Response of cortical and pial arteries to changes of arterial CO2 tension in rats--a morphometric study.

Changes of the internal (d) and external diameter (D) of cerebral arteries in response to the various levels of arterial pCO2 were studied in anesthetized rats, of which brains were frozen in situ with isopentane cooled in liquid nitrogen. The parietal cortex was fixed with osmium tetroxide and stained with toluidine blue for morphometry of the cerebral arteries. In comparison with control animals (pCO2 = 41.2 mm Hg), the d/D ratio in animals with hypercapnia (pCO2 = 69.9 mm Hg) was increased by 11.7% in the pial arteries and 7.9% in the cortical arteries, indicating vasodilatation. In contrast, the d/D ratio in those with hypocapnia (pCO2 = 27.7 mm Hg) was decreased by 6.2% and 13.0%, respectively, indicating vasoconstriction. There was a significant linear correlation existing between the d/D ratio of either pial or cortical arteries and pCO2. It is concluded that the cortical arteries respond to changes of arterial pCO2 in a similar manner to the pial arteries.