Noradrenaline-induced smooth muscle relaxation in the specific region of canine facial vein: implications for facial and cranial circulation.

This study was performed to investigate the heterogeneity of physiological and pharmacological properties in segments of the facial veins with special reference to selective brain cooling. Canine facial veins were isolated and the isometric tension of each segment was measured using the organ bath technique. Vessels in the segments of the facial veins that run opposite to the buccal cavity automatically produced myogenic tone and tended to show spontaneous contractions, but vessels in other segments did not. When no contractile agent was used for precontraction, noradrenaline and adrenaline produced dose-dependent relaxations in the former venous segments, but contractions in the latter ones. A Schild plot analysis for metoprolol against denopamine and for ICI118,551 against salbutamol showed that the venous segments running opposite the buccal cavity contained both beta(1)- and beta(2)-adrenoceptors, but the other venous segments contained only beta(2)-adrenoceptors. Electrical field stimulation-induced tetrodotoxin-sensitive relaxations in the former venous segments were diminished by pretreatment with metoprolol, but not with ICI118,551, indicating that the electrical stimulation-induced relaxation may be related to the activation of beta(1)-adrenoceptors in the venous smooth muscles. In conclusion, the heterogeneity of the functional properties, especially in the distribution of beta-adrenoceptors, in different segments of canine facial veins was observed in the present study, and autoregulatory mechanisms, humoral mechanisms, and neural mechanisms were suggested to affect cranial venous drainage.