Modification of cerebral laser-Doppler flow oscillations by halothane, PCO2, and nitric oxide synthase blockade.
We investigated whether nitric oxide (NO) played a role in the generation of cerebrocortical flow oscillations and their modification by hypocapnia, hypercapnia, and halothane administration. Parietal cortical laser-Doppler flow (LDF) was monitored transcranially in anesthetized (barbiturate + 0-1.0% halothane), artificially ventilated, adult male Sprague-Dawley rats. Thirty minutes after infusion of N omega-nitro-L-arginine methyl ester (L-NAME, 20 mg/kg i.v.) mean arterial pressure (MAP) increased from 105 +/- 10 to 132 +/- 15 mmHg (P < 0.02), while mean LDF decreased from 159 +/- 36 to 135 +/- 30 perfusion units (PU, P < 0.05). Oscillations in LDF at a frequency of 6.3-7.8 cycles/min and amplitude of 10% were induced or augmented by L-NAME but not by D-NAME or indomethacin (2 mg/kg i.p.). L-arginine (200 mg/kg) abolished the oscillations post-L-NAME at constant MAP. Sodium nitroprusside infusion (10(-5) M, 5-50 microliters/min) reversed the L-NAME-induced increase in MAP and decrease in mean LDF but did not attenuate the flow oscillations. Hypocapnia post-L-NAME decreased LDF to 110 +/- 20 PU (P < 0.001) and augmented the flow oscillations (amplitude: 11-31%). Hypercapnia (5% CO2) or halothane (0.4-1.0%) suspended the oscillations in the presence of L-NAME. The results suggest that NO synthase activity inhibits cerebrocortical flow oscillations, and NO is not an obligatory mediator of the effects of halothane, hypocapnia, and hypercapnia on oscillatory activity.
Hudetz
A G
AG
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, USA.
Smith
J J
JJ
Lee
J G
JG
Bosnjak
Z J
ZJ
Kampine
J P
JP
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D006221:Halothane / Q000494:pharmacology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D019001:Nitric Oxide Synthase; D009599:Nitroprusside / Q000494:pharmacology; D009991:Oscillometry; D010313:Partial Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley
D002245:Carbon Dioxide; D009599:Nitroprusside; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D006221:Halothane; D019331:NG-Nitroarginine Methyl Ester