The direct effect of the thyroid hormone on cardiac chronotropism.

Archives internationales de physiologie et de biochimie
M ValenteT De Leo

Abstract

To establish whether thyroid hormone modifies the heart rate directly or through an action on other neuroendocrine modulators, the authors have examined several animals models differing in the plasma levels of such compounds. Induction of the hypothyroid state in rats produced a slow onset of bradycardia, which may be removed by a prolonged triiodothyronine treatment. The involvement of TSH was excluded as, by comparing thyroidectomized, hypophysectomized and cold exposed rats, the heart rate was found to vary according to the thyroid levels and not to the TSH levels. Moreover growth hormone, corticotropin and gonadotropins do not influence the heart rate, as the bradycardia induced by hypophysectomy was fully removed by triiodothyronine treatment. The lack of influence by ACTH and GnH was confirmed by treatment of thyroidectomized rats with corticosteroids or testosterone, respectively. Finally, thyroid hormone did not act on the heart rate by changing the norepinephrine output at the sympathetic nerve endings in the heart. In fact, thyroidectomy produced a more intense bradycardia than sympathectomy, and such bradycardia was equally removed by triiodothyronine treatment in thyroidectomized rats and in thyroidectomized and the...Continue Reading

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Citations

Jun 15, 1996·Experientia·P de Martino RosarollT De Leo
Aug 1, 1993·Comparative Biochemistry and Physiology. Comparative Physiology·S Di MeoT de Leo
Oct 18, 2008·Thyroid : Official Journal of the American Thyroid Association·Joel A Dave, Ian L Ross
Sep 1, 1988·Journal of Endocrinological Investigation·P de Martino RosarollT De Leo
Jan 1, 1996·European Journal of Applied Physiology and Occupational Physiology·P VendittiS Di Meo
May 1, 1992·Clinical Endocrinology·B StablerL E Underwood
Nov 1, 1991·Australian Veterinary Journal·A HoeyR B Atwell
Aug 18, 1997·Biochemical and Biophysical Research Communications·S ShahraraC Sylvén

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