Compensatory renal hypertrophy. I. Evidence for a factor of renal origin inhibiting DNA synthesis.

Abstract

This study describes a method for the measurement and partial purification of a factor seemingly involved in the regulation of the renal mass.After homogenization at 4 °C, rabbit kidneys were centrifuged for 100 min at 105 000 g. The resulting supernatant (S-105) was lyophilized and tested on kidney slices obtained from rats mononephrectomized 48 h previously. We have developed a method based on the inhibition of DNA synthesis to measure the activity of the S-105. Slices of renal cortex, undergoing compensatory hypertrophy, were incubated in vitro in Hanks' medium at 37 °C, pH 7.4, in an O2–CO2 atmosphere in the presence of 0.144 μg (20 μCi (1 Ci = 37 GBq)) [3H]thymidine.An inhibition of DNA uptake of [3H]thymidine was noted in the presence of S-105. When other media (Hanks', sucrose, water) were used to extract S-105, the same type of inhibition was noted even though the sucrose buffer seemed ideal for the preservation of the inhibitory factor. The inhibitory effect was still observed after dialysis of S-105 against membranes permitting exclusion of molecules with molecular weight smaller than about 4000 (such as electrolytes and tissue thymidine). This inhibition seems to be specific, since other tissues such as liver in regeneration and rat intestine were not influenced by the dialyzed renal S-105. The dialyzable fraction did contain some inhibitors, but they were not specific for the kidney since they also acted on the liver and the jejunum.Our results suggest the existence, in the normal nephron, of a specific inhibitor of thymidine incorporation into DNA of kidneys undergoing a compensatory hypertrophy. This renal factor has a molecular weight of over 5000.