Effects of insulin-like growth factors I and II and insulin on the immortalized hypothalamic GTI-7 cell line
Abstract
Insulin and insulin-like growth factor I (IGF-I) participate in energy metabolism, regulate cellular growth and differentiation, and are thought to act locally in a paracrine manner through specific receptors. Systemic levels of these peptides in humans and primates are directly associated with levels of activity of the reproductive axis. To date, it is unclear whether these peptides participate in reproductive function by acting at the level of the GnRH neuron. In this study we examined the effects of IGF-I, IGF-II and insulin on immortalized GnRH-secreting neurons, the GTI-7 cell line. The GTI-7 cells expressed all three members of the insulin receptor family as determined by analysis of 125I-IGF-I, 125I-IGF-II and 125I-insulin binding sites. Insulin receptors bound insulin, IGF-II and IGF-I with a ratio of potency of 1:5:20. IGF-I and IGF-II receptors bound both IGF-I and IGF-II. The ratio of potency of IGF-I/IGF-II was 1:5 for the IGF-I receptor and 100:1 for the IGF-II receptor. The binding characteristics of the growth factors at 22 degrees C suggested the possibility that these cells may secrete IGF binding proteins. To ensure that changes in GnRH levels in the media were due to secretion and not to changes in cell numbe...Continue Reading
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