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1. The aim of this study was to investigate the time-dependency of the influence of dysthyroid states on the beta-adrenoceptor system in rat heart left ventricle. Therefore, the influence of acute and chronic hyper- and hypothyroidism on beta-adrenoceptor-induced left ventricular responses, beta-adrenoceptor density, cardiac noradrenaline tissue concentrations, Gs alpha-proteins, and basal and stimulated adenylate cyclase activities was determined. 2. Hyperthyroid rats were obtained by feeding with thyroxine (T4)-containing rat-chow for 1, 4 and 8 weeks. Hypothyroidism was induced by adding 0.05% propylthiouracil (PTU) to the drinking water. Rats of varying ages were used in order to compensate for the differences in the duration of the treatments. Rats were aged 3 and 5 months at the end of the experiments. 3. Thyroxine treatment for 4 and 8 weeks increased the cardiac sensitivity to isoprenaline, but maximal induced inotropic responses were decreased. Cardiac ventricular beta-adrenoceptor density was increased only in rats treated with T4 for 1 week. This transient effect of hyperthyroidism on cardiac beta-adrenoceptor density was not observed in older rats. The PTU treatment resulted in a stable decrease of cardiac beta-adrenoceptor density. 4. Left ventricular tissue noradrenaline concentrations were unaffected by hyperthyroidism, where a decrease was observed in hypothyroid rats. Density of Gs alpha proteins was increased in hearts from chronic hyperthyroid rats. 5. These results indicate that the increased sensitivity to beta-adrenoceptor-mediated stimulation in chronic hyperthyroidism cannot be attributed to changes in cardiac beta-adrenoceptor density, but is probably caused by an enhanced content of Gs alpha. Accordingly, in hyperthyroidism, the beta-adrenoceptor system is influenced time-dependently, whereas hypothyroidism affects the beta-adrenoceptor system independent of time.
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
January 1988,
Pharmacology & toxicology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
January 1984,
Journal of neural transmission,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
March 1988,
Neuroscience letters,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
August 1996,
British journal of pharmacology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
April 1995,
Journal of autonomic pharmacology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
February 2007,
Naunyn-Schmiedeberg's archives of pharmacology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
May 1984,
European journal of pharmacology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
December 2001,
The Journal of veterinary medical science,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
January 1991,
Fundamental & clinical pharmacology,
J Zwaveling, and
H D Batink, and
K Taguchi, and
J de Jong, and
M C Michel, and
M Pfaffendorf, and
A van Zwieten
September 1982,
British journal of clinical pharmacology,
