Thyroid/serum iodide ratio (T/S ratio), introduced by Vander Laan & Greer (1955), was examined from various view points as to its availability in appraisal of thyroidal function.
T/S ratio was maintained at a certain level after one time injection of 4-methyl-2 thiouracil and of 1-methyl-2 mercaptoimidazole. And time and dose necessary for this effect were sought. Administration of the latter for 2 consecutive weeks elevated T/S ratio, producing goiter.
Hypophysectomy in rats lowerde T/S ratio and thyroid weight. Feeding with seaweed rich in iodine resulted in far greater fall in these values, accompanied by a histological picture of hypothyroidism.
At 4 weeks after 1/4, 1/2and 3/4 thyroidectomy, T/S ratio in the remnant part increased to 2.02.5 times, and compensation hypertropy was in proportion with the size of the removed portion, increasing by 130% at 3/4 thyroidectomy. When excised unilateral lobe was transplanted below head skin, into the original site, or into the spleen, the result was unfavorable with its weight extremely reduced, T/S ratio in the remnant lobe increased samely as in the case of nontransplantation, and compensation hypertrophy far slighter.
Parahydroxyprophenon, which is said to have inhibitory effect on the hypophysis, was found utterly ineffective against increase in T/S ratio and compensation hypertrophy of the remnant part after 1/2 thyroidectomy. Methyozyl and Mercazole accelerated these, while Thyradin was strongly inhibitory.
After injection of 1000 i.u. of estradiol benzoate for 14 days, T/S ratio was elevated, while thyroid weight remained unchanged, histologically manifesting a picture of near hypothyroidism. Administration of estradiol benzoate for 2 consecutive weeks did not inhibit elevation of T/S ratio and swelling of thyroid, produced by consecutive administration of methyodile, but conversely accelerated them. Nor could it inhibit the same changes, produced by unilateral thyroidectomy.
Administration of 0.2ml of thyradine for 3 consecutive weeks decreased both thyroid weight and T/S ratio. After suspension of the administration, they gradually rose, surpassing the initial level in the end, and thus manifesting the rebound phenomenon. Concurrently measured weights of the hypophysis, ovary and uterus showed no remarkable change, but frequent estruses or lasting estrus was observed during Thyradine administration.
T/S ratio was evidently high in pregnancy, especially in the later pregnancy, and also in parturition.
Utilizing the Krieg's stereotaxic instrument, damage was electricly given to the anterior, medial and posterior area of the hypothalamus, and T/S ratio was found lowered by anterior and posterior damage, body weight decreased most heavily by posterior one, and estrus interrupted by anterior, medial and posterior one in the ascending order. Weights of the ovary and uterus were also remarkably reduced by posterior damage. In general persistence of corpus luteum was observed in the ovary.
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