title: Effect of phenylephrine on hemodynamics and splenic dimensions in horses.
abstract: Pharmacologically induced splenic contraction might be useful during certain medical or surgical procedures in horses. The effects of phenylephrine, an alpha 1-adrenergic receptor agonist, on hemodynamic function and splenic dimensions were examined in 6 healthy adult horses. Phenylephrine infusion (1, 3, or 6 micrograms/kg of body weight/min for 15 minutes) resulted in a dose-related increase in mean pulmonary artery pressure; right atrial pressure; systolic, mean, and diastolic arterial pressures; and packed cell volume (P = 0.0001). Concurrent decreases in heart rate and specific cardiac output (P = 0.0001) were detected, but stroke volume did not vary significantly. The rate-pressure product was increased only at the highest phenylephrine dosage (P = 0.012). Bradycardia was observed at all dosages during drug infusion, and second-degree atrioventricular block was detected in 88% of horses during infusion. Phenylephrine administration caused dose-dependent splenic contraction, as detected by ultrasonographic measurements of splenic area and thickness (P = 0.0001). At the 3- and 6-micrograms/kg/min infusion rates, splenic area was reduced to 28 and 17% of baseline measurement, respectively. Splenic dimensions had returned to baseline values by 35 minutes after the end of infusion. Infusion of phenylephrine at a dosage of 3 micrograms/kg/min for 15 minutes can be used to induce splenic contraction in horses.
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus.
authors.forename: J
authors.initials: J
authors.lastname: Hardy
authors.forename: R M
authors.initials: RM
authors.lastname: Bednarski
authors.forename: D S
authors.initials: DS
authors.lastname: Biller
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006439:Hemodynamics / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D007262:Infusions, Intravenous; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology*; D011651:Pulmonary Artery / Q000502:physiology; D011652:Pulmonary Circulation / Q000187:drug effects; D013154:Spleen / Q000033:anatomy & histology / Q000187:drug effects*; D013318:Stroke Volume / Q000187:drug effects; D013997:Time Factors; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D010656:Phenylephrine