Mitosis-stimulating activity of the pituitary growth hormone upon amphibian tissues as modified under the influences of thiourea treatment and denervation.

That certain hormones as well as neural agencies exert considerable effects upon the mitotic level of normal and regenerating tissues of Amphibia has been claimed from time to time. Denervation was stated to cause some measure of decrease in the mitotic activity of the regenerating tissues of adult newt(Singer and Craven, 1948). The mitotic responsiveness of epidermis of larval Amphibia to implanted nervous elements was reported by Overton(1950). Hypophysectomy inhibits the provocation of mitotic activity in the regenerating tissues of adult Amphibia(Inoue, 1956a). Growth hormone raises the mitotic level of normal epidermis and promotes mitotic activity of regenerating tissues and cortisone acts as an inhibitant for mitotic proliferation(Manner, 1955; Inoue, 1956b). As was reported previously, administration of daily constant dose of growth hormone induced a temporal mitotic stimulation upon the fin epidermis of larval bull-frog and the accerelation of metamorphosis. On the basis of such observations, several experiments were undertaken to analyse the phenomenon of the temporal mitotic stimulation. This report deals with the results of the experiments made on the relationship of thyroid function and mitotic activity in the epidermis when tadpoles were subjected to combined treatmets with growth hormone and thiourea. Observations were extended to the effect of growth hormone upon the provocation of mitotic activity in the denervated and regenerating forelimbs of the adult newt.