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Decreased Sensitivity of β-Adrenoceptors in Left Atria from Hypothyroid Rats

  • O.-E. Brodde
  • H. J. Schümann
  • J. Wagner

Abstract

In isolated electrically driven (1.0 Hz, 37°C) left atria of normal rats (NR) as well as of those made hypothyroid (HR) by feeding with propylthiouracil the β-sympathomimetic effects of isoprenaline (IPN) and of phenylephrine (PE) in the presence of 10−5M yohimbine on force of contraction and on the cAMP-level were investigated. In HR the dose-response curves for the positive inotropic effects (PIE) of IPN and PE were shifted to the right in comparison to NR; thus, the pD2-value for IPN was significantly decreased from 8.39±0.07(N=8) to 7.99±0.1(N=4), that for PE from 5.44±0.08(N=5) to 4.93±0.08 (N=9). In NR a submaximal effective concentration (EC80 for the PIE) of IPN(3 × 10−8M) increased the cAMP-level after 60sec by about 60%; in HR, however, the same concentration produced only a 25% increase in cAMP. The EC80 for the PIE of PE(10−5M) increased in NR the cAMP-level by approximately 35%, but failed to increase it in HR. When used in three times higher concentrations, however, both agents produced in HR an increase of the cAMP-level comparable with the effects in NR.

Keywords

Sodium NITROPRUSSIDE GUANYLATE Cyclase Positive Inotropic Effect Magnesium Acetate Coronary Smooth Muscle 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer-Verlag Berlin Heidelberg 1978

Authors and Affiliations

  • O.-E. Brodde
    • 1
  • H. J. Schümann
    • 1
  • J. Wagner
  1. 1.Institute of PharmacologyUniversity of EssenEssenGermany

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