Comparison of the effects of various amino acids on glycogen synthesis, lipogenesis and ketogenesis in isolated rat hepatocytes

Abstract

Several amino acids were found to stimulate glycogen synthesis and lipogenesis, and to inhibit ketogenesis in isolated rat hepatocytes. When hepatocytes were incubated in the presence of 20 mM-glucose, the amino acids could be classified in decreasing order of efficiency as follows: glutamine and proline, alanine, aminoisobutyric acid, asparagine and histidine for stimulation of glycogen synthesis; glutamine, proline and alanine for stimulation of lipogenesis; proline and glutamine for inhibition of ketogenesis. The study of the time course revealed that the rates were not linear and were preceded by a lag period. In all conditions studied, glutamine and proline were found to have similar quantitative effects on glycogen synthesis and lipid metabolism. However, their effects differ qualitatively. Indeed, the effects of proline on glycogen synthesis, lipogenesis and glutamate and aspartate content were faster. Moreover, proline increased the hydroxybutyrate/acetoacetate ratio, whereas glutamine did not change it. Incubation of hepatocytes with aminoisobutyric acid or under hypo-osmotic conditions, which increased cell volume and mimicked the amino acid-induced stimulation of glycogen synthesis, had little effect on lipogenesis. In hepatocytes incubated without glucose, ketogenesis was inhibited, in decreasing order of efficiency, by alanine, asparagine, glutamine and proline. Under these conditions, glutamine increased, alanine decreased and asparagine did not affect the concentration of malonyl-CoA. This indicates that the latter cannot be responsible for the inhibition of ketogenesis by alanine and asparagine.

Regulation of adipose branched-chain amino acid catabolism enzyme expression and cross-adipose amino acid flux in human obesity

“…This is consistent with reports using microdialysis in rat inguinal WAT (28,29) or using the human cross-SC WAT paradigm to measure these specific amino acids (15, 37a). The fate of SC WAT glutamate is not known, but, as an anaplerotic carbon source for the tricarboxylic acid cycle, it may serve as an adipocyte lipogenic substrate, as has been observed for liver (5).…”

Glutamina e turnover do carbono no tecido adiposo de leitões

“…Baquet et al (1991) verificaram que quando hepatócitos de ratos foram incubados na presença de 20 mM de glicose, a glutamina foi o aminoácido de maior eficiência no estímulo da lipogênese. Efeitos semelhantes da glutamina sobre a lipogênese foram encontrados por Lavoinne et al (1987).…”

“…Quando hepatócitos foram incubados em presença de glicose, a glutamina foi o aminoácido de maior eficiência no estímulo da lipogênese (Baquet et al, 1991). Entretanto, em cães mantidos em jejum por quatro dias, a infusão de glutamina atuou como potente inibidor da lipólise (Cersosimo et al, 1986).…”

Osmoregulatory reactions of frog erythrocytes under conditions of activation and blockade of Ca2+-channels

“…In several cases the regulatory volume decrease depends on Ca 2+ inflow to the cell [3], whereas in other cell types the response is associated with instant Ca 2+ efflux from the cellular depots [4]. In the same cell types the response to osmotic swelling includes an increase in glycogen synthesis and deceleration of glycolysis [5], an inhibition of proteolysis and in-reserve of caryolemma are practically absent. The goal of the performed work was study of kinetics of osmoregulatory reactions of nucleated erythrocytes-the whole cell and nucleus-at activation and blockade of Ca 2+ -membrane transport systems under conditions of hypoosmotic swelling.…”