PHENTOLAMINE AND ISOPROTERENOL - COMPARISON OF EFFECTS ON VASCULAR-RESISTANCE AND OXYGEN-UPTAKE IN SKELETAL-MUSCLE DURING HYPOTENSION

  • 1 January 1976
    • journal article
    • research article
    • Vol. 199  (2) , 353-359
Abstract
Effects of drugs on precapillary vessels and O2 uptake may differ from effects on resistance vessels and total flow in skeletal muscle. Effects of phentolamine and isoproterenol, 2 drugs which are used to treat shock, on O2 uptake in skeletal muscle were compared. O2 uptake of canine gracilis muscle (G.ovrhdot.VO2) was measured in muscles perfused at constant flow or constant pressure in normotensive dogs. Effects of the drugs were compared on O2 uptake at doses chosen so that both drugs produced comparable effects on vascular resistance. With flow constant, phentolamine increased but isoproterenol decreased or did not alter G.ovrhdot.VO2. With constant pressure, phentolamine produced significantly greater increases in G.ovrhdot.VO2. For example, increases in G.ovrhdot.VO2 occurred with all 3 doses of phentolamine, but only with the high dose of isoproterenol. Neither drug altered O2-Hb affinity of red blood cells or O2 consumption of skeletal muscle in vitro. Phentolamine produces more favorable effects than isoproterenol on O2 uptake in skeletal muscle, presumably because of greater dilator action on precapillary sphincters.