Changes in the Contents! of Multiple Components of Rat Pituitary Thyrotropin in Altered Thyroid States

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Abstract
Anterior pituitary glands from normal and hypothyroid rats were analyzed for the distribution of immunoreactive TSH using isoelectric focusing. More than four distinct components of immunoreactive TSH were present in the normal rat pituitary, mostly distributed over a region of isoe ectric point (pI) between pH 6.6–8.3. When rats were rendered hypothyroid by treatment with 6-methyl-2-thiouracil (MTU), the distribution pattern of these components as well as the total TSH content in the pituitary changed considerably. All of the TSH components in the pituitary decreased during the first week of MTU treatment and reaccumulated thereafter. Acidic TSH (pI 8.2) decreased to a lesser extent initially, returned to the normal level by 2 weeks, and exceeded it by 90% at 3 weeks of MTU treatment. Median TSH (pI 7.9) almost paralleled the variation in the total TSH content in the pituitary. In rats given both MTU and L-T4, the relative amount of acidic TSH increased, whereas that of alkaline TSH decreased. Thus, the abnormal distribution pattern of multiple forms of TSH in MTUtreated rats was nearly restored to normal by treatment with LT4. These data indicate that the contents and distribution of individual components of TSH in the pituitary are affected differentially by circulating thyroid hormone.