A comparison of changes in whole body and skin amino acid metabolism of sheep in response to 24 h continuous infusions of variants of insulin-like growth factor 1

Abstract

. 1997. A comparison of changes in whole body and skin amino acid metabolism of sheep in response to 24 h continuous infusions of variants of insulin-like growth factor 1. Can. J. Anim. Sci. 77: 695-706. Because of the economic significance of wool to many sheep production systems, attempts to partition amino acids towards skin and wool protein synthesis have included both nutritional and hormonal methods of manipulation. A variant of insulin-like growth factor 1 (IGF-1) has previously been shown to transiently increase protein synthesis in the skin of sheep and the current study extended that work by comparing the effects of a 24 h, close-arterial, skin infusion of IGF-1, in the form of either recombinant human (rhIGF-1) or an extended variant (LR 3 IGF-1), on both whole body and skin amino acid metabolism adult, castrated Romney sheep, with three animals allocated to each treatment. There were no differences in food intake between the two treatment groups. The plasma concentration of immunoreactive IGF-1 of sheep infused with rhIGF-1 increased (P < 0.01) with time of administration, but decreased (P < 0.05) after 24 h of LR 3 IGF-1 infusion. Administration of both IGF-1 variants caused a substantial and sustained decrease in arterial insulin to less than 50% (P < 0.05) of pre-infusion values, while arterial plasma glucose concentrations were only reduced by 7%. Alterations in whole body and skin protein metabolism were assessed from continuous infusions of mixed [U-13 C] AA, [2,6 ring 3 H]phenylalanine and [ 35 S]cysteine. Within 4 h both AA concentrations and whole body plasma ILR of essential and non-essential AA were decreased (P < 0.05 for seven AA) by IGF-1 infusions. Both IGF-1 variants caused acute increases (P < 0.05) in skin blood flow and, for 13 of the 15 AA measured, isotopic transfers (range 50-220%; P < 0.05 for cysteine and tyrosine), which probably reflect increased protein synthesis. By 24 h skin blood flow, AA uptake and protein synthesis had returned to pre-infusion values. Strategies based on exogenous application, or enhanced endogenous production, of IGF-1 are unlikely, therefore, to produce persistent anabolic responses.Key words: Insulin-like growth factor 1, skin, sheep, protein synthesis Lobley, G. E., Lee, J., Hocking Edwards, J. et Harris, P. M. 1997. Comparaison des changements du métabolisme des acides aminés de l'organisme entier et de la peau des moutons en réponse à une perfusion de 24 h de variants de somatomédine-C. Can. J. Anim. Sci. 77: 695-706. À cause de l'importance économique de la laine pour plusieurs systèmes de production ovine, les tentatives de partition des acides aminés (AA) vers la synthèse protéique de la peau et la laine ont été effectuées par l'utilisation de méthodes hormonales et nutritionnelles. Dans une étude antérieure, une augmentation temporaire de la synthèse protéique de la peau et de la laine a été obtenue chez les moutons perfusés avec un variant de somatomédine (SM-C). Dans la présente étude, une comparaison des effets d'une perfusion artérielle l...

Metabolic hormones and tissue concentrations of mRNA for IGF-I in lines of sheep that differ in their protein synthesis response to feed intake

“…Protein degradation rate is sensitive to a number of hormones, including IGF-I (Oddy & Owens 1996), cortisol (Rooyackers & Nair 1997) and insulin (Oddy 1993). Certainly, any increase in protein synthesis rate caused by infusion with IGF-I is usually only temporary (Lobley et al 1997). In the SS+ sheep used in the current study, changes in whole body protein degradation rate were even less responsive to nutrition than synthesis rate (Adams et al 2000), which would also explain the greater loss of liveweight by SS+ sheep than SS-sheep when fed below M (Adams et al 1997).…”

A Model of Net Amino Acid Absorption and Utilization by the Portal-Drained Viscera of the Lactating Dairy Cow

“…Net hepatic use was generally as great or greater than PDV use (Table 9 and Table 14), suggesting that greater than two-thirds of postabsorptive losses of EAA could be accounted for by splanchnic use. Although mammary tissue is able to catabolize a number of AA, net catabolism of total AA appears to be small (Hanigan et al, 2001b) suggesting that the remaining losses occur primarily in other peripheral tissues such as muscle and skin (Lobley et al, 1997(Lobley et al, , 2000.…”