Development and steroidogenic activity of preantral follicles in the neonatal rat ovary.

The neonatal rat ovary is completely devoid of antral follicles until the twelfth day of age. During this period the ovary becomes steroidogenically active and responsive to gonadotrophins. The aim of this study was to correlate the onset of ovarian androgen and oestrogen production in vitro with the first appearance of distinct granulosa and theca cells. Although ovarian aromatase activity increased significantly on day 7 of age, ovarian oestrogen production was limited by low progesterone and testosterone production until day 12 of age. Increased aromatase activity on day 7 and androgen production on day 12 were coincident with the first appearance of granulosa and theca cells respectively. These functional and morphological changes were not associated with significant alterations in ovarian weight or concentrations of LH or FSH in serum.