Stimulation of cell division in pronephros of embryonic grafts following partial nephrectomy in the host (

Following partial nephrectomy in juvenile metamorphosed Xenopus laevis the mitotic activity in the regenerating kidney reached its maximum on the 6th day and returned to its normal level by the 16th day. The mitotic activity was measured in the pronephros and epidermis of prefeeding Xenopus larvae (stage 38) at different intervals after their implantation into the lymph sacs of partially nephrectomized and control metamorphosed hosts. Ten days after partial nephrectomy, during the period of increased mitotic activity in the regenerating kidney of the host, the mitotic activity in the implant pronephros was twice as high as that in the implant pronephros of the control hosts. Eighteen days after partial nephrectomy when the mitotic activity in the regenerating host kidney had returned to normal, there was no difference between the mitotic activity of pronephros of implants in nephrectomized and control hosts. There was no significant difference between the mitotic activity of epidermis of the implants in nephrectomized and control hosts, nor was there any difference between the epidermal mitotic activity in implants examined 10 and 18 days after host nephrectomy. It was concluded that a circulating factor (or factors) responsible for the control of mitotic activity in the regenerating host kidney enters the implant through its vascular supply and influences the mitotic activity in the homologous embryonic tissue. It is possible that this factor is a tissue-specific mitotic inhibitor synthesized by the host kidney.