Physiological Studies on Gonadal Maturation of Fishes-I

Sexual Difference in Composition of Plasma Protein of Ayu in Relation to Gonadal Maturation

Abstract

Differences by sex in the composition of plasma protein, its hormonal control and relation-ship between plasma protein and yolk protein of Ayu, Plecoglossus altivelis, were studied elec-trophoretically and immunologically. In immunoelectrophoresis, two new proteins (Fm-a and Fm-b) appeared in the female plasma with the commencement of vitellogenesis. Fm-a was composed of two fractions (fractions 9 and 11) in starch-gel electrophoresis, which increased in the maturing female plasma. In males, the appearance of new protein was not observed. Estradiol-17β and estradiol-benzoate induced the dose-dependent synthesis of the new specific proteins in male fish, but testosterone, testosterone-propionate, hydrocortisone acetate and progesterone failed to produce the specific proteins. Ovarian extract caused three precipitin bands (Eg-a, Eg-b and Eg-c) in response to anti-maturing female Ayu plasma. Fm-a and Eg-a (a dominant fraction of ovarian extract) had the same antigenic component and binding sub-stances such as calcium, lipid and polysaccharide. Eg-a was also composed of two fractions in starch-gel electr ophoresis. In maturing females, plasma calcium increased simultaneously with the appearance of new specific protein and in estrogen-treated males (dose-dependent). These results suggest that in maturing female Ayu, new specific proteins, formed outside the ovary with the stimulation of estrogen, appear in the female plasma and then are taken up by the oocyte with the commencement of vitellogenesis.