Liver and kidney growth hormone (GH) receptors are regulated differently in diabetic GH and GH antagonist transgenic mice

Elevated GH levels are frequently seen in poorly controlled type I diabetics and have been implicated in diabetic complications. Studies of GH and GH antagonist (GHA) transgenic mice with streptozotocin (STZ)-induced diabetes have revealed that GH has a permissive effect for diabetic nephropathy, and that expression of a GHA gene protected mice against diabetic kidney lesions. To investigate whether kidney GH receptor (GHR) and/or GH-binding protein mag play a role in diabetic nephropathy, we evaluated CH-specific binding and messenger RNA levels for GHR/GH-binding protein in mouse livers and kidneys from bovine (b) GH or bGHA transgenic (TG) mice and their nontransgenic (NTg) littermates with or without STZ-induced diabetes. We found that liver-specific GH binding is significantly higher in both bGH- and bGHA-Tg mice compared to that in their NTg controls. In contrast, kidney GK binding is significantly lower in bGH-Tg mice compared to that in NTg littermates. These results indicate that regulation of mouse GHR expression is tissue specific. STZ-induced diabetes decreased GH-specitic binding in both liver and kidney of NTg and GHA-Tg mice, but not in bGH-Tg mice. The lowered GHR binding in diabetic NTg and GHA-Tg mice suggests the involvement of insulin in the regulation of GHR expression. The down-regulation of kidney GHR in GHA-Tg mice in combination with the presence of GHA may partially explain the protective mechanism of GHA against diabetic kidney lesions.