Abstract
The concentration of T 3 nuclear receptors may be modulated by thyroid hormones. We have examined the effect of thyroid hormone excess and deficiency in the rat on the in vitro binding of T 3 to anterior pituitary nuclear receptors. Nuclei prepared from hypothyroid, hyperthyroid and control rats by homogenisation and centrifugation were incubated with [ 125I]T 3 and unlabelled T 3 at increasing concentrations. After incubation for 60 min at 37 °C, nuclei were separated by filtration and bound radioactivity counted. Scatchard analysis of binding data revealed no significant difference in binding affinity or capacity for T 3 between nuclei from hypothyroid and control rats. Results from hyperthyroid and control animals revealed no change in affinity, but a marked reduction in binding capacity was observed, suggesting depletion of receptor number. This finding of down-regulation may represent a protective mechanism against the effects of high circulating thyroid hormone levels on the tissues.
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