A. Ruiztorres et al., INCREASE IN INSULIN-SECRETION WITH AGE - ITS CLINICAL IMPORTANCE IN EVALUATING ABNORMAL SECRETIONS FOCUSED ON DIABETES TYPE-II AND OBESITY, Archives of gerontology and geriatrics, 22(1), 1996, pp. 39-47
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.