Turnover of plasma oleic acid measured by radio-gas chromatography

Gas-liquid chromatography with radioactivity detection (Radio-GLC) was investigated as an analytical means of determining the fractional turnover rates of plasma free fatty acids. For this purpose normal dogs were infused with 1.838 muCi/min of [1-14C]oleic acid complexed with albumin and plasma samples were taken at 0 to 110 minutes. The plasma free fatty acids were isolated by a modified Dole extraction and the methyl esters, prepared by diazomethylation, were identified and quantitated by GLC and radio-GLC using radioactive methyl heptadecanoate as internal standard. The study demonstrates that physiologically feasible infusion rates and loads of radioactive acids can be found which permit accurate analyses of plasma free fatty acids by radio-GLC. During a 2-hour infusion no labeled acid other than oleic appeared in plasma indicating that the method could be used to study the turnover of a mixture of fatty acids simultaneously. These results also indicate that conventional methods of determination of radioactivity in purified extracts can be employed without concern for recycling of label among the fatty acids, at least over short periods of time. The radio-GLC technique described yields approximately 20% higher fractional turnover times for oleic acid than do standard methods.

Effect of glucagon on glucose turnover and plasma free fatty acids in depancreatized dogs maintained on matched insulin infusions

It has been shown previously that glucagon can increase the turnover of glucose in normal dogs and can enhance the secretion of insulin. The aim of this study was to determine the metabolic effects of glucagon independent of the effects of the insulin it releases directly through an action on β cells, and indirectly through hyperglycemia. Eight conscious dogs which could not mobilize extra insulin were obtained by replacing the endogenous insulin secretion of each with an equivalent intraportal infusion of the hormone immediately following removal of a remnant pancreatic autograft. Such infusions (200 μU/kg-min) maintained normal plasma concentrations of glucose and free fatty acids (FFA), as well as normal tracer-determined rates of glucose appearance (Ra) and disappearance (Rd) prior to glucagon infusion.There was a highly significant regression of the increments in glucose production on the rate of glucagon infusion (1.00–3.00 μg/kg-h). Rd increased proportionally to glucose levels, and there was therefore no significant change in the metabolic clearance of glucose. Hence a direct inhibitory effect of glucagon on glucose utilization could not be demonstrated. Corrections for recycling of the infused label did not appreciably affect the observed changes in Ra or Rd. Glucagon infusions did not increase the FFA level in plasma; when hyperglycemia was prominent a small decrease occurred. The role of glucagon in the net release of FFA from adipocytes in dogs is therefore questioned.