Effect of diet and ration on the relationship between plasma GH and IGF-1 concentrations in Arctic charr, Salvelinus alpinus (L.) (original) (raw)

The purpose of the study was to investigate whether dietary ration or diet composition in£uence the relationship between plasma growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in Arctic charr (Salvelinus alpinus L.). The pattern of changes in plasma GH and IGF-1 concentrations was examined in ¢sh fed at di¡erent ration levels (0%, 0.35% and 0.70% BWday À1 ) for 5 weeks, and in ¢sh fed diets containing di¡erent lipid:crude protein (LCP) ratios. Ration level signi¢cantly a¡ected plasma GH and IGF-1 concentrations; at 5 weeks the levels of both hormones in the food-deprived group were signi¢cantly lower than in ¢sh fed the 0.70% BWday À1 ration. Also, plasma IGF-1 levels in ¢sh of each ration treatment group were signi¢cantly correlated with individual ¢nal body weight; no such correlation was found for GH. To examine the e¡ects of dietary LCP ratios, ¢sh were fed for up to 18 weeks, with one of four formulated diets that had LCP ratios (dry matter basis) of 0.35 (Diet 1), 0.43 (Diet 2), 0.51 (Diet 3) or 0.59 (Diet 4), or a commercial diet (Diet 5) which had an LCP ratio of 0.38. Statistical di¡erences in plasma GH and IGF-1 concentrations were found only after 18 weeks. Growth hormone was signi¢cantly lower in ¢sh fed Diets 1 and 2 compared with Diets 3 and 5, and IGF-1 was signi¢cantly lower in ¢sh fed Diet 1 compared with Diets 2 and 5. Signi¢cant correlations between plasma GH and IGF-1 concentrations were found only for ¢sh fed Diets 1 and 5, suggesting that the in£uence of diet composition on the relationship between GH and IGF-1varies with the dietary LCP ra-tio in this species. The decline in plasma IGF-1 concentrations during food deprivation is similar to that described in other species; however, the unexpected decrease in plasma GH during food deprivation in this study may represent a species-speci¢c response.