title: Phenylephrine-induced elevations in arterial blood pressure are attenuated in heat-stressed humans.
abstract: To test the hypothesis that phenylephrine-induced elevations in blood pressure are attenuated in heat-stressed humans, blood pressure was elevated via steady-state infusion of three doses of phenylephrine HCl in 10 healthy subjects in both normothermic and heat stress conditions. Whole body heating significantly increased sublingual temperature by ~0.5 degrees C, muscle sympathetic nerve activity (MSNA), heart rate, and cardiac output and decreased total peripheral vascular resistance (TPR; all P < 0.005) but did not change mean arterial blood pressure (MAP; P > 0.05). At the highest dose of phenylephrine, the increase in MAP and TPR from predrug baselines was significantly attenuated during the heat stress [DeltaMAP 8.4 +/- 1.2 mmHg; DeltaTPR 0.96 +/- 0.85 peripheral resistance units (PRU)] compared with normothermia (DeltaMAP 15.4 +/- 1.4 mmHg, DeltaTPR 7.13 +/- 1.18 PRU; all P < 0.001). The sensitivity of baroreflex control of MSNA and heart rate, expressed as the slope of the relationship between MSNA and diastolic blood pressure, as well as the slope of the relationship between heart rate and systolic blood pressure, respectively, was similar between thermal conditions (each P > 0.05). These data suggest that phenylephrine-induced elevations in MAP are attenuated in heat-stressed humans without affecting baroreflex control of MSNA or heart rate.
authors.affiliation: Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, Texas 75231, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Cui
authors.forename: Thad E
authors.initials: TE
authors.lastname: Wilson
authors.forename: Craig G
authors.initials: CG
authors.lastname: Crandall
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects*; D001831:Body Temperature; D002302:Cardiac Output / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology*; D013268:Stimulation, Chemical; D017779:Sympathetic Fibers, Postganglionic / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D014662:Vasoconstrictor Agents; D010656:Phenylephrine