Mitotic activity in the remaining kidneys of unilaterally nephrectomized rats reaches a peak about 48 hours after operation. To test for the possible existence of tissue-specific growth-regulating factors, such rats were given injections of various tissue homogenates ca. 30 hours after uninephrectomy. Intraperitoneal administration of homogenates of fresh, cooked, or frozen kidneys, or suspensions of trypsin-dissociated kidneys, all reduced the 48-hour mitotic peak of hyperplastic kidneys by approximately 50 per cent. Saline-injected controls were insignificantly altered. Subcutaneous injections of frozen kidney homogenates did not adversely affect compensatory renal hyperplasia.

Intraperitoneal injections of fresh liver, testis, spleen, and blood homogenates inhibited renal mitosis as effectively as did kidney homogenates. Blood plasma from normal or uninephrectomized rats, however, were not effective. Egg albumin suppressed mitosis, but egg yolk did not.

In view of these failures to demonstrate a tissue-specific effect of homogenates on renal mitosis, together with similar discrepancies in comparable studies of liver, the existence of growth-regulating agents related to organ mass per se, and distinct from other functional demands, must remain problematical.


This investigation has been supported in part by a research grant (B-923) from the National Institutes of Health, and in part by a fellowship from the Department of Embryology of the Carnegie Institution of Washington.

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