EFFECT OF EXPERIMENTALLY INDUCED HYPO- AND HYPERTHYROID STATES UPON PITUITARY LACTOGENIC HORMONE CONCENTRATION IN RATS1

The lactogenic hormone concentration in the pituitary glands of intact and ovariectomized rats was estimated by the pigeon intradermal method of assay. Administration of Tapazole for 2 weeks caused a large reduction in lactogcnic hormone concentration. Reversal of the Tapazole-induced hypothyroid state, i.e. prevention of goitre, with euthyroid doses of thyroxine increased lactogenic hormone concentration considerably above untreated control levels. Injection of hyperthyroid levels of thyroxine caused no apparent change in lactogenic hormone concentration. The same pattern of results was obtained in both intact and ovariectomized groups. It is suggested that the metabolic processes operative in lactogenic. hormone synthesis are acutely sensitive to the circulating level of thyroxine.