title: Low cost of pulmonary ventilation in American alligators (Alligator mississippiensis) stimulated with doxapram.
abstract: To determine the costs of pulmonary ventilation without imposing severe oxygen limitations or acidosis that normally accompany exposures to hypoxia or hypercapnia, we opted to pharmacologically stimulate ventilation with doxapram (5 and 10 mg kg(-1)) in alligators. Doxapram is used clinically to alleviate ventilatory depression in response to anaesthesia and acts primarily on the peripheral oxygen-sensitive chemoreceptors. Using this approach, we investigated the hypothesis that pulmonary ventilation is relatively modest in comparison to resting metabolic rate in crocodilians and equipped seven juvenile alligators with masks for concurrent determination of ventilation and oxygen uptake. Doxapram elicited a dose-dependent and up to fourfold rise in ventilation, primarily by increasing ventilatory frequency. The accompanying rise in oxygen uptake was very small; ventilation in resting animals constitutes no more than 5% of resting metabolic rate. The conclusion that pulmonary ventilation is energetically cheap is consistent with earlier studies on alligators where ventilation was stimulated by hypoxia or hypercapnia.
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark nini.jensen@bios.au.dk.
authors.forename: Nini
authors.initials: N
authors.lastname: Skovgaard
authors.affiliation: Developmental Integrative Biology Cluster, Department of Biological Sciences, University of North Texas, Denton, TX 76203, USA.
authors.forename: Dane A
authors.initials: DA
authors.lastname: Crossley
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
mesh_terms: D000489:Alligators and Crocodiles / Q000502:physiology*; D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D004315:Doxapram / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000187:drug effects*; D056152:Respiratory Rate / Q000187:drug effects*; D019141:Respiratory System Agents / Q000494:pharmacology*; D014481:United States
chemical_list: D019141:Respiratory System Agents; D004315:Doxapram
keywords: Chemoreceptor; Cost of ventilation; Oxygen consumption; Reptile; Ventilator stimulant; Ventilatory response