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Functional link between myocardial α 1 ‐ and β 1 ‐adrenoceptors in neonatal rabbits
Author(s) -
Varma Daya R.
Publication year - 1991
Publication title -
drug development research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.582
H-Index - 60
eISSN - 1098-2299
pISSN - 0272-4391
DOI - 10.1002/ddr.430240306
Subject(s) - chronotropic , inotrope , medicine , phenylephrine , prazosin , epinephrine , endocrinology , norepinephrine , propranolol , isoprenaline , adrenergic receptor , antagonist , heart rate , receptor , blood pressure , stimulation , dopamine
Ontogeny of inotropic responses of the left atria and chronotropic responses of the right atria of rabbits was studied in vitro. The maximal inotropic effect (efficacy) of isoproterenol on atria from neonatal (1.5 weeks old) rabbits was significantly less than that of norepinephrine and epinephrine. The inotropic efficacy of isoproterenol increased with age and reached adult levels at 6 weeks. There was no difference in the potency and efficacy of inotropic effects of epinephrine and norepinephrine on neonatal and adult (∼40 weeks old) rabbit atria. At threshold concentrations, phenylephrine synergistically potentiated the inotropic effects of isoproterenol on atria from neonatal but not on atria from adult rabbits. The potentiation of the inotropic effects of isoproterenol by phenylephrine on neonatal rabbit atria was abolished by prazosin. There was no difference in the chronotropic effects of isoproterenol on atria from neonatal and adult rabbits. It is speculated that α 1 ‐ and β 1 ‐myocardial adrenoceptors are functionally linked in early life and a full expression of inotropic responses requires a concomitant activation of both receptor types.