Effect of Insulin on the Phosphorus-32 Mononucleotide Labelling of the Isolated Rat Diaphragm in the Controlled Absence of Extracellular Glucose

Abstract

EXTENSIVE work on glucose transport into the cell under the influence of insulin and on the metabolic consequences of this transport has been carried out on the eviscerated animal¹, the isolated rat diaphragm², the isolated perfused heart³ and the isolated epididymal fat pad^4,5. Insulin stimulation seems to involve not only an enhanced transport-rate, but also an increased intracellular distribution space as measured with non-metabolizable sugars² and amino-acids^6,7. However, some recent reports^8,9 dealing primarily with incorporation of carbon-14 into proteins of rat diaphragm, in the absence of added glucose, demonstrated a striking insulin effect, which could not be explained by an increased accumulation of amino-acid precursors of the labelled protein. This effect may be correlated¹⁰ with another report mentioning the action of insulin on endoplasmic reticulum proliferation in the fat pad¹¹. Whatever the mechanism of action of insulin may be, stimulation of glucose transport, protein synthesis or any other metabolic event is bound to be reflected in the turnover of free mononucleotides and especially adenosine nucleotides, the role of which is essential in the activation of sugars, fatty acids¹² and amino-acids¹³.