THE INSULIN-LIKE-GROWTH-FACTOR AXIS AND PLASMA-LIPID LEVELS IN THE ELDERLY

The activity of the hypothalamic-GH-insulin-like growth factor (IGF) n etwork. declines with age. It has recently been shown that increased c ardiovascular mortality occurs in adults with GH deficiency. As hyperc holesterolemia is common in GH-deficient adults, and because there is experimental evidence that GH may play a role in regulating plasma cho lesterol, we decided to investigate the activity of the GH-IGF axis in an elderly population by measuring serum IGF-I, IGF-LI, and IGF-bindi ng protein-3 (IGFBP-3) levels and to study their relationship with blo od lipid levels. One hundred and thirty-two elderly subjects, 52 men a nd 80 women, were studied (age range, 60-91 yr). Men had significantly lower levels of IGFBP-3, high density lipoprotein cholesterol (HDL-C) and apoprotein Al (ApoAl) compared to the women, whereas IGF-I and IG F-II were only slightly lower. Using Linear regression analysis, we ob served an inverse relationship of age with IGF-I (r = -0.35; P < 0.001 ), IGF-II (r = 0.40; P < 0.001), IGFBP-3 (r = 0.52; P < 0.001), body m ass index, and lipid levels. Univariate regression analysis showed a s trong and positive correlation of both IGF-I and IGFBP-3 with HDL-C an d ApoAl. Partial correlation analysis, after adjustment for age and bo dy mass index, showed that IGFBP-3 and IGF-II were still significantly and positively related to HDL-C and ApoAl. Furthermore, a strong asso ciation was documented among IGF-I, IGF-II, and IGFBP-3. These data de monstrate that even in an elderly population, further aging is accompa nied by a progressive decline in circulating IGF-I, IGF-II, and IGFBP- 3, suggesting a continuing diminution of the GH-IGF axis throughout ag ing. Moreover, the strong correlation between HDL-C and an index of GH secretion, such as IGFBP-3, suggests that GH might play an important role in lipid metabolism in healthy elderly subjects.