X-ray induced inhibition of DNA synthesis and mitosis in internal tissues during the initiation of limb regeneration in the adult newt.

Left front limbs of adult male newts were given 2000r of X-irradiation at least four weeks prior to amputation of both forelimbs. Internal stump tissues were evaluated for the ability to incorporate 3H-thymidine and accumulate colchicine-blocked mitotic figures. In otherwise uninjured limbs, irradiation stimulated low levels of DNA synthesis which did not increase significantly after amputation. Thus, as soon as DNA synthesis increased significantly in normal limbs as a result of amputation, it was demonstrably higher than in X-rayed limbs. In general, mitotic activity in both groups reflected the DNA synthetic rates. Since others have shown that denervation at the time of amputation blocks subsequent mitosis in internal stump tissues yet allows normal levels of DNA synthesis for eight days, we conclude that X-irradiation and denervation prevent cell division in potential blastema cells by different mechanisms.