Abstract
Isolated fat cells were used for the study of in vitro effects of insulin on glucose metabolism in human and rat adipose tissue. In human subcutaneous fat cells, effects of insulin could be detected at concentrations of glucose in the medium from 1 to 10 micro moles/ml. Cellular responsiveness was inversely proportional to the glucose level. At a constant concentration of 6 micro moles of glucose per ml, the effects of insulin at various concentrations up to 500 micro U/ml were investigated. At the highest concentration, which gave the maximal response, there was a 100% increase in the conversion of glucose-U-(14)C to glyceride-glycerol and a 40% increase in glucose oxidation. The dose-response curve was steepest between 2 and 20 micro U/ml. Rat epididymal fat cells were much more responsive to insulin. Glucose lipogenesis and pentose cycle activity could also be demonstrated in rat cells, whereas these activities could not be shown in fat cells from human omental and subcutaneous tissue. The findings for human cells are attributed to changes in cellular activity during preparation.
Highlights
In human subcutaneous fat cells, effects of insulin could be detected at concentrations of glucose in the medium from 1 to 10 pmoles/ml
The percentage changes in glucose oxidation were somewhat less than those observed with glyceride synthesis, and for the most part appeared to be independent of the glucose concentration; at 10 pmoles of glucose per ml no insulin effect on I4CO2production could be demonstrated
These findings indicate that glucose uptake by adipose cells was influenced by the extracellular concentration of glucose and by the presence of insulin
Summary
In human subcutaneous fat cells, effects of insulin could be detected at concentrations of glucose in the medium from 1 to 10 pmoles/ml. Rat epididymal fat cells were much more responsive to insulin. Glucose lipogenesis and pentose cycle activity could be demonstrated in rat cells, whereas these activities could not be shown in fat cellsfrom human omental and subcutaneous tissue. In vitro response to changes in insulin concentration over the physiological range has yet to be demonstrated in human adipose tissue. The present investigation was undertaken to further explore the effects of insulin on glucose metabolism in adipose tissue from adult man. The results obtained here indicate that the uptake of glucose and its conversion to glyceride-glycerol by human fat cells are stimulated by concentrations of insulin similar to those assayed in plasma after glucose ingestion.
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