Abstract
Summary
The thyroid hormone secretion rate (TSR) of female Sprague-Dawley-Rolfs-meyer rats has previously been shown to decline markedly from weaning time to about 4 months of age. In the present study it was shown that the pituitary and plasma levels of TSH were low at weaning time and gradually increased until 80 or 95 days of age, then showed a slight decline. In order-to explain the observations of a declining TSR associated with an increase in plasma TSH, it has been suggested that (1) the sensitivity of the thyroid gland to TSH decreases with age, (2) the t½ of TSH may decrease with increasing age, and (3) the secretion of L-T3 in the immature rat may be high and decline with age.
Get full access to this article
View all access options for this article.