INCREASE IN INSULIN-SECRETION WITH AGE - ITS CLINICAL IMPORTANCE IN EVALUATING ABNORMAL SECRETIONS FOCUSED ON DIABETES TYPE-II AND OBESITY

The urinary C-peptide excretion was measured in a healthy standardized population sample of 160 subjects from 20 to 90 years of age, homogen eously distributed by age and sex. Urinary C-peptide excretion corresp onded to 7% of the total amount released. The daily C-peptide excretio n was 61.23 +/- 2.2 (S.E.) mu g in the whole sample which corresponds to 41.9 +/- 1.5 IU of insulin secreted/day (I(CP)(d)), without sex dif ferences. There is an increase of the I(CP), value from the young to t he healthy middle-aged person, but when the results were corrected for standard amounts of excreted creatinine (1 g) and urea (22 g) the age -dependent increase is to be observed during the whole adult life span . Assuming that cross-sectionally observed data are representative of the individual changes, it is concluded that age alone increases insul in secretion. The results which may be useful as reference values for clinical application were as follows: (A) in 5 diabetes type II patien ts in which the I(CP)(d) value was measured several times a week, the intraindividual variation coefficient was 10.9 +/- 7.2%; (B) in a samp le of 47 type II diabetic patients of both sexes, between 51 and 70 ye ars of age, a clear correlation was found between I(CP)(d) and the res ults of the glucagon stimulation test, mainly regarding the relationsh ip between I(CP)(d) and the planimetrically measured area under the cu rve (r = 0.7, P < 0.0001); (C) in 7 obese non-diabetic individuals of similar ages the influence of the hypocaloric diet on the I(CP)(d) val ue was more evident than the use of C-peptide blood determinations bef ore or after glucagon. Finally, the I(CP)d values of type II diabetes patients with insulin requirement (n = 27) were significantly lower th an in the healthy control group (31.1 +/- 24.0 vs. 45.0 +/- 20.4), whi le diabetic patients without insulin requirement showed significantly higher values (73.0 +/- 33.0) (n = 27). These clinical studies primari ly focused on the physiology of human ageing justify the measurement o f C-peptide urinary excretion for evaluating daily insulin secretion i n patients with type II diabetes.