ISSN:
1573-4919
Keywords:
atria
;
thyroid hormones
;
β-adrenergic effect
;
sarcoplasmic reticulum
;
phospholamban
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract This paper discusses the mechanisms of two basic effects of thyroid hormones on atrial responses to β-adrenergic agonists, i.e. increased inotropic sensitivity and decreased maximal contractile responsiveness. The increased sensitivity of atria to β-adrenergic agonists under thyroid hormones appears to be related to increases in β-adrenoceptor density and Gs/Gi protein ratio, leading to activation of Gs-mediated pathway, but suppression of Gi-mediated pathway of adenylate cyclase regulation. Therefore, the i/c concentrations of cAMP and corresponding inotropic responses achieve their maximums at lower doses of β-adrenergic agonist. Thyroid hormones also decrease the expression of phospholamban, but increase the expression of sarcoplasmic reticulum Ca+2-pump. As a result, the basal activity of sarcoplasmic reticulum Ca+2-pump increases, but its β-adrenergic activation through phosphorylation of phospholamban decreases. It is suggested that these changes are causal for decreased maximal inotropic and lusitropic responses of atria to β-adrenergic agonists.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1006835213108
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