Ovarian HCG-binding capacity during the oestrous cycle of the rat.

Binding in 125I-labelled HCG to rat ovary varies during the oestrus cycle. The highest amount of binding was found in dioestrous-II rats (7.33 X 10(-15) mol of HCG per mg wet weight), while the lowest binding was observed in oestrous rats (1.67 X 10(-15) mol of HCG per mg wet weight) of circulation LH. It is concluded that the low binding capacity of the rat ovary in the oestrous stage is due to masking of the specific receptors by the excessively high LH hormone secretion in pro-oestrus.