Insulin-like growth factor-I, but not growth hormone, is dependent on a high protein intake to increase nitrogen balance in the rat

Abstract

The aim of the present study was to investigate the influence of dietary protein level on the protein anabolic effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I). Female growing rats were fed on either a high- or a low-protein diet with crude protein contents of 222 and 83 g/kg respectively. The diets contained the same amount of metabolizable energy (15·1 MJ/kg) and were given during a 14 d period. During the same time, three groups of rats (n 8) on each diet received subcutaneous infusions of either saline, recombinant human GH (rhGH) or recombinant human IGF-I (rhIGF-I). rhGH and rhIGF-I were given in doses of 360 and 500 μg/d respectively. The low-protein diet alone reduced significantly (P < 0·05) IGF-I concentrations in serum and in tissue taken from the gastrocnemius muscle as well as IGF-I mRNA from the same muscle. The responses to rhGH and rhIGF-I in terms of muscle IGF-I and its mRNA were variable. However, when rhIGF-I was infused into rats on the high-protein diet, significantly elevated levels of IGF-I in muscle tissues could be observed. This was associated with a significantly (P < 0·05) increased N balance, whereas rhGH significantly (P < 0·05) enhanced the N balance in rats on the low-protein diet. Thus, it can be concluded that the level of dietary protein ingested regulates not only the effect of IGF-I on whole-body N economy but also the regulation of IGF-I gene expression in muscles. The exact mechanism by which GH exerts its protein anabolic effect, however, remains to be elucidated.

An ecologic study of dietary and solar ultraviolet‐B links to breast carcinoma mortality rates

“…Insulin‐like growth factor–1 has been linked to diet in several ways. Insulin‐like growth factor–1 serum and tissue levels increase with obesity,81 energy‐dense diets,82 and dietary protein levels,83, 84 and are reduced in caloric restriction diets85 and vegan diets 86. These links are consistent with the ecologic study results presented here.…”

A Chronic Oral Toxicity Study of Marine Collagen Peptides Preparation from Chum Salmon (Oncorhynchus keta) Skin Using Sprague-Dawley Rat

“…Second, the administration of collagen peptides of 16.6 g/kg·bw/day increased the diet protein content to 34%. As we know, high content of protein may induce renal growth by the induction of insulin-like growth factor-I [17]. So this adverse effect might be due to the high dietary protein content.…”

T-Cell Populations and Cytokine Expression Are Impaired in Thymus and Spleen of Protein Malnourished BALB/c Mice Infected with Leishmania infantum

“…The animals had free access to water and food. Food rations per cage were daily weighed and feed consumption was calculated [31] . Diets were chosen based on previous reports that 4% protein diet induces protein deficiency but not energy deficiency whereas 14% protein diet has been reported to provide standard protein requirements for supporting normal growth in mice [32] .…”