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RATE, FORCE AND CYCLIC ADENOSINE 3′, 5′‐MONOPHOSPHATE RESPONSES TO (—)‐ADRENALINE IN NEONATAL RAT HEART TISSUE
Author(s) -
AU T.L.S.,
COLLINS G.A.,
WALKER M.J.A.
Publication year - 1980
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1980.tb07910.x
Subject(s) - propranolol , medicine , endocrinology , inotrope , adenosine , heart rate , epinephrine , circulatory system , chemistry , blood pressure
1 (–)‐Adrenaline sensitivity in 1 to 20 day‐old rat heart tissue was investigated as rate, force and cyclic adenosine 3′, 5′‐monophosphate (cyclic AMP) production responses together with sensitivity to (±)‐propranolol blockade. 2 Resting performances were measured and responsiveness to (–)‐adrenaline then determined as ED 50 values and maximal responses together with sensitivity to propranolol (pA 2 values). 3 Resting force, corrected for sample size, did not change with age, whereas resting atrial rate doubled between 1 and 20 days. 4 ED 50 concentrations in atria were constant with age, but decreased in ventricles. Cocaine (10 −5 m ) and other drugs did not consistently affect ED 50 values. 5 Maximal responses were not age‐dependent in right atria, but increased in left atria. In 2 to 5 day‐old hearts there was no inotropic response to adrenaline and the very small maximal response in ventricles rose 5 to 7 fold by 20 days. 6 Propranolol sensitivity increased slightly (2 to 4 times) with age in all tissue from a pA 2 value of 7.5 at 2 days to 8.2 at 20 days. 7 Control cyclic AMP was higher in 2 day than in 20 day‐old tissue and in atria than ventricular strips or hearts. In 2 and 20 day‐old atria, hearts and ventricles, force increases with different adrenaline concentrations correlated linearly with the log of the increase in cyclic AMP. Such a correlation was not seen in 2 day hearts and ventricles for cyclic AMP rose without corresponding force increases. 8 Results suggest slight maturational changes in atrial β‐receptors. In 1 to 5 day‐old ventricles, normal ED 50 concentrations and good cyclic AMP response in the presence of a much reduced force response may indicate receptor‐response transduction inefficiency, assuming a β 1 ‐receptor occupation and cyclic AMP production response mechanism for inotropism with adrenaline.