AbstractThe lumbar sympathetic chain was electrically stimulated in different species before and after blocking the adrenergic vasoconstrictor nervous response. Blood flow in the hind limb skeletal muscles was measured. In all species studied, fox, sheep, goat, monkey (five different strains), polecat, rat, badger, opossum rat and hare, stimulation of the lumbar chain before adrenergic blockade resulted in a vasoconstriction. After blocking the vasoconstrictor nervous response stimulation elicited a blood flow increase in fox, sheep and goat. After atropine, the response to stimulation was blocked, indicating that sympathetic cholinergic nerves had been activated. In the other species studied no vasodilator response was observed upon sympathetic chain stimulation. The results suggest that the role attributed to the vasodilator nerves, anticipatory to muscle exercise, are played by other mechanisms in species lacking sympathetic cholinergic vasodilator nerves.