Effect of EGF on initiation of primordial follicle growth in ovary of newborn rat

The present study was designed to look at the effect of epidermal growth factor (EGF) and follicle-stimulating hormone (FSH) on initiation of primordial follicle growth and differentiation in the ovary of newborn rat with a sensitive marker of proliferating cell nuclear antigen (PCNA). The results showed that more cuboidal granulosa cells (GC) were found in the ovary two days after injection of EGF. More proliferative GC were observed on D4. No such action of FSH on primordial follicles was demonstrated. Using in situ hybridization, inhibin a mRNA expression in GC was detected from D5, while FSH receptor (FSHR) mRNA expression started from D6 after birth. Both mRNAs increased following further development of the follicles. These results suggest that it is EGF, but not FSH, that may play a certain role in initiation of primordial follicle growth. FSH may be involved in further differentiation and growth of the early developmental follicles.