Endogenous and exogenous insulin responses in patients with cystic fibrosis.

Eight male patients with cystic fibrosis, normal nutrition, normal physical activity, relatively 
mild pulmonary disease, no evidence of liver disease and no family 
history of diabetes mellitus underwent a series of carbohydrate tolerance tests 
in comparison with a group of 18 normal male subjects matched 
for age and body weight. Compared with the normal group, the 
patients with cystic fibrosis had significantly impaired glucose tolerance and significantly 
lower serum immunoreactive insulin levels during oral and intravenous glucose tolerance 
tests; serum insulin levels were also significantly lower after intravenous administration 
of tolbutamide in the patients with cystic fibrosis, but the reduction 
in blood glucose concentration in each group was not significantly different. 
During an intravenous insulin test, the decrease in blood glucose concentration 
was the same for both groups, in spite of significantly lower 
serum insulin levels in the patients with cystic fibrosis .The percentage 
fall in plasma free fatty acids was at least as great 
in the patients with cystic fibrosis as in normals during the 
test procedures; while a significant decrease in plasma alpha-amino nitrogen after 
intravenously administered insulin was seen only in the patients with cystic 
fibrosis. These studies suggest that the carbohydrate intolerance of cystic fibrosis 
is consequent upon an impaired insulin response to glucose, but that 
this insulin deficiency is partly compensated for by increased peripheral tissue 
sensitivity to insulin. 