In vitro binding of 125I-HCG to the rat ovary from birth to puberty.

Neither homogenates nor frozen ovarian sections of rats aged 1, 5 and 7 days demonstrated specific binding of 125I-HCG. However, from day 10 to day 35, the homogenates could bind specifically, with an equilibrium association constant in the range of 0.9-2.7 x 10(10) M-1. The binding capacity increased from 5.8 fmol/mg tissue at day 10 to 15.7 fmol/mg tissue at day 35. As revealed by autoradiograpy, the frozen ovarian sections from 10-day-old rats showed 125I-HCG binding localized over the interstitial and thecal tissues and, in the older age groups, also in the granulosa cells of follicles larger than 500 micrometers in diameter. These results indicate that LH/HCG receptors appear in the rat ovary at the beginning of the second postnatal week, and that the interstitial cells are the main site of action of LH before puberty.