Effects of pCO(2) on the CSF turnover rate in rats monitored by Gd-DTPA enhanced T-1-weighted magnetic resonance imaging

The cerebrospinal fluid (CSF) secretion of rat was monitored by longitudina l relaxation time-weighted magnetic resonance imaging (T-1-weighted MRI) in combination with a ventricular injection of a T-1-relaxation reagent: gado linium-diethylene triamine-N,N,N',N",N"-pentaacetic acid (Gd-DTPA). A cannu la was inserted in the left lateral ventricle, and 5 mul of 8.5 mm Gd-DTPA was injected as a CSF marker. Changes in the image intensity of the CSF wer e measured every 30 s, and the turnover rate of CSF (k) in the left lateral ventricle was obtained from the dilution of Gd-DTPA, based on the assumpti on of a single compartment model. In the control conditions, k was 0.158 +/ - 0.009 min(-1) at an arterial blood CO2 tension (pCO(2)) of 38.6 +/- 2.2 m mHg (n=10), which corresponds to the CSF secretion rate of 3.6 mul min(-1). The k value was decreased (0.078 +/- 0.010 min(-1), n=4) by a carbonic-anh ydrase inhibitor (acetazolamide). The turnover rate was decreased by hypoca pnia (0.094+/-0.019 min(-1), pCO(2)=24.7 +/- 2.9 mmHg, n=4), and it increas ed gradually and reached a plateau level as a result of hypercapnia (0.194 +/- 0.011 min(-1), pCO(2)=104.5 +/- 7.1 mmHg, n=10). These results suggeste d that CO2 upregulates the secretion of CSF in the rat.