PLASMA INSULIN AND GROWTH HORMONE LEVELS IN OBESITY AND DIABETES

A close relationship between obesity and maturity-onset diabetes has long been appreciated but not clearly understood. The study of carbohydrate metabolism and its hormonal regulation in the obese is therefore of interest. The present communication is concerned with the effects of glucose administration on the secretion of insulin and growth hormone in obese and nonobese, diabetic and nondiabetic subjects. Since the fractional rate of degradation of these hormones is independent of hormone concentration over wide limits,'-3 acute changes in plasma concentration may fairly be taken to reflect changes in secretory rate provided that certain kinetic features of hormonal distribution and degradation are fully appreciated.' I t is particularly worth noting that both insulin' and growth hormone5 distribute rapidly (within 30-45 minutes) into an apparent volume five to eight times the plasma volume, and undergo metabolic degradation with half times averaging about 35 minutes' and 20-30 minute^^.^ Tespectively. "The nature of the obesity-diabetes relationship" is the subject of a recent excellent review by Smith and Levine7 to which reference may be made for a more complete bibliography. Here we summarize only several well established observations: A relatively high percentage of adult-onset diabetics are obese and were so long before the onset of clinical diabetes. Diabetes occurs far more frequently in obese than in nonobese subjects. Obese patients without clinically manifest diabetes exhibit impaired glucose tolerance with abnormally high frequency. Weight reduction to normal or near normal levels is frequently followed by a t least temporary remission of overt diabetes and even by the attainment of normal glucose tolerance. Nevertheless, diabetes cannot be considered to be an inevitable consequence even of long standing extreme obesity but rather occurs principally in those with a family history of diabetes; moreover, in most of these who experience remission following weight reduction a residual abnormality is expressed in a positive cortisone-glucose tolerance test.' It seems reasonable to conclude from these generally accepted observations that obesity can provide an additional stress in those who carry an inherited tendency to diabetes but does not in itself necessarily constitute a prediabetic state.