A pharmacologic study on CO2 responsiveness of intracranial pressure in rats with chronic hypercapnia.
OBJECTIVE
To investigate intracranial pressure (ICP) changes and their mechanisms in chronic hypercapnia.


METHODS
After 12 male Wistar rats were maintained in CO2-mixed air (mean PaCO2, 71.0 mm Hg) for 21 weeks, their ICP levels were measured during the breathing of 0, 5, 10, 12, and 14% CO2-mixed air before and after the i.v. administration of nitro-L-arginine methyl ester (L-NAME). The ICP responses to i.v. norepinephrine and i.v. adenosine were also tested. Ten rats that were maintained in room air served as the control group.


RESULTS
The mean ICP in the study group (5.9 mm Hg) was not significantly different from the mean ICP in the control group. In the study group, the ICP response to changes in PaCO2 was significantly blunted when compared to the response seen in the control group. In both groups, i.v. norepinephrine significantly increased the ICP. In the control group but not in the study group, i.v. L-NAME suppressed the ICP response to changes in PaCO2. In both groups, i.v. adenosine significantly increased the ICP.


CONCLUSIONS
The ICP response to PaCO2 was blunted in rats with chronic hypercapnia, and the mechanism of this reduced response may involve nitric oxide.
Kondo
T
T
Department of Medicine, Tokai University School of Medicine, Isehara, Kanagawa, Japan. tetsuri@is.icc.u-tokai.ac.jp
Kumagai
M
M
Takei
F
F
Ohta
Y
Y
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000494:pharmacology*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D006935:Hypercapnia / Q000503:physiopathology*; D007427:Intracranial Pressure / Q000187:drug effects; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D002245:Carbon Dioxide; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D000241:Adenosine; D019331:NG-Nitroarginine Methyl Ester; D009638:Norepinephrine