Dependency of pial arterial and arteriolar diameter on perivascular osmolarity in the cat. A microapplication study.

The effect of perivascular osmolarity on the diameter of pial arteries was studied in cats by the microapplication technique. Between 251 and 360 mosmoles/ liter, concentration-response curves were obtained for single vessels. Constriction occurred when perivascular osmolarity was decreased below 317 mosmoles /liter, and dilation occurred at osmolarities above this value. The effect was the same whether the osmolarity was changed by addition of mannitol or NaCl. Reduction of sodium concentration from 156 to 133 mEq/liter at constant osmolarity did not affect arteriolar diameter, but greater reductions in sodium concentration induced vasoconstriction. The results indicate that the resistance of pial arteries can be influenced by local changes in perivascular osmolarity.