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Responses to triiodothyronine are similar in normal mice and mice lacking receptors for sympathetic-nervous-system hormones
The background of the study. Thyroid
hormones and sympathetic-nervous-system hormones (catecholamines)
have similar cardiovascular and metabolic actions. This study evaluated
the cardiovascular and metabolic actions of thyroid hormone in animals
lacking receptors for catecholamines.
How the study was done. The study
animals were normal mice and mice lacking the genes for all forms
of the 
-catecholamine
receptor. The two types of mice had similar weights and serum thyroxine
(T4) and triiodothyronine (T3) concentrations. Cardiovascular responsiveness
to -receptor
activation was determined by measurements of cardiac dynamics and
heart weight after administration of the -receptor-activating
drug isoproterenol. Thyroid hormone responsiveness was determined
in the same way, and also by measurements of cardiac genes and oxygen
consumption after injections of T3 or saline for 14 days.
The results of the study. The mice
lacking -receptors
had a lower rate of oxygen consumption and a slower heart rate than
the normal mice. Blood pressure, cardiac contractility, and cardiac
weight were similar in the two groups. Treatment with isoproterernol
increased heart rate and heart weight in the normal mice, but not
in the mice lacking -receptors.
Administration of T3 increased oxygen consumption similarly in normal
mice and mice lacking -receptors,
but body weight did not change. Heart rate and cardiac contractility
increased to the same extent in both groups of mice; cardiac weight
increased more in response to T3 in the normal mice.
The conclusions of the study. Mice
with no -receptors
and normal mice have similar cardiovascular and metabolic responses
to T3, indicating that these actions of T3 are not mediated by activation
of the sympathetic nervous system.
The original article. Bachman ES,
Hampton TG, Dhillon H, Amende I, Wang J, Morgan JP, Hollenberg AN.
The metabolic and cardiovascular effects of hyperthyroidism are
largely independent of -adrenergic
stimulation. Endocrinology 2004;145:2767-74.
Next Article: Several clinical findings
predict the outcome of hyperthyroidism caused by Graves’
disease
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| Thyroid Digest Index | | | July 2004 Thyroid Digest |
