The Effect of Thiouracil Hypothyroidism on Reproduction in the Rat

IT HAS long been assumed that there is some relationship between thyroid activity and the reproductive system. Although much experimental work has been done in an effort to elucidate the problem, results have been conflicting. Most of the literature deals with the histologic and metabolic effects of thyroidectomy on special tissues, the effect on the estrus cycle as reflected in vaginal smears, or the physiological effect on the pituitary gland as judged by extraction or implantation experiments. Direct mating experiments are rare. The technical difficulties associated with thyroidectomy contribute largely to the confusion of results as the regenerative powers of the thyroid gland are so great that even the presence of a few thyroid cells after operation may alter the experimental findings. With the advent of thiouracil and related compounds a method was offered for the study of hypothyroidism which obviated the technical difficulties and sources of error associated with thyroid ablation. Using the thiouracil technique, a series of experiments were planned in an effort to demonstrate what specific effect hypothyroidism might exert on the ability of rats to reproduce.