We have compared the kidneys of two inbred strains of rats (Lewis and Lewis-Dwarf) 7 days after the induction of diabetes mellitus with streptozotocin, in order to examine the influence of a selective growth hormone (GH) deficiency on diabetic renal growth and insulin-like growth factor-I (IGF-I) content of the kidneys. Insulin-like growth factor-I was measured by radioimmunoassay and its distribution within the kidney by immunohistochemical staining. We detected a significant increase in both the wet weight (32.9±5.3,P=0.0085) and dry weight (16.3±6.3,P=0.046) of the kidneys of diabetic Lewis rats but dwarf rats, selectively deficient in GH, did not show a significant increase in either parameter. Extractable IGF-I increased within the kidneys of diabetic rats of both strains but to a lesser extent in the dwarf rats (+105±28and+65±21respectively,P<0.0l). In diabetic Lewis rats a positive correlation was noted between the severity of glycaemia and kidney IGF-I content (r=0.604,P<0.05) but no such correlation was noted in dwarf rats.Insulin-like growth factor-I immunostaining increased in diabetic rats of both strains, mainly within cells of the thick ascending limb of the loop of Henle including damaged and vacuolated cells. However, morphometric analysis of the staining showed that it was significantly less widespread in the diabetic dwarf rats (P=0.026). We conclude that growth hormone deficiency blunts experimental diabetic renal growth and restricts the increase in the kidney IGF-I content. These findings raise further questions concerning the contribution of GH and IGF-I to the early stages of experimental diabetic renal dise
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