Hypoxia elicits an increase in pulmonary vasculature resistance in anaesthetised turtles (Trachemys scripta)

In mammals and birds, low oxygen levels in the lungs cause a constriction o f the pulmonary vasculature, This response is locally mediated and is consi dered to be important for local matching of perfusion and ventilation. It i s not known whether reptiles respond in a similar fashion. The present stud y describes the effects of altering lung oxygen levels (at a constant F-CO2 of 0.03) on systemic and pulmonary blood flows and pressures in anaestheti sed (Nembumal, 50 mg kg(-1)) and artificially ventilated turtles Trachemys scripta. During severe hypoxia (1.5-3 kPa P-O2), pulmonary blood flow decre ased in all animals; systemic blood flow increased, resulting in an increas ed net right-to-left shunt blood flow, The redistribution of blood flows wa s associated with reciprocal changes in the vascular resistances within the pulmonary and the systemic circulations (R-pul and R-sys, respectively), A t 1.5kPa O-2, R-pul increased from 0.09+/-0.01 to 0.15+/-0.03 kPa ml(-1) mi n kg during normoxia (means +/-1 S.E.M., N=5), Concurrently, R-sys tended t o decrease from a normoxic value of 0.12+/-0.01 to 0.09+/-0.02kPa ml(-1) mi n kg (P=0.08), The effects of hypoxia on the haemodynamic variables persist ed following atropinisation (1 mg kg(-1)) and cervical vagotomy, suggesting that the increased R-pul during hypoxia is locally mediated. This study th erefore demonstrates that turtles exhibit hypoxic pulmonary vasoconstrictio n, although the threshold is low compared with that of mammals.