Hepatic expression of growth hormone receptor/binding protein and insulin-like growth factor I genes in uremic rats. Influence of nutritional deficit.
The molecular basis for GH resistance in chronic renal failure is unknown. It may partly reside in a decreased number of hepatic GH receptors and subsequently reduced IGF-I synthesis. To investigate the hepatic expression of GH receptor/binding protein (GHBP) and IGF-I genes in chronic renal failure, mRNA levels and the concentrations of its splicing variants were measured by Northern Blot in male 5/6 nephrectomized rats (NX, n = 9), aged 26 +/- 1 days, and three groups of sham-operated rats: (1) fed ad libitum (SAL, n = 9); (2) pair-fed with NX (SPF, n = 7); and (3) pair-fed with NX in terms of protein ingestion but calorically supplemented up to the intake of SAL (SPF+, n = 8). NX rats had severe renal failure, serum urea nitrogen 106 +/- 11 mg/dl (mean +/- SEM), and were growth retarded. GH receptor/GHBP gene expression was detected as two bands of 4.7 and 1.2 kb, respectively. The amount of mRNA was lower (P < 0.0001) in NX than SAL, either when both bands were considered together or separately. No differences were found between NX, SPF, and SPF+. Serum GHBP concentrations were higher (P < 0.01) in NX rats than the other groups. For the IGF-I gene, two bands of 7.5 and 1.8-0.8 kb were identified. Expression of IGF-I gene was reduced (P < 0.05) in NX in comparison with SAL, this reduction being more marked for the 7.5 kb transcript (amount of mRNA equal to 56.6 +/- 2.6 vs 84.8 +/- 6.2% of values found in SAL rats). There were no differences between NX and SPF. Normalization of caloric intake in SPF+ resulted in partial recovery of the 7.5-kb band and did not modify the 1.8-0.8 kb mRNAs. Circulating IGF-I levels were no different among the four groups. These data confirm that expression of liver GH receptor/GHBP and IGF-I genes is markedly decreased in uremic rats. Nutritional deficiency and not uremia itself seems to be the main causal factor, with protein deficit playing a major role.
Martínez
V
V
Department of Pediatrics, School of Medicine and Hospital Central de Asturias, University of Oviedo, Spain.
Balbín
M
M
Ordóñez
F A
FA
Rodríguez
J
J
García
E
E
Medina
A
A
Santos
F
F
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D007676:Kidney Failure, Chronic / Q000150:complications / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D009748:Nutrition Disorders / Q000150:complications / Q000235:genetics* / Q000378:metabolism; D011502:Protein-Energy Malnutrition / Q000150:complications / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011986:Receptors, Somatotropin / Q000235:genetics*; D014511:Uremia / Q000150:complications / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; C051815:somatotropin-binding protein