Kidney insulin-like growth factor-I mRNA levels are increased in postpubertal diabetic rats

in Journal of Endocrinology
Authors:
L. A. Bach
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J. L. Stevenson
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T. J. Allen
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G. Jerums
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A. C. Herington
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ABSTRACT

Diabetes-associated renal enlargement is more marked in postpubertal than prepubertal rats, and in the postpubertal rat, is associated with increased kidney insulin-like growth factor-I (IGF-I) levels for the first 2 days. In order to determine whether local IGF-I production is the cause of this increase in tissue levels, IGF-I mRNA levels were determined in pre- and postpubertal Sprague–Dawley rats made diabetic with streptozotocin (STZ) and in control rats. RNA was extracted from kidneys and livers of rats at 0 h, 6 h, 12 h and days 1, 2, 3 and 7 after STZ injection. After Northern blotting and hybridization with an oligonucleotide probe complementary to an E domain of the IGF-I cDNA, four distinct bands (7·4, 4·8, 1·8 and 1·0 kb) were found. Densitometric analyses of the most prominent bands (7·4 and 1·0 kb), after normalization for 18S ribosomal RNA content, revealed a 50–100% increase in the kidneys of postpubertal diabetic rats compared with postpubertal controls 12 h after STZ injection (P < 0·05, diabetes vs control). Between days 2 and 7, kidney IGF-I mRNA levels in postpubertal diabetic rats fell to approximately 50% of control levels (P < 0·05, diabetes vs control). In contrast, kidney IGF-I mRNA levels in the prepubertal diabetic rats remained unchanged over the 7 days. Liver IGF-I mRNA levels did not rise during the first 24 h and fell to approximately 60% of control levels by day 7 in both pre- and postpubertal diabetic rats (P < 0·05, diabetes vs control). Increased local IGF-I production may underlie the initiation of renal enlargement associated with diabetes mellitus.

Journal of Endocrinology (1991) 129, 5–10

 

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