Sex steroid regulation of insulin-like growth factor system gene expression and proliferation in primate myometrium

To investigate the role of locally produced insulin-like growth factors (IGFs) in sex steroid-induced growth in the primate uterus, ovariectomized rhesus monkeys were treated with placebo (control), estradiol (E2) alone, or E2 plus progesterone (P4). After 2 weeks, uteri were removed, and serial thin uterine sections were analyzed by in situ hybridization for IGF-I, IGF-II, and IGF-I and -II receptor messenger ribonucleic acids (mRNAs) and by immunocytochemistry for the cell proliferation-specific antigen Ki-67. IGF-I and IGF-II and both IGF receptor mRNAs are coexpressed by smooth muscle cells, supporting the possibility of autocrine/paracrine IGF action in stimulating myometrial growth. IGF-I mRNA is barely detected in control myometrium, is significantly increased by E2 treatment, and is augmented even more by the combination of E2 and P4 treatment, whereas little change is noted in myometrial IGF-II or IGF-I receptor mRNA levels. Ki-67-positive myometrial nuclei are also significantly increased by E2 and are augmented even more by E2 plus P4 treatment, with a correlation between local IGF-I mRNA concentration and local Ki-67-positive cell count of r = 0.891 (P = 0.003). These data provide direct experimental evidence for regulation of IGF-I gene expression by sex steroids in the primate uterus in vivo and implicate local IGF-I action in both estrogen- and P4-induced myometrial growth.