Effect of Puberty on Initial Kidney Growth and Rise in Kidney IGF-I in Diabetic Rats

Prepubertal subjects have a low incidence of diabetic nephropathy compared with duration-matched postpubertal subjects. At puberty, there is an increase in insulinlike growth factor I (IGF-I) levels, and because IGF-I has been implicated in the early kidney enlargement of experimental diabetes, we studied the development of kidney enlargement and kidney IGF-I levels in prepubertal (aged 5 wk) and postpubertal (aged 13 wk) Sprague-Dawley rats during the 7 days after induction of diabetes with streptozocin. Kidney weight in postpubertal diabetic animals was significantly greater than in postpubertal controls by day 2 (1.46 +/- 0.06 vs. 1.16 +/- 0.09 g, P less than 0.05), and by day 7, kidney weight had increased by 36% (1.61 +/- 0.07 vs. 1.18 +/- 0.08 g, P less than 0.001). Despite comparable blood glucose levels in the prepubertal and postpubertal diabetic rats, kidney weight in prepubertal diabetic animals was significantly greater than in prepubertal controls by 14% on day 7 only (0.84 +/- 0.01 vs. 0.73 +/- 0.03 g, P less than 0.05). Kidney IGF-I content was significantly elevated in diabetic postpubertal rats, peaking on day 1 (diabetic vs. control, 1082 +/- 156 vs. 543 +/- 21 ng/g, P less than 0.001) and day 2 but not in prepubertal diabetic rats. Thus, prepubertal diabetic rats have reduced and retarded kidney growth and attenuated kidney IGF-I levels, suggesting that local IGF-I accumulation may play an important role in diabetes-associated kidney enlargement.