Influence of protein nutrition on the response of growing lambs to exogenous bovine growth hormone

Abstract

Interactions between protein supply and the anabolic response to exogenous bovine (b) GH have been examined in two experiments using 28-35 kg lambs sustained entirely by intragastric infusion of volatile fatty acids (700 kJ/kg W 0.75 per day) into the rumen and the casein (600 mg (low protein; LP) or 1200 mg (high protein; HP)/kg W 0.75 per day) into the abomasum. Sheep received continuous i.v. infusions of bGH for 6 days in experiment 1 and for 18 days in experiment 2. Nitrogen balances were determined daily throughout both experiments and blood samples, from indwelling catheters, were assayed for GH, insulin-like growth factor-I (IGF-I), insulin and glucose. Infusion of bGH increased plasma GH concentration by five- to sixfold in all animals. There was an increase in N retention in both HP and LP animals over the first 2-3 days of GH administration. HP animals sustained higher N retentions (31%; P less than 0.05) throughout the GH administration but LP animals did not. In contrast, plasma IGF-I concentrations increased progressively over the first 72 to 96 h of GH administration in all sheep and thereafter remained significantly (P less than 0.05) elevated until termination of the GH infusion. In lambs which received both HP and LP infusion in experiment 1 the increase in IGF-I and LP infusions in experiment 1 the increase in IGF-I concentration by day 6 of GH administration was significantly (P less than 0.05) greater when they received the higher protein intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone and amino acid supply interact synergistically to control insulin-like growth factor-I production and gene expression in cultured ovine hepatocytes

“…The data presented demonstrate that these cells behave similarly to rat hepatocytes (Thissen et al 1994) in that GH and amino acid supply interact synergistically to stimulate IGF-I gene expression. In addition this study is the first to demonstrate that this effect is also manifest at the level of IGF-I peptide release, further strengthening previous arguments based on in vivo data (MacRae et al 1991) that amino acid-GH interactions at the level of the liver may be important physiologically.…”

“…Consistent with this hypothesis, it has been shown that the IGF-I response to an intravenous GH challenge is increased by high levels of feed in several species (Breier et al 1988, Wyn et al 1991, Bates et al 1993. Experiments to determine the nutritional components responsible for this altered IGF-I responsiveness indicate that in sheep and in rats, the IGF-I plasma response may be modulated by levels of dietary protein, independently of energy status, suggesting that plasma amino acids may act as metabolic signals (MacRae et al 1991, VandeHaar et al 1991, Kriel et al 1992.…”

Impacts of restricted feeding and realimentation on bone development and plasma concentrations of bone-specific biomarkers in lambs

“…Limited, Victoria, Australia) while plasma concentration of P was measured photometrically at 340 nm (Cobas Mira, Roche Diagnostics Systems, Basel, Switzerland) using a Roche Diagnostics kit (Roche Diagnostics GmbH, Annheim, Germany). Plasma GH concentration was measured as described by MacRae et al (1991) while bone-specific alkaline phosphatase level was measured by immunoassay (Alkphase-B kit, Metra Biosystem, CA, USA). Plasma osteocalcin concentration was measured using an enzyme-linked immunoabsorbent assay test (ELISA) according to procedures described by Peterson et al (2005).…”

Effects of nutritional status and gonadal steroids on expression of appetite-regulatory genes in the hypothalamic arcuate nucleus of sheep

“…Leptin concentrations were determined by homologous RIA (Marie et al 2001) with sensitivity 0·5 ng/ml, intra-assay CV 12·0% and interassay CV 16%. The RIA for insulin (MacRae et al 1991) had sensitivity 0·2 µIU/ml, intra-assay CV 4·7% and interassay CV 4·9%. Finally, LH was measured by RIA (McNeilly et al 1986) with sensitivity 0·05 ng/ml and intra-and interassay CV 7·9% and 9·3% respectively.…”