Compensatory thyroid hyperplasia in hemithyroidectomized Snell dwarf mice

The effect of hemithyroidectomy (HEMITX) on the proliferation of follicular cells in the remaining thyroid lobe in Snell dwarf mice (dw/dw) and in phenotypically normal mice from the same strain (?/+) was examined by means of the colchicine metaphase-arrest technique. In both the normal and dwarf mice, the mean mitotic activity rate of the thyroid lobe 48 h after contralateral HEMITX was significantly higher than that in the animals with intact contralateral lobe (P less than 0.001), indicating the existence of compensatory thyroid hyperplasia (CTH). Since in Snell dwarfs not only GH and PRL but also TSH is lacking, it is concluded that extrapituitary factors, most probably neural pathways, are involved in CTH in these animals.