BINDING SITES FOR ATRIAL NATRIURETIC PEPTIDE IN HIGH CONCENTRATIONS IN HUMAN OVARY

As one approach to examining the molecular functions of atrial natriuretic peptide (ANP), we examined the binding capacities of four human ovaries, one with a developing follicle of 7 mm (a) in diameter, two preovulatory follicles (small one of 12 mm (b) and large one of 18 mm (c) in diameter just before ovulation) and one (d) at menopause. The number of ANP binding sites of the ovary with a Graafian follicle (c) was far greater than those previously observed in various tissues. Four ovaries showed a drastic difference in concentrations of ANP binding sites. The binding capacity of membrane fractions from the ovary with a Graafian follicle just before ovulation (c) was 18 times greater than that of the ovary at menopause (d), 7.2 times that of the developing follicle (a), and 3.8 times that of the ovary with a preovulatory follicle (b). However, the dissociation constant (Kd) values showed no major difference at any stage among three ovaries except ovary at menopause. These findings suggest that ANP is involved in events related to the reproductive process.