A technique for the isolation of chicken hepatocytes and their use in a study of gluconeogenesis

Metabolic and hormonal responses of growing modern meat-type chickens to fasting

1. The present study compared the effects of fasting on circulating concentrations of glucose, insulin and glucagon in male and female modern meat-type chickens (Ross 708) at three ages (19 d, 33 d and 47 d). 2. Plasma concentrations of glucose were reduced by fasting with reductions of 24.9% (19-d-old), 22.6% (33-d-old) and 17.9% (47-d-old) in broiler chickens fasted for 12 h. 3. Plasma concentrations of insulin decreased with fasting. For instance, circulating concentrations of insulin declined after 6 h of fasting by 45.7%, 54.7% and 50.0%, respectively, in 19-d-old, 33-d-old and 47-d-old broiler chickens. 4. Plasma concentrations of glucagon were increased by fasting. Plasma concentrations of glucagon were elevated by 3.79% (19-d-old), 3.51% (33-d-old) and 3.79% (47-d-old) with 6 h of fasting and remained elevated with 12 h, 18 h and 24 h of fasting.

Perspectives on the endocrinology of poultry growth and metabolism

Birds have rapid pre- and post-hatching growth rates. The major hormones required to support normal growth are growth hormone (GH), triiodothyronine (T(3)) and insulin-like growth factor-I (IGF-I). Optimal growth requires a "set-point" concentration of both IGF-I and T(3) in the circulation. Pituitary GH plays a role in controlling the circulating concentrations of both IGF-I and T(3). Nutritional restriction (energy, protein) leads to reductions in circulating concentrations of both IGF-I and T(3) with increased GH secretion due removal of negative feedback. Similarly, there is un-coupling of the GH-IGF-I axis in stunting disease. A critical control point is at the level of the liver and GH receptor/signal transduction. The major hormones controlling metabolism include glucagon, insulin, adrenal glucocorticoid hormone, corticosterone and potentially somatostatin. Chickens and turkeys have higher circulating concentrations of glucose than those of livestock mammals. What are not known include the following: the biological basis for the high basal glucose concentrations; the quantitative fluxes of key metabolites in the fed and fasted state through growth and development; the relative contribution of different organs to gluconeogenesis; the relative importance of insulin and somatostatin in controlling lipolysis and the role of gastro-intestinal hormones in the control of metabolism.

Insulin administration suppresses an increase in insulin-like growth factor binding protein-2 gene expression stimulated by fasting in the chicken

1. We examined the changes in plasma IGF-I concentration and tissue IGFBP-2 gene expression of young fasted chickens refed a commercial diet or administered bovine insulin intravenously. 2. Plasma IGF-I concentration was decreased by fasting for 2 d. Although plasma IGF-I concentration was increased by refeeding, it didn't recover to the level of chickens fed a commercial diet ad libitum. 3. Insulin administration lowered plasma IGF-I concentration compared to other groups. 4. Hepatic IGFBP-2 mRNA was increased by fasting for 2 d and decreased by refeeding for 6 h. Insulin administration also decreased hepatic IGFBP-2 gene expression stimulated by fasting to the level of refed chickens. 5. IGFBP-2 mRNA in the gizzard was increased by fasting for 2 d and tended to decrease after refeeding for 6 h. Insulin administration decreased gizzard IGFBP-2 gene expression to less than that in refed chickens. 6. There was no between-treatment difference in IGFBP-2 mRNA in the brain and kidney. 7. These results suggest that the changes in IGFBP-2 gene expression in the liver and gizzard by fasting and refeeding might be partly regulated by the alteration in plasma insulin concentration.

Effects of pantethine on lipogenesis and CO2 production in the isolated hepatocytes of the chick (Gallus domesticus)

1. Isolated hepatocytes from chicks were used to study the effects of pantethine supplementation to incubation medium on in vitro lipogenesis, CO2 production and beta-oxidation of fatty acid. 2. In vitro lipogenesis, determined by the incorporation of 1-[14C]acetate into total lipid and various lipid fractions, as depressed in concordance with the increase of pantethine concentration in the medium. 3. Incubation of isolated hepatocytes with pantethine resulted in a significant decrease (P < 0.01) in the activities of acetyl-CoA carboxylase and fatty acid synthetase. 4. The results suggest that in vitro fatty acid synthesis from 1-[14C]acetate was depressed and CO2 production was elevated in hepatocytes of chicks through pantethine addition to the medium at a low level.

Gluconeogenesis in isolated chicken hepatocytes: effect of fatty acids, beta-hydroxybutrate, ethanol, and various pyruvate/lactate ratios

The effect of fatty acids beta-hydroxybutyrate, ethanol, and different pyruvate/lactate ratios on gluconeogenesis in isolated chicken hepatocytes was investigated. Glucogenesis was significantly affected by a change in the oxidation-reduction (pyruvate/lactate) ratio, and this effect was greater than could be accounted for by the additive effects of these substrates. Substituting lactate with nongluconeogenic substrates, such as beta-hydroxybutyrate or ethanol, increased the formation of glucose by 80 and 200%, respectively, demonstrating the beneficial effect of the increased reducing equivalents in the hepatocytes. Oleic acid per se had no effect but when added complexed with albumin, it had a negative effect on gluconeogenesis.