypothermic cardiopulmonary bypass with possible ischemic cerebral injury and neurological sequelae.
authors.affiliation: Department of Cardiothoracic Surgery, Temple University School of Medicine, Philadelphia, Pennsylvania 19134.
authors.forename: G
authors.initials: G
authors.lastname: Speziali
authors.forename: P
authors.initials: P
authors.lastname: Russo
authors.forename: D A
authors.initials: DA
authors.lastname: Davis
authors.forename: L C
authors.initials: LC
authors.lastname: Wagerle
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D002536:Cerebral Arteries / Q000187:drug effects / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D007035:Hypothermia / Q000503:physiopathology*; D066298:In Vitro Techniques; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D012756:Sheep; D013696:Temperature; D014661:Vasoconstriction
chemical_list: D009599:Nitroprusside; D009569:Nitric Oxide; D001120:Arginine; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine; D010646:Phentolamine