Species variations in the relaxation of tail arteries to electrical stimulation

Relaxation in response to electrical stimulation has been studied in isolated tail arteries from rats, cats and pigs. Electrical stimulation elicited contractile responses in unstimulated strips, but caused frequency-dependent relaxations in tail arteries from all species studied, following contractile responses by various agents. The order of susceptibility to the relaxant effect of electrical stimulation in arteries from all three species was pig greater than cat greater than rat. Relaxations to electrical stimulation were unaffected by prior treatment of arteries with atropine, propranolol, tetrodotoxin, indomethacin, ouabain, pyrilamine and chemical denervation with 6-hydroxy-dopamine, but were prevented, dose-dependently, by cimetidine and aminophylline (antagonists of histamine H2-receptor and adenosine P1-receptor, respectively). The results suggest that relaxation of tail arteries from the rat, cat and pig in response to electrical stimulation is modulated by histamine and adenosine.