Inhibitory Effects of Dopamine on Noradrenaline-induced Constriction of Arterioles in vivo in the Striated Cremaster Muscle

The effect of dopamine on the arterioles (50.8 ~ 95.2 μm) in the cremaster muscle was examined to determine its effect on microcirculation. Anesthetized rats were used under a light microscope connected to a videocamera. Drugs were applied using small round filter paper (370 μm in diameter) containing the drug and placed in the immediate vicinity of the arteriole on the cremaster with a micromanipulator. The dose of the drug applied was represented by concentration of the drug solution in which the filter paper was immersed. Dopamine (10-6 ~10-4M) induced neither constriction nor dilation of the arteriole in the cremaster. Papaverine (10-2M) did not dilate the arteriole. However, the arterioles were constricted by noradrenaline (10-6 ~ 10-4M) and vasopressin (10-7M) in a dose-dependent manner. Noradrenaline (10-4M)-induced constriction was blocked by concomitant application of dopamine (10-4M). This effect of dopamine was antagonized by SCH23390 (10-3M). However, isoproterenol (10-3M) did not affect the arteriole, nor inhibit noradrenaline (10-4M)-induced constriction of the arterioles. While forskolin (10-2M) alone did not produce constriction or dilation of the arterioles, it inhibited noradrenaline (10-4M)-induced constriction of the arteriole. These results suggest that dopamine prevents the constriction of the arteriole induced by noradrenaline, by activation of DA 1 receptors, which activates adenylate cyclase.