POSITIVE INOTROPIC BUT NO RELAXANT EFFECTS OF PHENYLEPHRINE IN CAT PAPILLARY-MUSCLE

  • 1 January 1978
    • journal article
    • research article
    • Vol. 4  (4) , 291-298
Abstract
The effect of phenylephrine (30 .mu.M) in the presence of propranolol (1 .mu.M) on electrically induced isometric twitches and on KCl-contractures was studied in papillary muscles from reserpine-pretreated cats at 25.degree. C. Under these conditions phenylephrine was previously shown to act solely via .alpha.-adrenoceptors and not to increase c[cyclic]AMP. Phenylephrine increased force of contraction, time to peak tension and relaxation time. Contracture tension remained unaffected. The stimulation of cardiac .alpha.-adrenoceptors, in contrast to .beta.-adrenergic stimulation, does not lead to so-called relaxant effects. This qualitative difference between the 2 responses is probably due to the different capacity of both stimuli to increase cAMP.

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