Abstract
AbstractOntogeny 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 α1‐ and β1‐myocardial adrenoceptors are functionally linked in early life and a full expression of inotropic responses requires a concomitant activation of both receptor types.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
