Partial purification and characterization of a renotropic fraction from ovine pituitaries

It has been previously established that hypophysectomy leads to renal atrophy in rats and that a crude pituitary-derived fraction is effective in restoring kidney weight to the level expected for intact animals of the same body weight. This paper reports that considerable purification of the crude renotropic fraction from ovine pituitaries has been achieved and that the purified fraction is capable of restoring kidney weights of hypophysectomized castrated rats to normal values. For example, after five daily subcutaneous injections (135 micrograms/day) there were significant increases in dry kidney weight and total renal protein and DNA. The pituitary-derived fraction was devoid of somatotropin, contained only trace amounts of corticotropin, gamma-lipotropin, vasopressin, and prolactin, and had only low levels of thyrotropin and follitropin. Daily injections of prolactin, thyrotropin, and follitropin in doses of 20 micrograms each failed to stimulate renal growth in hypophysectomized rats. Thus, it seems highly unlikely that these factors are responsible for the observed renal hyperplasia after treatment with the pituitary fraction. The purified renotropic fraction had an isoelectric pH between 8 and 9. On polyacrylamide gel electrophoresis in the presence of detergent and a reducing agent, the renotropic fraction exhibited two major bands and one minor band with mobilities that corresponded to those of a standard lutropin preparation. The renotropic fraction exhibited considerable crossreactivity with an antiserum directed against the lutropin alpha subunit, suggesting the presence of the common glycoprotein hormone subunit. Moreover, the purified fraction stimulated steroid production by Leydig tumor cells in vitro. It is noteworthy, however, that standard ovine lutropin at 135 micrograms/day failed to exhibit renotropic activity in hypophysectomized castrated rats, although effects were noted at twice that dose. It appears that the renotropic activity represents a pituitary substance that can be separated from lutropin only with difficulty.