| Summary: | The innervation of the branchial vasculature of the blacktip reef shark, Carcharhinus melanopterus, appears similar to that described for other elasmobranchs, Isolated perfused gill arch preparations were used in a study of vascular responses to branchial nerve stimulation. The pre-addition of 10(-5) M concentrations of pancuronium to the perfusate prevented skeletal muscle contractions and significantly reduced (P < 0.001) changes in perfusion pressure in response to nerve stimulation, The adductor muscles received an extensive innervation by nerve fibres ramifying from the gill arch, In pharmacological studies, pancuronium completely antagonized the normal vasoconstrictive response to acetylcholine, At low concentrations, noradrenaline produced a vasoconstriction, but this changed to a vasodilatation at concentrations above 10(-5) M, The use of antagonists demonstrated the presence of both alpha-, and beta-adrenoceptors in the branchial vasculature, Anatomical studies failed to show adrenergic nerves in the gills, suggesting al lack of a spinal autonomic ('sympathetic') innervation, Adrenergic regulation of gill blood flow may involve the release of catecholamines into the blood stream from chromaffin tissue stores.
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