Studies with mouse pituitary thyrotropic tumors. I. Survival of implants during prolonged suppression by thyroid hormone.

Implants of dependent mouse pituitary thyrotropic tumors survived prolonged suppression of growth with thyroid hormone. With one dependent strain, 805~, no tumor became palpable after implantation in control mice with intact thyroid to 17 months. However, tumors regularly appeared in implanted radiothyroidectomized mice. The latent period to appearance of the tumor decreased with increasing time of suppression with thyroid hormone prior to thyroid ablation. The findings were similar with those of another radiothyroidectomized dependent strain, 4183, kept suppressed by thyroid feeding, then discontinued. With an autonomous responsive L ~4 strain, no tumors appeared in control mice with an intact thyroid, up to 10 months after implantation. Tumors appeared upon radiothyroidectomy, and the latent period was progressively less with more prolonged suppression. After 18 months, however, growths became palpable, even with an intact thyroid.