IGF-I LEVELS IN DIFFERENT CONDITIONS OF LOW SOMATOTROPE SECRETION IN ADULTHOOD - OBESITY IN COMPARISON WITH GH DEFICIENCY

Background. It is widely accepted that IGF-I synthesis and release dep end on GH secretion as well as on the nutritional status and vary with age. Based on these premises, after the definition of normal IGF-I le vels during lifespan, in a large population of normal subjects of both sexes, our aim was to verify IC;F-I levels in large groups of adult p atients with GH deficiency or obesity, a condition in which a reduced somatotrope secretion is well known. Methods. To this goal, IGF-I leve ls were assayed after acid-ethanol extraction, in 326 normal subjects (NS, 98 men and 228 women, age 20-80 Srs, BMI 17.9-26.1 kg/m(2)), 54 p atients with GH deficiency (GHD, 24 men and 30 women, age 20-80 yrs, B MI 18.2-27.1 kg/m(2)), and 195 patients with obesity (OB, 33 men and 1 62 women, age 17-71 yrs, BMI 27.7-64.9 kg/m(2)). In NS, IGF-I Levels w ere similar in both sexes and showed a progressive decrease with age. No correlation was present between IGF-I and BMI in NS. Median IGF-I l evels and the 3rd centile in NS when considered per decade were: III) 230 and 108.6; IV) 220 and 129.8; V) 150.5 and 72.4; VI) 163.0 and 62. 4; VII) 110 and 41.6; VIII) 82 and 24.7 mu g/l. In GHD, IGF-I levels w ere independent on sex and did not show reduction during lifespan. Mea n IGF-I levels in GHD were lower than that in NS (64.5+/-5.9 vs 171.3/-4.8 mu g/l, p<0.01) and did not correlate with age or BMI. Analyzing individual IGF-I levels, in GHD, in the III and IV decade 21/24 patie nts had IGF-I levels lower than 3rd centile while, up to the VIII deca de, only 10/30 had IGF-I levels below normal limits. In OB, IGF-I leve ls were independent on sex but, Like in NS, showed a progressive decre ase with age and were independently, negatively correlated with BMI bu t not with WHR. Analyzing individual IGF-I levels, in OB, IGF-I levels were below 3rd centile in 10/77 patients in the III and IV decade and in only 8/108 patients up to the VIII decade. Mean IGF-I levels in th e whole OB population (179.6+/-5.9 mu g/l) were higher (p<0.01) than t hose in GHD (64.5+/-5.9 mu g/l) while only in the TV decade IGF-I leve ls in OB group were Lower (p<0.02) than those in NS (184.7+/-12.6 mu g /l vs 224,0+/-9.2 mu g/l). Conclusions. In conclusion, present data co nfirm that IGF-I Levels depends on GH secretion as well as on nutritio nal status, being negatively and independently correlated with age and BMI. IGF-I assay is not a reliable test for the diagnosis of GH defic iency in adulthood though it gives good discrimination between GHD and normal subjects up to 40 yrs of age. In spite of low GH secretion, IG F-I levels are only slightly reduced in obesity, probably as consequen ce of hyperinsulinism.