Ovariectomy and gonadal hormone treatment: Effects on insulin-like growth factor-1 receptors in the rat brain

Various studies demonstrate that estradiol regulates structure and function of adult neurons. Long-term effect of estradiol in terms of neuroprotection is less documented compared to short-term one. It is well documented that estradiol interacts with insulin-like growth factor-1 (IGF-I) in the brain. The present study examines the effect of ovariectomy and two doses of ovarian hormone treatment on IGF-I receptor density in the adult rat by receptor autoradiography using ¹²⁵I-IGF-I as a ligand. Our result showed that ovariectomy decreased IGF-I receptor density in hippocampus, hypothalamus and parietal cortex compared to that of the sham-operated group. Treatment with low or high dose estrogen restored IGF-I receptor density to the control levels in nearly all areas studied in this investigation. It seems that low dose estrogen has more pronounced effect than the high dose in restoring IGF-I receptor density. On the other hand, progesterone treatment in high but not in low dose restored IGF-I receptor density to that of the control. These results demonstrate that both estrogen and progesterone significantly affects IGF-I receptor density in different areas of the brain. These effects indicate a dose-dependent modulator effect of ovarian hormones on IGF-I activity in the brain.