Effects of clenbuterol hydrochloride on pulmonary gas exchange and hemodynamics in anesthetized horses.
We evaluated the effects of clenbuterol HCl (0.8 micrograms/kg, of body weight, IV), a beta 2 agonist, on ventilation-perfusion matching and hemodynamic variables in anesthetized (by IV route), laterally recumbent horses. The multiple inert gas elimination technique was used to assess pulmonary gas exchange. Clenbuterol HCl induced a decrease in arterial oxygen tension (from 57.0 +/- 1.8 to 49.3 +/- 1.2 mm of Hg; mean +/- SEM) as a result of increased shunt fraction (from 6.6 +/- 2.1 to 14.4 +/- 3.1%) and ventilation to regions with high ventilation-perfusion ratios. In contrast, no changes in these variables were found in horses given sterile water. In horses given clenbuterol HCl, O2 consumption increased from 2.23 +/- 0.18 to 2.70 +/- 0.14 ml.min-1.kg-1, and respiratory exchange ratio decreased from 0.80 +/- 0.02 to 0.72 +/- 0.01. Respiratory exchange ratio and O2 consumption were not significantly modified in sterile water-treated (control) horses. Clenbuterol HCl administration was associated with increased cardiac index (from 57.4 +/- 4.0 to 84.2 +/- 6.3 ml.min-1.kg-1), decreased total peripheral vascular resistance (from 108.3 +/- 9.3 to 47.6 +/- 2.8 mm of Hg.s.kg.ml-1), and decreased pulmonary vascular resistance (from 31.3 +/- 3.8 to 13.6 +/- 0.7 mm of Hg.s.kg.ml-1). Our findings indicated that clenbuterol HCl may potentiate hypoxemia as a result of increased shunt fraction in horses anesthetized by the IV route, and caused changes in hemodynamic variables that were consistent with its ability to stimulate beta 2-adrenergic receptors.
Dodam
J R
JR
Department of Anatomy, Physiological Sciences and Radiology, College of Veterinary Medicine, North Carolina State University, Raleigh 27606.
Moon
R E
RE
Olson
N C
NC
Exposito
A J
AJ
Fawcett
T A
TA
Huang
Y C
YC
Theil
D R
DR
Camporesi
E
E
Swanson
C R
CR
D000768:Anesthesia, General / Q000662:veterinary; D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002976:Clenbuterol / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D008168:Lung / Q000187:drug effects / Q000502:physiology*; D010101:Oxygen Consumption / Q000187:drug effects*; D011652:Pulmonary Circulation / Q000187:drug effects*; D012119:Respiration / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects
D002976:Clenbuterol