Population-based reference values for IGF-I and IGF-binding protein-1: relations with metabolic and anthropometric variables.

Population-based reference values for IGF-I and IGF-binding protein-1 (IGFBP-1) have been established. One hundred and one women and the same number of men, 20-70 years old, were randomly selected from the population registry in the community of Linköping. Participation rate was 67%. Venous blood was drawn in the fasting state. Serum IGF-I was measured by RIA after acid-ethanol extraction and IGFBP-1 was determined by ELISA. IGF-I levels did not differ between genders and the decline with age was similar in men and women (men: Y = 366-3.28 x age (years), r = -0.61, P < 0.0001; women: Y = 386-3.49 x age, r = -0.57, P < 0.0001, P = 0.4 for difference in slope). There were negative correlations between IGF-I and plasma lipids and blood pressure in both genders, but none was independent of age. Serum angiotensin-converting enzyme activity correlated positively with IGF-I in men independently from age (r = 0.21, P = 0.01). The distribution of IGFBP-1 was positively skewed and it was higher in women than in men (5.9 +/- 4.8 micrograms/l and 4.0 +/- 3.3 micrograms/l respectively; Mann-Whitney, P = 0.002). In men and in the women not taking oestrogen, IGFBP-1 correlated positively with age (Spearman rank correlation (Spearman: men: r = 0.32, P = 0.002; women: r = 0.24, P = 0.03). C-peptide correlated negatively (Spearman: men: r = -0.38, P = 0.002; women: r = -0.49, P < 0.000) and sex hormone binding globulin positively with IGFBP-1 (Spearman: men: r = 0.50, P < 0.0001; women: r = 0.55, P < 0.0001). IGF-I declined with age while IGFBP-1, which is considered to modulate the free bioactive fraction of IGF-I, increased. This suggests that IGF-I activity might be even lower in elderly subjects than is accounted for by the low total IGF-I.

A population-based study of plasma cyclic guanosine monophosphate: relations to age, atrial natriuretic factor and angiotensin-converting enzyme activity.

In order to study the relations between plasma cyclic guanosine monophosphate (cGMP) and anthropometric variables, plasma atrial natriuretic factor (ANP) and serum angiotensin-converting enzyme activity (ACE), a population study with random selection of 217 subjects (49% men) 18-69 years old was performed. Venous blood was drawn at 08.00 h and ambulatory blood pressure (ABP) recording was then performed. There was no gender-difference in cGMP levels (men 2.2 +/- 1.1 nmol L-1, women 2.2 +/- 1.1 nmol L-1). A weak negative correlation was seen between cGMP and systolic ABP in both genders 20-44 years of age (r = -0.3, p = 0.05 for both), but this correlation did not persist in multivariate analysis with correction for ANP, age and ACE. In women, cGMP correlated positively with ANP (r = 0.27, p = 0.005) independently of ANP, ACE, ABP and age. ACE correlated negatively with cGMP in men (all; r = -0.22, p = 0.03, 45-69 years of age r = -0.49, p = 0.0002) and this correlation was independent of ANP, ACE, ABP and age. ACE catalyses the breakdown of bradykinin, which stimulates the release of NO. As the second messenger of NO is cGMP, the negative correlation between ACE and cGMP in men might be a reflection of reduced production of NO. Our results also suggest that there are gender differences in the stimuli for basal cGMP production.