THE EFFECT OF THYROXIN INJECTIONS ON THE THYROTROPHIN CONTENT OF THE ANTERIOR PITUITARY OF THE MALE ALBINO MOUSE1

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Abstract
Three series of adult [male] albino mice were injected with avg. total doses of 0.64, 1.32 and 2.66 mg. of thyroxin over periods of 21 and 23 days. The degree of hyperthyroidism produced by 1.34 mg., the avg. dose for the 3 series, was accompanied by a smaller body wt. increase than that in controls, though growth was not stopped, lessened the activity of the thyroids of the injected animals by 43.43% as judged by measurements of follicular epithelium in the treated and control animals, and decreased the absolute wt. of the pars anterior by 14.48% and its relative wt. by 6.00% compared with the figures in controls. The thyro-trophic potency of the ant. pituitaries of the thyroxin-injected mice and control mice was assayed by implanting individual pituitaries subcut. into day-old chicks, measuring the thyroid cell heights in the chicks 24 hrs. after implantation and comparing with similar measurements in control chicks. The avg. thyroid cell height of the chicks implanted with pituitaries of the 3 thyroxin-injected series was 2.26 [plus or minus] 0.01 [mu]; that of chicks with pituitaries of control mice was 3.36 [plus or minus] 0.02 [mu]; and that of control chicks (untreated or implanted with mouse brain) was 2.15 [plus or minus] 0.01 [mu]. Thus the thyrotrophic potency of the pituitaries of the thyroxin-injected mice was decreased by 92.71% compared with that of control mice. Furthermore, the avg. total dose of 0.64 mg. of thyroxin depleted the thyroid-stimulating content of the pars anterior as much as avg. doses of 1.32 and 2.66 mg. given over the same period of time.