title: Cardiorespiratory responses of the toad (Bufo marinus) to hypoxia at two different temperatures.
abstract: Central vascular blood flows and ventilation were measured in conscious toads (Bufo marinus) at 15 and 25 degrees C. The animals were exposed to hypoxia (Fi(O)(sum)=0.10 and 0.05, where Fi(O)(sum) is the fractional oxygen concentration of inspired air) at both temperatures. In addition, the cardiorespiratory responses to hypercapnia (Fi(CO)(sum)=0.05) and atropine injection (5 mg kg(-)(1); 7.4 micromol kg(-)(1)) were studied at 25 degrees C. At 25 degrees C, systemic blood flow ( q_dot (sys)) exceeded pulmocutaneous blood flow ( q_dot (pc)), indicating a large net right-to-left shunt ( q_dot (pc)/ q_dot (sys) was 0.39). q_dot (pc)/ q_dot (sys) was reduced significantly to 0.22 at 15 degrees C. At both temperatures, q_dot (pc) increased significantly during hypoxia (from 26.2 to 50.8 ml min(-)(1 )kg(-)(1) at 25 degrees C and from 11. 2 to 18.9 ml min(-)(1 )kg(-)(1) at 15 degrees C), whereas q_dot (sys) changed little (from 77.2 to 66.2 ml min(-)(1 )kg(-)(1) at 25 degrees C and from 54.3 to 50.1 ml min(-)(1 )kg(-)(1) at 15 degrees C). As a result, the net right-to-left shunt was greatly reduced, while total cardiac output remained almost unaffected. The ventilatory response was more pronounced during hypercapnia but, since q_dot (pc) and q_dot (sys) were affected similarly, there was no change in the shunt pattern. In undisturbed toads at 25 degrees C, atropine injection increased q_dot (pc) and eliminated the net right-to-left shunt. This is consistent with the known vagal innervation of the pulmonary artery. The present study shows that the cardiac right-to-left shunt that prevails in undisturbed and resting toads is reduced with increased temperature and during hypoxia. These findings are consistent with the general view that the cardiac right-to-left shunt is regulated and reduced whenever oxygen delivery is compromised or metabolic rate is increased.
authors.affiliation: Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada. t.wang.1@bham.ac.uk
authors.forename: A K
authors.initials: AK
authors.lastname: Gamperl
authors.forename: W K
authors.initials: WK
authors.lastname: Milsom
authors.forename: A P
authors.initials: AP
authors.lastname: Farrell
authors.forename: T
authors.initials: T
authors.lastname: Wang
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001783:Blood Flow Velocity / Q000187:drug effects; D002024:Bufo marinus; D003331:Coronary Vessels / Q000187:drug effects / Q000503:physiopathology; D006321:Heart / Q000187:drug effects / Q000503:physiopathology*; D006439:Hemodynamics / Q000187:drug effects; D006935:Hypercapnia / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000098:blood supply / Q000187:drug effects / Q000503:physiopathology*; D018727:Muscarinic Antagonists / Q000494:pharmacology; D012123:Pulmonary Ventilation / Q000187:drug effects; D013696:Temperature
chemical_list: D018727:Muscarinic Antagonists; D001285:Atropine