Abstract
Growth hormone (GH) and IGF-I are considered to be essential to adipocyte differentiation and may play a key role in fat mass accumulation in vivo. The aim of this study is to determine the effect of high lipid content diet (HL) on serum GH and tissue IGF-I mRNA levels in rats. Male Wistar rats were administered a diet containing 29% energy as lipid for 18 weeks. Significant body weight increase was observed in HL-treated rats at 28 weeks of age, comparing with normal control (CO) rats. Significantly increased fat accumlation was also shown in epididymal and subcutaneous adipose tissues in HL rats. Serum GH levels in HL rats were significantly lower than those in CO rats (HL=16.5±2.9 (SEM)ng/ml vs CO=31.7±6.0, p<0.01). Total RNA was extracted and applied to northern blot to hybridize with a rat IGF-I cDNA probe. IGF-I mRNAs were expressed at 7.5 kb with several minor bands in liver and white adipose tissue. Hepatic IGF-I mRNA/β-actin mRNA ratio in HL rats was significantly decreased (HL=0.74±0.07 vs CO=1.66±0.59, p<0.01) in accordance with decreased serum GH levels. The epididymal fat IGF-I mRNA/β-actin mRNA ratio in HL was also significantly lower than those in CO (HL=0.56±0.13 vs CO=0.81±0.14, p<0.02), whereas there was no significant difference in subcutaneous fat IGF-I mRNA/β-actin mRNA ratio between HL and CO (HL=1.61±0.31 vs CO=1.68±0.42, NS). IGF-I mRNA levels in both liver and epididymal fat in HL rats decreased proportionately to serum GH levels, suggesting that hepatic and epididymal fat IGF-I mRNA levels are mainly regulated by GH. In an obese state, increased visceral fat accumulation may be promoted by decreased serum GH levels or vice versa.
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