Bm. Murray et al., EFFECT OF DIETARY-PROTEIN INTAKE ON RENAL GROWTH - POSSIBLE ROLE OF INSULIN-LIKE GROWTH FACTOR-I, The Journal of laboratory and clinical medicine, 122(6), 1993, pp. 677-685
Insulin-like growth factor-I (IGF-I) has been implicated as a possible
mediator of renal hypertrophy after uninephrectomy and diabetes melli
tus. Because renal hypertrophy is also a consequence of high protein i
ntake, we studied the effect of varying concentrations of dietary prot
ein on circulating levels and renal tissue content of IGF-I. Male Spra
gue-Dawley rats were fed isocaloric diets containing high (50%, HP), n
ormal (20%, NP) or low (6%, LP) dietary protein for up to 14 days befo
re they were killed. As expected, renal size (dry kidney weight) was g
reater in HP-fed rats and smaller in LP-fed rats when compared with NP
-fed animals (HP, 1415 +/- 26 mg [p < 0.01 vs NP]; NP, 1148 +/- 27 mg;
LP, 838 +/- 16 mg [p < 0.01 vs NP]), and most of the relative changes
in kidney size occurred during the first week of ingestion of the exp
erimental diet. Renal hypertrophy in the HP-fed animals was accompanie
d at day 3 by a significant rise in kidney tissue IGF-I that remained
elevated at day 7 but had fallen to baseline values by day 14. The ris
e in renal IGF-I content in the HP-fed rat was accompanied by increase
s in circulating IGF-I on day 3 only. Both circulating and renal tissu
e IGF-I levels were suppressed in the LP-fed animals at 3, 7, and 14 d
ays. These data confirm that varying dietary protein intake has profou
nd effects on both circulating and renal IGF-I levels. They are consis
tent with a potential causal role of decreased hepatic and renal IGF-I
synthesis in the blunted somatic and renal growth that is seen in the
LP-fed rat. The data from the HP-fed animals also suggest that increa
sed renal synthesis of IGF-I may play an important role in the initial
hypertrophic response seen in response to an HP diet. However, persis
tent elevation of circulating or kidney IGF-I levels (or both) does no
t appear necessary for the maintenance of kidney hypertrophy in the HP
-fed rat.