Effects of the alpha 1-adrenoceptor agonist phenylephrine in pig heart. Study of the direct action on contractile proteins.
The effects of the alpha 1-adrenoceptor agonist phenylephrine (CAS 59-42-7) on Ca++ sensitivity of the contractile proteins and on force of contraction of the heart were studied in right ventricular preparations isolated from pigs. In contracting trabeculae phenylephrine (3-100 mumol/l) increased force of contraction in the presence of propranolol maximally by 91.8 +/- 36.2% (n = 5). The effect of phenylephrine was antagonized by prazosin, indicating an alpha-adrenoceptor-mediated positive inotropic effect. Glycerol- and Lubrol WX-extracted trabeculae ("chemically skinned") were activated by Ca(++)-concentrations between 0.01 and 47.7 mumol/l. Phenylephrine (0.1-100 mumol/l) did not affect the Ca++ activated force in these preparations. A direct intracellular action of phenylephrine on contractile proteins is thus rather unlikely to contribute to the positive inotropic effect of phenylephrine.
Meyer
W
W
Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, Universität Hamburg, Fed. Rep. of Germany.
Böhm
M
M
Herzig
J W
JW
Mügge
A
A
Schmitz
W
W
Scholz
H
H
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D003285:Contractile Proteins / Q000187:drug effects*; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013552:Swine
D000316:Adrenergic alpha-Agonists; D003285:Contractile Proteins; D010656:Phenylephrine; D002118:Calcium