Related Experiment Videos
Dietary protein restriction in artificially reared neonatal rats causes a reduction of insulin-like growth factor-I
B M Moats-Staats1, J L Brady, L E Underwood
1Department of Pediatrics, University of North Carolina, Chapel Hill 27599.
Insights
Neonatal protein restriction in rats significantly impacts growth and insulin-like growth factor-I (IGF-I) levels. Lower protein diets reduced weight gain and serum IGF-I, suggesting impaired gene expression.
Area of Science:
- Neonatal physiology
- Nutritional science
- Molecular biology
Background:
- Neonatal growth and development are critically dependent on adequate nutrition.
- Insulin-like growth factor-I (IGF-I) plays a vital role in growth regulation.
- Understanding the impact of nutrient restriction on IGF-I pathways is crucial for neonatal health.
Purpose of the Study:
- To investigate the effects of varying protein intake on neonatal rat growth.
- To assess serum IGF-I concentrations and IGF-I gene expression under protein restriction.
- To elucidate the relationship between dietary protein, growth, and IGF-I in neonates.
Main Methods:
- Artificial rearing of neonatal rats (days 6-18) via continuous milk infusion.
- Administration of isocaloric diets with 8%, 13.5%, or 18% lactalbumin protein.
- Comparison of artificially reared (AR) rats with mother-reared (MR) controls.
- Measurement of weight gain, tail length, serum IGF-I, and liver IGF-I mRNA levels.
Main Results:
- Growth (weight and tail length) in AR rats was dose-dependent on dietary protein levels.
- Serum IGF-I and liver IGF-I mRNA levels mirrored the growth patterns observed.
- Protein restriction led to significant reductions in serum IGF-I and IGF-I mRNA compared to controls.
- A specific 7.5-kilobase IGF-I mRNA size class was unexpectedly elevated in AR rats.
Conclusions:
- Neonatal protein restriction adversely affects growth and reduces serum IGF-I and IGF-I gene expression.
- These effects are likely mediated by decreased IGF-I gene expression at the transcriptional or RNA stabilization level.
- The independent regulation of a specific IGF-I mRNA size class warrants further investigation.
Abstract:
To determine in neonates the effects of protein restriction on growth, serum IGF-I, and IGF-I gene expression, we adapted a technique for rearing neonatal rats (days 6-18 of life) artificially by continuous infusion of milk through a gastrostomy. The artificially reared (AR) animals were given isocaloric diets containing 8%, 13.5%, or 18% lactalbumin protein. The AR rats were compared to rats reared by their mothers (MR) for 18 days. The growth of AR rats was related to the amount of dietary protein, with the pups given 18% protein having the best growth (25.55 g gained during the 12 days of the study) and those given 8% protein having the worst (13.42 g). The 13.5% protein-fed animals were intermediate in weight gain (18.39 g). The weight gains of the 18% and 8% protein-fed pups were significantly different from that of the MR animals (18.37 g). An identical pattern of tail length growth was noted among the groups. Mean serum IGF-I concentrations followed the same pattern (MR, 1.66 U/ml on day 18 of life; 18% AR, 2.53; 13.5% AR, 1.52; 8% AR, 1.31). Liver IGF-I mRNA was rank-ordered identically with weight gain and serum IGF-I [MR, 23.10 pg/micrograms poly(A+) RNA; 18% AR, 27.66; 13.5% AR, 21.02; 8% AR, 18.76]. Unexpectedly, the 7.5-kilobase IGF-I mRNA size class showed a 2- to 3-fold higher abundance in all groups of AR rats compared to that in MR controls (P less than 0.01), suggesting that this IGF-I size class is regulated independently of the other species. The reductions in serum IGF-I and IGF-I mRNA during protein restriction of neonatal rats suggest that these responses are mediated by decreased IGF-I gene expression at the level of transcription or RNA stabilization.