Digestion, rumen fermentation and circulating concentrations of insulin, growth hormone and IGF-1 in steers fed diets based on different proportions of maize silage and grass silage

Replacing grass silage with maize silage results in a fundamental change in the ratio of structural to non-structural carbohydrates with commensurate changes in rumen fermentation patterns and nutrient utilisation. This study investigated the effects of feeding four forage mixtures, namely grass silage (G); 67 g/100 g grass silage133 g/100 g maize silage (GGM); 67 g/100 g maize silage133/100 g grass silage (MMG); maize silage (M) to four ruminally and duodenally canulated Holstein Friesian steers. All diets were formulated to be isonitrogenous (22.4 g N/kg DM) using a concentrate mixture. Dietary dry matter (DM) and organic matter (OM) digestibility increased with ascending maize silage inclusion (P,0.1) whereas starch and neutral detergent fibre digestibility declined (P,0.05). Ratio of non-glucogenic to glucogenic precursors in the rumen fluid increased with maize silage inclusion (P,0.01) with a commensurate reduction in rumen pH (P,0.05). Mean circulating concentrations of insulin were greatest and similar in diets MMG and GGM, lower in diet M and lowest in diet G (P,0.01). There were no effects of diet on the mean circulating concentration of growth hormone (GH), or the frequency, amplitude and duration of GH pulses, or the mean circulating concentrations of IGF-1. Increasing levels of DM, OM and starch intakes with the substitution of grass silage with maize silage affected overall digestion, nutrient partitioning and subsequent circulating concentrations of insulin.

Digestion, rumen fermentation and circulating concentrations of insulin, growth hormone and IGF-1 in steers given maize silages harvested at three stages of maturity

Advancing maturity of forage maize is associated with increases in the proportion of dry matter (DM) and starch and decreases in the proportions of structural carbohydrates in the ensiled crop. Three maize silages (286 (low, L), 329 (medium, M) and 379 (high, H) g DM per kg fresh weight) plus a concentrate formulated to give isonitrogenous intakes were offered to Holstein-Friesian steers fitted with a cannula in the dorsal sac of the rumen and a 'T' piece cannula in the proximal duodenum in an experiment with a cross-over design that allowed four collection periods. Nutrient flow to the duodenum was estimated using chromium-EDTA. Steers consumed approximately 0(.)6 kg DM per day less of diet L compared with the other two diets (P=0(.)026), resulting in less DM being digested (P=0(.)005) but digestibility did not differ between diets. Similar results were obtained for organic matter. There were no differences between diets in the intake or digestibility of neutral-detergent fibre. Intake, duodenal flow and faecal output of starch were greater for steers offered diets M and H compared with those given diet L (P < 0(.)05). In all diets rumen digestion contributed to over 90% of total digestion of starch, although rumen digestibility declined significantly with advancing maize maturity (P=0(.)002). Molar proportions of acetic acid were higher in diet H (P < 0(.)05) whilst proportions of propionic acid and n-butyric acid were higher in diets M and L. There were no significant differences between diets in mean rumen pH or ammonia concentrations. Mean circulating concentrations of insulin were higher (P=0(.)009) in cattle given diets L and M compared with diet H. There were no differences between diets in the mean circulating concentration of growth hormone, or the frequency, amplitude and duration of growth hormone pulses, or the mean circulating concentrations of IGF-1. Changes in forage composition that accompany advancing maize maturity affect overall silage digestion and circulating concentrations of insulin.

Age-related increases in circulating inflammatory markers in men are independent of BMI, blood pressure and blood lipid concentrations

Objective: To examine whether age-related increase in concentrations of circulating inflammatory mediators is due to concurrent increases in cardiovascular risk factors or is independent of these. Methods and results: Cytokines (IL-6, IL-18), chemokines (6Ckine, MCP-1, IP-10), soluble adhesion molecules (sICAM-1, sVCAM-1, sE-selectin) and adipokines (adiponectin) were measured in the plasma of healthy male subjects aged 18-84 years (n = 162). These were related to known cardiovascular risk factors (age, BMI, systolic and diastolic blood pressure, plasma total cholesterol, LDL cholesterol, HDL cholesterol and triacylglycerol concentrations) in order to identify significant associations. Plasma concentrations of sVCAM-1, sE-selectin, IL-6, IL-18, MCP-1, 6Ckine, IP-10 and adiponectin, but not sICAM-1, were significantly positively correlated with age, as well as with several other cardiovascular risk factors. The correlations with other risk factors disappeared when age was controlled for. In contrast, the correlations with age remained significant for sVCAM-1, IL-6, MCP-1, 6Ckine and IP-10 when other cardiovascular risk factors were controlled for. Conclusions: Plasma concentrations of some inflammatory markers (sVCAM-1, IL-6, MCP-L 6Ckine, IP-10) are positively correlated with age, independent of other cardiovascular risk factors. This suggests that age-related inflammation may not be driven by recognised risk factors. (C) 2006 Elsevier Ireland Ltd. All rights reserved.

Modulation of interleukin signalling and gene expression in cardiac myocytes by endothelin-1

The related inflammatory cytokines, interleukin- (IL-) 1β and IL-33, are both implicated in the response of the heart to injury. They also activate mitogen-activated protein kinases (MAPKs) in cardiac myocytes. The hypertrophic Gq protein-coupled receptor agonist endothelin-1 is a potentially cardioprotective peptide and may modulate the inflammatory response. Endothelin-1 also stimulates (MAPKs) in cardiac myocytes and promotes rapid changes in expression of mRNAs encoding intercellular and intracellular signalling components including receptors for IL-33 (ST2) and phosphoprotein phosphatases. Prior exposure to endothelin-1 may specifically modulate the response to IL-33 and, more globally, influence MAPK activation by different stimuli. Neonatal rat ventricular myocytes were exposed to IL-1β or IL-33 with or without pre-exposure to endothelin-1 (5 h) and MAPK activation assessed. IL-33 activated ERK1/2, JNKs and p38-MAPK, but to a lesser degree than IL-1β. Endothelin-1 increased expression of soluble IL-33 receptors (sST2 receptors) which may prevent binding of IL-33 to the cell-surface receptors. However, pretreatment with endothelin-1 only inhibited activation of p38-MAPK by IL-33 with no significant influence on ERK1/2 and a small increase in activation of JNKs. Inhibition of p38-MAPK signalling following pretreatment with endothelin-1 was also detected with IL-1β, H2O2 or tumour necrosis factor α (TNFα) indicating an effect intrinsic to the signalling pathway. Endothelin-1 pretreatment suppressed the increase in expression of IL-6 mRNA induced by IL-1β and decreased the duration of expression of TNFα mRNA. Coupled with the general decrease in p38-MAPK signalling, we conclude that endothelin-1 attenuates the cardiac myocyte inflammatory response, potentially to confer cardioprotection.

Effects of dietary fatty acid composition on basal and hormonestimulated hepatic lipogenesis and on circulating lipids in the rat

Thirty male rats were randomly assigned to one of three dietary groups in which the source of dietary fat was either a mixed oil, maize oil or fish oil. Effects of dietary fatty acid composition on in virro rates of [U-'4C]glucose incorporation into hepatic total lipids and into hepatic triacylglycerol were measured under basal, insulin (4 nM)-, gastric inhibitory polypeptide (GIP; 6 mi)- and insulin + GIP (4 nM + 6 n ~ ) - stimulated conditions. Effects of the three diets on postprandial plasma triacylglycerol, cholesterol, insulin and GIP concentrations were also measured. The fish-oil diet decreased rates of basal glucose incorporation into hepatic total lipids (P < 0.05) and hepatic triacylglycerol (P < 0.01) compared with the mixed-oil diet. The presence of insulin + GIP in the incubation medium stimulated glucose incorporation into hepatic total lipids in the maize-oil (P < 0.01) and fish-oil groups (P < OW), as well as into hepatic triacylglycerol in the maize-oil group (P < 0.005). In addition, the fish-oil diet decreased postprandial plasma triacylglycerol levels compared with both other dietary groups (P < 0-05 both cases), and the mixed-oil diet markedly increased postprandial plasma insulin levels compared with the other dietary groups (P c 0.001).

The early transcriptomic response to interleukin 1β and interleukin 33 in rat neonatal cardiomyocytes

In the heart, inflammatory cytokines including interleukin (IL) 1β are implicated in regulating adaptive and maladaptive changes, whereas IL33 negatively regulates cardiomyocyte hypertrophy and promotes cardioprotection. These agonists signal through a common co-receptor but, in cardiomyocytes, IL1β more potently activates mitogen-activated protein kinases and NFκB, pathways that regulate gene expression. We compared the effects of external application of IL1β and IL33 on the cardiomyocyte transcriptome. Neonatal rat cardiomyocytes were exposed to IL1β or IL33 (0.5, 1 or 2h). Transcriptomic profiles were determined using Affymetrix rat genome 230 2.0 microarrays and data were validated by quantitative PCR. IL1β induced significant changes in more RNAs than IL33 and, generally, to a greater degree. It also had a significantly greater effect in downregulating mRNAs and in regulating mRNAs associated with selected pathways. IL33 had a greater effect on a small, select group of specific transcripts. Thus, differences in intensity of intracellular signals can deliver qualitatively different responses. Quantitatively different responses in production of receptor agonists and transcription factors may contribute to qualitative differences at later times resulting in different phenotypic cellular responses.