Limited role for nitric oxide in mediating cerebrovascular control of newborn piglets.
OBJECTIVE
To investigate the effects of the nitric oxide (NO) synthase inhibitor L-nitro-arginine methyl ester (L-NAME) on cerebral blood flow, and its response to alterations in arterial carbon dioxide tension (CBF-CO2 reactivity).


METHODS
Cerebral blood flow was measured six times at varying arterial carbon dioxide tension (PaCO2) using the intravenous 133Xenon clearance technique in eight mechanically ventilated piglets of less than 24 hours postnatal age. After the third measurement L-NAME was administered as a bolus (20 mg/kg) and subsequently infused (10 mg/kg/hour).


RESULTS
PaCO2 ranged between 2.7-8.9 kPa. Cerebral blood flow decreased by 14.0% (95% confidence interval 1.9-27.4) after L-NAME. CBF-CO2 reactivity was 18.4% per kPa (95% CI 14.1-22.2) before L-NAME and 15.2%/kPa (95% CI 11.1-19.3) afterwards; the difference between the CBF-CO2 reactivities was 3.2%/kPa (95% CI -0.4-6.8): these were not significantly different.


CONCLUSIONS
Inhibition of nitric oxide synthesis reduces cerebral blood flow no more than a 0.5-1.0 kPa fall in PaCO2. Nitric oxide is not an important mediator of CBF-CO2 reactivity.
Patel
J
J
Royal Postgraduate Medical School, Hammersmith Hospital, London.
Pryds
O
O
Roberts
I
I
Harris
D
D
Edwards
A D
AD
D000818:Animals; D000831:Animals, Newborn; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D010313:Partial Pressure; D013552:Swine; D014980:Xenon Radioisotopes
D014980:Xenon Radioisotopes; D002245:Carbon Dioxide; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester