Levels of thyroid and thyrotrophic hormones in the blood of rats at various stages of the oestrous cycle.

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A COMPARISON was made between the levels of thyroid and thyrotrophic hormones in the blood of female albino rats during the four stages of the œstrous cycle. The procedure used was that adopted by D'Angello and Gordon1, namely, ‘the stasis tadpole method’. Serum was obtained from the blood of the rats, which were divided into four groups of five or six each according to the vaginal smear reading. These groups were of pro-œstrous, œstrous, metœstrous and diœstrous rats. The tadpoles were divided into five groups, one of which was the untreated control. The others were injected with seven injections of 0.01 ml. of serum obtained from the four groups of rats on alternate days. Twenty-four hours after the last injection the tadpoles were killed with chloroform, fixed in susa and stored in 80 per cent alcohol. Their hindlimbs were then measured with a micrometer; this was used as a criterion of thyroid hormone activity. The height of the epithelial cells of the thyroids of tadpoles was used as an indication of the level of thyrotrophic hormone in the blood of the different groups of rats. The results are shown in Table 1.