Human growth hormone and insulin-like growth factor-I inhibit erythropoietin secretion from the kidneys of adult rats

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) play important roles in erythropoiesis and erythro-poietin (EPO) secretion. We examined the effects of GH and IGF-I on EPO production in adult rat kidney and liver in vivo and in vitro. Male Wistar rats aged 8-10 weeks were used. Recombinant human GH (hGH) was continuously infused (20 mug/kg per h) subcutaneously for 48 h using a micro-osmotic infusion pump. Octreotide (10 mug/kg) was subcutaneously injected every 12 h beginning 12 h before the hGH treatment. GH increased plasma EPO levels earlier than it increased plasma IGF-I levels. At 24 h, the IGF-I content in the liver and kidney was increased from 172.8+/-14.6 to 232.6+/-17.8 ng/g tissue (means+/-S.E.) and from 53.8+/-3.1 to 112.8+/-7.2 ng/g tissue, respectively. The EPO content in the liver was increased from 7.5+/-1.2 to 15.1+/-1.4 mIU/g tissue at 48 h, whereas the EPO content in the kidney was decreased at 12, 24, and 48 h after the start of hGH treatment. When the kidneys were organ-cultured, hGH considerably decreased EPO levels in the culture medium in a dose-related manner. The addition of anti-hGH IgG blunted the GH-induced inhibition of EPO secretion from the kidneys. IGF-I also decreased EPO levels in the medium in a dose-related manner. The addition of anti-IGF-I IgG blunted the IGF-I-induced inhibition of EPO secretion from the kidneys, whereas the GH-induced inhibition of EPO secretion was not affected. These findings suggest that both hGH and IGF-I have direct inhibitory effects on EPO secretion from adult rat kidneys.