Similar Hormonal Changes in Sera from Scorbutic and Fasted (Vitamin C-Supplemented) Guinea Pigs, Including Decreased IGF-I and Appearance of an IGF-I Reversible Mitogenic Inhibitor

Abstract

We previously proposed that the decreased rates of synthesis of collagen and proteoglycans in vitamin C-deficient guinea pigs were unrelated to the role of ascorbate in proline hydroxylation but might result from modulation of hormones known to change during fasting. In the present studies, we found that sera from guinea pigs on an ascorbate-free diet for 24–28 days or from those fasted for 4 days, with vitamin C supplementation, showed similar changes in the concentrations of several hormones. EGF and IGF-II concentrations were unchanged, but cortisol was increased 3–5 times and growth hormone was increased to approximately twice normal levels. Thyroxine and IGF-I concentrations were decreased to 40% and 25–33% of normal levels, respectively. The decrease in serum IGF-I must occur by a growth hormone-independent pathway. The extent of changes in hormone concentrations in sera from ascorbate-deficient guinea pigs was correlated with the extent of weight loss. Sera from scorbutic and fasted guinea pigs failed to stimulate DNA synthesis in quiescent BALB 3T3 cells in the presence of saturating concentrations of EGF and PDGF. Addition of experimental sera to normal serum showed that lack of mitogenic activity was due to the presence of an inhibitor. Inhibition was not related to IGF-I concentrations in the sera, although it was reversed by the addition of IGF-I to sera from scorbutic or fasted animals. These results support our proposed model and suggest that IGF-I, as well as an inhibitor of its activity, plays a role in the regulation of growth by vitamin C and other nutrients.

Key Words:

• Growth factor
• growth inhibitor
• ascorbate
• fasting
• nutrition