J. Grizard

Lack of an effect of a high leucine test meal on plasma insulin in preruminant lambs

Abstract The experiment was performed to determine the effects of dietary leucine excess on plasma insulin, glucagon and cortisol levels in preruminant lambs. The animals received either a control test meal or a high leucine test meal. High leucine meal resulted in an about 5 fold increase in plasma leucine and α-ketoisocaproate on 1–2h period after meal feeding when compared to the respective period in controls. Postprandial plasma glucose was unmodified by leucine excess when compared to control meal. In contrast, postprandial levels in free valine, lysine, tyrosine, phenylalanine and methionine decreased. Surprisingly postprandial levels of insulin, glucagon and cortisol were not significantly modified by dietary leucine excess.

Binding and degradation of 125I-glucagon by highly purified rat liver plasma membranes

125I-glucagon binding and degradation were studied in highly purified plasma membranes from rat livers. Specific 125I-glucagon binding increased rapidly with time at 30 degrees C and reached a maximum between 30 and 120 min. At 120 min the labelled material present in the supernatants from incubation mixtures had extensively lost its ability to rebind to fresh membranes whatever the glucagon concentration. This impairment was not due to the release of a degradative activity into the incubation mixture, suggesting a membrane-mediated process. The presence of proteinase inhibitors (bacitracin/aprotinin) resulted both in an increase in specific 125I-glucagon binding to membranes and an improvement in the ability of the labelled material from the supernatant to rebind to fresh membranes. When analysed by Bio-Gel P-10 chromatography the loss in the ability of the labelled material in the supernatants to rebind to fresh membranes correlated with a decrease in the labelled material which eluted as 125I-glucagon from the column. Chromatographic analysis overestimated 125I-glucagon when compared to the radioreceptor assay. The labelled material extracted from membranes by Triton X-100 solubilization or dissociated from membranes after exposure to an excess of unlabelled glucagon mainly eluted as 125I-glucagon. However, a significant amount (20-30%) of the labelled material eluted in the low molecular weight region.