Tissue-specific mitotic inhibition in the kidneys of embryonic grafts and partially nephrectomized host Xenopus laevis.

Immature Xenopus laevis were unilaterally nephrectomized and implanted subcutaneously with stage 38 (prefeeding) larvae. Rat kidney extract was injected 8 and 16 days after the operation and the mitotic incidence (MI) in the host and implant tissues was measured by the colcemid metaphase arrest technique. The MI in the kidney of nephrectomized hosts was higher than normal at 8 days but had returned to the control level at 16 days. Injection of kidney extract inhibited mitosis in the host kidney both at 8 and 16 days after partial nephrectomy. The MI of implant pronephros was higher in nephrectomized than in control hosts both at 8 and 16 days. Injection of kidney extract into nephrectomized hosts inhibited mitosis in the implant pronephros both at 8 and 16 days. Neither host nephrectomy nor injection of kidney extract had any effect on the MI in the epidermis of the implants. Unoperated immature Xenopus were injected with rat kidney or liver extracts. Kidney extract inhibited mitosis in the kidney but not in the liver, while liver extract inhibited mitosis in the liver but not in the kidney. The rate of mitosis in the kidney and liver of normal animals may be controlled by tissuespecific inhibitors of cell division.