Growth hormone inhibits renotropic action of luteinizing hormone-isoform(s).

We recently purified luteinizing hormone (LH)-isoforms with renotropic activity from ovine pituitaries based on the stimulation of [3H] thymidine incorporation into renal DNA of castrated-hypophysectomized rats. In this study, we examined the hormonal interactions between ovine growth hormone (GH) and this LH-isoform in renal DNA synthesis. A single injection of LH-isoform (40 micrograms) significantly increased [3H] thymidine incorporation, but an injection of GH (200 micrograms) did not, during experimental periods of up to 26 hours. Repetitive ovine GH treatment (5 days) did not change basal [3H] thymidine incorporation, either, although its biological activity was evidenced by an increase in insulin-like growth factor-I (IGF-I). Stimulated [3H] thymidine incorporation by LH-isoform (100 micrograms) was significantly suppressed by an injection of GH (200 micrograms) and was, to a greater extent, by repetitive treatment with GH (200 micrograms/day, for 3 or 5 consecutive days). These results demonstrated one example of the effect of complex hormonal interactions on kidney growth.