title: Effects of serotonin agonists and doxapram on respiratory depression and hypoxemia in etorphine-immobilized impala (Aepyceros melampus).
abstract: Respiratory depression is a common side effect when opioids are used to immobilize wildlife. Serotonergic ligands have the potential to reverse opioid-induced respiratory depression. We examined whether any of three serotonergic ligands could reverse this depression in etorphine-immobilized (0.07 mg/kg) impala (Aepyceros melampus). The study took place in September-December 2007. Impala received intravenous injections of metoclopramide (10 mg/kg, n=6), buspirone (0.05 mg/kg, n=8), pimozide (1 mg/kg, n=8), doxapram (1 mg/kg, n=6), and control solutions on separate occasions. During the immobilization, partial pressures of oxygen (PaO(2), mmHg) and carbon dioxide (PaCO(2), mmHg), respiratory rate (breaths/min), ventilation (l/min), peripheral O(2) saturation (%), tidal volume (l), and respiratory exchange ratio were measured before and after injection of the experimental drugs. Etorphine immobilization caused respiratory depression and hypoxia (mean+/-SD, PaCO(2)=51+/-2 mmHg, PaO(2)=40+/-3 mmHg). Metoclopramide and buspirone, but not pimozide, attenuated the hypoxic effects of etorphine; 3 min after injection, metoclopramide increased the PaO(2) by 7.5+/-6.3 mmHg and buspirone by 6+/-6.6 mmHg (F=3.9, P=0.02). These effects were similar to those of doxapram (8+/-7 mmHg, F=3.9; P>0.05). Neither metoclopramide nor buspirone significantly increased ventilation, but they increased PaO(2) by significantly improving the alveolar-arterial oxygen partial pressure gradient (A-a gradient, F=1.4, P<0.05), indicating improved oxygen diffusion. Metoclopramide and buspirone transiently improved blood oxygenation of opioid-immobilized impala, probably by improving ventilation-perfusion ratios, without reversing catatonic immobilization.
authors.affiliation: Brain Function Research Group, School of Physiology, University of the Witwatersrand, 7 York Road, Parktown, 2193, South Africa. Leith.Meyer@wits.ac.za
authors.forename: Leith C R
authors.initials: LC
authors.lastname: Meyer
authors.forename: Robyn S
authors.initials: RS
authors.lastname: Hetem
authors.forename: Linda G
authors.initials: LG
authors.lastname: Fick
authors.forename: Duncan
authors.initials: D
authors.lastname: Mitchell
authors.forename: Andrea
authors.initials: A
authors.lastname: Fuller
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects; D000818:Animals; D000835:Animals, Wild; D000866:Antelopes / Q000502:physiology*; D002245:Carbon Dioxide / Q000032:analysis; D004315:Doxapram / Q000494:pharmacology*; D005048:Etorphine / Q000008:administration & dosage / Q000009:adverse effects*; D000860:Hypoxia / Q000139:chemically induced / Q000662:veterinary*; D007103:Immobilization / Q000379:methods / Q000502:physiology / Q000662:veterinary; D010100:Oxygen / Q000032:analysis; D010101:Oxygen Consumption; D010313:Partial Pressure; D012131:Respiratory Insufficiency / Q000139:chemically induced / Q000662:veterinary*; D056152:Respiratory Rate / Q000187:drug effects; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013990:Tidal Volume / Q000187:drug effects; D014692:Ventilation-Perfusion Ratio / Q000187:drug effects
chemical_list: D000701:Analgesics, Opioid; D017366:Serotonin Receptor Agonists; D002245:Carbon Dioxide; D005048:Etorphine; D004315:Doxapram; D010100:Oxygen