Pharmacological investigations of the vasodilator nerves supplying the duck's foot

Vasodilator responses to electrical nerve stimulation and to various putative autonomic inhibitory neurotransmitters were studied in the Krebs-perfused foot of the domestic duck. Electrical stimulation resulted in frequency-dependent vasoconstrictor responses which were abolished by the infusion of guanethidine. After abolition of the vasoconstriction, electrical stimulation produced a frequency-dependent vasodilatation. The putative inhibitory transmitter substances tested were substance P, somatostatin, vasoactive intestinal polypeptide, adenosine triphosphate and dopamine. Of these only dopamine produced dilator responses similar in appearance to those following nerve stimulation. Infusion of metoclopramide (170 microM) greatly reduced dilator responses to nerve stimulation and to dopamine but not those to glyceryl trinitrate. These results suggest that the vasculature of the duck foot may be supplied by dopaminergic vasodilator nerves.