Phylogenetic expression of hypoxic vasoconstriction

Hypoxic vasoactivity is universally dose‐ and location‐dependent. Whereas hypoxic vasoconstriction is a common feature in respiratory vascular beds among every vertebrate class studied, hypoxic vasodilation is the predominant response in the mammalian systemic vasculature. In jawless fishes, which represent the lowest class of extant vertebrates, a profound systemic hypoxic vasoconstriction is elicited in post‐gill, but not pre‐gill vessels, suggesting an early antecedent to hypoxic pulmonary vasoconstriction outside vertebrate respiratory circuits. The present study examined hypoxic vasoactivity in multiple vertebrate classes in order to establish the phylogenetic lineage of hypoxic vasoconstriction. Hypoxic vasoactivity was examined in systemic, and where applicable, respiratory vessels from Agnatha (sea lamprey, Petromyzon marinus), Osteichthyes, (Yellowfin tuna, Thunnus albacares), Amphibia (American bullfrog, Rana catesbeiana), Reptilia (American alligator, Alligator mississippiensis), Aves (Pekin duck, Anas platyrhynchos domesticus; chicken, gallus domesticus), and Mammalia (white rat, rattus rattus). Hypoxic vasoconstriction was noted in post‐, but not pre‐gill systemic vessels in fish, it was present in systemic vessels from every class except Mammalia, and it was noted in all pulmonary vessels tested. These results show that hypoxic vasoconstriction is an ancient regulatory mechanism with a long lineage in the systemic circulation that has only recently evolved into an exclusively respiratory response. This work was supported in part by NSF Grant IBN0235223 (KRO) and American Heart Association Postdoctoral Fellowship #0320037z.