Investigation of a substance of renal origin which inhibits the growth of renal cortex explant in vitro

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Abstract
Explants of renal cortex from 7-day mice or 5-day rats were reared on plasma clots, in the presence or absence of chick embryo metanephros. The size of outgrowth, estimated after 48 h, was similar for renal cortex of both species. When reared in chick embryo extract in the presence or absence of metanephros, the outgrowth estimated after 48 h was 2·08 ± 0·092 greater than that of the initial explant. Addition of supernatant fluid from a homogenate of renal cortex of adult mouse, rat, guinea-pig, rabbit or pig inhibited the outgrowth of renal cortex explant from neonate mouse or rat. The supernatant fluid from a homogenate of adult renal medulla had no significant effect. The inhibitory activity of the supernatant fluid from a homogenate of renal cortex from adult animals was destroyed by heating at 99 °C. The compound with growth-inhibitory activity appeared to be cortex-specific but not species-specific. Extracts of liver, spleen, duodenum, and heart muscle of adult animals had no significant effect on the outgrowth of renal explants of neonate animals; and extracts from renal cortex of adult mammals had no significant effect on the growth of other tissues from neonate mice or rats. The degree of growth inhibition was related to the amount of protein in the extract of renal cortex. Maximum inhibition was observed with extracts of renal cortex containing 2·5 mg protein/0·5 ml. Immune serum samples were obtained from rabbits and guinea-pigs immunized against extracts of renal cortex and medulla and liver from rats and mice. Only the serum from either rabbit or guinea-pig immunized against extracts of renal cortex blocked the growth-inhibitory action of renal cortex extracts.