Demonstration in Tupaia papillary muscle preparations of alpha-adrenoceptors mediating positive inotropic effects: comparison with guinea-pigs

Br J Pharmacol. 1989 Oct;98(2):552-6. doi: 10.1111/j.1476-5381.1989.tb12629.x.


1. Positive inotropic responses to alpha- and beta-adrenoceptor agonists of isolated papillary muscles from the tree shrew (Tupaia), were compared with those from guinea-pigs. 2. In Tupaia, the concentration-response curve for phenylephrine, unlike that for isoprenaline, was not affected by pindolol in a concentration (10(-8) M) sufficient to block beta-adrenoceptor-mediated responses, but it was significantly shifted to the right by phentolamine (10(-6) M). In guinea-pig papillary muscles, however, the concentration-response curve for phenylephrine, like that for isoprenaline, was shifted to the right by pindolol (10(-8) M) but was unaltered by phentolamine (10(-6) M). Furthermore, when the mean concentrations of agonists inducing maximal positive inotropic responses were compared (relative to that of isoprenaline = 1.0), phenylephrine was found to be only slightly less potent (0.84 +/- 0.04; n = 5) in Tupaia and much less potent (0.33 +/- 0.06; n = 5) in the guinea-pig. 3. Although in Tupaia papillary muscles the increase in developed tension induced by a combination of phenylephrine and isoprenaline did not significantly differ from that by phenylephrine alone, it was approximately 3 times larger than that produced by phenylephrine alone in guinea-pigs. 4. These results indicate that in papillary muscles from Tupaia, unlike the guinea-pig, the positive inotropic effects of phenylephrine can be mediated by alpha-adrenoceptors.

Publication types

  • Comparative Study

MeSH terms

  • Adrenergic alpha-Agonists / pharmacology
  • Adrenergic beta-Agonists / pharmacology
  • Animals
  • Female
  • Guinea Pigs
  • Heart / drug effects*
  • In Vitro Techniques
  • Isometric Contraction
  • Isoproterenol / pharmacology
  • Male
  • Myocardial Contraction / drug effects*
  • Papillary Muscles / drug effects
  • Phenylephrine / pharmacology
  • Receptors, Adrenergic, alpha / drug effects*
  • Tupaia / physiology*
  • Tupaiidae / physiology*


  • Adrenergic alpha-Agonists
  • Adrenergic beta-Agonists
  • Receptors, Adrenergic, alpha
  • Phenylephrine
  • Isoproterenol